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USGS2012

Variation in migratory behavior influences regional genetic diversity and structure among American kestrel populations (Falco sparverius) in North America

Birds employ numerous strategies to cope with seasonal fluctuations in high-quality habitat availability. Long distance migration is a common tactic; however, partial migration is especially common among broadly distributed species. Under partial migration systems, a portion of a species migrates, whereas the remainder inhabits breeding grounds year round. In this study, we identified effects of migratory behavior variation on genetic structure and diversity of American Kestrels (Falco sparverius), a widespread partial migrant in North America. American Kestrels generally migrate; however, a resident group inhabits the southeastern United States year round. The southeastern group is designated as a separate subspecies (F. s. paulus) from the migratory group (F. s. sparverius). Using mitochondrial DNA and microsatellites from 183 and 211 individuals, respectively, we illustrate that genetic structure is stronger among nonmigratory populations, with differentiation measures ranging from 0.060 to 0.189 depending on genetic marker and analysis approach. In contrast, measures from western North American populations ranged from 0 to 0.032. These findings suggest that seasonal migratory behavior is also associated with natal and breeding dispersal tendencies. We likewise detected significantly lower genetic diversity within nonmigratory populations, reflecting the greater influence of genetic drift in small populations. We identified the signal of population expansion among nonmigratory populations, consistent with the recent establishment of higher latitude breeding locations following Pleistocene glacial retreat. Differentiation of F. s. paulus and F. s. sparverius reflected subtle differences in allele frequencies. Because migratory behavior can evolve quickly, our analyses suggest recent origins of migratory American Kestrel populations in North America.

Journal of Heredity↗

USGS2022

Increased mercury and reduced insect diversity in linked stream-riparian food webs downstream of a historical mercury mine

Historical mining left a legacy of abandoned mines and waste rock in remote headwaters of major river systems in the western United States. Understanding the influence of these legacy mines on culturally and ecological important downstream ecosystems is not always straight-forward because of elevated natural levels of mineralization in mining-impacted watersheds. To test the ecological effects of historic mining in the headwaters of the upper Salmon River watershed (USA), we measured multiple community and chemical endpoints in downstream linked aquatic-terrestrial food webs. Mining inputs impacted downstream food webs through increased mercury accumulation and decreased insect biodiversity. Total mercury (THg) in seston, aquatic insect larvae, adult aquatic insects, riparian spiders, and fish at sites up to 7.6 km downstream of mining was in much higher concentrations (1.3 to 11.3-fold) and isotopically distinct compared with sites immediately upstream of mining inputs. Methylmercury (MeHg) concentrations in bull trout and riparian spiders were sufficiently high (732 – 918 and 347 – 1,140 ng MeHg g -1 dw) to affect humans, birds, and piscivorous fish. Furthermore, the alpha-diversity of benthic insects was locally depressed by 12-20% within 4.3 to 5.7 km downstream of from the mine. However, because total insect biomass was not affected by mine inputs, the mass of mercury in benthic insects at a site (i.e., ng Hg m -2 ) was extremely elevated downstream (10 – 1,778-fold) compared with directly upstream of mining inputs. Downstream adult aquatic insect-mediated fluxes of total mercury were also high (~16 ng THg m -2 d -1 ). Abandoned mines can have ecologically important effects on downstream communities, including reduced biodiversity and increased mercury flux to higher order consumers, including fish, birds, and humans.

Idaho↗

USGS2013

Tamarix and Diorhabda leaf beetle interactions: implications for Tamarix water use and riparian habitat

Tamarix leaf beetles (Diorhabda carinulata) have been widely released on western United States rivers to control introduced shrubs in the genus Tamarix, with the goals of saving water through removal of an assumed high water-use plant, and of improving habitat value by removing a competitor of native riparian trees. We review recent studies addressing three questions: (1) to what extent are Tamarix weakened or killed by recurrent cycles of defoliation; (2) can significant water salvage be expected from defoliation; and (3) what are the effects of defoliation on riparian ecology, particularly on avian habit? Defoliation has been patchy at many sites, and shrubs at some sites recover each year even after multiple years of defoliation. Tamarix evapotranspiration (ET) is much lower than originally assumed in estimates of potential water savings, and are the same or lower than possible replacement plants. There is concern that the endangered southwestern willow flycatcher (Empidonax trailli extimus) will be negatively affected by defoliation because the birds build nests early in the season when Tamarix is still green, but are still on their nests during the period of summer defoliation. Affected river systems will require continued monitoring and development of adaptive management practices to maintain or enhance riparian habitat values. Multiplatform remote sensing methods are playing an essential role in monitoring defoliation and rates of ET on affected river systems.

JAWRA↗

USGS1999

The 1992 epizootic of Newcastle disease in double-crested cormorants in North America

In the summer of 1992, morbidity and mortality in juvenile double-crested cormorants (Phalacrocorax auritus; DCC) attributable to Newcastle disease virus (NDV) was observed for the first time in seven northern USA states and one Canadian province, and recurred in three western Canadian provinces. Based on clinical signs and laboratory diagnostic findings, DCC mortality from NDV occurred in 59 of the 63 nesting colonies and two of three non-colony sites investigated. An estimate of in excess of 20,000 DCC died, with mortality rates ranging from < 1 to 37% in Great Lakes colonies to 20 to 92% in Minnesota (USA) and North and South Dakota (USA) colonies. Sick juvenile white pelicans (Pelecanus erythrorhynchos) exhibiting signs similar to sick cormorants, and dead pelicans were observed in Minnesota and North Dakota. Mortality rates in pelican colonies were as high as in the adjacent cormorant colonies, but no cause for the mortality of an estimated 5,000 pelicans was determined. No evidence of NDV was found in other species nesting in proximity to affected cormorants. Although the source of the NDV infection is unknown in cormorants, the simultaneous onset of the epizootics in juvenile birds over a wide geographic area implies that the virus was acquired by adults prior to migration and was carried back to nest sites, exposing susceptible nestlings. The possible transmission of this virus from free-ranging wild birds to domestic poultry is a concern. Based on repeated epizootics in cormorants since 1990, NDV seems to be established in DCC.

Journal of Wildlife Diseases↗

USGS2016

Using resilience and resistance concepts to manage threats to sagebrush ecosystems, Gunnison sage-grouse, and Greater sage-grouse in their eastern range: A strategic multi-scale approach

This report provides a strategic approach developed by a Western Association of Fish and Wildlife Agencies interagency working group for conservation of sagebrush ecosystems, Greater sage-grouse, and Gunnison sage-grouse. It uses information on (1) factors that influence sagebrush ecosystem resilience to disturbance and resistance to nonnative invasive annual grasses and (2) distribution and relative abundance of sage-grouse populations to address persistent ecosystem threats, such as invasive annual grasses and wildfire, and land use and development threats, such as oil and gas development and cropland conversion, to develop effective management strategies. A sage-grouse habitat matrix links relative resilience and resistance of sagebrush ecosystems with modeled sage-grouse breeding habitat probabilities to help decisionmakers assess risks and determine appropriate management strategies at both landscape and site scales. Areas for targeted management are assessed by overlaying matrix components with Greater sage-grouse Priority Areas for Conservation and Gunnison sage-grouse critical habitat and linkages, breeding bird concentration areas, and specific habitat threats. Decision tools are discussed for determining the suitability of target areas for management and the most appropriate management actions. A similar approach was developed for the Great Basin that was incorporated into the Federal land use plan amendments and served as the basis of a Bureau of Land Management Fire and Invasives Assessment Tool, which was used to prioritize sage-grouse habitat for targeted management activities.

General Technical Report↗

USGS2023

Turkey Vulture survival is reduced in areas of greater road density

The demography of, and factors that influence these metrics, are largely unknown for most vultures in the Americas. Survivorship of Turkey Vultures ( Cathartes aura ) may be influenced by landscape heterogeneity and human disturbance. We quantified the effects of landscape composition (Shannon’s diversity index) and configuration (contagion, edge density, and largest patch index), and human disturbance (road density) on the annual and seasonal survival probabilities of the three North American breeding populations (western, central, and eastern) of Turkey Vultures that spend the nonbreeding season in the southeastern portion of the Nearctic and the northern Neotropics during a 17-year period. We used Cox’s proportional hazards models with time-varying covariates to estimate spatial and temporal changes in survival rates of adult Turkey Vultures. Road density, but not landscape composition or configuration, influenced survival rates in space and time. Overall annual survival averaged 0.87 (95% confidence interval [CI]: 0.74–0.98). Mortality risk was low in western and central populations (hazard ratio < 1) but was 3.7 times greater for vultures in the eastern population. Survival during the breeding (0.97, 95% CI: 0.96–0.98) and outbound migration (1.0, 95% CI: 1–1) seasons was significantly higher than the other seasons. Average survival tended to be higher for nonbreeding (0.81, 95% CI: 0.71–0.88) compared to return migration (0.69, 95% CI: 0.56–0.81) seasons. The risk of mortality for all vulture populations increased with road density, and this was greater during the nonbreeding and return migration seasons. The spatial variation in road density across the Americas may generate a network of ecological traps for Turkey Vultures induced to stop in areas of greater road-kill abundance. Road-killed animals acting as an attractant for vultures can increase the occurrence of vulture–vehicle collisions and potentially aggravate human–wildlife conflicts. Further analyses are needed to address survivorship and mortality factors for young birds. Our results may help the implementation of specific mitigation efforts to reduce human–vulture conflicts and vulture mortality. For instance, concentrating efforts to remove road-killed animals in areas where road density is highest can likely reduce vulture–vehicle collisions and associated mortalities of these birds.

Article↗

USGS2002

Three geese resembling Gray-Bellied Brant/Lawrence's Brant from Long Island, New York

Three oddly plumaged brant, intermediate in several respects between 'Atlantic' or 'Pale-bellied Brant' (hrota) and ?Black Brant? (nigricans) were photographed and described on western Long Island, New York during 2002 (two in March, the third in October). Their plumage corresponded to that of the little-studied, and apparently genetically distinctive small population known among goose biologists as 'Gray-bellied Brant,' which breeds only on a few islands in the western Canadian High Arctic, stages in migration in the inner Aleutians, and winters in a small portion of the Greater Puget Sound area. But Gray-bellied Brant also wander, having recently been found in winter as far from Puget Sound as Baja California in the west, and Iceland and the British Isles to the east?these strays presumably having migrated southwest with Pacific-wintering nigricans and southeast with Atlantic-wintering hrota, respectively. Despite their tendency to associate with locally wintering hrota and nigricans, mixed pairs or hybrid young involving these vagrants have never been demonstrated in North America?nor have mixed pairs or hybrid young between hrota and nigricans, despite widespread belief to the contrary. Complicating the picture is that the type specimen of nigricans, a distinctive New Jersey specimen collected in 1846, also differs from 'true' Pacific Coast Black Brant in several respects, in a manner qualitatively similar to the LI birds described herein. The appearance of the type, often referred to informally as 'Lawrence?s Brant,' differs from typical Black Brant to such an extent that Delacour and Zimmer (1952) rejected application of nigricans to Pacific Black Brant, to which the name orientalis would have to be applied instead. Recent examination of museum specimens of breeding- and winter-area Gray-bellies confirms that Lawrence?s Brant closely resembles some of them?as do these three Long Island birds. Whatever the ultimate statuses of Gray-bellied and Lawrence's Brant prove to be?and however the relationships among them and the three currently recognized other taxa of brant eventually play out?birds resembling Gray-bellied/Lawrence?s are occurring on both Atlantic and Pacific coasts and perhaps also in interior North America, so knowledge of their plumage variation should now be factored into the identification of all oddly-plumaged or out-of-range brant, but especially of putative 'nigricans' inland or on the Atlantic Coast.

North American Birds↗

USGS1998

Geographic, temporal, and age-specific variation in diets of Glaucous Gulls in western Alaska

We collected boluses and food remains of adult Glaucous Gulls (Larus hyperboreus) at or near nests and chicks, and digestive tracts from adults at three sites on the Yukon-Kuskokwim Delta, Alaska that differed in proximity to marine and terrestrial foods. We observed both geographic and temporal variation in diet; gulls consumed proportionately more terrestrial prey after peak hatch in late June, and gulls near the coast consumed proportionately more marine prey than gulls at two inland areas. Goslings occurred in > 60% of all samples from these inland areas. We compared these data to those from a previous study in western Alaska and found no marked differences. Evidence for similar patterns of geographic and temporal variation in diet was found using measurements of stable-carbon and nitrogen isotopes in gull and prey tissues. Stable isotope analysis further revealed that adult gulls consumed proportionately more marine prey (saffron cod, Eleginus gracilis) than they fed to their young. Using isotopic models, we estimated that 7-22% and 10-23% of the diet of adult and juvenile Glaucous Gulls, respectively, was comprised of terrestrial species. In addition to significant age-related variation, dietary estimates varied among geographic areas and between pre- and post-hatch periods. Overall, our isotopic estimates of the contribution of terrestrial prey to the diet of Glaucous Gulls was less than what may be inferred from conventional methods of diet analysis. Our study emphasizes the benefit of combining stable-isotope and conventional analyses to infer temporal and geographic changes in diet of wild birds and other organisms.

Condor↗

USGS2024

Risk of invasive waterfowl interaction with poultry production: Understanding potential for avian pathogen transmission via species distribution models

Recent outbreaks of highly pathogenic avian influenza have devastated poultry production across the United States, with more than 77 million birds culled in 2022–2024 alone. Wild waterfowl, including various invasive species, host numerous pathogens, including highly pathogenic avian influenza virus (HPAIV), and have been implicated as catalysts of disease outbreaks among native fauna and domestic birds. In major poultry-producing states like Arkansas, USA, where the poultry sector is responsible for significant economic activity (>$4 billion USD in 2022), understanding the risk of invasive waterfowl interactions with domestic poultry is critical. Here, we assessed the risk of invasive waterfowl-poultry interaction in Arkansas by comparing the density of poultry production sites (chicken houses) to areas of high habitat suitability for two invasive waterfowl species, (Egyptian Goose [ Alopochen aegyptiaca ] and Mute Swan [ Cygnus olor ]), known to host significant pathogens, including avian influenza viruses. The percentage of urban land cover was the most important habitat characteristic for both invasive waterfowl species. At the 95% confidence interval, chicken house densities in areas highly suitable for both species (Egyptian Goose = 0.91 ± 0.11 chicken houses/km 2 ; Mute Swan = 0.61 ± 0.03 chicken houses/km 2 ) were three to five times higher than chicken house densities across the state (0.17 ± 0.01 chicken houses/km 2 ). We show that northwestern and western Arkansas, both areas of high importance for poultry production, are also at high risk of invasive waterfowl presence. Our results suggest that targeted monitoring efforts for waterfowl-poultry contact in these areas could help mitigate the risk of avian pathogen exposure in Arkansas and similar regions with high poultry production.

Biological Invasions↗

USGS2016

Population dynamics of mallards breeding in eastern Washington

Variation in regional population trends for mallards breeding in the western United States indicates that additional research into factors that influence demographics could contribute to management and understanding the population demographics of mallards across North America. We estimated breeding incidence and adult female, nest, and brood survival in eastern Washington in 2006 and 2007 by monitoring female mallards with radio telemetry and tested how those parameters were influenced by study year (2006 vs. 2007), landscape type (agricultural vs. natural), and age (second year [SY] vs. after second year [ASY]). We also investigated the effects of female body condition and capture date on breeding incidence, and nest initiation date and hatch date on nest and brood survival, respectively. We included population parameters in a stage-based demographic model and conducted a perturbation analysis to identify which vital rates were most influential on population growth rate (λ). Adult female survival was best modeled with a constant weekly survival rate (0.994, SE = 0.003). Breeding incidence differed between years and was higher for birds in better body condition. Nest survival was higher for ASY females (0.276, SE = 0.118) than SY females (0.066, SE = 0.052), and higher on publicly managed lands (0.383, SE = 0.212) than agricultural (0.114, SE = 0.058) landscapes. Brood survival was best modeled with a constant rate for the 7-week monitoring period (0.50, SE = 0.155). The single variable having the greatest influence on λ was non-breeding season survival, but the combination of parameters from the breeding grounds explained a greater percent of the variance in λ. Mallard population growth rate was most sensitive to changes in non-breeding survival, nest success, brood survival, and breeding incidence. Future management decisions should focus on activities that improve these vital rates if managers want to increase the production of mallards in eastern Washington.

Washington↗

USGS2011

Characterization of winter foraging locations of Adélie penguins along the Western Antarctic Peninsula, 2001–2002

In accord with the hypotheses driving the Southern Ocean Global Ocean Ecosystems Dynamics (SO GLOBEC) program, we tested the hypothesis that the winter foraging ecology of a major top predator in waters off the Western Antarctic Peninsula (WAP), the Adélie penguin ( Pygoscelis adeliae ), is constrained by oceanographic features related to the physiography of the region. This hypothesis grew from the supposition that breeding colonies in the WAP during summer are located adjacent to areas of complex bathymetry where circulation and upwelling processes appear to ensure predictable food resources. Therefore, we tested the additional hypothesis that these areas continue to contribute to the foraging strategy of this species throughout the non-breeding winter season. We used satellite telemetry data collected as part of the SO GLOBEC program during the austral winters of 2001 and 2002 to characterize individual penguin foraging locations in relation to bathymetry, sea ice variability within the pack ice, and wind velocity and divergence (as a proxy for potential areas with cracks and leads). We also explored differences between males and females in core foraging area overlap. Ocean depth was the most influential variable in the determination of foraging location, with most birds focusing their effort on shallow (<200 m) waters near land and on mixed-layer (200–500 m) waters near the edge of deep troughs. Within-ice variability and wind (as a proxy for potential areas with cracks and leads) were not found to be influential variables, which is likely because of the low resolution satellite imagery and model outputs that were available. Throughout the study period, all individuals maintained a core foraging area separated from other individuals with very little overlap. However, from a year with light sea ice to one with heavy ice cover (2001–2002), we observed an increase in the overlap of individual female foraging areas with those of other birds, likely due to restricted access to the water column, reduced prey abundance, or higher prey concentration. Male birds maintained separate core foraging areas with the same small amount of overlap, showing no difference in overlap between the years. While complex bathymetry was an important physical variable influencing the Adélie penguin's foraging, the analysis of sea ice data of a higher resolution than was available for this study may help elucidate the role of sea ice in affecting Adélie penguin winter foraging behavior within the pack ice.

Deep-Sea Research Part II: Topical Studies in Ocea↗

USGS2006

Can hunting of translocated nuisance Canada geese reduce local conflicts?

Resident Canada geese (Branta canadensis) nest or reside in the temperate latitudes of North America. In past years, translocation-the capture and subsequent release of geese at distant locations-has been used to establish resident goose populations and to reduce nuisance problems. However, with new special hunting seasons designed to target resident Canada geese, we can now evaluate translocation as a management tool when hunting is allowed at release sites. We selected 2 study sites, representative of urban and suburban locations with nuisance resident geese, in central and western New York, USA. In June 2003, we translocated 80 neck-banded adult geese, 14 radiomarked adult females, and 83 juveniles 150 km east and southwest from urban and suburban problem sites in western New York to state-owned Wildlife Management Areas. At these same capture sites, we used 151 neck-banded adult geese, 12 radiomarked females, and 100 juveniles as controls to compare dispersal movements and harvest vulnerability to translocated geese. All observations (n = 45) of translocated radiomarked geese were <20 km from release sites, in areas where hunting was permitted. Only 25 of 538 observations (4.6%) of radiomarked geese at control sites were in areas open to hunting. The remainder of observations occurred at nonhunting locations within 10 km of control sites. More translocated adult geese (23.8%) were harvested than control geese (6.6%; ??2 = 72.98, P = 0.0009). More translocated juvenile geese were harvested (22.9%) than juvenile controls (5.0%; ??2 = 72.30, P = 0.0005). Only 7 (8.8%) translocated adult geese returned to the original capture sites during Canada goose hunting seasons. Translocation of adult and juvenile geese in family groups may alleviate nuisance problems at conflict sites through increased harvest, reducing the number of birds returning in subsequent years.

Wildlife Society Bulletin↗

USGS2014

Bouse Formation in the Bristol basin near Amboy, California, USA

Limestone beds underlain and overlain by alluvial fan conglomerate near Amboy, California, are very similar in many respects to parts of the Bouse Formation, suggesting that an arm of the Pliocene Bouse water body extended across a wide part of the southern Mojave Desert. The deposits are north of the town of Amboy at and below an elevation of 290 m, along the northern piedmont of the Bristol “dry” Lake basin. The Amboy outcrops contain the Lawlor Tuff (4.83 Ma), which is also found in an outcrop of the Bouse Formation in the Blythe basin near Buzzards Peak in the Chocolate Mountains, 180 km southeast of Amboy. Bouse exposures near Amboy are &sim;3.4 m thick, white, distinctly bedded, with limestone and calcareous sandstone as well as stromatolite mounds; we interpret these as nearshore deposits. The Bouse at Amboy contains ostracodes, diatoms, and mollusks that indicate saline lake or estuarine environments with an admixture of fresh-water forms. Along with wading bird tracks and a spine from a marine fish, these fossils suggest that the deposits formed in saline waters near a fresh-water source such as a perennial stream. Beds of the outcrop dip southward and are 113 m above the surface of Bristol Playa, where similar age sediments are buried 270+ m deep, indicating significant faulting and vertical tectonics in this part of the Eastern California Shear Zone during the past 5 m.y. Confirmation of the Bouse Formation at Amboy strengthens previous assignments to the Bouse Formation for mudstones in driller logs at Danby “dry” Lake, California, and suggests that areally extensive arms of the Bouse water body were west of the Blythe basin. The Bristol basin arm of the lower Bouse basin probably was restricted from the main water body by narrow passages, but Bouse sediment there is similar to that in the Blythe basin, suggesting generally similar water chemistry and environmental conditions. Examining the degree to which Bouse deposits in the western arms differed from Bouse deposits in the Blythe basin offers an approach to test whether the southernmost Bouse water body was deposited in an estuarine or lacustrine setting.

California↗

USGS2025

Combining ecological and genomic diversity surveys to inform conservation and restoration of an endangered wetland plant, soft salty bird’s-beak (Chloropyron molle ssp. molle)

Emergent tidal wetlands are declining globally as a result of sea level rise and land use change. This habitat loss can keenly affect rare plant species within wetlands, and may require restoration to meet species recovery goals related to retaining populations throughout species' ranges. Soft salty bird’s-beak ( Chloropyron molle ssp. molle ) is a federally- and state-endangered hemi-parasitic plant that occurs at the upper marsh transition zone in the San Francisco Bay–Delta, California, USA. We combined field surveys to document habitat associations and trends in abundance with genomic surveys to understand patterns of genetic structure in this rare endemic. We found that C . molle ssp. molle persisted at nine previously occupied marsh sites, although four sites (Hill Slough, MOTCO East, Fagan Marsh, and Joice Island) were smaller in population size than when surveyed in the 1990s. Additionally, twelve sites contained plots with suitable but unoccupied habitat that could be further assessed for restoration. Genomic analysis of over 40,000 single-nucleotide polymorphisms (SNPs) and 253 individuals grouped C . molle ssp. molle into six to seven regional genetic clusters with isolation by distance, and confirmed that C . molle ssp. molle is genetically distinct from adjacent populations of its closest relative ( C . molle ssp. hispidum ). The western-most C . molle ssp. molle sites of Point Pinole and Fagan Marsh were the most genetically and geographically isolated and had the lowest genome-wide diversity. Heterozygosity in sets of genes associated with tidal elevation, salinity, and annual and summer precipitation varied independently across populations. Overall, these genomic patterns indicate that selecting donor sites with similar environmental conditions and utilizing composite seeding approaches from multiple sites could allow for local adaptation to a range of possible environmental conditions. This comprehensive survey of habitat and genomic patterns can allow for the development of restoration actions and build climate-adaptation planning to help prevent the loss of a rare plant.

California↗

USGS2021

Shifts in the wintering distribution and abundance of Emperor Geese in Alaska

For wildlife species that winter at northern latitudes, harsh overwinter conditions can play an important role in population dynamics. Recent changes in global temperatures have resulted in distributional shifts of wildlife species, as well as amelioration of winter climates in northern landscapes. The emperor goose ( Anser canagicus ), an endemic migratory bird of the Bering Sea region, winters across a large area of the subarctic, with potential differences in migration strategies and costs among individuals. As a long-standing species of conservation concern due to decreased population size, understanding the response of emperor geese to changing conditions has become critical to on-going management. We sought to evaluate changes in wintering distribution and arrival/departure dates over time, by comparing spatial and temporal patterns of wintering emperor geese from 2015 to 2017 (using geolocator data) to satellite telemetry data collected from 1999 to 2004. Further, we quantified changes in spatial patterns of winter abundance by comparing historical and contemporary aerial and ground surveys at three island complexes encompassing most of their winter distribution. Our results indicate that emperor geese are arriving at wintering areas earlier and spending more time at these areas than in the past. Our comparisons among historical aerial and ground surveys suggests that increasing numbers of emperor geese are wintering closer to breeding areas in western Alaska; a change likely related to increasing habitat availability due to shifting environmental conditions. Our results also showed that fewer emperor geese are using an area in the core of their wintering range, suggesting either decreased habitat quality or a reduction in migration distance via alternative wintering locations. Overall, our study highlights a rapid response to apparent habitat change likely due to warming temperatures and a reduction in ice cover and emphasizes the importance of understanding complex interactions among migration distance, the environment, and habitat in interpreting site selection.

Alaska↗

USGS2007

Comparison of immune responses of brown-headed cowbird and related blackbirds to West Nile and other mosquito-borne encephalitis viruses

The rapid geographic spread of West Nile virus (family Flaviviridae , genus Flavivirus , WNV) across the United States has stimulated interest in comparative host infection studies to delineate competent avian hosts critical for viral amplification. We compared the host competence of four taxonomically related blackbird species (Icteridae) after experimental infection with WNV and with two endemic, mosquito-borne encephalitis viruses, western equine encephalomyelitis virus (family Togaviridae , genus Alphavirus , WEEV), and St, Louis encephalitis virus (family Flaviviridae , genus Flavivirus , SLEV). We predicted differences in disease resistance among the blackbird species based on differences in life history, because they differ in geographic range and life history traits that include mating and breeding systems. Differences were observed among the response of these hosts to all three viruses, Red-winged Blackbirds were more susceptible to SLEV than Brewer's Blackbirds, whereas Brewer's Blackbirds were more susceptible to WEEV than Red-winged Blackbirds. In response to WNV infection, cowbirds showed the lowest mean viremias, cleared their infections faster, and showed lower antibody levels than concurrently infected species. Brown-headed Cowbirds also exhibited significantly lower viremia responses after infection with SLEV and WEEV as well as coinfection with WEEV and WNV than concurrently infected icterids. We concluded that cowbirds may be more resistant to infection to both native and introduced viruses because they experience heightened exposure to a variety of pathogens of parenting birds during the course of their parasitic life style.

Journal of Wildlife Diseases↗

USGS2001

Contaminant profiles of two species of shorebirds foraging together at two neighboring sites in south San Francisco Bay, California

The San Francisco Bay estuary isused by over one million shorebirds during springmigration and is home to several hundred thousandduring the winter. Most shorebird use occurs in thesouthern reach of the estuary (South Bay). Thereduced water circulation and discharge fromindustrial sources in the South Bay are responsiblefor the highest levels of some trace elements in theestuary. Wintering shorebirds have been found to havestrong site fidelity to areas as small as a fewkilometers in the South Bay, which may increase theirexposure to contaminants near local point sources. Inaddition, different shorebird species foraging at thesame site have been shown to have differentcontaminant burdens. Thus, our objectives were totest whether contaminant burdens differed by species,or whether contaminant burdens differed in shorebirdscollected at adjacent sites. We examined thecontaminant profiles of two species of shorebirds,long-billed dowitchers ( Limnodromus scolopaceus )and western sandpipers ( Calidris mauri ) thatforage together at two sites, Hayward and Newark,separated by 8 km in the South Bay. We usedmultivariate analysis of variance tests to compare thecomposition of 14 elemental analytes in their livertissues and estimated their molar ratios of Hg and Se. Composite samples were used for contaminant analysesbecause of the small body size of the shorebirds. Seven elemental analytes (Ag, Ba, Be, Cr, Ni, Pb, V)were below detection limits in a majority of thesamples so statistical analyses were precluded. Inthe measurable analytes (As, Cd, Cu, Hg, Mn, Se, Zn),we found no significant intra-site differences ofcontaminant profiles for the two species. We pooledthe samples to examine inter-site differences andfound significant differences in contaminant profilesbetween shorebirds at the neighboring sites ( P = 0.03). Shorebirds at Newark had higher ( P < 0.05) concentrations of As, Cd, and Se than those at Hayward. Dowitchers at Newark had concentrations of Hg and Se which were highly correlated ( P < 0.003) in a mean molar ratio of 1:19, similar tothat reported in other birds. In the larger dowitcherspecies, we also examined exposure to 20organochlorine compounds. Organic analyses showedthat the dowitchers had been exposed to DDE, PCBs,dieldrin and trans-nonachlor, but with no significantdifferences in concentrations between Hayward andNewark ( P > 0.05).

Environmental Monitoring and Assessment↗

USGS1999

Productivity, diets, and environmental contaminants in nesting bald eagles from the Aleutian Archipelago

We studied productivity, diets, and environmental contaminants in nesting bald eagles from the western Aleutian Islands, Alaska, USA, during the summers of 1993 and 1994. Productivity on Adak, Tanaga, and Amchitka Islands ranged from 0.88 to 1.24 young produced per occupied site and was comparable to that of healthy populations in the lower 48 United States. However, productivity on Kiska Island was depressed, averaging 0.67 young per occupied site. The lower reproductive success on Kiska was associated with elevated levels of dichlorodiphenyldichloroethylene and other organochlorine pesticides. Many of the organochlorine pesticides were elevated in bald eagle eggs from the four islands, but concentrations of these contaminants and Hg were significantly higher in eggs from Kiska Island than in eggs from the other islands. In contrast, polychlorinated biphenyl concentrations were higher in eggs from Adak, Amchitka, and Kiska (where military facilities have been installed) than in those from Tanaga (which has had little military activity). The most likely source of these contaminants in bald eagles was from their diets, which were variable spatially and temporally. Fish made up most (56%) of the eagles' diet on Adak and Tanaga Islands, followed by birds (25%) and mammals (19%). In contrast, birds comprised the majority (60%) of bald eagle diets on Amchitka and Kiska Islands, followed by mammals (30%) and fish (10%). The high proportion of seabirds in the diet of eagles from Kiska Island could be the major source of organochlorine and Hg contamination. Elevated concentrations of organochlorines in bald eagle eggs from the Aleutian Archipelago was surprising, because of the distance to agricultural areas. The results indicate that these contaminants can be transported long distances and affect wildlife populations in remote and pristine areas. We also discuss potential sources and transport mechanisms of these contaminants to the Aleutian Islands.

Environmental Toxicology and Chemistry↗