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At least 559 records · Page 31Linked to original sources
USGS2006

Testing the junk-food hypothesis on marine birds: Effects of prey type on growth and development

The junk-food hypothesis attributes declines in productivity of marine birds and mammals to changes in the species of prey they consume and corresponding differences in nutritional quality of those prey. To test this hypothesis nestling Black-legged Kittiwakes (Rissa tridactyla) and Tufted Puffins (Fratercula cirrhata) were raised in captivity under controlled conditions to determine whether the type and quality of fish consumed by young seabirds constrains their growth and development. Some nestlings were fed rations of Capelin (Mallotus villosus), Herring (Clupea pallasi) or Sand Lance (Ammodytes hexapterus) and their growth was compared with nestlings raised on equal biomass rations of Walleye Pollock (Theragra chalcograma). Nestlings fed rations of herring, sand lance, or capelin experienced higher growth increments than nestlings fed pollock. The energy density of forage fish fed to nestlings had a marked effect on growth increments and could be expected to have an effect on pre- and post-fledging survival of nestlings in the wild. These results provide empirical support for the junk-food hypothesis.

Waterbirds↗
USGS2006

Breeding ecology and nesting habitat associations of five marsh bird species in western New York

Nesting habitats and nest success of five species of marsh birds were studied during 1997 and 1998 at the Iroquois National Wildlife Refuge (NWR) and the adjacent Oak Orchard and Tonawanda State Wildlife Management Areas (WMA) located in western New York. Nest searches located 18 American Bittern (Botaurus lentiginosus), 117 Least Bittern (Ixobrychus exilis), 189 Pied-billed Grebe (Podilymbus podiceps), 23 Sora (Porzana carolina), and 72 Virginia Rail (Rallus limicola) nests. Average nest densities in 1998, our best nest searching year, ranged from 0.01/ha for Soras (N = 8) to 0.28/ha for Pied-billed Grebes (N = 160). Mayfield nest success estimates for Least Bittern were 80% (N = 16) in 1997 and 46% (N = 37) in 1998. Nest success estimates were 72% (N = 55) for Pied-billed Grebe, 43% (N = 6) for Sora, and 38% (N = 20) for Virginia Rail. Nests of all five species were located in ???70% emergent vegetation with a mean water depth of 24-56 cm and an average vegetation height that ranged from 69-133 cm. Logistic regression models were developed for each species using habitat variables at nest and random site locations. Each model was ranked with Akaike's Information Criterion for small sample size (AICc). In general, our best models indicated that increased emergent vegetation and horizontal cover with shallow water depths improved the odds of encountering marsh bird nests in the wetlands of western New York. We suggest that managing wetlands as a complex, at different stages of succession, would best benefit marsh bird species.

Waterbirds↗
USGS2006

Traversing a boreal forest landscape: Summer movements of Tule Greater White-fronted Geese

We monitored the movement, distribution and site affinities of radio-marked Tule Greater White-fronted Geese (Anser albifrons elgasi) during spring and summer in Alaska, 1994-1997 and 2004. Our assessment of summer movements was comprehensive, as locations were obtained during prenesting, nesting, and molt for over 90% of geese with active radios captured during winter or the previous summer in Alaska. Geese arrived to coastal and interior marshes in the Cook Inlet Basin (CIB) from mid April to early May, after which they moved to nesting areas in the upper CIB. Nesting birds used coastal staging areas in close proximity to eventual nest site location. Molting sites included a sub-glacial lake system in the upper CIB, although up to 50% of geese underwent a molt migration to wetlands across the Alaska Range, 400-600 km west of the CIB. Geese that molted at distant sites returned to the CIB before autumn migration. Length of stay in the CIB varied among years from 108-119 days, and averaged 116 days. Summer home-range sizes, exclusive of molting areas, averaged >273,000 ha, and were substantially larger than reported for other northern-nesting waterfowl. No radio-marked geese were found nesting in the vicinity of Redoubt Bay on the west side of Cook Inlet, and few nested near the Susitna Flats, the only other previously known nesting areas. The absence of nesting geese from Redoubt Bay corroborates aerial survey data showing a precipitous decline in the use of the west side of Cook Inlet between the early 1980s and early 1990s. The change in distribution of geese is likely related to a major eruption of Redoubt Volcano in 1989 that significantly altered landscapes used by nesting, brood rearing, and molting geese in the vicinity of Redoubt Bay. High inter-site movements of Greater White-fronted Geese throughout summer in south central Alaska likely increases exposure to predation, but also promotes social interactions and facilitates pioneering of distant, and diverse habitats in a vast, patchy, and often unpredictable landscape.

Alaska↗
USGS2006

Different time and energy budgets of Lesser Snow Geese in rice-prairies and coastal marshes in southwest Louisiana

Many bird species use human-made habitats and an important issue is whether these are equally suitable foraging habitats as are historical, natural habitats. Historically, Lesser Snow Geese (Chen caerulescens caerulescens, hereafter Snow Geese) wintered in coastal marshes in Louisiana but began using rice-prairies within the last 60 years. Time spent feeding was used as an indicator of habitat suitability and time and energy budgets of Snow Geese were compared between rice-prairies and coastal marshes in southwest Louisiana. Composite diets of Snow Geese have a lower energy density in the rice-prairies than in coastal marshes; thus, we predicted that Snow Geese would spend relatively more time feeding in rice-praires to obtain existence energy. However, time spent feeding was higher in coastal marshes and thus, not proportional to energy density of composite diets. Snow Geese in coastal marshes ingested less apparent metabolizable energy than did Snow Geese in rice-prairies. In rice-prairies, juveniles spent more time feeding than did adults; however, time spent feeding was similar between age classes in coastal marshes. Undeveloped foraging skills probably cause juvenile Snow Geese to forage less efficiently in coastal marshes than in rice-prairies. These findings are consistent with recent trends in Snow Goose numbers, which increased in rice-prairies but remained stable in coastal marshes.

Waterbirds↗
USGS2006

Sexing Forster's Terns using morphometric measurements

Forester's Terns (Sterna forsteri), like most seabirds, are monomorphic and are difficult to sex without extensive behavioral observations or genetic sexing. We conducted the first morphological study and discriminant function analysis on Forster's Terns to develop a method to accurately identify their sex in the field. A sample of 84 terns from the San Francisco Bay estuary were captured or collected, measured, and the sex of 40 female and 44 male terns was confirmed by genetic analyses or via necropsy. Male Forster's Terns were larger than females for 7 of 9 morphological measurements, with head-bill length showing the least amount of overlap between the sexes, followed by culmen length and culmen depth at the gonys. Sexual size dimorphism was greatest with retrix R6 length, followed by culmen width, and culmen depth. A discriminant function including only head-bill length accurately sexed 82% of Forster's Terns, whereas a second discriminant function incorporating both head-bill length and culmen depth at the gonys increased sexing accuracy to 87%. When we used a 75% posterior probability or greater of accurately sexing Forster's Terns, we excluded only 18% of the sample that overlapped and accurately sexed 94% of the remaining individuals. Our results indicate that Forster's Terns can be accurately sexed in the field using only 2 morphological measurements.

Waterbirds↗
USGS2007

Temporal changes of populations and trophic relationships of wintering diving ducks in Chesapeake Bay

Population and trophic relationships among diving ducks in Chesapeake Bay are diverse and complex as they include five species of bay ducks (Aythya spp.), nine species of seaducks (Tribe Mergini), and the Ruddy Duck (Oxyura jamaicensis). Here we considered the relationships between population changes and diet over the past half century to assess the importance of prey changes to wintering waterfowl in the Bay. Food habits of 643 diving ducks collected from Chesapeake Bay during 1999-2006 were determined by analyses of their gullet (esophagus and proventriculus) and gizzard contents and compared to historical data (1885-1979) of 1,541 diving ducks. Aerial waterfowl surveys, in general, suggest that six species of seaducks were more commonly located in the meso- to polyhaline areas of the Bay, whereas five species of bay ducks and Ruddy Ducks were in the oligo- to mesohaline areas. Seaducks fed on a molluscan diet of Hooked Mussel (Ischadium recurvum), Amethyst Gemclam (Gemma gemma), and Dwarf Surfclarn (Mulinia lateralis). Bay ducks and Ruddy Ducks fed more on Baltic Macoma (Macoma balthica), the adventive Atlantic Rangia (Rangia cuneata), and submerged aquatic vegetation (SAV). Mergansers were found over the widest salinity range in the Bay, probably because of their piscivorous diet. Each diving duck species appears to fill a unique foraging niche, although there is much overlap of selected prey. When current food habits are compared to historic data, only the Canvasback (Aythya valisineria) has had major diet changes, although SAV now accounts for less food volume for all diving duck species, except the Redhead (Aythya americana). Understanding the trophic-habitat relationships of diving ducks in coastal wintering areas will give managers a better understanding of the ecological effects of future environmental changes. Intensive restoration efforts on SAV and oyster beds should greatly benefit diving duck populations.

Waterbirds↗
USGS2007

Longterm trends in nest counts of colonial seabirds in South Carolina, USA

We analyzed temporal and spatial trends in annual nest counts of Brown Pelicans (Pelecanus occidentalis), Royal Terns (Sterna maxima), and Sandwich Terns (Sterna sandvicensis) throughout South Carolina from 1969 through 2005. There was an increase in the number of active pelican nests from 1969 through the mid 1980s, although this was followed by a steady decline that continued through 2005. Numbers of Royal Tern nests have declined during the study period, especially since 1990. In contrast, annual counts of active Sandwich Tern nests remained relatively stable through the mid 1980s, then increased substantially and have since remained stable. During the early years of the study, a greater proportion of nests from each species occurred on colonies within the Cape Romain region, although this distribution appears to have shifted with a greater proportion of nests now occurring along the southern coast. At the statewide level and at each of the primary colonies, we observed a positive correlation in counts of Brown Pelican and Royal Tern nests. Mechanisms underlying the observed trends are unclear. We suggest that priorities for research include (1) determination of diet and foraging locales for all three species, (2) impacts of ectoparasites on condition and survival of pelican chicks, and (3) metapopulation structure of all three species. Management activities should focus primarily on protection of colony sites.

Waterbirds↗
USGS2007

Scale-dependent habitat selection of nesting Great Egrets and Snowy Egrets

Foraging habitat selection of nesting Great Egrets (Ardea alba) and Snowy Egrets (Egretta thula) was investigated within an estuary with extensive impounded salt marsh habitat. Using a geographic information system, available habitat was partitioned into concentric bands at five, ten, and 15 km radius from nesting colonies to assess the relative effects of habitat composition and distance on habitat selection. Snowy Egrets were more likely than Great Egrets to depart colonies and travel to foraging sites in groups, but both species usually arrived at sites that were occupied by other wading birds. Mean flight distances were 6.2 km (SE = 0.4, N = 28, range 1.8-10.7 km) for Great Egrets and 4.7 km (SE = 0.48, N = 31, range 0.7-12.5 km) for Snowy Egrets. At the broadest spatial scale both species used impounded (mostly salt marsh) and estuarine edge habitat more than expected based on availability while avoiding unimpounded (mostly fresh water wetland) habitat. At more local scales habitat use matched availability. Interpretation of habitat preference differed with the types of habitat that were included and the maximum distance that habitat was considered available. These results illustrate that caution is needed when interpreting the results of habitat preference studies when individuals are constrained in their choice of habitats, such as for central place foragers.

Waterbirds↗
USGS2007

Responses of California Brown Pelicans to disturbances at a large Oregon roost

Numbers of California Brown Pelicans (Pelecanus occidentalis californicus) along the coast of Oregon and Washington have increased sharply in recent years. We identified East Sand Island in the Columbia River estuary as the site of the largest pelican roost within this region. Numbers of pelicans roosting on East Sand Island have increased from less than 100 during 1979-1986 to a high count of 10,852 in 2002. The East Sand Island roost is currently the site of a major non-breeding aggregation of this endangered subspecies. Total numbers of pelicans roosting on East Sand Island increased seasonally from April to September or October, and then declined sharply with the onset of winter storms. Pelicans appeared to forage more during low tides, and return to the roost during high tides; therefore, pelican numbers on the island were positively associated with tide height. Land-based human disturbance was negatively associated with total pelican numbers, whereas water-based human disturbance had no significant effect on total pelican numbers on the island. Natural disturbances, although more frequent than human disturbances, apparently did not influence the total number of pelicans on the island.

Waterbirds↗
USGS2007

Daily foraging patterns of adult Double-crested Cormorants during the breeding season

We recorded the daily presence of Double-crested Cormorants (Phalacrocorax auritus) at the nesting island on Oneida Lake, New York, by monitoring the activities of 15 radio-tagged adults from July through September, 2000, using an automated data-logging receiver. A total of 24,464 acceptable detections was obtained for adult cormorants actively attempting to nest on the lake. Tagged cormorants had a bimodal dally activity pattern during the first month, with the fewest birds detected on the island at 09.00 h and 15.00 h Eastern daylight time. The pattern of activity appeared to change slightly in the second month of the study, representative of a post-breeding period for the colony, with a shift from a less synchronous pattern of departures to a greater focus on morning activity also centered around 09.30 h. These results correspond with daily observations of Great Cormorant (P. carbo) foraging activities reported for colonies in Africa and Poland. The data also support the possibility of nocturnal foraging activity, not previously reported for this species on their summer breeding grounds. No correlation was found between total number of daily detections and climatalogical factors or events.

Waterbirds↗
USGS2007

Egg flotation estimates nest age for Pacific and Red-throated Loons

We used Pacific Loon (Gavia pacifica) and Red-throated Loon (G. stellata) nests with known ages to gauge the efficacy of egg flotation for determining nest age in coastal Alaska. Egg flotation accurately estimated nest age for both species; the mean ± 1SD difference between known age and age determined with egg flotation was - 0.05 ± 2.00 d and -0.02 ± 1.63 d for Pacific and Red-throated Loons, respectively. Day of nest initiation did not influence the relationship between known nest age and nest age estimated with egg flotation, indicating incubation period was not shortened in nests initiated later in the season. Additionally, we found no difference in the ability of egg flotation to estimate nest age between two widely dispersed study sites for Pacific Loons, and only a small difference between two of three widely dispersed study sites for Red-throated Loons. Thus, our described relationships between egg flotation categories and nest age should be broadly applicable for these holarctic species. We conclude that for Pacific and Red-throated Loons, egg flotation is a useful technique for determining nest age in the field to better monitor nest fate, and to quantify nest age effects on nest daily survival rate.

Waterbirds↗
USGS2007

Mercury and selenium in American White Pelicans breeding at Pyramid Lake, Nevada

American White Pelicans (Pelecanus erythrorhynchos) that breed on Anaho Island, Pyramid Lake, Nevada, are potentially exposed to a variety of contaminants. Therefore, the reproductive success of this colony was monitored in 1996 and eggs, blood and feathers from nestlings, livers from adults and nestlings, regurgitated fish from nestlings, and fish from representative feeding areas were collected and analyzed for mercury and selenium to determine exposure to the pelicans and sources of contamination. Additional samples were collected and analyzed in 1988, 1992, and 2004. Reproductive success at the Anaho Island colony was normal in 1996 based on hatching rates of eggs (???75% in undisturbed areas) and survival of nestlings. Mercury and selenium concentrations in eggs were generally below known effect levels and did not appear to have an adverse impact on hatching success. Mercury and selenium concentrations in fish ranged widely, with mercury of greatest concern. Microscopic lesions characteristic of mercury toxicity were absent in pre-fledging nestlings in 1996. Some adult pelicans had elevated mercury concentrations in their livers; however, the potential toxic effects were difficult to evaluate because of probable demethylation of mercury, thereby possibly providing protection from toxicity. Exposure of pelicans to mercury varied among years, most likely in relation to wet-dry cycles and available feeding areas.

Waterbirds↗
USGS2008

Assessing habitat use by breeding Great Blue Herons (Ardea herodias) on the Upper Mississippi River, USA

Approximately 7,610 to 3,175 pairs of Great Blue Herons ( Ardea herodias ) nested along 420 river km of the Upper Mississippi River (UMR) from 1993 to 2003. Numbers declined precipitously in the mid-1990s stabilizing somewhat in the early 2000s. The average number of nests in colonies was 349 (SD = 283). Annual colony turn over rate for the eleven year period was 0.15 and ranged from 0.06 to 0.29 each year. The number of years that a colony was active was positively correlated with the average number of nests present while the colony was active. Of the eight colonies active in 1993 that averaged more than 349 nests, four were abandoned by 2003. Only one colony grew to greater than 349 nests during the study period. Custer et al. (2004) suggested that herons on the UMR may be limited by forage resources or foraging habitat and social factors, as evidenced by the even spacing of colonies that reflects the maximum feeding range of herons on the river. To rule out nesting and foraging habitat limitation, landscape habitat features of terrestrial and aquatic areas were examined for colony areas and areas without colonies. Available fish monitoring data were used to examine potential interactions between herons and forage resources. Colony areas did not differ from areas without colonies in any habitat feature. Indices of potential heron forage fish increased from 1993 to 2002, although low indices of fish abundance in 1993 were likely influenced by flood conditions that year. Although fish availability to herons is related to flows and water levels, available data suggested that herons did not negatively impact their potential forage base. Numbers of herons were not correlated with indices of fish abundance from the preceding year on a pool-wide scale. Indices of fish abundance were higher within 5 km of colonies than farther than 5 km from colonies, and indices of fish abundance increased from June through August both near and far from colonies. Numbers of herons and locations and sizes of colonies varied annually, whereas landscape features typically vary little if at all from year to year. Indices of fish abundance also varied greatly by sample location and year. Disturbance, particularly by humans in this highly used river, should be examined in relation to limiting foraging opportunities and influencing behavior (colony and individual) and productivity in colonies.

Illinois, Iowa, Minnesota, Missouri, Wisconsin↗
USGS2008

Diets of Lesser Scaup during spring migration throughout the upper-Midwest are consistent with the spring condition hypothesis

The spring condition hypothesis (SCH) states that the current decline of the North American scaup population (Lesser [Aythya affinis] and Greater Scaup [A. marila] combined) is due to a decline in quality or availability of scaup foods on wintering, spring migration, or breeding areas that has caused a reduction in female body condition and subsequent reproductive success. Our previous research indicated that forage quality in diets of Lesser Scaup (hereafter scaup) at two sites in Northwestern Minnesota was lower in springs 2000-2001 than that reported for springs 1986-1988, consistent with the SCH. Accordingly, we further tested the SCH at a landscape scale, by comparing amounts of amphipods in diets (index of forage quality) of scaup (N = 263) collected in springs 2003-2005 from seven eco-physiographic regions in Iowa, Minnesota, and North Dakota in relation to data from Northwestern Minnesota during springs 2000-2001. We found that aggregate percentages of Gammarus lacustris and Hyalella azteca (amphipods) in scaup diets during springs 2000-2001 in Northwest Minnesota were similar to those in the Iowa Prairie Pothole, Minnesota Morainal, Minnesota Glaciated Plains, Red River Valley, and Northwestern Minnesota in springs 2003-2005; however, scaup consumed relatively higher aggregate percentages of Gammarus lacustris and Hyalella azteca in North Dakota Missouri Coteau and North Dakota Glaciated Plains. Females in Iowa were over three times less likely to have consumed food than those in North Dakota, despite previous research indicating similar foraging rates among these regions. Mean mass of scaup diet samples throughout the upper-Midwest were 77 mg (49%) and 87 mg (52%) lower than those of historical studies in Minnesota and Manitoba, respectively. We conclude that there has been a decrease in forage quality for scaup in Iowa and Minnesota and a decrease in the amount of forage consumed throughout the upper-Midwest, consistent with the SCH.

Minnesota↗
USGS2008

Space use by Forster's Terns breeding in South San Francisco Bay

Parental care behaviors often differ in dimorphic seabirds, leading to sex-specific differences in foraging behaviors. However, few studies have examined sex-specific foraging behaviors in monomorphic seabirds. Using radio-telemetry, we studied Forster's Terns (Sterna forsteri) - a monomorphic and socially monogamous seabird - breeding in the South San Francisco Bay, California. Space use did not differ between males and females. Instead, space use varied by breeding stage and colony affiliation. Forster's Terns were located farthest from the nest during pre-breeding and post-breeding time periods, and closest to the nest during incubation and chick-rearing. Home-range size and core-use areas decreased as the breeding season progressed and were most concentrated in the post-breeding stage. The results of this and other studies indicate that tems, unlike other monomorphic seabirds studied, do not exhibit sex-specific differences in space use.

Waterbirds↗
USGS2008

Breeding stage influences space use of female American avocets in San Francisco Bay, California

Female American Avocets (Recurvirostra americana) were radio-marked (N=15) and tracked in the South San Francisco Bay, California, to determine if space use varied by breeding stage. Visual observations were used to determine breeding stage (pre-incubation, incubation, brood-rearing, post-breeding) of marked avocets. Space use measurements (linear movements, home ranges, core areas, and average distance from nest) varied significantly among breeding stages. Space use was greatest for the post-breeding stage, followed by pre-incubation, incubation, and brood-rearing. Most avocet nests (93%) were located within their pre-incubation core area boundaries, whereas only 36% of nests were within post-breeding core areas. Distance between daily location and future nest sites decreased significantly as the number of days prior to incubation decreased, suggesting that avocets prospected future nest sites several weeks prior to nesting. These data indicate that breeding stage influences space use of female American Avocets and illustrates the importance of delineating breeding stages to better understand space use of avian species.

Waterbirds↗
USGS2008

Breeding phenology and reproductive success of the Brandt's Cormorant at three nearshore colonies in central California, 1997-2001

Brandt's Cormorant ( Phalacrocorax penicillatus ) breeding effort, phenology and success were studied in 1997-2001 at three colonies spanning approximately 200 km of the central California coast: Point Reyes (PR); Devil's Slide Rock and Mainland (DS); and Castle-Hurricane Colony Complex (CH). Breeding effort was reduced at all three colonies in the 1998 El Niño event. Mean clutch initiation dates differed significantly among colonies, with cormorants at the southernmost colony (CH) laying earliest, and those at the northernmost colony (PR) laying latest. Productivity at individual colonies varied greatly among years (range 0.7-2.5 fledglings per pair). Overall colony means were lowest (1.6 fledglings/pair) during the 1998 El Niño event and highest (2.5 fledglings/pair) in the 1999 La Niña event. Productivity at CH (1.7 fledglings/pair) was significantly lower than at PR (2.2 fledglings/pair), and interannual variation was greatest at CH. Late-nesting birds laid fewer eggs, hatched fewer chicks, and fledged fewer chicks per pair than early-nesters. The rapid rate of growth at some nearshore colonies in central California suggests immigration from elsewhere, most likely the large offshore colony at the South Farallon Islands. Variation in timing of breeding and reproductive success among colonies demonstrates a value in maintaining multiple study locations when assessing Brandt's Cormorant population parameters in the California Current System.

Waterbirds↗
USGS2008

Low prevalence of avian influenza virus in shorebirds on the Pacific coast of North America

The emergence of highly pathogenic avian influenza (HPAI) H5N1 has elevated concerns about wild birds as virus hosts; however, little is known about the ecological and epidemiological factors of transmission by shorebirds. Here we summarize results for 2,773 shorebirds that were live-trapped on the Pacific coast of the United States during 2006-2007 and tested for avian influenza virus using real-time reverse transcriptase-polymerase chain reaction (RT-PCR) and virus isolation. As was the case throughout North America, HPAI H5N1 was not detected in shorebirds during this interval. Contrary to other wild bird groups, most notably waterfowl, the prevalence of even low pathogenicity virus among shorebirds in our study areas in California, Washington, and Alaska was extremely low (0.5%). Virus was detected by RT-PCR from four different species, including, Dunlin (Calidris alpina; N = 3), Western Sandpiper (C. mauri; N = 8), Long-billed Dowitcher (Limnodromus scolopaceus; N = 1), and American Avocet (Recurvirostra americana; N = 1), with the detections in the latter three constituting the first published records for these birds. Based on studies in the eastern United States, we expected, but did not detect (H 1 = 1.6, P = 0.21) elevated avian influenza prevalence among shorebirds during spring migration. Diagnostic tests, which were designed to evaluate testing and sampling methods, indicated poor functioning of traditional virus isolation methods and no improvement in detection likelihood by collecting oropharyngeal swabs in addition to cloacal swab samples for low pathogenicity viruses (Z 1 = 0.7, P = 0.48).

Waterbirds↗