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A study of the diet of nestlings and the overlap of trophic and spatial niches of sympatric Scarlet Ibis (Eudocimus ruber) and Yellow-crowned Night Heron (Nyctanassa violacea) in a northern Brazilian mangrove swamp was made from 1993 to 1997. A collection of regurgitates from nestlings was taken and stratified samples were taken at foraging areas. Both species fed mainly on saltwater ocypodid crabs, the night heron being more stenophagous than the ibis. About 90% of the prey of the night heron were Mangrove Land Crabs (Ucides cordatus) in the range 11-100 g, while fiddler crabs (Ucaspp.) were 64% of the diet of ibises, being mostly in the range 1.1-10 g. The niche of the ibis was broader than that of the night heron, both in trophic and spatial dimensions. The distribution in foraging areas of the Yellow-crowned Night Heron showed a significant, positive spatial correlation with its main prey. The land crab formed a significantly greater proportion in the bird’s diet than its relative abundance in the field. Scarlet Ibis distribution showed no significant spatial correlation with its prey. The niche overlap of the two birds was only moderate, and they seemed to use adjacent regions of the ecological space. As Mangrove Land Crabs and fiddler crabs are similar, the main factor of prey segregation between the two bird species seemed to be prey size. In relation to other geographical areas, both Yellow-crowned Night Heron and Scarlet Ibis occupied more restricted trophic niches, which may be related to the high availability of prey in northern Brazilian mangroves. Prey availability is more stable in saltwater ecosystems than in freshwater ones, so the high levels of niche overlap should not be attributed to seasonally relaxed competition. Competition does not seem to play a significant role in defining guild structure. It is not clear if the Scarlet Ibis in Brazil suffers physiological constraints from dietary salt, as has been reported from North America.
Radio-telemetry was used to continuously monitor the at-sea activity of an adult Marbled Murrelet (Brachyramphus marmoratus) nesting in Santa Cruz County, California. From 05.39 h on 28 May 1997, to 05.14 h on 29 May 1997, the murrelet was followed by tracking teams at Año Nuevo Bay. Between 05.44 h and 20.19 h on 28 May, the bird engaged in eleven dive bouts, with a mean duration of 18.8 ± 5.4 min. Mean dive duration was 24.8 ± 15.7 s; mean surface between dives was 15.2 ± 12.7 s. No dives were initiated after 20.19 h. The bird spent 12.3% of the at-sea period and 23.4% of daylight hours engaged in diving bouts. This relatively small amount of time spent diving allows for considerable flexibility in activity budget.
Fourteen male Common Terns (Sterna hirundo) of known age (3-21 yr) were handicapped by shortening their wings early in the incubation period, and were then followed through chick-raising. The study was conducted at Bird Island, Massachusetts, USA, in 1996, a year when chick growth and survival appeared to be limited by food availability. Chick growth and survival were used as indirect measures of allocation of resources to current reproduction. Rates of change of body-mass and feather re-growth (ptilochronology) were used as indirect measures of allocation of resources to self-maintenance. The birds’ mates were studied similarly, but were not handicapped. Experimental birds and pairs were compared to controls matched for laying date and clutch-size. Handicapped males re-grew tail-feathers pulled for ptilochronology significantly more slowly than controls. They and their mates raised significantly more young than controls. Older handicapped males lost more body-mass during chick-raising than their matched controls, whereas younger males lost less. These results conflict with the prediction of life-history theory that long-lived birds faced with increased costs of reproduction should allocate these costs to their offspring rather than to themselves. However, we point out several problems in using handicapping to test such predictions. The assumed effects of handicapping on the cost of flight and on foraging ability have not been verified or measured. Changes in reproductive effort are not measured directly, and the end points that have been investigated are often ambiguous. The assumption that older individuals consistently have lower residual reproductive value than younger individuals may be incorrect if there is selective survival of high-quality individuals within the study population.
Colony-site tenacity commonly reflects the stability of nesting habitats. The match between nesting substrate and coloration pattern of the eggs in two reproductive groups of the Gull-billed Tern (Gelochelidon nilotica) in the south of Iberian Peninsula was investigated to tests the adaptiveness of colony-site tenacity. The terns showing high colony-site tenacity had 1) a closer match in color between the eggs and the nesting substrate and 2) a lower richness and diversity of egg colors and 3) a lower rate of egg loss from predation than the low colony-site tenacity ones. These results appear to be adaptive, resulting from a long-standing renesting in the same colony-site. However, such mimicry would be difficult to achieve for terns with low site-tenacity, where breeding occur in unstable habitats. These birds were frequently obliged to move from one location to another due to weather irregularity and water level in the reservoirs they bred. In addition, the occasional high predation pressures on both adults and chicks, manifested by the low-tenacity tern group studied, was also involved. The attainment of such egg-crypsis could be an important adaptive advantage favoring colony-site tenacity. In unstable habitats, however, there would be a trade-off between the benefits linked to colony-site tenacity and the negative effects of suboptimal reproduction. Additional experimental design and studies are, however, necessary to confirm these results and predictions.
The first case of cooperative polyandry in the Common Tern (Sterna hirundo) is reported. During the breeding season of 2000 two males, originating from the same brood, bred together with a female, who was paired in the previous season with one of the males. Both males copulated with the female. All three terns incubated the eggs, brooded and fed the chicks, but in different proportions. Despite poor food supply and bad weather conditions during the breeding season 2000, this polyandrous trio reared two fledglings, one of which has returned to the native colony in 2002. In another case, a two-year old, unrelated male incubated a clutch belonging to a pair of terns for a few days. Possible reasons for this deviation from the common monogamous mating system are discussed.
We examined the movements of flightless Long-tailed Ducks (Clangula hyemalis) during the wing molt in the near-shore lagoons of the Beaufort Sea in Alaska. Estimates of site fidelity during the 21-day flightless period ranged from 1-100%, with considerable variation among locations and within locations among years. There was no effect of low-level experimental disturbance or an underwater seismic survey on site fidelity of molting Long-tailed Ducks. Birds molting along a relatively consistent habitat gradient were more likely to move than those molting in a fragmented habitat. While flocks of birds are consistently observed in the same locations, these data suggest considerable turnover within these aggregations. These results, in conjunction with other studies, suggest that forage is relatively uniformly distributed within lagoons. We conclude that habitat selection by molting Long-tailed Ducks is likely influenced by protection from wind and associated waves.
From 1989-1998, in Canada’s Atlantic Provinces and eastern sub-arctic region, migrant Canada Geese (Branta canadensis), wintering American Black Duck (Anas rubripes), Mallard (A. platyrhynchos) and incubating Common Eider (Somateria mollissima) were captured and examined with a fluoroscope to determine if shotgun pellets were embedded in their tissues. Of 1,624 birds examined, 25% carried embedded shotgun pellets. The highest proportion of birds carrying pellets was recorded in the sample of female Common Eider captured on nests in Labrador, followed by female eiders nesting in Newfoundland, Quebec and Nova Scotia and migrant Canada Geese in spring in Prince Edward Island.
This study measured the summer mortality rate of breeding waterbirds during a period of three years (1998-2000) in the El Hondo wetland, Spain, an ecosystem of international importance for ornithological diversity. On average, 874 birds died each summer in the study period, but varied from 199 birds in 1998, to 1,690 in 1999. When the observed mortality was expressed as a percentage of the initial breeding populations, the death rates ranged from 1.6% per month in 1998 to 7.7% in 1999. Many of the dead birds gave positive results for the presence of different enterocolic bacteria (30% to 60%) and for the presence of lead shot in their gizzards (30%). These results cannot be however interpreted as percentages causing the ultimate death because many individuals could be only carriers of enterocolic infections and, in addition, many of our positive results for the presence of lead correspond to sub-lethal values. Nevertheless, our results suggest that a significant decrease in the summer mortality rate of waterbirds could be probably achieved by improving the water quality of the ponds in periods of low water levels and by extracting the sources of lead either manually or mechanically.
Stiff-tailed ducks (Oxyurini) are reputed to be unique among waterfowl in having two complete wing and tail molts annually. We examined molt patterns in wild Ruddy Ducks (Oxyura jamaicensis) and in captives of known age. Adults of both groups underwent a complete wing molt in early autumn. A spring wing molt was very rare in wild Ruddy Ducks, but occurred more often in captives, especially in adult females. Ruddy Ducks replace rectrices twice annually. These molts are complete but unusual in that feathers are typically replaced in two waves, in which (1) every other rectrix is lost and largely re-grown before (2) the intervening feathers are molted. As a result, the molt is protracted and the tail plumage, at times, includes feathers of two generations. The pattern ensures that a functional tail is maintained at all times.
We investigated the incidence of injuries caused by lost or discarded fishing tackle on the Mute Swan (Cygnus olor) admitted to a wildlife hospital in the English Midlands between January 2000 and December 2002. Injuries caused by lost or discarded fishing tackle was the largest single attributable cause of admission over this period, accounting for 17% of a total of 1,491 swans admitted over the three year period. Treatment success was high with 87% subsequently released, although the majority of these birds would probably have died without treatment. We also conducted a survey of blood lead levels in 921 swans over the same period and 74% were found to have elevated blood lead levels over 1.21 μmol/l. Over three-quarters of swans with elevated blood lead levels (>1.21 μmol/l) were successfully treated with the chelating agent EDTA and were subsequently released following treatment.
A 28-year (1974-2002) study of the Cattle Egret (Bubulcus ibis) was conducted on Bird Island and Telfair Island at Cedar Creek Reservoir in northeast Texas to determine trends and dynamics of clutch/brood sizes, hatching success, chick mortality, and nest-site vegetation. For the breeding colonies on these islands, annual mean clutch size ranged from 2.71-3.73 (overall mean = 2.98) and from 2.56-4.18 (overall mean = 3.33); annual mean brood sizes ranged from 2.20-3.08 (overall mean = 2.60) and from 2.38-3.67 (overall mean = 2.87). Annual mean hatching success on the islands was high throughout the study (78%-94% [overall mean = 88%] and 71%-96% [overall mean = 86%]). Annual mean chick mortality was low (0.5%-13% [overall mean = 4.5%] and 0%-10% [overall mean = 2.1%]). Among marked broods on both islands, only 6.5% lost chicks, for which the mean loss was 1.16 chicks/brood. Generally, within these broods, there was higher mortality of the younger chicks. In broods of more than two chicks, the mortality ratio between 1st- and 2nd-hatched chicks was lower than other combinations of sibling rank. Decline of nest density coincided with the cumulative adverse effects of guanotrophication on nest-site vegetation. The original native nest-site vegetation was replaced by Chinaberry (Melia azedarach), an exotic tree that provided optimal nest sites until it too became intolerant to guanotrophy, which resulted in a continued decline in nest-site vegetation. During the time of declining availability of nest-site vegetation, the egrets began ground nesting; by 2002, 48% of nests were on the ground.
In 2001, predator exclosures were used to protect nests of the Western Sandpiper (Calidris mauri) in western Alaska. During the exclosure experiment, nest contents in exclosures had significantly higher daily survival rates than control nests, however, late in the study predators began to cue in on exclosures and predate the nest contents. An Arctic Fox (Alopex lagopus) dug under one exclosure and took the newly hatched chicks, and Long-tailed Jaegers (Stercorarius longicaudus) learned to associate exclosures with active nests and repeatedly visited them. The jaegers attempted to gain access to exclosed nests and pursued adult sandpipers as they emerged from the exclosures. The exclosures were removed to reduce potential mortality to adult and young sandpipers, but subsequently, post-exclosure nests had lower daily survival rates than controls during the same time period. Predation of post-exclosure eggs and chicks highlighted the lasting influence of the exclosure treatment on offspring survival because predators probably remembered nest locations. Researchers are urged to use caution when considering use of predator exclosures in areas where jaegers occur.
South Carolina winters a large proportion (over 1/3) of the eastern race of the American Oystercatcher (Haematopus palliatus), a declining species. During December of 1999-2002 ground surveys were conducted to provide baseline data on the abundance, age class partitioning and distribution of wintering American Oystercatchers in South Carolina. The number of oystercatchers in South Carolina was stable during this study (3,536, 95% CI: 3,030, 4,042). A single comprehensive survey can estimate the number of oystercatchers with enough precision to detect changes in the population of 13% and greater, but location of flocks and the range of tidal heights needed to concentrate flocks must be known prior to conducting the survey. About 89% of the birds in 2002 roosted on washed shell rakes and 9% had immature bill coloration. Winter surveys of the proportion of immature oystercatchers may provide an index of regional reproductive success, an important parameter for conservation plans. Because South Carolina winters a large number of oystercatchers, future surveys could be used to verify suspected declines on a regional scale.
We studied aspects of the reproduction of Kittlitz’s Murrelet (Brachyramphus brevirostris) in Prince William Sound, Alaska, in 1996-1998. Productivity in all bays was extremely low in all years: only one fledgling in 1996, none in 1997, and evidence of breeding (but no fledglings seen) in 1998. Other evidence suggested that these birds spent such short periods in two of the bays that they could not have bred successfully. We also observed what appeared to be mixed-species “pairs” of Kittlitz’s and Marbled Murrelets (B. marmoratus) in early summer 1997 and on all late-summer cruises. Although breeding failures may not be uncommon in Kittlitz’s Murrelet, the low reproductive output in all three years and the occurrence of mixed-species pairs are sources of conservation concern and suggest that this species may be experiencing problems reproducing successfully in Prince William Sound.
The Yellow-eyed Penguin (Megadyptes antipodes) is monomorphic but exhibits subtle sexual morphometric dimorphism. Information on the sexes of these birds is needed for informed management of the species and the construction of accurate population models. Using DNA analysis and Discriminant Function Analysis on head and foot measurements, we tested whether adults and fledglings of Yellow-eyed Penguin can be sexed using morphometry. We found that head and foot measurements can be used to correctly sex up to 93% of adults. Using only foot length, 88% of fledglings can be sexed accurately. As age until fledging was found to have an effect on morphometric variables, sexing should be conducted as synchronized as possible when chicks are over 90 days of age. We recommend that error rates inherent in sexing fledglings be taken into account when publishing sex-ratio data and subsequent analyses, particularly when age of fledglings could not be determined. The use of whole-skull measurements for sexing may be useful in other species in which bill measurements between the sexes are only slightly dimorphic or contains large degrees of overlap.
In eastern Canada during the early 1990s, a shift in the distribution of Capelin (Mallotus villosus) resulted in a prolonged absence (at least 8 years) of the preferred prey for the Atlantic Puffin (Fratercula arctica) breeding at Gannet Islands, Labrador. It has been documented that there is no suitable alternative prey to Capelin in the northwest Atlantic for seabirds, thus these extreme changes in food supply may have negative effects on reproduction and adult survivorship. In this study, foraging behavior, chick growth and productivity of Atlantic Puffins at the Gannet Islands, Labrador during 1996-1998 were compared to data in a study undertaken in 1981-1983, prior to the decline in Capelin abundance. It was confirmed that the dramatic change in Capelin abundance was reflected in chick diet as Atlantic Puffin chicks received 50-70% (by mass) less Capelin in 1996-1998 than in 1981-1983. Hatch dates did not differ among decades and breeding success, chick wing growth and fledge mass were unaffected. The only breeding parameter significantly affected by the change in food supply was chick growth (mass gain). Taken together, our data indicated that following a decline in Capelin abundance, the Atlantic Puffin did not experience breeding failure and effectively reared young utilizing suitable alternative prey which included post-larval sandlance and other small fish and invertebrates.
Nesting chronology, habitat use, subcolony use, and hatchability were documented for the Black-crowned Night Heron (Nycticorax nycticorax) nesting at Alcatraz Island, San Francisco Bay, California during 1990-2002. Reproductive success was estimated using the Mayfield method and compared among years. Totals of monitored nests per year ranged from 68 in 2001 to 341 in 1996, with a trend of declining numbers since 1996. An increase in numbers of the Western Gull (Larus occidentalis), the Black-crowned Night Heron’s primary competitor, occurred during the same period. Overall reproductive success of the Black-crowned Night Heron at Alcatraz Island was below the 13-year average of 56.4% since 1996. During the study, the average number of chicks fledged per nest each year ranged from 0.46 to 1.27, which is less than the two chicks per nest suggested as a requirement for a sustained population. Embryos in five of 187 failed Black-crowned Night Heron eggs were deformed. In 1990 and 1991, eggs were analyzed for a wide range of contaminants, but none appeared to be sufficiently elevated to have caused the observed deformities. Based on these relatively low levels of contaminants, a high hatchability rate (94.5%), and relatively low levels of embryotoxicity, contaminants did not appear to significantly affect Black-crowned Night Heron reproduction at Alcatraz Island. However, predation by the Common Raven (Corvus corax) and Western Gull, interspecific competition with the Western Gull, habitat deterioration, and possible human disturbance are likely factors contributing to the decline in Black-crowned Night Heron reproductive success on Alcatraz Island in recent years.
We counted the heronries at two study areas in China, where important but unknown numbers breed. At Poyang Lake, within a 1,800 km2 area, we found ten heronries with Little Egret (Egretta garzetta), Intermediate Egret (Egretta intermedia), Great White Egret (Ardea alba), Cattle Egret (Bubulcus ibis), Chinese Pond Heron (Ardeola bacchus), and Black-crowned Night Heron (Nycticorax nycticorax), and at Tai Lake we found five heronries within a 4000 km2 area. Heronry size ranged from a few hundred nests to 36,400 nests. Several heronries were located within human settlements, in contrast with the sites used in Europe and in North America, where herons tend to avoid human disturbance. An extrapolation of the mean densities observed at the two study areas, for all the zones of mainland China that are cultivated mostly with rice, provide a first estimate of a total numbers of up to some five million nests of herons and egrets, which is much higher than previously suggested for China.