Double-crested Cormorants (Phalacrcorax auritus) and other piscivorous birds are frequently implicated in having negative effects on commercial and sport fisheries despite the fact that several studies suggest that such effects may be infrequent. Increases in cormorant populations in North America over the last decades have fueled the debate further and population controls, official and unofficial, are in effect in several jurisdictions. Of importance to the management community is the need to obtain the best information on actual diets of cormorants throughout their annual cycle but particularly on the temperate breeding grounds where they frequently overlap with fisheries. Despite success in quantifying seabird diets, managers have yet to exploit the potential of the stable isotope approach to examine trophodynamics of cormorants where they can potentially interfere with fisheries. Here, the use of stable isotope methods (δ15N and δ13C) to quantitatively predict trophic interactions between cormorants and their prey are recommended to augment conventional dietary approaches. The stable isotope approach is particularly suited to situations where birds feed at a single, well-defined lake or waterbody. The approach can provide a quantitative estimate of fish consumption to species or species groups in cases where such groups are isotopically distinct. This paper is intended to provide the research and management communities with the necessary background to apply stable isotope methods to better assess diets of cormorants and other piscivorous waterbirds.

Prey items fed to chicks of eight individually-marked and known specialist Thick-billed Murres (Una lomvia) were watched over a 15–year period at Coats Island, Nunavut, and time-depth recorders attached to eight birds in two separate years. Two males were amphipod specialists, one male a cod specialist and another male a shanny specialist; two females were sculpin specialists and two capelin specialists. Although there was likely some gender-related component to diet, there were clear specializations within each gender. Specialization in diet was mirrored by specialization in foraging behavior: amphipod specialists made V-shaped dives and had short foraging ranges, shanny/cod specialists made many shallow dives, sculpin specialists made deep, U-shaped dives, while capelin specialists made V- or W-shaped dives to moderate depths. There was no clear pattern between specialties and age or reproductive success. The use of longitudinal studies in foraging behavior, as long-term studies of individuals can complement existing knowledge of the flexibility or specialization of waterbirds, is encouraged.

Beginning in the 1960s, Ring-billed Gulls' (Larus delawarensis) historic breeding range expanded from inland habitats and freshwater wetlands to marine sites in Atlantic North America. Adults winter on salt water but salt tolerance may entail costs (e.g. maintenance of salt glands) and favor reduced parental use of marine resources for feeding chicks. Diets of Ring-billed Gull chicks nesting on a marine island off Prince Edward Island, Canada, were investigated using soft regurgitant collection and stable isotope (δ¹³C and δ¹⁵N) analysis of both regurgitants and blood samples. Isotopic signatures in blood of chicks of Ring-billed and sympatrically-nesting Herring (L. argentatus) and Great Black-backed Gulls (L. marinus) were also compared. Regurgitants of Ring-billed Gull chicks contained freshwater/ terrestrial and marine invertebrates and fish. A stable isotope mixing model incorporating both δ¹³C and δ¹⁵N in chick regurgitants and blood estimated that 42.2% of Ring-billed Gull chick diet came from the marine environment, whereas estimates from blood for Herring and Great Black-backed Gulls were 43.6%, and 73.5%, respectively. Further, differences existed among gull species in estimates for dietary contribution from various food sources from marine and terrestrial/freshwater environments. Although Ring-billed Gulls can use marine food sources to feed their young, whether salt in marine food imposes a physiological cost on these young in comparison to young reared exclusively on non-marine foods is unclear.

The Black-winged Stilt (Himantopus himantopus) is a long-distance migratory wader common in Europe, North Africa, Asia and Australia. Diets of Black-winged Stilt chicks collected from breeding sites in southwestern Taiwan between April and September 1999–2001 were investigated. The contents of 305 stomachs were examined and 12,176 food items categorized into seven classes, 17 orders, 39 families and 48 species of animals. Prey importance was determined by the index of Acosta (I'a); i.e. the sum of the relative frequency of occurrence, relative abundance and relative estimated volume. The mean abundance and estimated volume of animal contents per stomach were 39 ± 6 items and 80 ± 10 mm³, respectively. The main aquatic invertebrate prey (I'a > 10) were water scavenger beetles (Hydrophilidae), biting midges (Ceratopogonidae), chironomid midges (Chironomidae), shore flies (Ephydridae), house flies (Muscidae) and brine shrimp (Artemiidae). The total relative frequency of occurrence, relative abundance and relative estimated volume of these six families were over 64%, 87% and 72%, respectively. The major prey size range of stilt chicks was 2.7–7.4 mm³, which comprised only 18% of the total relative abundance of diet items while contributing 42% of the total estimated diet volume. Two alien (an Oreochromis hybrid and Gambusia affinis) and one indigenous (Yongeichthys caninus) fish species were also important contributors to the relative estimated volume (17% in total). The findings suggest that water-level management may improve the feeding habitats of stilts.

The Argentinean Pampas is an ecologically disturbed region where patchy wetlands form complex habitats with surrounding agricultural areas. Numerous bird species concentrate in these sites at breeding colonies and communal roosts. For two consecutive years, point censuses were made of birds in the vicinity of a roosting and breeding area at Los Padres Lake in the south-east Pampas's plain. In parallel with these censuses, limnological analyses (e.g. nutrient concentration, conductivity, water transparency and temperature) were conducted to correlate changes in the structure of waterbird assemblages with environmental variability. Seasonal variability in the structure of waterbird assemblages could be due to changes in the birds' habitat use and reproductive phenology through the year (e.g. colonies, foraging and roosting sites) and land use in neighboring areas (e.g. for agricultural practices). Waterbird abundance in July and August correlated with phosphorus and nitrogen concentrations, which were linked to changes of waterbird assemblages and their feeding behavior. The present study shows the potential importance of waterbird communities in contributing biotic nutrients to Pampas wetlands.

Many salt ponds around the Mediterranean are being either abandoned or converted into aquaculture enterprises, which affects their use by migratory shorebirds. Effective management of salt ponds can improve their attractiveness to birds but requires a better understanding of the shorebirds' response to variations in environmental conditions of the ponds. The main objectives of this study were to analyze the relative importance of different types of salt pond (industrial, traditional and inactive) to shorebirds throughout the tidal cycle, as well as determine the environmental factors that affect the use of salt ponds by shorebirds. Birds were counted during low and high tides on salt ponds in the Guadiana estuary, southeast Portugal. Simultaneously, the environmental conditions of each of the 212 pans studied were recorded and their importance analyzed using logistic regression models. Although more birds used the salt ponds during the high-tide, many species stayed in the study area during lowtide, suggesting a preference to feed on salt ponds as compared to tidal flats. Industrial salt ponds were preferred by most of the species. Water depth, salinity and area were major factors in explaining the presence of the shorebirds and, hence, are the most important environmental variables to take into consideration when devising management plans for salt ponds.

Reproduction within a recently re-introduced resident flock of Whooping Cranes ( Grus americana) in Florida during 1992–2007 was poor compared to an established wild flock. Pairing and nesting increased with average age of the flock, but fertility, hatching and fledging were variable among years, suggestive of an environmental influence. For climatic variables measured during the incubation period, only maximum soil temperature was associated with the failure of late nests in dry years. However, pre-nesting winter precipitation and water elevation were positively correlated with an index of nesting effort. Winter precipitation was associated with fertility and hatchability, whereas winter marsh water levels were associated with earlier nesting dates and increased egg volume. Both winter precipitation (>8 cm mean monthly) and water elevation (>20.3 m above mean sea level or 68% of full marsh surface area or perimeter) greater than a threshold level appeared to be good predictors for successful reproduction in central Florida, but occurred together in only four of ten study period years. Pairs delayed nesting, had smaller eggs, and hatched and fledged fewer chicks in years with low winter water elevation. Low winter precipitation associated with decreased fertility of eggs may explain the failure of fully incubated nests to hatch in some years. Insufficient stimulation of the neuroendocrine system due to limited rainfall and poor physiological condition due to poor food resources in low water marshes are proposed mechanisms for low fertility and delayed nesting and egg size, respectively. Drought appears to encourage birds to use lake edges for nesting which have increased hazards. Thus, conservation of wetlands for cranes should include deep marshes and lake edges with controlled boat usage during the nesting season. Further investigation is recommended for pre-nesting and incubation behaviors, diseases of eggs, and egg volumes.

Wintering diving duck (Aythya spp.) time-activity budgets have been developed for many species in different regions. As such, direct comparisons can be made among studies where substantial deviations in “normal” activity budgets can provide insight as to how location, food resources, habitat, weather and human disturbance may differentially influence behavior (s) during winter. To examine how diving ducks use large reservoirs in eastern Texas, 1,275 individual time-activity budgets were quantified for Canvasback (Aythya valisineria), Lesser Scaup (A. affinis) and Ring-necked Duck (A. collaris) wintering on B.A. Steinhagen, Sam Rayburn and Toledo Bend Reservoirs during winter 2003/2004 and 2004/2005. Behaviors varied among species (P< 0.001), where food acquisition, locomotion and resting-related behaviors dominated time-activity budgets. All three species spent similar time feeding compared to other studies in the southeastern United States, but spent substantially more time locomoting than previously reported. Human disturbances from boat traffic were associated with time spent locomoting, but no species dramatically increased time feeding to compensate for increased time locomoting. Wintering diving duck activity budgets on these large eastern Texas reservoirs were generally similar to previous studies in the southeast. However, the (in) direct impacts of boat disturbances warrants closer investigation, specifically related to wintering waterfowl responses and the potential utility or value of voluntary avoidance areas during winter.

The reduced mobility of flightless waterbirds during wing-feather molt should influence time allocation during the day, but time-budget studies are lacking in most species. Here, time budgets of flightless and fully-winged individuals at Lake Constance, Central Europe, were compared for five waterbird species with different feeding ecology and varying sensitivity to disturbances or predation pressure. Significant differences in diurnal activity budgets of flightless and fully-winged birds were observed in all five species. Different behaviors were responsible for the observed differences. Flightless Mute Swans Cygnus olor spent more time feeding while decreasing locomotory activity. Red-crested Pochard Netta rufina also increased feeding, but, in addition, had increased locomotory activity while resting less. In contrast, flightless individuals of both Gadwall Anas strepera and Tufted Ducks Aythya fuligula spent less time foraging, while there was no such change in Eurasian Coot Fulica atra. More consistent patterns were observed in vigilance behavior, which increased in three of the five species. Comfort activities, such as preening, increased in two species, and were unchanged in the remaining three. Social interactions, which constituted only a small part of the daily budget, only changed in Gadwall. The present data suggest that the five waterbird species meet the increased energy demands during molt by either one or a combination of behavioral adaptations, i.e. different strategies, such as higher nutrient intake (e.g. Mute Swan, Red-crested Pochard), lower energy consumption by reducing the locomotory component (e.g. Mute Swan, Tufted Duck) or a breakdown of energy reserves deposited prior to the molting period resulting in more time spent resting (e.g. Gadwall). Also, increased resting times during the day may indicate nocturnal feeding, which needs to be examined in more detail.

Many studies on the effects of human disturbance on birds have focused on adults and report mainly negative effects. Few focus on effects on chicks. Here, an experimental approach was used to determine effects of human disturbance on chick growth. Cassin's Auklet chicks were assigned to one of three groups (control, low and high disturbance). In experimental groups, a person walked close to the burrow entrance four times or eight times a day, according to the disturbance level assigned. Growth (mass increment and wing length increase) was measured and compared between the three groups. Since adults are absent from the nest during the day, chicks, but not their parents, experienced the disturbance regime. Body condition and experience (age) of the parents did not influence peak or fledging mass of chicks subject to disturbance. Chicks were not affected by disturbance in the early stages of growth, while chicks in the experimental groups stopped gaining weight sooner than controls and fledged at lower weights (6 to 9% less) compared to chicks in the control group. Chicks in the high disturbance group had a lower peak (F_2,68 = 7.53, P < 0.001) and fledging mass (F_2,68 = 17.274, P < 0.001) compared to chicks in the control group, while chicks in the low disturbance group had a lower fledging mass (F_2,68 = 17.274, P < 0.001) but similar peak mass. As subsequent survival of chicks is likely to be affected by their mass at fledging, the results show that it is necessary to consider the chick growth stage when making management plans for areas with burrow-nesting seabirds.

King Rails (Rallus elegans) and Clapper Rails (Rallus longirostris) are large, secretive waterbirds whose ranges overlap in brackish marshes along the Atlantic and Gulf Coasts. King and Clapper Rails are difficult to separate by physical appearance and there is currently no reliable method to distinguish between the two species. Here, the relative effectiveness of using discriminant analysis of morphometric measurements to identify and sex King and Clapper Rails was examined. Mean measurements of wing, tarsus, and weight were different between male King and Clapper Rails and between female King and Clapper Rails. However, for all measurements except culmen, male Clapper Rails and female King Rails were not different. Discriminate analysis of morphometric measurements revealed that wing, tarsus, and culmen measurements differentiated between King and Clapper Rails, but cross-validation results for male Clapper Rails were only 73%. Male King Rails were larger than female King Rails for all morphometric measurements and male Clapper Rails were larger than female Clapper Rails for all morphometric measurements except for the tail. Wing and tarsus measurements differentiated between male and female King Rails and wing, tarsus, and culmen measurements differentiated between male and female Clapper Rails.

Although DDE caused reproductive failures in a wide variety of bird species during the 1950s–1970s, the mechanism(s) by which it acted have still not been fully elucidated. This experimental study was designed to test an hypothesis that the primary mechanism by which DDE caused hatching failure in Common Terns (Sterna hirundo) was by disrupting the structure of the eggshell, leading to reduced exchange of O₂ and CO₂ through the shell to and from the embryo. In the study, gas exchange through two groups of Common Tern eggshells was reduced by 12% or 28% by sealing parts of the surface with acrylic resin. Contrary to predictions from the hypothesis, all treated eggs hatched and there were no other changes in breeding success relative to untreated controls. The result suggests that DDE caused embryonic deaths in Common Terns by mechanisms acting within the egg rather than by modification of the structure or respiratory properties of the shell.

Previous reports of female-female pairings in seabirds concerned surface-nesting species only and the genetic relatedness between the two females has been determined only once. Here, the first observation of a female-female pair (detected by molecular sexing) in a burrow-nesting seabird is documented. In 2003, two female Cory's Shearwaters (Calonectris diomedea) were found incubating the same egg, from which a chick hatched. A genetic (microsatellite) analysis showed that the two females were unrelated. This study provides additional evidence that petrel mating systems may be more flexible than initially thought. Female-female pairing in burrow-nesting seabirds might be promoted by similar factors to surface-nesting seabirds, and might have remained undetected until now due to the secretive habits of burrow-nesting seabirds and the low number of genetic studies conducted.

Skin collections show that the Shandong coast of China used to harbor a breeding population of the Chinese Crested Tern, Thalasseus Bemsteini, in the 1930s. However, the current status of this Critically Endangered population is poorly documented. From June to July 2006 a survey was conducted along the southern Shandong coast. The results suggest that the species has likely been extirpated. The extirpation of the regional breeding population may have resulted from anthropogenic colonization and development on the breeding islands starting during the 1950s.

Reptiles are uncommon as seabird predators on islands. While conducting a study on Cory's Shearwaters (Calonectris diomedea) on Selvagem Grande, North Atlantic, incidental observations during 2006 early hatching period indicated that some chicks were being killed by Madeiran Wall Lizards (Teira dugesii). In the same year and in 2007, the phenomenon was further examined and samples of 78 and 153 nests, respectively, were followed. Also, non-systematic visits were made to other nests. A total of 40 episodes of lizards depredating Cory's Shearwaters hatchlings was recorded. This hitherto unknown source of predation for this shearwater accounted for the failure of four (5.1%) study nests in 2006 and eight (5.2%) study nests in 2007. All recorded predation cases took place either during or shortly after hatching. Also, non-systematic observations indicated that three other species of burrowing petrels (Bulwer's Petrel, Bulweria bulwerii; Madeiran Storm-petrel, Oceanodroma castro, White-faced Storm-petrel, Pelagodroma marina) were preyed upon by Madeiran Wall Lizards. Predation by lizards is apparently a phenomenon of lesser concern for Cory's Shearwaters but the potentially higher impact over the smaller petrel species is not known.