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At least 577 records · Page 32Linked to original sources
USGS1997

Reproduction of black-crowned night-herons related to predation and contaminants in Oregon and Washington, USA

We studied reproductive characteristics of Black-crowned Night-Herons ( Nycticorax nycticorax ) at four colonies in south central Washington and one colony in north central Oregon in 1991. Nest success, adjusted using the Mayfield method, was significantly different between colonies and ranged from 12-84% to hatching and 12-73% to 14 days post-hatching. The mean number of young surviving to 14 days of age in each colony ranged from 0.47-1.94 per nesting female (includes recycling efforts that involve laying more than one clutch). They were marked intercolony differences in clutch size and incidence of recycling. Predation (primarily avian) was a major factor that adversely affected nest success in three colonies and was relatively unimportant in two colonies. Residues of DDE, total polychlorinated biphenyls, 2,3,7,8-tetrachlorodibenzo-p-dioxin, and other compounds in eggs were generally low and apparently had little influence on reproductive success at any of the colonies. Mean eggshell thinning ranged from 7-1 1 % in comparison to a pre-1947 norm for eggs measured in museum collections. Cytochrome P450 enzyme (EROD, PROD, and BROD) induction in livers of pipped embryos by colony ranged from low to average in comparison with other colonies throughout the U.S. Average EROD and BROD activities were highest at Sand Dune Island and were lowest at Potholes Reservoir which was designated the reference colony. In relation to our study of three of the five colonies in the early 1980s, residues of DDE and several related compounds appeared to decline, nest predation rates increased, and nest success decreased at all three colonies.

Oregon, Washington↗
USGS1997

Nesting season food habits of 4 species of herons and egrets at Lake Okeechobee, Florida

Based on the composition of nestling regurgitations collected during 3 breeding seasons, fish were the most important prey group for Great Egrets (Ardea alba: N = 200 nest-day samples; aggregate percent biomass [APB] = 73.4%), Snowy Egrets (Egretta thula: N = 115; APB = 91.4%), and Tricolored Herons (E. tricolor: N = 68; APB = 97.3%). For Little Blue Herons (E. caerulea: N = 57), grass shrimp (Palaemonetes paludosus; APB = 39.7%) ranked higher in overall importance than all fishes combined (APB = 36.5%). Dietary overlap, as measured by Schoener's Similarity Index, was greatest between Snowy Egrets and Tricolored Herons (77%) and lowest between Tricolored Herons and Little Blue Herons (30%). Diet diversity, as measured by Shannon's Index, was highest for Great Egrets (2.04), intermediate for Snowy Egrets (1.71) and Tricolored Herons (1.68), and lowest for Little Blue Herons (1.60). Great Egrets ate a wider variety of fish species and sizes, especially larger fishes, and more crayfish than the other species. Little Blue Herons ate fewer fish and more grass shrimp and insects, and ate smaller forage fishes than Tricolored Herons but similar-sized fish as Snowy Egrets. The coarse-scale trophic composition of Snowy Egret and Tricolored Heron diets did not differ significantly, but Tricolored Herons ate larger forage fishes than Snowy Egrets. Pronounced interannual and intercolony variation in diet composition suggested that Great Egrets and Little Blue Herons switched prey types as hydrologic conditions and habitat availability changed. Conversely, lack of such variation suggested that Snowy Egrets and Tricolored Herons adjusted their foraging tactics to ensure continued encounters with preferred prey despite changing habitat conditions. These results are generally consistent with other published data, help confirm some generalizations about foraging strategies and patterns of niche differentiation among these ecologically similar species, and have implications for managing the Lake Okeechobee ecosystem.

Florida↗
USGS1998

Key areas for wintering North American herons

Nearly all North American heron populations are migratory, but details of where they winter are little known. Locations where North American herons winter were identified using banding recovery data. North American herons winter from Canada through northern South America but especially in eastern North America south of New York, Florida, California, Louisiana, Texas, Mexico and Cuba, these areas accounting for 63% of winter recoveries. We identified regions where recoveries for various species clustered as 'key areas.' These forty-three areas constitute a network of areas that hold sites that likely are important to wintering herons. The relative importance of each area and site within the network must be evaluated by further on the ground inventory. Because of biases inherent in the available data, these hypothesized key areas are indicative rather than exhaustive. As a first cut, this network of areas can serve to inform further inventory activities and can provide an initial basis to begin planning for the year-round conservation of North American heron populations.

Colonial Waterbirds↗
USGS1998

Hermit crabs in the diet of Pigeon Guillemots at Kachemak Bay, Alaska

Guillemots ( Cepphus spp.) feed their chicks a diet that is almost exclusively fish. We observed Pigeon Guillemots ( C. columba ) at two colonies in Alaska where hermit crabs (Crustacea: Anomura) were a major part of the diet for some nestlings. Hermit crabs were delivered to three of five observed nests at one colony, comprised between 2% and 22% of the items delivered at those nests, and were the second most common food type at one nest. Hermit crabs may be an attractive prey item when lipid-rich forage fish are scarce, and crabs living in gastropod shells that have been softened by encrustations of Suberites sponges may be vulnerable to guillemot predation.

Alaska↗
USGS2000

Population estimates of Nearctic shorebirds

Estimates are presented for the population sizes of 53 species of Nearctic shorebirds occurring regularly in North America, plus four species that breed occasionally. Shorebird population sizes were derived from data obtained by a variety of methods from breeding, migration and wintering areas, and formal assessments of accuracy of counts or estimates are rarely available. Accurate estimates exist only for a few species that have been the subject of detailed investigation, and the likely accuracy of most estimates is considered poor or low. Population estimates range from a few tens to several millions. Overall, population estimates most commonly fell in the range of hundreds of thousands, particularly the low hundreds of thousands; estimated population sizes for large shorebird species currently all fall below 500,000. Population size was inversely related to size (mass) of the species, with a statistically significant negative regression between log (population size) and log (mass). Two outlying groups were evident on the regression graph: one, with populations lower than predicted, included species considered either to be "at risk" or particularly hard to count, and a second, with populations higher than predicted, included two species that are hunted. Population estimates are an integral part of conservation plans being developed for shorebirds in the United States and Canada, and may be used to identify areas of key international and regional importance.

Waterbirds↗
USGS2000

Temporal variability in abundance of Marbled Murrelets at sea in southeast Alaska

We examined effects of season, time of day, tide stage, tidal oscillation, and sea surface temperature on Marbled Murrelet ( Brachyramphus marmoratus ) abundance and distribution at sea. We also evaluated whether constraining surveys to specific time periods or tide stages would reduce temporal variability in counts. Murrelets were surveyed daily from small boats and from shore in Auke Bay and Fritz Cove, Alaska, from May through August in 1992 and 1993. Murrelet numbers were high before egg-laying, declined by more than half during egg-laying and incubation and were highly variable during chick-rearing and fledging. Murrelet numbers were highest in early and late morning and declined throughout the day, sometimes increasing slightly in the evening. Peak murrelet numbers occurred on high or falling morning tides, especially in shallow areas where Pacific sand lance ( Ammodytes hexapterus ) were abundant. Differences between years in murrelet abundance and breeding phenology probably resulted from interannual differences in the pattern of seasonal warming and subsequent effects on production at lower trophic levels. We recommend that surveys for trends in abundance in Southeast Alaska be conducted in early morning, in June, at high or falling tides. Power analyses indicated that surveys conducted in this manner would minimize the number of years required to detect a significant change in abundance.

Alaska↗
USGS2000

Sexing adult black-legged kittiwakes by DNA, behavior, and morphology

We sexed adult Black-legged Kittiwakes ( Rissa tridactyla ) using DNA-based genetic techniques, behavior and morphology and compared results from these techniques. Genetic and morphology data were collected on 605 breeding kittiwakes and sex-specific behaviors were recorded for a sub-sample of 285 of these individuals. We compared sex classification based on both genetic and behavioral techniques for this sub-sample to assess the accuracy of the genetic technique. DNA-based techniques correctly sexed 97.2% and sex-specific behaviors, 96.5% of this sub-sample. We used the corrected genetic classifications from this sub-sample and the genetic classifications for the remaining birds, under the assumption they were correct, to develop predictive morphometric discriminant function models for all 605 birds. These models accurately predicted the sex of 73-96% of individuals examined, depending on the sample of birds used and the characters included. The most accurate single measurement for determining sex was length of head plus bill, which correctly classified 88% of individuals tested. When both members of a pair were measured, classification levels improved and approached the accuracy of both behavioral observations and genetic analyses. Morphometric techniques were only slightly less accurate than genetic techniques but were easier to implement in the field and less costly. Behavioral observations, while highly accurate, required that birds be easily observable during the breeding season and that birds be identifiable. As such, sex-specific behaviors may best be applied as a confirmation of sex for previously marked birds. All three techniques thus have the potential to be highly accurate, and the selection of one or more will depend on the circumstances of any particular field study.

Alaska↗
USGS2000

Predictable interregional movements by female northern pintails during winter

Factors influencing initiation of regional and interregional movements by nonbreeding ducks are poorly understood, especially during winter. During winters 1990-1991 through 1992-1993, we radiotagged 347 female Northern Pintails (Anas acuta) in southwestern Louisiana and monitored their movements to three regions: (1) the Gulf Coast Region of Louisiana and Texas (outside of southwestern Louisiana), (2) the Rice Prairie Region of Texas, and (3) the Mississippi Alluvial Valley. We found that adult females were 1.9 times more likely than were immatures to emigrate from southwestern Louisiana during winter. During winters 1990-1991 and 1991-1992, females were more likely to emigrate during stormy than during fair weather, whereas they were more likely to emigrate during fair weather in 1992-1993. Females were more likely to emigrate during duck-hunting seasons than during nonhunting seasons, regardless of weather. Daily emigration probabilities did not differ in relation to body condition when released (body mass adjusted for body size) or to number of previous emigration events. Each winter, large numbers of females consistently moved from the Gulf Coast Region to areas with abundant rice (Oryza sativa) agriculture within the Mississippi Alluvial Valley. We conclude that destination of interregional movements by this population of Northern Pintails is highly predictable, and that initiation of such movements is influenced by female age and long-term winter precipitation patterns in the Mississippi Alluvial Valley. Furthermore, timing of these movements is predictable, based not on calendar date, but rather on duck-hunting seasons and, usually, the environmental cues to habitat availability provided by stormy weather.

Waterbirds↗
USGS2002

Nesting ecology of tundra swans on the coastal Yukon-Kuskokwim Delta, Alaska

Nesting ecology of Tundra Swans (Cygnus columbianus columbianus) was studies the Kashunuk River near Old Chevak (61A?26a??N, 165A?27a??W), on the Yukon-Kuskokwim Delta of western Alaska from 1988-2000. Annual variation in snow-melt chronology, nesting phenology, nesting density, clutch size and nest success was examined. The same area (approximately 23 kmA?) was searched each year and nests were found as early as possible in the laying period. Laying initiation dates ranged from 1-27 May and hatch dates from 12 June a?? 4 July among pairs and years of study. The peak arrival of Tundra Swans and the phenology of nest initiation and hatch were highly correlated with the progression of ice and snow melt in spring. Nest density averaged 0.71 kmA? and 89% of nesting pairs hatched at least one egg. Incubation period ranged from 26 to 33 days with a median of 30 days. Clutch size varied significantly among years, driven by a low mean value of 3.4 eggs in 1999. Clutch sizes were generally larger than found in previous investigations on the Yukon-Kuskokwim Delta, and nearly one egg larger than reported for clutches from Alaskaa??s North Slope (=70A?N). There was no indication of reduced clutch size in years of late spring snow melt, although nesting density tended to be lower.

Waterbirds↗
USGS2001

Using resampling to assess reliability of audio-visual survey strategies for marbled murrelets at inland forest sites

Marbled Murrelets (Brachyramphus marmoratus) are threatened seabirds that nest in coastal old-growth coniferous forests throughout much of their breeding range. Currently, observer-based audio-visual surveys are conducted at inland forest sites during the breeding season primarily to determine nesting distribution and breeding status and are being used to estimate temporal or spatial trends in murrelet detections. Our goal was to assess the feasibility of using audio-visual survey data for such monitoring. We used an intensive field-based survey effort to record daily murrelet detections at seven survey stations in the Oregon Coast Range. We then used computer-aided resampling techniques to assess the effectiveness of twelve survey strategies with varying scheduling and a sampling intensity of 4-14 surveys per breeding season to estimate known means and SDs of murrelet detections. Most survey strategies we tested failed to provide estimates of detection means and SDs that were within A?20% of actual means and SDs. Estimates of daily detections were, however, frequently estimated to within A?50% of field data with sampling efforts of 14 days/breeding season. Additional resampling analyses with statistically generated detection data indicated that the temporal variability in detection data had a great effect on the reliability of the mean and SD estimates calculated from the twelve survey strategies, while the value of the mean had little effect. Effectiveness at estimating multi-year trends in detection data was similarly poor, indicating that audio-visual surveys might be reliably used to estimate annual declines in murrelet detections of the order of 50% per year.

Waterbirds↗
USGS2002

Parental care in Tundra Swans during the pre-fledgling period

Among studies that have quantified the care of precocial young, few have investigated forms of parental care other than vigilance. During the pre-fledging period, Tundra Swan (Cygnus columbianus columbianus) parents provided simultaneous biparental care by foraging near each other and their cygnets, and cygnets spent more time foraging during bouts in which both parents were foraging nearby than when only one parent was foraging nearby. Parents spent nearly twice as much foraging time on land than did non-parents, a habitat in which cygnets foraged more intensely than parents (i.e., spent more time foraging during foraging bouts) and could graze on protein-rich sedges rather than use more difficult below-water foraging methods. Parents also spent more than twice as much time being vigilant and more than three times as much time defending their territory than non-parents, behaviors that presumably benefited cygents by decreasing predation risk and indirect foraging competition, respectively. Parents therefore incurred the costs of foraging less intensely during foraging bouts, spending more time interacting, more time in vigilance, and less time sleeping/preening than non-parents.

Waterbirds↗
USGS1988

Organochlorine residues in great blue herons from the northwestern United States

We collected eggs or young Great Blue Herons from eight nesting colonies in the northwestern United States from 1977 through 1982. Subadults were collected at three estuarine areas in Puget Sound in 1981 and dead young or adults were collected at various localities. Nearly all samples analyzed contained organochlorine residues. There was no evidence that nay of the organochlorines detected were related to lethal or serious sublethal effects.

Colonial Waterbirds↗
USGS1986

Waterfowl and wetlands management in the coastal zone of the Atlantic Flyway: Meeting and summary comments

A conference on waterfowl and wetlands along the Atlantic coast of North America was held in Wilmington, Delaware in September 1986. Discussions centered around coastal impoundments and Open Marsh Water Management as methods of mosquito control and waterfowl enhancement. Single purpose management of coastal marshes, whether for mosquito control or waterfowl, may not be the most beneficial approach. Where management options are available, the management for habitat heterogeneity may be indicated.

Colonial Waterbirds↗
USGS1999

Predicting chick survival and productivity of Roseate Terns from data on early growth

Early growth of Roseate Tern (Sterna dougallii) chicks is a strong predictor of chick survival and hence of productivity. We developed discriminant functions to predict chick survival from body-masses measured during the first 3 days of life. Productivity is estimated by assuming that almost all A-chicks (first-hatched in each brood) survive to fledging, and using the discriminant functions to predict survival of B-chicks (second-hatched in each brood). A relation between survival rates and classification rates is derived, allowing discriminant function results to be used in predicting survival rates. In the absence of predation, the resulting estimates of chick survival and productivity are almost as good as those obtained by more intensive methods, but require much less effort and much less disturbance. This approach might be useful for other seabird species in which chick survival is determined primarily by parental performance.

Waterbirds↗
USGS1999

Aspects of chick growth in Gull-billed Terns in coastal Virginia

Because of concerns about apparent population declines and low productivity of Gull-billed Terns (Sterna nilotica) along the coast of Virginia, we investigated whether food limitations may result in retarded growth rates of young. Several colonies of Gull-billed Terns were monitored from May to July each year from 1994 to 1996 on both sandy barrier islands and marsh/shellpile islands in coastal Virginia. Nests were visited one to three times a week to monitor clutch size and hatching success, and enclosures were installed around selected nests to monitor chick growth from hatching to at least two weeks of age. When comparing chick growth, we found significant year, habitat and hatch order effects. Chicks from marsh shellpiles had higher mass and culmen growth rates than did those from barrier islands, and first-hatched (A) chicks had significantly higher culmen growth rates than did second-hatched (B) chicks. Year effects were only found for mass growth rates. Growth rates of Gull- billed Terns in these Virginia colonies seem to be low relative to those of six other North American tern species from other geographic areas. These findings suggest that growth rates of young Gull-billed Terns, as well as other reproductive parameters, need to be examined in detail in other coastal areas such as Texas, where the species is more abundant, to determine whether our growth results are species- or region-specific.

Waterbirds↗
USGS1999

Aspects of hatching success and chick survival in Gull-billed Terns in coastal Virginia

Because of a long-term population decline in Gull-billed Terns (Sterna nilotica) nesting along the coast of Virginia, we began a three year study in 1994 to monitor hatching success and survival of Gull-billed Tern chicks at several Virginia colony sites. Colonies were located on either small, storm-deposited shellpiles along marsh fringes or large, sandshell overwash fans of barrier islands. Nests were monitored one to three times a week for hatching success, and enclosures were installed around selected nests to monitor chick survival from hatching to about two weeks of age. Hatching success was lower in marsh colonies than island colonies, and was lower in 1995 than in 1994 and 1996, primarily because of flooding. The average brood size of nests where at least one chick hatched was 1.99 chicks. Survival rates of chicks to 14 days depended on hatch order and year but not brood size (one vs. two or more) or time of season. A-chicks had higher survival rates than B-chicks and third-hatched C-chicks (0.661 compared to 0.442 and 0.357, respectively). The year effect was significant only for A-chicks, with lower survival in 1994 (0.50) than in 1995 (0.765) or 1996 (0.758). Overall, productivity was low (0.53 chick per nest) compared to estimates for colonies in Denmark, and was attributable to nest flooding by spring and storm-driven high tides and chick predation, presumably mostly by Great Horned Owls (Bubo virginianus).

Waterbirds↗
USGS1999

Contribution of research to management and recovery of the roseate tern: review of a twelve-year project

The Northwest Atlantic population of the Roseate Tern (Sterna dougallii) is largely confined to a small breeding area along the northeast coast of the USA between 40? and 42?N. This population was listed as endangered in the USA in 1987 because it was dangerously concentrated into a few breeding sites (85% on two islands in the 1980s). The nesting population in the area from Long Island, New York to Cape Cod, Massachusetts has been studied intensively since 1987, in conjunction with a program of management of the breeding colonies. This paper summarizes the results of the research program and discusses the extent to which it has contributed to effective management. The regional population now numbers about 4,000 breeding pairs and has been increasing slowly since 1987, except between 1991 and 1992 when it declined by about 17%. This decline was probably caused by Hurricane `Bob' in August 1991. Roseate Terns have specialized foraging habits and are concentrated into a small number of foraging areas near the nesting colonies. The historically important breeding sites were taken over by large gulls between 1930 and 1972. Many of the terns moved to less suitable sites near the mainland, where they are subject to predation by mainland-based predators. Despite this, Roseate Terns breed with high success at many sites. The sex-ratio is skewed towards females; about 12% of nests are attended by female-female pairs. The annual adult survival rate (0.83) is unusually low for a seabird. Most mortality occurs away from the breeding grounds, but the winter quarters remained unknown until one roost site was found in Brazil in 1995-1997. A major management goal has been to restore former colony-sites by eliminating nesting gulls, but the success of some of these projects has been questionable because they may have attracted birds to sites with higher levels of predation. Although the research has yielded important information about the biology and demography of the species, it has taken longer than expected to obtain and analyze data from multiple sites on this long-lived species. Most work has been carried out at breeding sites: critical studies on feeding ecology and winter ecology have been hampered by insufficient funding and the paucity of self-motivated biologists. Hence, the program has not yet provided all the keys to restoring the population.

Waterbirds↗