Translator Disclaimer
1 December 1995 Impacts of hunting disturbance on waterbirds - a review
Jesper Madsen, Anthony D. Fox
Author Affiliations +

Waterbird hunting is a widespread activity in wetlands throughout Europe and constitutes one of the most significant sources of disturbance during autumn and winter. The biological evidence for effects of hunting disturbance on the behaviour and distribution of migratory and wintering waterbirds and its possible impacts on population dynamics is reviewed. Most of the literature has been concerned with local effects of disturbance, focussing on quarry geese and dabbling ducks. Comparatively little is known about effects on diving ducks and waders, while there is no direct evidence for impacts at the population level for any waterbird species. Hunting disturbance can cause temporary disruption of normal activities of waterbirds, alter their diurnal rhythms and increase escape flight distances. It can displace waterbirds from preferred feeding and roosting habitats at local or regional level and increase turnover, so that the carrying capacity of a site is not reached. Quarry waterbirds, and those occurring in large inshore concentrations, such as many dabbling ducks, geese and waders, are potentially most sensitive to disturbance. Hunting disturbance can disrupt pair-bonds and family structures which may affect reproductive output. Evidence is provided that many waterbird populations are limited by winter conditions and that the majority of studied waterbird species lose body reserves during winter. Because hunting disturbance causes under-exploitation of potential feeding grounds where population limitation is considered to occur, such disturbance will, by definition, have an impact at the population level. However, the magnitude of this impact has not been quantified and requires a modelling approach.

Hunting affects waterbird population dynamics as a direct result of the harvest kill (e.g. Anderson & Burnham 1976, Nichols 1991, Ebbinge 1991), but the indirect results of disturbance caused by shooting activity remain controversial. It has proved relatively simple to demonstrate that hunting activity can have an effect on waterbirds, i.e. that shooting activity can affect the behaviour, numbers and distribution of waterbirds using a wetland area (see reviews by Meltofte 1982 and Bell & Owen 1990). However, because most waterbirds are migratory, the impacts of hunting disturbance, i.e. the long-term consequences for a population measured in terms of changes in mortality or recruitment processes, have proved comparatively difficult to demonstrate (Bell & Owen 1990). Many confounding factors other than disturbance affect population dynamics making key variables difficult to isolate (Cayford 1993), and impacts may only become manifest thousands of kilometres away from the point of disturbance (Davidson & Rothwell 1993).

This review uses scientific publications and reports to evaluate current knowledge of the impact of hunting disturbance on waterbirds. We review a hierarchy of demonstrated effects and impacts, ranging from behavioural and distributional responses to consequences for body condition and, ultimately, survival and fecundity (sensu Cole & Knight 1991, Stock et al. 1994). Since it is difficult to demonstrate direct impacts of disturbance on population dynamics, we examine the indirect evidence to support the hypothesis that such impacts occur. Hence, we look for evidence that 1) hunting disturbance causes a significant displacement of birds from potential food resources which would otherwise have been exploited and, 2) waterbird populations are limited by food resources during winter. If populations are primarily limited by factors operating on the breeding grounds, hunting disturbance during autumn and winter is unlikely to exert a major influence on population change. Implicit in these assumptions is the fact that birds face energetic bottlenecks during this period of their life cycle, a feature that can only be measured indirectly by changes in individual body condition. In addition, this review addresses other factors that may impact upon individual survival or fecundity probabilities.

Behavioural effects of hunting disturbance

Escape flight distances

The escape flight distance, i.e. the distance at which a bird or a flock of birds takes flight approached by a disturbance stimulus, is often used as a measure of the effect of disturbance. However, the measure is highly variable, depending on the species, flock size, the type, frequency, predictability and previous experience of stimuli, the site and weather conditions (Madsen 1985, Keller 1989, Madsen et al. 1992a, Keller 1992, Smit & Visser 1993).

An increase in escape flight distance in response to hunting has often been claimed, but the evidence is restricted to few controlled studies where distances have been measured before and during the open season or in shot-over sites versus areas not shot-over. Most work has been carried out on geese (brent geese Branta bernicla: Owens 1977, Madsen 1988; bean geese Anser fabalis and white-fronted geese Anser albifrons: Gerdes & Reepmayer 1983; pink-footed geese Anser brachyrhynchus: Madsen 1985) while information is very restricted on ducks (dabbling ducks: Arctander et al. 1984) and waders (common snipe Gallinago gallinago: Arctander et al. 1984). Generally, escape flight distances approximately doubled after hunting seasons opened, amongst geese increasing from 150–211 metres to 367–500 metres. In most studies, the controlled stimulus eliciting escape flight was human approach, which indirectly shows that hunting activity has a synergistic disturbance effect, enhancing bird responses to other forms of human activity in the absence of hunting.

Activity patterns

Usually, waterbirds are shot at in flight and birds not killed fly away from the hunter or dive. However, shooting may affect birds feeding or resting nearby, including non-target species. Their reactions may range from no reaction to escape flight, with intermediate reactions such as increased alertness and walking/swimming away from the hunter.

The disturbance period, i.e. the time it takes for a flock of birds to resume the activity performed before escaping from a source of disturbance, varies according to species and stimulus, and hunting activity can elicit a stronger response than other activities (greater snow geese Anser caerulescens atlanticus: Bélanger & Bedárd 1989, wigeon Anas penelope and mute swan Cygnus olor: Madsen et al. 1992a). Stationary shooting punts caused an eight-minute disruption to feeding wigeon (no different from a spontaneous flight), whereas mobile shooting punts pursuing the ducks caused 46 minutes of disturbance, significantly longer than that caused by fishing boats (20 minutes). Wigeon disturbed a second time by a mobile punt took 168 minutes to resume feeding (Madsen et al. 1992a). In protected mute swans, the disturbance period elicited by mobile punts was on average 95 minutes.

The ability of waterbirds to compensate for lost foraging time depends on the energetic cost incurred by the disturbance, measured in terms of the increased flight time and the disturbance period, as well as feeding strategy of the species. Generally, the longer feeding time a species requires to fulfill its daily energy demands, the less able it is to compensate. The wigeon mentioned above spent most of the daytime foraging in autumn and winter, and were thus unable to compensate for lost feeding time, even if only disturbed by one mobile punt per day. They lost up to 25% of foraging time on days with repeated disturbance. By comparison, mute swans spent less time foraging, and compensated for the lost feeding time within the same day (Madsen et al. 1992a). Bell et al. (1991) found that wigeon and brent geese foraging in an estuary outside refuges together lost 14% of the daily feeding time due to disturbance. In the refuge part of the estuary, the birds lost 7% of the foraging time. Furthermore, because access to their inter-tidal feeding resource is already restricted by tidal inundation, such birds have little opportunity to compensate by increasing feeding time throughout the daily cycle (Mudge 1989, Fox et al. 1993). Likewise, greater snow geese which spend most of the daytime foraging were unable to compensate for time lost to disturbance, especially by low-flying aircraft and hunting (Bélanger & Bedárd 1989, 1990).

Hunting activity may modify diurnal activity of waterbirds: in British refuge areas, wigeon mostly feed by day, but are night-time foragers on most sites outside the refuges (Owen & Williams 1976). A similar pattern occurs amongst wigeon in the Danish Wadden Sea (Madsen 1988) and black ducks Anas rubripes, mallards Anas platyrhynchos and diving ducks in North America (Conroy et al. 1987, Girard 1941, Thornburg 1973). In Greece, undisturbed wigeon, shoveler Anas clypeata, pintail Anas acuta and coot Fulica atra actively fed by day, when teal Anas crecca roosted. On shooting days, shoveler and pintail completely stopped feeding, while wigeon and coot continued feeding, although at lower intensity. Some wigeon ceased foraging by day altogether, solely foraging at night (Joensen & Madsen 1985).

Distributional effects of hunting disturbance

Local distribution

Local redistribution, i.e. a temporary spatial displacement of waterbirds when hunters are present, not necessarily resulting in an under-use of resources, has been shown for cormorant Phalacrocorax carbo sinensis (Madsen et al. 1992b), mute swan (Madsen et al. 1992a,b), snow geese (Burton & Hudson 1975) brent geese (Denson & Murrell 1962, Kramer et al. 1979, Madsen 1988), wigeon (Joensen & Madsen 1985, Bell et al. 1991), black duck (Conroy et al. 1987), Anatidae (Bossenmaier & Marshall 1958, Thomas 1976, Gomes cited in Hirons & Thomas 1993, Gerhard 1994), eider Somateria mollissima (Salvig et al. 1994), waders (Meltofte 1980, Gomes cited in Hirons & Thomas 1993), lapwing Vanellus vanellus and golden plover Pluvialis apricaria (Meltofte 1981), whooper swan Cygnus cygnus and curlew Numenius arquata (Schneider-Jacoby et al. 1991, Meile 1991).

Several accounts report reductions in waterbird numbers, representing an under-use of local food resources either by comparing ecologically similar areas with intensive shooting to areas with low shooting intensities (Anatidae: Reichholf 1973, Schneider 1986, Frenzel & Schneider 1987, Ziegler 1987, Ziegler & Hanke 1988, Meile 1991, Frikke & Laursen 1994a; wigeon and teal: Madsen 1988) or by comparison of years with different shooting intensities (wigeon: Townsend & O'Connor 1993).

In 18 cases, the number and distribution of birds have been compared before and after reserve creation. In 14 of these, dramatic increases in numbers were reported (Anatidae: Geroudet 1967, Andersson 1977, Jepsen 1983, Owen & Salmon 1984, Frenzel & Schneider 1987, Hirons & Thomas 1993; greylag geese Anser anser: Roos & Lindskog 1976, Hirons & Thomas 1993, Rasmussen 1994, waders: Campredon 1979); in the remaining four cases, no effects were observed (Anatidae: Owen & Salmon 1984).

The above studies suffer from the lack of experimental study of disturbance effects and lack of monitoring of confounding environmental variables (e.g. available food stocks). Experimental reserves were established on two Danish wetlands to test whether hunting activity caused disturbance. It was hypothesised that, if hunting caused disturbance, reserve creation would cause a local redistribution and overall increase in bird numbers, especially quarry species. Following four years of base-line observations, refuge positions were changed each year for three hunting seasons, after which permanent refuge areas were established. Local food stocks (mainly submerged vegetation), weather and water levels, hunting pressure and overall population levels were monitored throughout (Madsen et al.1992a,b,c,d, 1995, Madsen 1995). In both areas, waterbird numbers increased following reserve creation and the highest bird concentrations occurred in the shooting-free zones. Quarry species responded most strongly (by three to forty fold increases compared to base-line years), but some protected species (especially lapwing and golden plover) also increased. None of the local increases could be explained by changes in food stocks, weather or water level conditions or human use of the areas inside and adjacent to the reserves; only in few species could the increases be explained by changes in overall flyway population levels (Madsen et al. 1995).

The consequence of long escape flight distances or increased wariness induced by hunting disturbance as described above, is a restriction of local site use (Owen 1972, Owens 1977, Madsen 1985, Smit & Visser 1993). For example, pink-footed geese staging at a refuge in Denmark during autumn were unable to effectively exploit approximately one third of the refuge grassland area because hunting took place along the borders (Madsen 1980). In some cases, the birds may be able to compensate and use the unexploited resource at times of the 24hour cycle when human activity ceases or at other times of the season (Owens 1977, Gerdes & Reepmayer 1983, Madsen 1988). However, in other cases this is not possible, either because the resource has dropped in quality or has disappeared at the time of closure of shooting (Madsen 1985, 1988).

Regional distribution

There have been some attempts to look at the wider-scale effects of hunting disturbance on waterbird distribution, comparing numbers and distribution of birds in relation to regional/national patterns of hunting practises (Tamisier & Saint-Gerand 1981) or refuge distribution (Jepsen 1983, Bell et al. 1991). The results of these studies can, however, be disputed either because they did not take into account the available habitat resources, or because the scale of the habitat areas were too crudely determined to address the problem effectively.

In Britain, Owen & Salmon (1984) showed that during a 23-year period, numbers of dabbling ducks increased significantly in refuge areas but not in shot-over areas. Wigeon numbers greatly increased on reserves and decreased outside. Outside the open season this relationship was not apparent, suggesting that it was primarily disturbance and not improved habitat quality on the reserves that was the cause. The study suggested that the observed developments were due to redistributions. However, it is unknown to what extent improved survival and body condition (which may affect breeding output) of birds using the protected areas contributed to the increase in numbers. In Denmark, the autumn staging population of wigeon was almost doubled following the creation of two reserves; the increase happened within 3–4 years, excluding a general population increase being the main cause but suggesting a redistribution within the northwest European fly way (Madsen 1995).

In geese, progressive protection of feeding areas and ultimately a full shooting ban was followed by a gradual increase in numbers and expansion in range of Anser geese in Belgium and the Lower Rhine area in Germany (Meire & Kuijken 1991, Mooij 1991), the rate of increase exceeding the general rate of increase in the overall northwest European wintering population levels. In Denmark, autumn staging populations of pink-footed geese and greylag geese are concentrated on sites with low shooting intensities; outside the shooting season both species have a much wider distribution (Madsen 1982, 1986). Similarly, despite the fact that geese are protected in Italy, they are concentrated in few sites which have some protection from hunting (Perco 1991). Shooting of pinkfooted geese in the two major autumn staging sites in Denmark can result in an exodus of almost the entire population to the Netherlands within one day (Madsen & Jepsen 1992, Jakobsen 1993). Similarly, most of the Norwegian greylag geese emigrate southwards to staging grounds in Denmark and the Netherlands prior to or during the first days of the open season, and the early massdeparture is ascribed to the disturbance associated with the hunting (Lorentsen 1988, Follestad 1994).

In golden plovers and curlews staging in Denmark, Meltofte (1981) described a differential distribution in spring compared to autumn; in autumn, proportionally fewer birds occurred in areas with high shooting intensity compared to areas with no or moderate shooting intensity. In other species of waders, there was no clear relationship.


The number of birds present in an area is obviously determined by the numbers immigrating and emigrating at any one time. Both these parameters are affected by intrinsic (e.g the food resource, predation risk) and extrinsic factors (e.g. the quality of known sites further along the flyway), but together they produce an observed rate of turnover amongst birds using a site. If we assume stable population size and regular duration of migration periods between years, the most important parameter affecting the number of birds using a site is the average length of stay of individuals at that site (Thompson 1993). Whilst assessment of the mean length of stay is difficult (e.g. requiring intensive capture/recapture programmes), daily counts provide phenology data which enable calculation of total number of bird days at a site. This provides an indirect measure of the effects of disturbance on mean length of stay.

Three papers document prolonged staging periods following refuge creation, based upon phenology curves and the numbers of bird days (Anatidae: Geroudet 1967, dabbling ducks and waders: Madsen et al. 1992c,d). In the Danish experimental reserves, some spring- and autumnstaging migrants have started to overwinter. While the numbers of birds grew in the two study sites, there were no concurrent reductions in neighbouring staging areas. This suggests that, rather than ‘draining’ birds from adjacent areas, increases were due to the cumulative effect of increasing numbers of birds prolonging their stay, hence birds were ‘captured’ by the refuges and ‘lost’ from areas farther down the fly way (Madsen et al; 1995).

While increases in turnover can be demonstrated as a result of hunting disturbance, the scale of this effect is more difficult to determine. How many birds are lost to a site as a result of disturbance relative to the number actually killed? By using a multifactorial simulation model, Frederick et al. (1987) attempted to describe lesser snow goose Anser caerulescens caerulescens use of refuge areas, based on many parameters using data gathered from real-life situations. Data input to the model included food availability, numbers of geese, feeding behaviour, energetics and migration patterns, as well as details of human hunting activities, although some of these parameters were not derived empirically. The results of the model showed that increasing hunting activity not only increased the kill, but induced greater numbers of geese to move out of the refuges to other sites on the basis of reduced feeding efficiency caused by disruption from the hunting activity. The main conclusion from the work was that the direct effect of hunting mortality was far less important in reducing numbers within a managed area than the associated disturbance which greatly enhanced emigration. Similarly, field investigations of the effects of hunting on mallard in Germany showed that out of an initial 650 ducks, 256 were shot during one day of intensive shooting, but only 100 birds remained in the lake system, implying that 300 ducks emigrated as a result of hunting disturbance (Jettka 1986). In one of the Danish experimental reserves, the annual hunting kill of wigeon was ca 3,000, compared to an increase in peak counts of more than 21,000 after creation of refuge areas (Madsen et al. 1992a, 1995).

Species-specific sensitivity to disturbance

Outside the breeding season most waterbird species exhibit ecological characteristics which are reflected in their distribution, food choice and behaviour, and which have implications for the sensitivity of each species to disturbance. It is therefore important to be able to determine the differential vulnerability to disturbance of the different species.

Bell & Owen (1990, based on Mayhew 1988) used the proportion of the 24 hours a species has to feed to meet its energetic demands as a prime indicator of vulnerability, which seems plausible as birds which have to feed much, e.g. wigeon, have less time to compensate for disturbance. Species with distributions restricted to the intertidal zone were also classified as vulnerable, because this is the zone where hunting is most prevalent and where tidal inundation of feeding areas may further restrict access to feeding opportunity.

Madsen & Pihl (1993) devised a multifactorial classification of sensitivity of wildfowl and coot to disturbance, based on their potential risk of being affected by disturbance. From this analysis the following species were regarded as potentially most sensitive to disturbance: whooper swans and Bewick's swans Cygnus bewickii, geese (all species), dabbling ducks (all species except mallard), pochard Aythya ferina, tufted duck Aythya fuligula and scaup Aythya marila. Generally, these species stay close to the coast or inland, and are concentrated, mostly in relatively large flocks. Most are herbivorous and are popular quarry species, except whooper and Bewick's swans which are protected and often feed on arable land in isolated flocks, hence making them less susceptible to hunting disturbance. Larger diving ducks and sawbills were regarded as being the least sensitive.

Generally, quarry species are the most sensitive to hunting disturbance (Madsen et al. 1995). However, as protected species often mix on the roost or feeding grounds with quarry species, these also suffer disturbance (Madsen 1988, Meile 1991, Madsen et al. 1992a,b, 1995, Schneider-Jacoby et al. 1993).

The scale of the problem

Hunting of waterbirds is a popular recreational activity; in Europe and the Mediterranean basin, 10–15 million ducks and geese are shot annually by approximately 3.2 million hunters (Scott 1982). However, shooting is only one of many human activities which may cause disturbance to waterbirds and it is relevant to judge the importance of other sources as well. Furthermore, whilst other activities operating in isolation may not be as disturbing as hunting, the effects of multiple disturbance from different sources can have a synergistic or cumulative effect on birds. All sources of disturbance have the same net effect: the presence of human activity denies access to resources (be it loafing, sleeping, feeding or other areas used by waterbirds) and this may reduce exploitation rates below those which would be attained in the absence of such activity. In this respect, all disturbance activities can be considered to equate to net habitat loss.

Few field studies have quantified the intensities, distribution, phenology, diurnal patterns and hence the potential disturbance effects of the various human activities operating in areas used by waterbirds. In two Danish coastal wetlands of international importance for waterbirds, Madsen et al. (1992a,b) found that hunting and fishing were the most frequent human activities during the open season, whereas leisure activities, such as boating, windsurfing and beach walking, were primarily confined to the summer period. In autumn, fishing gradually stopped, while hunting continued whilst quarry waterbird species were present. Hunting took place in the core feeding areas of the waterbirds, i.e., in shallow water zones with submerged vegetation or in adjacent marshes, while fishing was mainly restricted to deeper water, outside core waterbird feeding areas. In intertidal areas, beach activities, including bait digging, are more frequent and year-round (e.g. Kirby et al. 1993, Laursen 1982, Salvig et al. 1994). However, hunting activity was under-represented in those studies, because most hunting takes place at dawn and dusk (e.g. Frikke & Laursen 1994a,b).

In the non-refuge part of the Exe Estuary in southern England, a variety of human activities occurred throughout the winter season. Free-roaming dogs, bait diggers, windsurfers and walkers were the most frequent potential disturbance sources; however, in terms of the frequency and duration by which brent geese and wigeon were dis- turbed, hunters represented quantitatively the most important source of disturbance (Bell et al. 1991).

In the Greek Amvrakikos wetlands, hunting was the most frequent winter activity, followed by boat fishing (Joensen & Madsen 1985). Most hunting took place from the shore during dawn and dusk, but motorised punts were also used.

At Lake Constance (Germany/Switzerland) waterbird hunting is only one of several human activities causing disturbance to wintering waterbirds, of which canoeing, boating, wind-surfing and walking on the lake shores, together with hunting, are the most disturbing (Schneider 1986, Frenzel & Schneider 1987, Bauer et al. 1992, Schneider-Jacoby et al. 1993).

The available information is too patchy to allow an extrapolation of the above studies to a wider European scale. There is a great need for more information about the distribution of human activities and their spatial and temporal overlap with roosting and feeding areas of waterbirds in wetlands. A comparison of the disturbance effects of hunting versus other activities can only be achieved effectively against such a background. Judging from the few examples available, hunting activity seems to be more disruptive in terms of interruption of feeding activity than other studied surface activities, comparable only with the effects of low-flying aircraft (Bélanger & Bedárd 1990, Bell et al. 1991, Madsen et al. 1992a). The increase in escape flight distances of geese and dabbling ducks during the open season indicates that hunting activity is the critical source of disturbance affecting the strength of that response, which in turn implies that in the absence of hunting, escape flight distances would be shorter.

Impacts on body condition, survival and reproduction

Support for the hypothesis that waterbird populations are limited by factors away from the breeding areas can be derived from two sources; firstly, from evidence of population limitation during winter and secondly, from identification of particular energetic bottlenecks in the life cycle of the animals which offer clues to the likely role of key factors affecting survival and reproduction.

Migration and regulation of populations

The mobility of birds facilitates their exploitation of different habitats, including some unsuitable for reproduction. The relative availability of resources remote from a populations' breeding area may therefore affect overall breeding success and survival. Waterbirds exhibit a range of migratory strategies adapted to different circumstances (e.g. Alerstam & Högstedt 1982).

Several studies suggest that wintering habitat limits wader and duck populations. Loss of wintering habitat has been shown to reduce the numbers of overwintering waterbirds (e.g. Teesmouth in the UK, Evans 1980), and reductions in wintering dunlin Calidris alpina numbers in the UK have coincided with loss of mudflat habitat due to Spartina encroachment (Goss-Custard & Moser 1988). Baltic-breeding eider and tufted duck numbers varied with changes in winter food supply (Pehrsson 1978, 1984), and studies suggest that mallard overwinter mortality determines breeding population size in the United States (Anderson & Burnham 1976, Bergan & Smith 1993, although Reinecke et al. 1987 and Blohm et al. 1987 do not support this suggestion) and in the UK (Hill 1984). Cavity-nesting goldeneyes Bucephala clangula are primarily limited by availability of nest sites, since provision of artificial nestboxes initially increased breeding numbers. However, when supplied with an over-abundance of artificial nest sites, above a certain threshold, the population varied in a way unattributable to any factor related to breeding population or habitat (Fredga & Dow 1984). Finnish studies of dabbling duck assemblages show that most species are not in competitive equilibrium, since densities are well below potential carrying capacities of the environment in most years (Pöysä 1984).

Factors influencing bird numbers using an area may vary in time and space, which confounds attempts to understand such processes at a single point in time. For example, the grey plover Pluvialis squatarola increase on UK estuaries was attributed to factors outside of wintering areas, where there was a sequential expansion in numbers using different wintering sites. Preferred habitats were already “filled” prior to the increase and showed no change during the period of increase (Moser 1988). Similarly, protection from hunting of Greenland white-fronted geese Anser albifrons flavirostris at Wexford in southeast Ireland resulted in a rapid increase in wintering numbers, which has since stabilised at a higher level, perhaps restricted by food availability (Fox et al. 1994). Other populations, such as Baltic-breeding long-tailed ducks Clangula hyemalis (Pehrsson 1984) show no relationship with winter food supply.

Bell & Owen (1990) extensively reviewed the literature and concluded that there is supportive evidence for the view that “waterfowl populations are limited by the carrying capacity of their wintering and staging areas rather than by resources on the breeding areas” and Meltofte (1993) concluded that there was very little evidence that wader population regulation occurred on breeding areas. Exceptions, however, may be those species of waders and wildfowl that predominantly use artificial habitats, or colonial nesters, like the eider.

Seasonal changes in body mass

Whether or not waterbirds are limited by non-breeding habitats, they may become more susceptible to the effects of disturbance at certain periods in the annual life cycle. Most waterbird species undergo regular patterns of body mass increase and decline throughout the course of their annual cycle, reflecting the accumulation and use of body stores and reserves (sensu van der Meer & Piersma 1994) in response to seasonal changes in the present and future requirements of the individual (e.g. mallard: Owen & Cook 1977, dunlin: Pienkowski et al. 1979, teal: Fox et al. 1992, brent goose: Ebbinge 1989, barnacle goose Branta leucopsis: Owen et al. 1992, knot Calidris canutus: Piersma 1994). From these patterns, it is possible to determine periods of greatest potential stress (i.e. when reserves are being depleted or stores need to be accumulated rapidly) and hence pin-point periods when enhanced energetic expenditure (through flight from disturbance) or reduced availability (through denial of access to food resource) may prove critical.

Periods of low body nutrient levels

Waterbirds generally exhibit lowest body mass in late winter and in summer immediately after hatching of young (e.g. Owen 1980), although the latter need not concern the discussion here. Most species of waterbirds are able to maintain a positive energy balance (and hence are able to lay down body stores) until the end of December, taking advantage of the food resource along the flyway to ultimate wintering areas. However, after December, most species show a decline in body weight which in at least two studies has been shown to be the result of a lack of sufficient food availability and was hence a consequence of birds depleting a stored resource accumulated earlier in the season (Owen et al. 1992, Kestenholz 1994). Furthermore, all the descriptive wader studies argue that the mid-winter peak in body mass reflects an accumulation of nutrient stores to overcome subsequent food shortage after this time of the year (Dick & Pienkowski 1979, Davidson 1981, Johnson 1985). The late winter period is particularly critical for waterbirds, since this marks the time when body mass has been depleted during a period of net energy loss, but which may be further exacerbated by factors such as unusually severe weather conditions which has been shown to significantly increase the recovery rates of ringed Anatidae and waders (Baillie et al. 1986, Ridgill & Fox 1990). Since body weights may reach very low levels at this time, and maximal foraging efforts fail to maintain condition during these periods, further reductions in foraging efficiency and/or enhanced energetic costs caused by disturbance are likely to further stress individuals at such times. Body mass may then hit its lowest level before the upturn in spring food availability enables recouping of lost stores (e.g. Owen et al. 1992).

An alternative explanation is that mid-winter weight loss is adaptive, a hypothesis supported by studies of the weight dynamics of captive birds fed ad libitum (Reinecke et al. 1982, Perry et al. 1987). However, whatever the cause, the reduction in body stores still inhibits the ability of the individual to meet enhanced energetic demands, as in the case of severe weather or elevated levels of disturbance.

These periods of lowest nutrient reserves may be periods of sensitivity for some species, and whilst mass starvation events are rare, many individuals approach critical levels of reserve depletion in the absence of adequate food supplies. In a very few cases, dramatic mass starvation events have been described for some diving ducks species experiencing severe weather very late in the winter, the result of a combination of food shortage and extra energy demands (e.g. eiders: Wrånes 1988; pochard and tufted ducks: Suter & van Eerden 1992; waders: Piersma 1994). During severe weather in March 1986, more than 20,000 birds starved in two studied areas of Switzerland and The Netherlands as a result of unusually cold weather encountered during the return spring migration when food stocks were low (Suter & van Eerden 1992). Late winter hunting disturbance in wintering areas (German and Swiss lakes) may contribute to exhaustion because birds are denied access to foraging areas and/or because of increased energy expenditure (Meile 1991). Similarly, there are documented cases of widespread starvation of waders, also most frequently as a result of the onset of hard weather late in the winter period when stores are at their lowest (e.g. Davidson & Evans 1982).

Accumulation of stores

Waterbirds also accumulate body stores to meet anticipated future needs, as for example to obtain enough fuel stores to fly successfully between staging areas of suitable habitat over terrain which may be hostile in terms of high predation risk or poor feeding opportunity. Waterbirds must also store nutrients in spring in preparation for investment in reproductive effort, especially when many long-distance migratory waterbird populations breed in areas where food may be extremely scarce prior to egglaying (as is the case for most arctic and northern breeding waders and Anatidae). Hence the opportunity for periods of rapid nutrient accumulation (at least in undisturbed situations) also has critical consequences for the fitness of the individual.

Hunting disturbance may affect the acquisition of nutrient stores in two major ways:

  • Denial of access to best feeding resources: Birds subject to hunting pressure may be displaced from areas of high-est feeding profitability as a result of the associated disturbance, as has been shown for the wigeon, which respond by movement into improved feeding opportunities after the closure of the season (Mayhew & Houston 1989) or in the absence of hunting disturbance (Madsen 1988). Unless birds can compensate for this loss of feeding opportunity, the reduction in food intake rate below the level in the absence of hunting disturbance must have fitness consequences.

  • Loss of feeding opportunity and the extra energetic costs of disturbance: Owens (1977) showed that disturbance to brent geese caused them to fly 1.7% more and feed 3.5% less than in the absence of disruption. These differences may appear small, and may easily be recouped by faster intake rates, sacrificing trivial activity or extending the feeding period (such as feeding at night). However, flying is energetically costly (approximately 12–15 times basal metabolic rate compared with 1.4 times for resting in dabbling ducks, Wooley & Owen 1977) and in situations where tide, daylight, predation risk or other factors limit access to food resources, the effects of these restrictions may be considerable. Indeed, White-Robinson (1982) calculated that disturbance to brent geese increased their net daily energy expenditure by 31%, similar to the results of Bélanger & Bedárd (1990) for greater snow geese. Several other authors have also used energy budgets to assess the impacts of disturbance (see Keller 1995).

Evidence for the ultimate impact of these effects on the individual are lacking. In a study of the mallard, Watmough (1983) showed that recreational disturbance increased the daytime energy expenditure by 20%, but since the ducks spent most of the day loafing, this was unlikely to have any overall effect. Indeed, the author argued that the birds would be unlikely to stay within the area if they failed to attain the necessary energy balance at the site. Birds will show a range of responses to compensate for lack of feeding opportunity and the range of responses makes the study of the effects of disturbance difficult to interpret. Waterbirds will often feed at night when disturbance is much reduced, to compensate for feeding in a situation where predation risk may be high during daylight. Owen & Williams (1976), for example, showed that wigeon fed by day on sites which were undisturbed, but in non-refuge areas the same species remained on inaccessible undisturbed refuges and fed only at night. Despite this, increasing the need to feed under cover of darkness may enhance predation risk, so that remaining in an area subject to hunting and maintaining an energy balance may carry a survival cost to the individual. Unfortunately, relatively few studies have adequately addressed the effects of disturbance on a 24-hour basis.

Birds may also increase their feeding rates if the time they are able to spend feeding is reduced in some way. Oystercatchers Haematopus ostralegus, for example, can modify their intake rates by reducing search and handling time to accommodate up to 33% reductions in feeding time (Swennen et al. 1989), although these results were obtained from caged birds and may not be directly applicable to natural situations because this experiment obviously did not consider the role of predation risk on the part of the study animals.

Stores for migration

Flight between wintering and summering areas requires fuel which is usually stored in the form of body fat in waterbirds, accumulated by feeding on appropriate high energy foods and stored within the body in deposits readily available for use en route during migration (e.g. Davidson & Wilson 1992, Evans 1992, Piersma 1994). Birds may use a series of staging areas en route to ultimate breeding areas, and migration strategies of some populations have evolved specifically to exploit such a chain of stopping-off sites for ‘refuelling’. Loss of such sites along a migration corridor may then have severe implications for these species (e.g. Evans & Davidson 1990, Evans et al. 1991).

Although there have been few direct studies relating fat storage to migration survival, evidence from studies of birds embarking upon migration show that those in poor body condition are less likely to survive than those in better condition (barnacle geese: Owen & Black 1989, knot: Davidson & Wilson in press). However, there is considerable circumstantial evidence that losses on migration amongst quarry species correlate with population size, and evidence from several studies of non-passerine birds suggests that migration mortality is an important factor in these populations (Owen & Black 1990).

Impacts on reproduction

Most waterbird species lay eggs which are large and energy-rich relative to body size and have relatively long incubation periods (Alisauskas & Ankney 1992, Krapu & Reinecke 1992). Both traits are considered to have evolved to enable the precocial young to hatch in an advanced state of development where they can rapidly locate their own food and avoid predation without high levels of investment from the parents. Often the female incubates the clutch alone, so as well as obtaining the nutrient stores for egg production, she must store nutrients to sustain her through a prolonged incubation period as well. These life history traits impose severe demands on the females of long-distance migratory waterbirds during the prelude to breeding which may represent bottlenecks in the annual cycle of waterbird populations (Fox in press).

Studies have shown that larger forms such as swans and geese may accumulate nutrients stores throughout the winter (in particular in the form of fat and protein stores) in preparation for migration and ultimately for breeding (Alisauskas & Ankney 1992. Krapu & Reinecke 1992). However, many smaller forms depend upon a much more rapid accumulation of stores in spring (Ebbinge 1989. Piersma 1994), making them more vulnerable during this period.

Madsen (1995) demonstrated the impacts on subsequent reproductive output in pink-footed geese subjected to disturbance during the spring migration period. These birds failed to accumulate nutrient stores as well as those not disturbed using the same area and subsequently produced less young. Although these impacts were demonstrated on spring staging areas, it is likely that mid-winter depletion of reserves, or the failure to attain critical spring levels of nutrient stores prior to migration to breeding areas may affect reproductive output in waterbird species depending on endogenous stores for successful breeding attempts.

Many dabbling duck species derive much of their protein stores for reproduction from the breeding areas (Krapu & Reinecke 1992). because protein sources are usually abundant in ultimate nesting areas. The same may be true of the Aythya and other small diving duck species, but in long-lived species, such as the eider, protein stores are accumulated prior to nesting and transported to the breeding areas for investment in egg formation just as in geese and swans (Krapu & Reinecke 1992). However, most studied duck species accumulate fat stores in areas far from their breeding grounds for investment in reproduction, such that any factors reducing their ability to acquire stores may also affect subsequent nesting success. Unfortunately, there have been no studies of the effects of any form of disturbance on the accumulation of adequate fat stores of ducks and its consequent influence on fitness (in terms of reproductive output or survival). This remains a major research priority for the future.

Such investigations as have taken place also support the hypothesis that shorebirds carry protein stores for reproduction in their flight musculature to the breeding areas (e.g. Davidson & Evans 1988. Piersma 1994).

In conclusion, hunting disturbance is likely to have its greatest impact on survival during the late winter period when body reserves reach their lowest point. Disturbance is most likely to have its greatest impact on breeding output during the subsequent recovery stage, when waterbirds exploit increasingly nutritious feeding resources to restore condition and accumulate stores in preparation for long-distance migration and ultimate breeding.

Break-up of pair-bonds and social units

Some species of waterbirds show complex social structure, where association with a mate (e.g. gadwall Anas streperer: Paulus 1983) or extended family groups (especially amongst long-lived species, e.g. geese: Boyd 1953, Warren 1994) enhances social status and hence access to the best feeding opportunity (Hepp & Hair 1984). Early pairing in mallard confers adaptive advantages on both partners, giving the female protection during pre-breeding nutrient acquisition and ensuring that the male can guard his mate during the prelude to breeding (Rohwer & Anderson 1988). Since the nutritional status of female mallard is known to affect her reproductive success (Krapu 1981). the presence of an associated male has direct consequences for her reproductive output. Similarly, paired gadwall displaced lone birds, giving females access to the best feeding opportunities during the late winter period, well before departure for ultimate breeding areas (Paulus 1983, 1984).

Duck pair-bonds tend to be of relatively short duration, although there is accumulating evidence for some between-year mate fidelity (e.g. mallard: Mjelstad & Sætersdal 1990, gadwall: Köhler et al. 1995 and wigeon: C. Mitchell pers. comm.). Geese and swans tend to pair for life, and annual divorce rates in undisturbed situations are low (e.g. 2% or less in protected barnacle geese. Owen et al. 1988. Black & Owen 1995). There is a cost to separation from an established mate in studied populations, since a bird losing its mate had an 8% probability of successful breeding in the year following the loss, compared with 21% amongst geese remaining with their partners (Owen et al. 1988).

Radio-tracking studies of Canada geese Branta canadensis showed that hunting reduced cohesion amongst family units and thereby increased mortality (Bartelt 1987). Snow geese also showed greater rates of family disintegration as a result of hunting disturbance which in turn reduced survival of young (Prevn et l & MacInnes 1980). Amongst the non-hunted population of barnacle geese, ‘orphaned’ goslings which had lost parents and siblings suffered harassment from other flock members, were denied access to good feeding opportunity and showed reduced survival compared with young remaining in family units (Black et al. 1992).

These studies suggest that any factor affecting the pair bond or other social groupings may affect the survival or reproductive potential of the members, especially if this disruption continues into spring. Since some studies have shown that disturbance can make it more difficult for pairs or families to remain together, this factor may have an important role to play in reducing survival and reproduction in hunted populations. Indeed, Owen et al. (1988) suggested that disturbance, especially hunting disturbance in autumn, was responsible to a large extent for the lack of persistent pair and family cohesion in some North American goose populations (e.g. Jones & Jones 1966, Craven & Rusch 1983).


The review of case studies investigating the effects of hunting disturbance outlined above has shown that the presence of hunters in the vicinity of waterbirds modifies the distribution and abundance of those birds in space (e.g. movement away from heavily hunted feeding areas) and time (e.g. faster turnover at a staging site). The degree to which this modification occurs also varies in time and space, modified by the difference in behavioural trade-offs birds may make between feeding opportunity and predation risk (see review by Lima & Dill 1990). These factors also vary in time and space, as for example during severe winter weather (an example of an unpredictable factor) or during the pre-breeding acquisition of nutrients required for reproduction (a more regular and predictable feature of the life history). Nevertheless, from the review of the available material, the conclusion must be that the net effect of hunting disturbance is to reduce the potential of a site to support numbers of waterbirds to a level below that which would be achieved in the absence of hunting disturbance. Hence hunting disturbance (as is the case with any other form of disruption to natural patterns of waterbird exploitation of a site) reduces the capacity of a site below that which is potentially available.

This review has shown the considerable bias existing in the current literature with regard to coverage of the subject of hunting disturbance (Table 1). Much emphasis has been placed upon the study of quarry geese and dabbling ducks, to the neglect of protected species, waders and diving ducks. The focus has also been placed on studies of the local effects of hunting disturbance, which are relatively easy to demonstrate. However, we still understand little about the direct impact of such disturbance at the population level.

The review does, however, provide evidence to support the hypothesis that many waterbird populations are limited by conditions prevailing in winter. Because we can demonstrate local and even regional effects from changes in hunting disturbance, we conclude there is reason for concern that hunting disturbance has an impact at the population level.

Table 1.

Summary table of the number of literature references to demonstrated effects and impacts of hunting disturbance on waterbirds.

It can be argued that hunting disturbance cannot be a serious factor impacting on population levels of waterbirds in the Western Palearctic, since many species have recovered in numbers in recent years (e.g. Rose & Scott 1994). The increases, at least in geese, however, have been attributed mainly to improved protection from hunting (Ebbinge 1991). It is known for many species that the overall kill has declined in recent years (Ebbinge 1991, Noer et al. 1995), but there has been no assessment of the apparently secondary impact of the reduction in disturbance associated with this trend.

We still know little about the potential magnitude of the impact of hunting disturbance. Unless we are able to structure complex experimental work, there appears little scope for empirical quantification of its scale. The example of Norwegian-staging pink-footed geese (Madsen 1995) remains one of the few such studies able to demonstrate that any form of disturbance has a direct impact on an individual's reproductive success. However, it still remains to be resolved as to how this impact is expressed at the overall population level. Furthermore, this is a highly specific situation; a small goose population with few stopover sites. Therefore, it is unlikely that this approach can be used as a model for looking at commoner species with wider distributions and more complex interactions.

If we are ever to progress in this field, it is vital that modelling be employed to assess the potential scale of impacts of hunting disturbance, backed by good empirical data to input as model parameters. For instance, what will be the effect of large-scale implementation of reserve networks (such as those described from Denmark) on the overall wintering distribution of birds along the flyway? Using existing data from the experimental reserves, modelling of the effects of changes in turnover is already a possibility. Furthermore, mate loss may appear trivial in the population dynamics of an organism, but data exists on the costs (in terms of reproductive output) of mate loss and repairing. It is therefore feasible to explore the consequences of this at the population level, based on simulated and observed levels of occurrence, to assess its impact.

From a management point of view, the wealth of empirical data on the effects of hunting disturbance have proved valuable for site management (e.g. establishing buffer zone widths from escape flight distances). However, with increasing emphasis on international conservation and management planning organised at the population fly way level, international collaboration under legislation and conventions require a more strategic, coordinated approach to management of hunting disturbance. The challenge for the future is to develop population models which identify specific bottlenecks in the annual life cycle of waterbirds. Hunting disturbance can then be set in such a framework, establishing its relative influence and geographical distribution in order to develop international management policies.


the review is the synthesis of a reference document prepared for the Commission of the European Communities by the The Danish National Environmental Research Institute and the International Waterfowl and Wetlands Research Bureau (IWRB) on the impacts of hunting disturbance on waterbird population dynamics and etho-ecology. Henning Noer and Mike Moser are thanked for collaboration on the report and for giving advice on the manuscript. Jim Nichols, Nick Davidson, an anonymous referee and Hannu Pöysä improved an earlier draft of the manuscript.



Alisauskas, R.T. & Ankney, C.D. 1992: The cost of egg-laying and its relationship to nutrient reserves in waterfowl. - In: Batt, B.D.J., Afton, A.D., Anderson, M.G., Ankney, C.D., Johnson, D.H., Kadlec, J.A. & Krapu. G.L. (eds.); Ecology and Management of Breeding Waterfowl. University of Minnesota Press, Minneapolis, pp. 30–61. Google Scholar


Alerstam, T. & Högstedt, G. 1982: Bird migration and reproduction in relation to habitats for survival and breeding. - Ornis Scandinavica 13: 25–37. Google Scholar


Anderson, D.R. & Burnham, K.P. 1976: Population ecology of the Mallard. VI The effect of exploitation on survival. - US Fish & Wildlife Service Resource Publication 128. Google Scholar


Andersson, Å. 1977: Andjakten i Hullsjön. - Report, Skogshögskolan, Uppsala, 30 pp. (In Swedish). Google Scholar


Arctander, P., Fjeldså, J. & Jensen, A. 1984: Sejlads med luftpudebåde, jagt og andre forstyrrelser af fugle og sæler ved Saltholm maj-september 1984. - Miljøministeriet, Fredningsstyrelsen, Denmark, 103 pp. (In Danish). Google Scholar


Baillie, S.R., Clark, N.A. & Ogilvie, M.A. 1986: Cold weather movements of waterfowl and waders: an analysis of ringing recoveries. - Report. British Trust for Ornithology, Tring, 56 pp. Google Scholar


Bartelt, G.A. 1987: Effects of disturbance and hunting on the behaviour of Canada Goose family groups in Wisconsin. - Journal of Wildlife Management 51: 517–522. Google Scholar


Bauer, H.-G., Stark, H. & Frenzei, P. 1992: Der Einfluss von Störungen auf überwinternde Wasservögel am westlichen Bodensee. - Ornithologische Beobachter 89: 93–110. (In German). Google Scholar


Bélanger, L. & Bédard, J. 1989: Responses of Staging Greater Snow Geese to human disturbance. - Journal of Wildlife Management 53: 713–719. Google Scholar


Bélanger, L. & Bédard, J. 1990: Energetic cost of man-induced disturbance to staging Greater Snow Geese. - Journal of Wildlife Management 54: 36–41. Google Scholar


Bell, D.V., Fox, P., Owen, M. & Bell, M.C. 1991: Field studies of the relationship between wildfowl and disturbance. - In: Bell, D.V. & Fox, P. (eds.); Shooting disturbance: an assessment of its impact and effects on overwintering waterfowl populations and their distribution in the United Kingdom. Unpublished report, WWT/BASC, Slimbridge/Rossett, UK, pp. 153–198. Google Scholar


Bell, D.V. & Owen, M. 1990: Shooting disturbance - a review. - In: Matthews, G.V.T. (ed.); Managing waterfowl populations. IWRB Special Publication No. 12. Slimbridge. UK, pp. 159–171. Google Scholar


Bergan, J.F. & Smith, L.M. 1993: Survival rates of female mallards wintering in the playa lakes region. - Journal of Wildlife Management 57: 570–577. Google Scholar


Black, J.M., Carbone, C., Owen, M. & Wells, R. 1992: Foraging dynamics in goose flocks: the cost of living on the edge. - Animal Behaviour 44: 41–50. Google Scholar


Black, J. & Owen, M. 1995: Reproductive performance and assortative pairing in relation to age in Barnacle Geese. - Journal of Animal Ecology 64: 234–244. Google Scholar


Blohm, R.J., Reynolds, R.E., Bladen, J.P., Nichols, J.D., Hines, J.E., Pollock, K.H. & Eberhardt, R.T. 1987: Mallard mortality rates on key breeding and wintering areas. - Transactions North American Wildlife and Natural Resources Conference 52: 246–257. Google Scholar


Bossenmaier, E.F. & Marshall, W.H. 1958: Field-feeding by waterfowl in southwestern Manitoba. - Wildlife Monograph 1, 32 pp. Google Scholar


Boyd, H. 1953: On encounters between wild White-fronted Geese in winter flocks. - Behaviour 5: 85–129. Google Scholar


Burton, R.A. & Hudson, R.J. 1975: Activity budgets of lesser snow geese wintering on the Fraser River Estuary, British Columbia. - Wildfowl 29: 111–117. Google Scholar


Campredon P. 1979: Quelques donnees concernant 1 hivernage des limicoles sur le Bassin d Arcachon (Gironde). - L Oiseau 49: 113– 131. (In French). Google Scholar


Cayford, J. 1993: Wader disturbance: A theoretical overview. - Wader Study Group Bulletin 68: 3–5. Google Scholar


Craven, S.R. & Rusch, D.H. 1983: Winter distribution and affinities of Canada Geese marked in Hudson and James Bays. - Journal of Wildlife Management 47: 307–319. Google Scholar


Cole, D.N. & Knight, R.L. 1991: Wildlife preservation and recreational use: Conflicting goals of wildland management. - Transactions North American Wildlife and Natural Resources Conference 56: 233–237. Google Scholar


Conroy, M.J., Costanzo, G.R. & Stotts, D.B. 1987: Winter movements of American black ducks in relation to natural and impounded wetlands in New Jersey. - In: Whitman, W.R. & Meredith, W.H. (eds.); Waterfowl and wetlands symposium. Delaware Department of Natural Resources and Environment Control, Dover, Delaware, pp. 31–45. Google Scholar


Davidson, N.C. 1981: Survival of shorebirds (Charadrii) during severe weather: the role of nutrient reserves. - In: Jones, N.V. & Wolff, W.J. (eds.); Feeding and survival strategies of estuarine organisms. Plenum Press, New York, pp. 231–249. Google Scholar


Davidson, N.C. & Evans, P.R. 1982: Mortality of redshanks and oystercatchers from starvation during severe weather. - Bird Study 29: 183–188. Google Scholar


Davidson, N.C. & Evans, P.R. 1988: Prebreeding accumulation of fat and muscle protein by arctic-breeding shorebirds. - Proceedings of XIX International Congress, Ottawa: 342–352. Google Scholar


Davidson, N.C. & Rothwell, P.I. 1993: Human disturbance to waterfowl on estuaries: conservation and coastal management implications of current knowledge. - Wader Study Group Bulletin 68: 97–105. Google Scholar


Davidson, N.C. & Wilson, J.R. 1992: The migration system of European-wintering Knots Calidris canutus islandica. - Wader Study Group Bulletin 64: Supplement: 39–51. Google Scholar


Davidson, N.C. & Wilson, J.W. in press: Does nutritional stress in spring influence the breeding ground survival of shorebirds? - Journal of Avian Biology. Google Scholar


Denson, E.P. Jr. & Murrell, S.L. 1962: Black brant populations of Humboldt Bay, California, - Journal of Wildlife Management 26: 257–262. Google Scholar


Dick, W.J.A. & Pienkowski, M.W. 1979: Autumn and early winter weights of waders in North-West Africa. - Ornis Scandinavica 10: 117–123. Google Scholar


Dill, L.M. 1987: Animal decision making and its ecological consequences: the future of aquatic ecology and behaviour. - Canadian Journal of Zoology 65: 803–811. Google Scholar


Ebbinge, B.S. 1989: A multifactorial explanation for variation in breeding performance of Brent Geese Branta bernicla. - Ibis 131: 196–204. Google Scholar


Ebbinge, B.S. 1991: The impact of hunting on mortality rates and spatial distribution of geese wintering in the western Palearctic. - Ardea 79: 197–210. Google Scholar


Evans, P.R. 1980: Reclamation of intertidal land: some effects on the Shelduck and wader populations in the Tees Estuary. - Vereinigung Ornithologischer Gesellschaft in Bayern 23: 147–168. Google Scholar


Evans, P.R. 1992: The use of Balsfjord. north Norway, as a staging post by Knot during spring migration: fat deposition, muscle hypertrophy and flight strategies. - Wader Study Group Bulletin 63 Supplement: 126–128. Google Scholar


Evans, P.R. & Davidson, N.C. 1990: Migration strategies and tactics of waders breeding in arctic and north temperate latitudes. - In: Gwinner, G. (ed.); Bird Migration. Springer Verlag, Berlin, pp. 387–398. Google Scholar


Evans, P.R., Davidson, N.C., Piersma, T. & Pienkowski, M.W. 1991: Implications for habitat loss at migration staging posts for shorebird populations. - Proceedings of XX International Ornithological Congress, New Zealand: 2228–2235. Google Scholar


Follestad, A. 1994: Innspill til en forvaltningsplan for gjess i Norge. - Norsk Instituit for Naturforskning, NINA Utredning 65: 1–78. (In Norwegian). Google Scholar


Fox, A.D. in press: Female condition and reproductive output in Northern Hemisphere migratory Anatidae. - Gibier Faune Sauvage. Google Scholar


Fox, A.D., King, R. & Watkin, J. 1992: Seasonal variation in weight, body measurements and condition of free-living Teal. - Bird Study 39: 53–62. Google Scholar


Fox A.D., Bell, D.V. & Mudge, G.P. 1993: A preliminary study of the effects of disturbance on feeding Wigeon grazing on Eel-grass Zostera. - Wader Study Group Bulletin 68: 67–71. Google Scholar


Fox, A.D., Norriss, D.W., Stroud, D.A. & Wilson. H.J. 1994: Greenland White-fronted Geese in Ireland and Britain 1982/83– 1993/94. - GWGS Research Report 8, Aberystwyth. 54 pp. Google Scholar


Frederick, R.B., Clark, W.H. & Kaas, E.E. 1987: Behaviour, energetics and management of refuging waterfowl: a simulation model. - Wildlife Monographs 96: 1–35. Google Scholar


Fredga, S. & Dow, H. 1984: Factors affecting the size of a local population of Goldeneye Bucephala clangula (L.) breeding in Sweden. - Viltrevy 13: 225–255. Google Scholar


Frenzel, P. & Schneider, M. 1987: Ökologische Untersuchungen an überwinternden Wasservögeln im Ermatinger Becken (Bodensee): Die Auswirkungen von Jagd, Schiffahrt und Freizeitaktivitäten. - Ornithologisches Jahresbuch Baden-Württemberg 3: 53–79. (In German). Google Scholar


Frikke, J. & Laursen, K. 1994a: Forlandsjagt i Vadehavet. Med en analyse af betydningen for andefugle. - Danmarks Miljeunderspgelser, Faglig Rapport fra DMU, No. 102, 55 pp. (In Danish). Google Scholar


Frikke, J. & Laursen, K. 1994b: Jagt i Ballum-området. - Danmarks Miljøundersøgelser, Faglig Rapport fra DMU, No. 104, 41 pp. (In Danish). Google Scholar


Gerdes, K. & Reepmayer, H. 1983: Zur raumlichen Verteilung überwinternder Saat- und Blessgänse (Anser fabalis und Anser albifrons) in Abhängigkeit von naturschutzschadlichen und fordernden Einflussen. - Die Vogelwelt 104: 141–153. (In German). Google Scholar


Gerhard, M. 1994: Ursachen und kurzfristige Auswirkungen von Störungen auf den Wasservogelbestand des Biebersteiner Weihers. - Charadri us 30: 70–76. (In German). Google Scholar


Geroudet, P. 1967: L evolution du stationnement des Anatides dans une reserve de chasse sur le Rhone en aval de Geneve. - Nos Oiseaux 24: 141–153. (In French). Google Scholar


Girard, G.L. 1941: The mallard: its management in western Manitoba. - Journal of Wildlife Management 5: 233–259. Google Scholar


Goss-Custard, J.D. & Moser, M. 1988: Rates of change in the numbers of Dunlin Calidris alpina wintering in British estuaries in relation to the spread of Spartina anglica. - Journal of Applied Ecology 25: 543–554. Google Scholar


Hepp, G.R. & Hair, J.D. 1984: Dominance in wintering waterfowl (Anatini): effects on distribution of sexes. - Condor 86: 251–257. Google Scholar


Hill, D.A. 1984: Population regulation in the Mallard (Anas platyrhynchos). - Journal of Animal Ecology 53: 191–202. Google Scholar


Hirons, G. & Thomas, G. 1993: Disturbance on estuaries: RSPB nature reserve experience. - Wader Study Group Bulletin 68: 72–78. Google Scholar


Jakobsen, B. 1993: Indvirkerjagt på fuglebestandes træktider? - Vár Fuglefauna Supplement 1: 62–64. (In Danish). Google Scholar


Jepsen, P.U. 1983: Vildtreservaterne som led i den samlede naturforvaltning. - Proceedings 3rd Nordic Ornithological Conference 1981: 133–142. (In Danish). Google Scholar


Jettka, H. 1986: Jagdstreckenauswertung der Stockenten (Anas platyrhynchos L.) in einem Revierdes Münsterlandes in Nordrhein-Westfalen. - Zeitschrift für Jagdwissenschaft 32: 90–96. (In German). Google Scholar


Joensen, A.H. & Madsen, J. 1985: Waterfowl and raptors wintering in wetlands of Western Greece, 1983–85. - Natura Jutlandica 21 (II): 169–200. Google Scholar


Johnson, C. 1985: Patterns of seasonal weight variation in waders in the Wash. - Ringing and Migration 6: 19–32. Google Scholar


Jones, R.D. & Jones, D.M. 1966: The progress of family disintegration in the Black Brant. - Wildfowl Trust Annual Report 17: 75– 78. Google Scholar


Keller, V. 1989: Variations in the response of Great Crested Grebes Podiceps cristatus to human disturbance - a sign of adaptation? - Biological Conservation 49: 31–45. Google Scholar


Keller, V. 1992: Schutzzonen für Wasservögel zur Vermeidung von Störungen durch Menschen: Wissenschaftliche Grundlagen und ihre Umsetzung in die Praxis. - Ornithologische Beobachter 89: 225–229. (In German). Google Scholar


Keller, V. 1995: Auswirkungen menschlicher Störungen auf Vögel - eine Literaturübersicht. - Ornithologische Beobachter 92: 3–38. (In German). Google Scholar


Kestenholz, M. 1994: Body mass dynamics of wintering Tufted Ducks Aythya fuligula and Pochard A. ferina in Switzerland. - Wildfowl 45: 147–158. Google Scholar


Kirby, J.S., Clee, C. & Seager, V. 1993: Impact and extent of recreational disturbance to wader roosts on the Dee estuary: some preliminary results. - Wader Study Group Bulletin 68: 53–58. Google Scholar


Köhler, P., Köhler, U., Pykal, J., Krosigk, E. von & Firsching, U. 1995: Dauerpaare trotz Mauserzug? Paarbildung während der Familienauflösung bei Schnatterenten Anas strepera. (In German with English summary: Sustained pair-bonds during moult migration? Pair-formation during break up of family groups in Gadwall Anas strepera.). - Journal für Ornithologie 136: 167–175. Google Scholar


Kramer, G.W., Rauen, L.R. & Harris, S.W. 1979: Populations, hunting mortality and habitat use of black brant at San Quintin Bay, Baja California, Mexico. - In: Jarvis, R.L. & Bartonek, J.C. (eds.); Proceedings of the Symposium on Management and Biology of Pacific Flyway Geese. The Wildlife Society, Washington, D.C., pp. 242–254. Google Scholar


Krapu, G.L. 1981: The role of nutrient reserves in Mallard reproduction. - Auk 98: 29–38. Google Scholar


Krapu, G.L. & Reinecke, K.J. 1992: Foraging Ecology and Nutrition. - In: Batt, B.D.J., Afton, A.D., Anderson, M.G., Ankney, C.D., Johnson, D.H., Kadlec, J.A. & Krapu, G.L. (eds.); Ecology and Management of Breeding Waterfowl. University of Minnesota Press, Minneapolis, pp.1–29. Google Scholar


Laursen, K. 1982: Recreational activities and wildlife aspects in the Danish Wadden Sea. - Schriftenreihe des Bundesministers für Ernährung, Landwirtschaft und Forsten No. 275: 63–83. Google Scholar


Lima, L. & Dill, L.M.. 1990: Behavioral decisions made under the risk of predation: a review and prospectus. - Canadian Journal of Zoology 68: 619–640. Google Scholar


Lorentsen, Ø. 1988: Tidlig jakt på grågås. Erfaringer fra forsøk på Smøla 1982–1984. - DN-rapport 5, Norsk Direktorat for Naturforvaltning, 15 pp. (In Norwegian). Google Scholar


Madsen, J. 1980: Forekomst, habitatvalg og overnatning hos Kortnæbbet Gås Anser brachyrhynchus på Tipperne 1972–1978. (In Danish with English summary: Occurrence, habitat selection and roosting by Pink-footed Geese Anser brachyrhynchus at Tipperne, 1972–1978.).- Dansk ornitologisk Forenings Tidsskrift 74: 45–58. Google Scholar


Madsen, J. 1982: Observations on the Svalbard population of Anser brachyrhynchus in Denmark: (a) numbers, distribution and breeding success 1980/81 and (b) population trends 1931–1980. - Aquila 89: 133–140. Google Scholar


Madsen, J. 1985: Impact of disturbance on field utilization of Pink-footed Geese in West Jutland, Denmark. - Biological Conservation 33: 53–63. Google Scholar


Madsen, J. 1986: Danske rastepladser for gæs. (In Danish with English summary: Status of the staging goose populations and their haunts in Denmark, 1980–1983.). - Miljøministeriet, Skov- og Naturstyrelsen, 114 pp. Google Scholar


Madsen, J. 1988: Autumn feeding ecology of herbivorous wildfowl in the Danish Wadden Sea and the impacts of food supplies and shooting on movements. - Danish Review of Game Biology 13 (4): 1–32. Google Scholar


Madsen, J. 1995: Impacts of disturbance on migratory waterfowl. - Ibis 137: 67–74. Google Scholar


Madsen, J., Frikke, J., Kristensen, J.B., Bøgebjerg, E. & Hounisen, J.P. 1992a: Forsøgsreservat Nibe Bredning: Baggrundsundersøgelser efteråret 1985 til foråret 1989. - Danmarks Miljøundersøgelser, Faglig Rapport fra DMU No. 46, 50 pp. (In Danish). Google Scholar


Madsen, J., Bøgebjerg, E., Kristensen, J.B., Frikke, J. & Hounisen, J.P. 1992b: Forsøgsreservat Ulvshale-Nyord: Baggrundsundersøgelser efteråret 1985 til foråret 1989. - Danmarks Miljøundersøgelser, Faglig Rapport fra DMU No. 47, 57 pp. (In Danish). Google Scholar


Madsen, J., Hounisen, J.P., Bøgebjerg, E. & Frikke, J. 1992c: Forsøgsreservat Nibe Bredning: Resultater af eksperimenter 1989–1991. - Danmarks Miljøundersøgelser, Faglig Rapport fra DMU No. 53, 43 pp. (In Danish). Google Scholar


Madsen, J., Bøgebjerg, E., Hounisen, J.P., Kristensen, J.B. & Frikke, J. 1992d: Forsøgsreservat Ulvshale-Nyord: Resultater af eksperimenter 1989–1991. - Danmarks Miljøundersøgelser, Faglig Rapport fra DMU No. 55, 61 pp. (In Danish). Google Scholar


Madsen, J., Hounisen, J.P., Bøgebjerg, E. & Jørgensen, H.E. 1995: Udviklingen i de rastende bestande af vandfugle i forsøgsreservaterne 1985–1993. - Danmarks Milj0undersøgelser, Faglig Rapport fra DMU No. 132, 40 pp. (In Danish). Google Scholar


Madsen, J. & Jepsen, P.U. 1992: Passing the buck. Need for a flyway management plan for the Svalbard Pink-footed Goose. - In: van Roomen, M. & Madsen, J. (eds.); Waterfowl and agriculture: review and future perspective of the crop damage conflict in Europe. IWRB Special Publication No. 21, Slimbridge, UK, pp. 109–110. Google Scholar


Madsen, J. & Pihl, S. 1993: Jagt- og forstyrrelsesfrie kerneområder for vandfugle i Danmark. - Danmarks Miljøundersøgelser, Faglig Rapport fra DMU No. 72, 135 pp. (In Danish). Google Scholar


Mayhew, P. 1988: The daily energy intake of European Wigeon in winter. - Ornis Scandinavica 19: 217–223. Google Scholar


Mayhew, P.W. & Houston, D.C. 1989: Feeding site selection by Wigeon Anas penelope in relation to water. - Ibis 131: 1–8. Google Scholar


Meile, P. 1991: Die Bedeutung der ‘Gemeinschaftlichen’ Wasserjagd für überwinternde Wasservögel am Ermantinger Becken. - Ornithologische Beobachter 88: 27–55. (In German). Google Scholar


Meire, P. & Kuijken, E. 1991: Factors affecting the number and distribution of wintering geese and some implications for their conservation in Flanders, Belgium. - Ardea 79: 143–158. Google Scholar


Meltofte, H. 1980: Fugle i Vadehavet. Vadefugletællinger i Vadehavet 1974–1978. (In Danish with English summary: Wader counts in the Danish part of the Wadden Sea 1974–1978.). - Fredningsstyrelsen, Miljøministeriet, 50 pp. Google Scholar


Meltofte, H. 1981: Danske rastepladser for vadefugle. (In Danish with English summary: Wader counts in Denmark.). - Vadefuglegruppen, Dansk Ornithologisk Forening/Miljøministeriet, 194 pp. Google Scholar


Meltofte, H. 1982: Jagtlige forstyrrelser af svømme- og vadefugle. (In Danish with English summary: Shooting disturbance of waterfowl.). - Dansk ornitologisk Forenings Tidsskrift 76: 21–35. Google Scholar


Meltofte, H. 1993: Vadefugletrækket gennem Danmark. (In Danish with English summary: Wader migration through Denmark: populations, non-breeding phenology and migratory strategies.) - Dansk ornitologisk Forenings Tidsskrift 87: 1–180. Google Scholar


Mjelstad, H. & Sætersdal, M. 1990: Reforming of resident Mallard pairs, rule rather than exception? - Wildfowl 41: 150–151. Google Scholar


Mooij, J.H. 1991: Numbers and distribution of grey geese (genus Anser) in the Federal Republic of Germany, with special reference to the Lower Rhine Region. - Ardea 79: 125–134. Google Scholar


Moser, M. 1988: Limits to the numbers of Grey Plovers Pluvialis squatarola wintering on British estuaries: an analysis of long term population trends. - Journal of Applied Ecology 25: 473–485. Google Scholar


Mudge, G.P. 1989: Night shooting of wildfowl: an assessment of its prevalence, intensity and disturbance impact. - Report to NCC, Wildfowl & Wetlands Trust, Slimbridge, UK, 34 pp. Google Scholar


Nichols, J.D. 1991: Responses of North American duck populations to exploitation. - In: Perrins, C.M., Lebreton, J.-D. & Hirons, G.J.M. (eds.); Bird population studies. Oxford University Press, Oxford, pp. 498–525. Google Scholar


Noer, H., Clausager, I. & Asferg, T. 1995: The bag of Eider Somateria mollissima in Denmark 1958–1990. - Danish Review of Game Biology 14 (5): 1–24. Google Scholar


Owen, M. 1972: Some factors affecting food intake and selection in White-fronted Geese. - Journal of Applied Ecology 41: 79–92. Google Scholar


Owen, M. 1980: Wild Geese of the world. - Batsford, London, 236 pp. Google Scholar


Owen, M., Black, J.M. & Liber, H. 1988: Pair bond duration and timing of its formation in Barnacle Geese (Branta leucopsis). - In: Weller, M.W. (ed.); Waterfowl in Winter. University of Minnesota Press, Minneapolis, pp. 257–269. Google Scholar


Owen, M. & Black, J.M. 1989: Factors affecting the survival of Barnacle Geese on migration from the breeding grounds. - Journal of Animal Ecology 58: 603–618. Google Scholar


Owen, M. & Black J.M. 1990: The importance of migration mortality in non-passerine birds. - In: Perrins, C.M., Lebreton, J.D. & Hirons, G.J.M. (eds); Bird population studies: Relevance to conservation and management. Oxford University Press, Oxford, pp. 360–372. Google Scholar


Owen, M. & Cook, W.A. 1977: Variations in body weight, wing length and condition of Mallard Anas platyrhynchos platyrhynchos and their relationship to environmental changes. - Journal of Zoology London 183: 377–395. Google Scholar


Owen, M. & Salmon, D.G. 1984: Wildfowl distribution in relation to reserves and shooting. - Shooting Disturbance Seminar, B.A.S.C. Rossett, 1984. Unpublished Report, Wildfowl and Wetlands Trust, Slimbridge, UK. 18 pp. Google Scholar


Owen, M. & Williams, G. 1976: Winter distribution and habitat requirements of Wigeon in Britain. - Wildfowl 27: 83–90. Google Scholar


Owen, M., Wells, R.L. & Black, J.M. 1992: Energy budgets of wintering Barnacle Geese : the effects of declining food resources. - Ornis Scandinavica 23: 451–458. Google Scholar


Owens, N.W. 1977: Responses of wintering Brent Geese to human disturbance. - Wildfowl 28: 5–14. Google Scholar


Paulus, S.L. 1983: Dominance relations, resource use and pairing chronology of Gadwalls in winter. - Auk 100: 947–952. Google Scholar


Paulus, S.L. 1984: Activity budgets of non-breeding Gadwalls in Louisiana. - Journal of Wildlife Management 48: 371–380. Google Scholar


Pehrsson, O. 1978: A ten-year fluctuation pattern of the Common Eider Somateria mollissima on the Swedish west coast as a result of food availability. - In: Andersson, Å. & Fredga, S. (eds.); Proceedings from the Symposium on Sea Ducks, June 16–17 1975, Stockholm, Sweden. IWRB, Slimbridge, UK, pp. 91–98. Google Scholar


Pehrsson, O. 1984: Diving duck populations in relation to their food supplies. - In: Evans, P.R., Goss-Custard, J.D. & Hale, W.G. (eds.); Coastal waders and wildfowl in winter. Cambridge University Press, Cambridge, pp. 101–116. Google Scholar


Perco, F. 1991 : Recent changes in size of goose populations in Italy. - Ardea 78: 169–172. Google Scholar


Perry, M.C., Nichols, J.D., Conroy, M.J., Obrecht, H.H. & Williams, B.K. 1987: Sex-specificity of behavioral dominance and fasting endurance in wintering canvasbacks: experimental results. - In: Weller, M.W. (ed.); Waterfowl in winter. University of Minnesota Press, Minneapolis, pp. 103–121. Google Scholar


Pienkowski, M.W., Lloyd, C.S. & Minton, C.D.T. 1979: Seasonal and migrational weight changes in Dunlins. - Bird Study 26: 134– 148. Google Scholar


Piersma, T. 1994: Close to the edge: energetic bottlenecks and the evolution of migratory pathways in Knots. - Doctoral Thesis, University of Groningen, The Netherlands, 366 pp. Google Scholar


Pöysä, H. 1984: Temporal and spatial dynamics of waterfowl populations in a wetland area - a community ecological approach. - Ornis Fennica 61: 99–108. Google Scholar


Preven, J.P. & MacInnes, C.D. 1980: Family and other social groups in Snow Geese. - Wildlife Monograph 71: 1–46. Google Scholar


Rasmussen, L.M. 1994: Overvågning af Saltvandssøen og Margrethe Kog 1993. - Report, Miljø- og Energiministeriet, Skov- og Naturstyrelsen, 69 pp. (In Danish). Google Scholar


Reichholf, J. 1973: Begrundung einer ökologischen Strategie der Jagd auf Enten. - Anzeiger Ornithologischer Gesellschaft Bayern 12: 237–247. (In German). Google Scholar


Reinecke, K.J., Stone, T.L. & Owen, R.B. Jr . 1982: Seasonal carcass composition and energy balance of female black ducks in Maine. - Condor 84: 420–426. Google Scholar


Reinecke, K.J., Shaiffer, C.W. & Delnicki, D. 1987: Winter survival of female mallards in the Lower Mississippi Valley. - Transactions North American Wildlife and Natural Resources Conference 52: 258–263. Google Scholar


Ridgill, S.C. & Fox, A.D. 1990: Cold Weather Movements of Waterfowl in western Europe. - IWRB Publication No. 13. IWRB, Slimbridge, UK, 89 pp. Google Scholar


Rohwer, F.C. & Anderson, M.G. 1988: Female biased philopatry, monogamy and the timing of pair-bond formation in waterfowl. - In: Johnson, R.F. (ed.); Current Ornithology. Plenum Press, New York, pp. 187–221. Google Scholar


Roos, G. & Lindskog, H. 1976: En ny rastplats för grågås Anser anser på Måkläppen i sydvästra Skåne. - Anser 15: 101–108. (In Swedish). Google Scholar


Rose, P.M. & Scott, D.A. 1994: Waterfowl Population Estimates. - IWRB Publication No. 29. IWRB, Slimbridge, UK. 102 pp. Google Scholar


Salvig, J., Laursen, K. & Frikke, J. 1994: Surveys of human activities and their effects on numbers and distribution of waterfowl in the Danish Wadden Sea. - Ophelia Supplement 6: 333–337. Google Scholar


Scott, D.A. 1982: Problems in the management of waterfowl populations. - Proceedings 2nd Technical Meeting Western Palearctic Migratory Bird Management, Paris 1979. IWRB, Slimbridge, UK, pp. 89–106. Google Scholar


Schneider, M. 1986: Auswirkungen eines Jagdschongebietes auf die Wasservögel im Ermatinger Becken (Bodensee). - Ornithologisches Jahresbuch Baden-Württemberg 2: 1–46. (In German). Google Scholar


Schneider-Jacoby, M., Frenzel, P., Jacoby, H., Knötzsch, G. & Kolb, K.-H. 1991 : The impact of hunting disturbance on a protected species, the Whooper Swan Cygnus cygnus at Lake Constance. - Wildfowl Supplement 1: 378–382. Google Scholar


Schneider-Jacoby, M, Bauer, H.-G. & Schultze, W. 1993: Untersuchungen über den Einfluss von Störungen auf den Wasservogelbestand im Gnadensee (Untersee/Bodensee). - Ornithologisches Jahresbuch Baden-Württemberg 9: 1–24. (In German). Google Scholar


Smit, C.J. & Visser, G.J.M. 1993: Effects of disturbance on shorebirds: a summary of existing knowledge from the Dutch Wadden Sea and Delta area. - Wader Study Group Bulletin 68: 6–19. Google Scholar


Stock, M., Bergmann, H.-H., Helb, H.-W., Keller, V., SchniedrigPetrig, R. & Zehnter, H.-C. 1994: Der Begriff Störung in naturschutzorientierter Forschung: ein Diskussionsbeitrag aus ornithologischer Sicht. - Zeitschrift für Ökologie und Naturschutz 3: 25–33. (In German). Google Scholar


Suter, W. & Eerden, M. van 1992: Simultaneous mass starvation of wintering diving ducks in Switzerland and The Netherlands: a wrong decision in the right strategy? - Ardea 80: 229–242. Google Scholar


Swennen, C., Leopold, M.F. & de Bruijn, L.L.M. 1989: Timestressed Oystercatchers Haematopus ostralegus can increase their intake rate. - Animal Behaviour 38: 8–22. Google Scholar


Tamisier, A. & Saint-Gerand, T. 1981: Stationnements d'Oiseaux d'Eau et chasse de nuit dans les departements cotiers de France. - Alauda 49: 81–93. (In French). Google Scholar


Thomas, G. 1976: Habitat usage of wintering ducks at the Ouse Washes, England. - Wildfowl 27: 148–152. Google Scholar


Thompson, J.J. 1993: Modelling the local abundance of shorebirds staging on migration. - Theoretical Population Biology 44: 299– 315. Google Scholar


Thornburg, D.D. 1973: Diving duck movements on Keokuk Pool, Mississippi River. - Journal of Wildlife Management 37: 382– 389. Google Scholar


Townsend, D.J. & O'Connor, D.A. 1993: Some effects of disturbance to waterfowl from bait-digging and wildfowling at Lindisfarne National Nature Reserve, north-east England. - Wader Study Group Bulletin 68: 47–52. Google Scholar


van der Meer J.. & Piersma, T. 1994: Physiologically inspired regression models for estimating and predicting nutrient stores and their composition in birds. - Physiological Zoology 67: 305–329. Google Scholar


Warren, S.M. 1994: Individual performance in the Canada Goose Branta canadensis. - Ph D thesis. University of East Anglia, 188 pp. Google Scholar


Watmough, B. 1983: The effects on wildfowl of recreation at reservoirs in the mid-Trent Valley, England. - Severn-Trent Water: Research and Development Project Report. Birmingham, 105 pp. Google Scholar


White-Robinson, R.. 1982: Inland and saltmarsh feeding by wintering Brent Geese in Essex. - Wildfowl 33: 113–118. Google Scholar


Wooley, J.B. & Owen, Jr., R.B. 1977: Energy costs of activity and daily energy expenditure in the black duck. - Journal of Wildlife Management 42: 739–745. Google Scholar


Wrånes, E. 1988: Massedød av aerfugl på Sørlandet vinteren 1981/82. - Vår Fuglefauna 11: 71–74. (In Norwegian). Google Scholar


Ziegler, G. 1987: Zur Entstehung eines Mauserplatzes der Reiherente (Aythya fuligula) von überregionaler Bedeutung im nördlichen Westfalen. - Die Vogelwelt 108: 67–70. (In German). Google Scholar


Ziegler, G. & Hanke, W. 1988: Entwicklung von Stockenten (Anas platyrhynchos) Beständen in der Häverner Marsch unter dem Einfluss der Jagd. - Vogelwelt 109: 118–124. (In German). Google Scholar
Jesper Madsen and Anthony D. Fox "Impacts of hunting disturbance on waterbirds - a review," Wildlife Biology 1(4), 193-207, (1 December 1995).
Received: 18 August 1995; Accepted: 29 November 1995; Published: 1 December 1995

Back to Top