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Tuesday, 10 November 2015

The Condor, Volume 117: Issue 4. November 2015

The Condor

Volume 117, Issue 4. November 2015



Winter site fidelity and winter movements in Common Loons (Gavia immer) across North America

James D. Paruk, Michael D. Chickering, Darwin Long, Hannah Uher-Koch, Andrew East, Daniel Poleschook, Virginia Gumm, William Hanson, Evan M. Adams, Kristin A. Kovach and David C. Evers
Biodiversity Research Institute, Portland, Maine, USA

In many avian species, breeding site fidelity has been more thoroughly investigated than winter site fidelity, yet the latter may have a greater impact on survivorship. The Common Loon (Gavia immer) is an example of a species whose breeding site fidelity has been well established, but whether it exhibits winter site fidelity remains unknown. Because Common Loons primarily winter in marine waters off coastal shores, winter site fidelity has been challenging to document. We investigated winter site fidelity in Common Loons across North America using satellite transmitters, recaptures, and resightings of previously color-marked individuals. Color-marked adults returned in consecutive years to the same coastal wintering locations in California, Washington, Louisiana, Maryland, and Massachusetts, USA. We estimated adult annual apparent survival as 77% (0.48–0.93) and adult winter site fidelity as 85% (0.35–0.98). This finding has important conservation implications in the aftermath of recent marine oil spills; if Common Loons return to the same contaminated wintering areas annually, decreased fitness and survivorship could result in population-level effects.

Comparing models of Red Knot population dynamics

Conor P. McGowan

U.S. Geological Survey, Alabama Cooperative Fish and Wildlife Research Unit, School of Forestry and Wildlife Science, Auburn University, Auburn, Alabama, USA

Predictive population modeling contributes to our basic scientific understanding of population dynamics, but can also inform management decisions by evaluating alternative actions in virtual environments. Quantitative models mathematically reflect scientific hypotheses about how a system functions. In Delaware Bay, mid-Atlantic Coast, USA, to more effectively manage horseshoe crab (Limulus polyphemus) harvests and protect Red Knot (Calidris canutus rufa) populations, models are used to compare harvest actions and predict the impacts on crab and knot populations. Management has been chiefly driven by the core hypothesis that horseshoe crab egg abundance governs the survival and reproduction of migrating Red Knots that stopover in the Bay during spring migration. However, recently, hypotheses proposing that knot dynamics are governed by cyclical lemming dynamics garnered some support in data analyses. In this paper, I present alternative models of Red Knot population dynamics to reflect alternative hypotheses. Using 2 models with different lemming population cycle lengths and 2 models with different horseshoe crab effects, I project the knot population into the future under environmental stochasticity and parametric uncertainty with each model. I then compare each model's predictions to 10 yr of population monitoring from Delaware Bay. Using Bayes' theorem and model weight updating, models can accrue weight or support for one or another hypothesis of population dynamics. With 4 models of Red Knot population dynamics and only 10 yr of data, no hypothesis clearly predicted population count data better than another. The collapsed lemming cycle model performed best, accruing ~35% of the model weight, followed closely by the horseshoe crab egg abundance model, which accrued ~30% of the weight. The models that predicted no decline or stable populations (i.e. the 4-yr lemming cycle model and the weak horseshoe crab effect model) were the most weakly supported.

Will representation targets based on area protect critical resources for the conservation of the Tucuman Parrot?

Anna M. Pidgeon, Luis Rivera, Sebastian Martinuzzi, Natalia Politi and Brooke Bateman
Department of Forest and Wildlife Ecology, University of Wisconsin–Madison, Madison, Wisconsin, USAFacultad de Ciencias Agrarias, Universidad Nacional de Jujuy, CONICET, Jujuy, Argentina

The Tucuman Parrot (Amazona tucumana), which is restricted to Southern Yungas forest of Argentina and Bolivia, has not recovered from severe population declines in the 1980s. We assessed habitat conservation targets for this species and asked, “What constitutes the right target?” For species with small ranges, maximizing the proportion of the range under protection is an established strategy to safeguard against threats. However, designating an amount for protection based on range alone (i.e. a ‘representation target') may set a misguided conservation target if critical resources are not considered. We used an ensemble model (‘biomod2’) to map suitable breeding and nonbreeding habitat of the Tucuman Parrot based on environmental variables and key resources (breeding) or the species' occurrence (nonbreeding). Pino blanco (Podocarpus parlatorei) seeds are critical food for Tucuman Parrot nestlings, so we modeled the distribution of this tree as a proxy for potential breeding habitat. We then examined the adequacy of current habitat protection relative to representation targets and in light of known threats, including forest degradation and loss, and poaching. Overall, 17% of the 110,122 km2Southern Yungas is protected, which is close to the proportion recommended (the target; 22%), based on the ecoregion's size, for inclusion in a conservation network. Similarly, 26% of the 46,263 km2 of nonbreeding habitat is protected, also relatively successful at 71% of the target (36%). However, of the scant ~21,000 km2of breeding habitat, only 15% is protected, much less than the representation target (49%) recommended for maximizing the probability of population persistence. Poaching of nestlings further undermines the value of some nesting habitat in Bolivia. For Tucuman Parrots, increased enforcement of protection in Bolivia and protection of additional nesting habitat in Argentina are the most efficient ways to enhance persistence. Our results illustrate how habitat conservation targets based on area alone may be inadequate if important biological information is overlooked.

Wintering ecology of sympatric subspecies of Sandhill Crane: Correlations between body size, site fidelity, and movement patterns

Gary L. Ivey, Bruce D. Dugger, Caroline P. Herziger, Michael L. Casazza and Joseph P. Fleskes

International Crane Foundation, Bend, Oregon, USADepartment of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon, USA Western Ecological Research Center, U.S. Geological Survey, Dixon, California, USA
Body size is known to correlate with many aspects of life history in birds, and this knowledge can be used to manage and conserve bird species. However, few studies have compared the wintering ecology of sympatric subspecies that vary significantly in body size. We used radiotelemetry to examine the relationship between body size and site fidelity, movements, and home range in 2 subspecies of Sandhill Crane (Grus canadensis) wintering in the Sacramento–San Joaquin Delta of California, USA. Both subspecies showed high interannual return rates to the Delta study area, but Greater Sandhill Cranes (G. c. tabida) showed stronger within-winter fidelity to landscapes in our study region and to roost complexes within landscapes than did Lesser Sandhill Cranes (G. c. canadensis). Foraging flights from roost sites were shorter for G. c. tabida than for G. c. canadensis (1.9 ± 0.01 km vs. 4.5 ± 0.01 km, respectively) and, consequently, the mean size of 95% fixed-kernel winter home ranges was an order of magnitude smaller for G. c. tabida than for G. c. canadensis (1.9 ± 0.4 km2 vs. 21.9 ± 1.9 km2, respectively). Strong site fidelity indicates that conservation planning to manage for adequate food resources around traditional roost sites can be effective for meeting the habitat needs of these cranes, but the scale of conservation efforts should differ by subspecies. Analysis of movement patterns suggests that conservation planners and managers should consider all habitats within 5 km of a known G. c. tabida roost and within 10 km of a G. c. canadensis roost when planning for habitat management, mitigation, acquisition, and easements.

Genetic structure of Greater Sage-Grouse (Centrocercus urophasianus) in a declining, peripheral population

Dawn M. Davis, Kerry P. Reese, Scott C. Gardner and Krista L. Bird
U.S. Fish and Wildlife Service, Portland, Oregon, USADepartment of Fish and Wildlife Sciences, University of Idaho, Moscow, Idaho, USA California Department of Fish and Wildlife, Sacramento, California, USA
Loss of suitable habitat and subsequent fragmentation of populations are recognized as important factors in the decline and extinction of many species because they result in smaller, more isolated populations with reduced genetic diversity. The Greater Sage-Grouse (Centrocercus urophasianus), having declined in distribution and abundance throughout its range, is a candidate species under the U.S. Endangered Species Act and a species of special concern in California. Because the relationships between dispersal, gene flow, and genetic structure are interrelated and affect the long-term persistence of Greater Sage-Grouse, we assessed the genetic structure and patterns of dispersal among Greater Sage-Grouse in a declining, peripheral population in northeastern California. We genotyped 19 microsatellite loci from 167 individuals from 13 leks and 20 individuals captured off lek. Greater Sage-Grouse in northeastern California appear to maintain gene flow and genetic diversity across the sampled region. Despite population declines and habitat loss, leks were not genetically differentiated. Our results showed significant isolation-by-distance among males, which suggests that male Greater Sage-Grouse are more philopatric than females. Spatial autocorrelation analysis revealed stronger spatial structuring for males than for females. Results from the corrected assignment index also confirmed female-biased dispersal, although differences between sexes were not significant. While more research is needed on the proximate and ultimate causes behind the patterns we observed, our results serve as an important step toward understanding genetic structure and patterns of sex-biased dispersal in Greater Sage-Grouse occupying the periphery of the species' geographic distribution.

Scalar considerations in population trend estimates: Implications for recovery strategy planning for species of conservation concern

Danielle M. Ethier and Thomas D. Nudds
Department of Integrative Biology, University of Guelph, Guelph, Ontario, Canada

Broad-scale population trends are often used to identify and list species of conservation concern and as baselines to surmise which recovery actions might arrest or reverse declines. It is therefore important that trends are quantified regionally, so that finer-scale assessments can be made about the plausible causes of declines and targeted conservation actions can be implemented. We estimated regional population trends for a grassland bird, the Bobolink (Dolichonyx oryzivorus), to compare with trends from provincial analyses used for risk assessment, to identify the regions contributing most substantially to population declines. We used 45 yr of count data from the North American Breeding Bird Survey, across 35 agricultural census divisions in southern Ontario, Canada, to develop spatially explicit hierarchical Bayesian models of regional population trends. Population trends were negative in 30 of 35 census divisions, 6 of which had 95% credibility intervals (CI) that did not include zero. In 34 of 35 census divisions, the CI included the provincial short-term recovery goal of a population trend of −1%. Between 1998 and 2011, corresponding to the time series used for provincial risk assessment, the CI for 3 of 21 negative trends did not include 0 or −1. Our results indicate that most regional trend estimates currently exceed the goal set out in the recovery strategy, insofar as they have been stable and not necessarily declining. This suggests a more optimistic picture of the state of Bobolink population trends than that obtained from analyses at broader spatial scales, which masked important regional variation. This result demonstrates the need for consideration of scale variance in trend estimation during risk assessment and management planning, and the application of spatially explicit trend estimation for small geographic areas to aid in this process.

Summer vs. winter: Examining the temporal distribution of avian biodiversity to inform conservation

Kristen E. Dybala, Melanie L. TruanAndrew Engilis
Point Blue Conservation Science, Petaluma, California, USAMuseum of Wildlife and Fish Biology, Department of Wildlife, Fish & Conservation Biology, University of California, Davis, California, USA

Winter habitat quality plays a key role in avian population regulation, and conservation of winter habitat is a priority for waterfowl, shorebirds, and Neotropical migrant landbirds. Yet, there has been little discussion of the importance of conserving temperate wintering habitat for landbirds, including the billions of Neotemperate migratory landbirds that winter in the United States. The value and impact of conservation initiatives in the U.S. could be maximized by accommodating the habitat requirements of bird communities throughout the full annual cycle, particularly in the southern and western U.S. where winter species richness is concentrated. To estimate the degree to which winter bird communities should be a conservation priority, we examined the temporal distribution of avian diversity using riparian habitat in the lower Cosumnes River and lower Putah Creek watersheds in California's Central Valley. We used hierarchical multispecies occupancy models to estimate seasonal species richness and phylogenetic diversity in each watershed. We found that total species richness was equally as high in winter as in summer, and that phylogenetic diversity was higher in winter, with a considerable proportion of the winter avian diversity attributable to boreal-breeding Neotemperate migrants. Our results provide evidence that maintaining and restoring high-quality riparian habitat for winter bird communities in California is an important conservation opportunity. Broader recognition of the diversity of temperate winter bird communities and additional research into the factors affecting body condition and survival would facilitate effective conservation of high-quality winter habitat, benefiting Neotemperate migrants and year-round residents during a season that can have important impacts on their population dynamics.

Biases in nest survival associated with choice of exposure period: A case study in North American upland game birds

Erik J. Blomber, Daniel Gibson and James S. Sedinger
Department of Wildlife Ecology, University of Maine, Orono, Maine, USAProgram in Ecology, Evolution and Conservation Biology, Department of Natural Resources and Environmental Science, University of Nevada Reno, Reno, Nevada, USA
Estimated probability of daily nest survival is commonly used to derive cumulative nest survival for a specified nest-exposure period. For many species of birds, the presence of a parent is an important cue used by researchers to locate nests, but in some cases nest detection rates are reduced during egg laying, when parents spend a greater amount of time away from the nest. As a result, sample size becomes limited during the laying stage. Researchers must then choose between 2 alternative strategies for deriving cumulative nest survival, based on either (1) exposure length for only the incubation period or (2) exposure length for laying plus incubation. Both approaches carry implicit assumptions, the violation of which can result in bias. We reviewed recent literature and describe the extent to which these 2 strategies were used in studies of galliform birds (including grouse, quail, and Wild Turkey [Meleagris gallopavo]) in North America. We then evaluated the theoretical potential for bias under each approach across a range of daily nest survival probabilities and for 3 different life-history scenarios. The incubation-only strategy was most commonly applied, with 62% of publications reporting its use. We found that the incubation-only strategy was biased except under an assumption of zero nest failure during egg laying. Fewer studies reported using the laying-plus-incubation strategy, which was unbiased in situations where risk of failure was equivalent among laying and incubation stages. This strategy also minimized bias across the broadest range of situations, and accordingly we recommend its use where the daily survival rate during egg laying is unknown. We recommend that both the laying and incubation periods should be used to define the length of nest exposure when estimating cumulative nest survival, particularly for species with large clutches and long laying periods.

Physical, human disturbance, and regional social factors influencing Common Loon occupancy and reproductive success

Maxwell Field and Thomas M. Gehring
Department of Biology, Central Michigan University, Mount Pleasant, Michigan, USA

Common Loons (Gavia immer) appear to use physical habitat, human disturbance, and social cues when selecting territories; however, recent loon habitat models suggest that the importance of each of these cues may vary depending on population density. We conducted loon detection surveys on lakes (n = 42) in the Lower Peninsula of Michigan, USA, during 2007–2008, and developed territory occupancy and nest success models. We found that occupancy was positively associated with lake area and the presence of islands, whereas road density (human disturbance) and the number of loon pairs within 10 km (social cue) were not important predictors of occupancy. Similarly, loon nest success was positively associated with lake area and the presence of islands. Both models performed well when applied to an independent dataset of 85 lakes (AUC = 0.743 and 0.724, respectively), indicating that these models could be used for identifying suitable habitat during conservation efforts. Our results suggest that managers should first focus efforts on maintaining or creating nesting islands on lakes, and then assess regional loon occupancy rates once physical habitat conditions are met. Comparing our results with recent loon habitat models, we suggest that social cue covariates are most important at low population densities, whereas physical habitat covariates are dominant predictors of occupancy at higher population densities of loons. Loon response to human disturbance appears to be location-specific, depending on the level of human development around lakes and local conservation efforts, particularly the provision of artificial nest platforms.

Using local dispersal data to reduce bias in annual apparent survival and mate fidelity

Caz M. Taylor, David B. Lank and Brett K. Sandercock

Department of Ecology and Evolutionary Biology, Tulane University, New Orleans, Louisiana, USACentre for Wildlife Ecology, Department of Biological Sciences, Simon Fraser University, Burnaby, British Columbia, CanadaDivision of Biology, Kansas State University, Manhattan, Kansas, USA


In mark–recapture studies conducted on fixed-area study sites, apparent (or “local”) survival (ϕ) is the product of the probabilities of true survival (S) and site fidelity to the sampling area (F). If marked individuals permanently emigrate from the study site, apparent survival will be biased low relative to true survival. Similarly, estimates of mate fidelity will be biased high because site fidelity is typically higher for individuals that reunite with their previous mates than among pairs that divorce. Here, we develop a method for calculating site fidelity that takes plot boundaries into account, based on a dispersal model estimated from local movements within a fixed study site. We use dispersal estimates to adjust apparent survival and mate fidelity for the effects of short-distance movements out of a fixed area. We demonstrate our method with a retrospective analysis of a published study of 2 species of sandpipers breeding sympatrically at a field site in western Alaska. Estimates of survival probability increased by 0.01–0.03 for males and 0.07–0.08 for females in both species. The larger adjustments for females were expected based on their longer local dispersal movements. Adjusted mate fidelity estimates were lower than the original estimates by 0.04–0.07. Use of local movement data to estimate site fidelity cannot account for permanent emigration due to long-distance movements and, if such movements occur, our adjusted estimates of ϕ remain a function of true survival and site fidelity. Nevertheless, our method can reduce bias in demographic parameters resulting from local dispersal movements, improving estimates of annual survival and mate fidelity for use in demographic models.

Habitat selection, nest survival, and nest predators of Rusty Blackbirds in northern New England, USA

Shannon H. Buckley Luepold, Thomas P. Hodgman, Stacy A. McNulty, Jonathan Cohen and Carol R. Foss

Department of Environmental and Forest Biology, State University of New York College of Environmental Science and Forestry, Syracuse, New York, USA
Bird Group, Maine Department of Inland Fisheries and Wildlife, Bangor, Maine, USA
Adirondack Ecological Center, State University of New York College of Environmental Science and Forestry, Newcomb, New York, USA
Audubon Society of New Hampshire, Concord, New Hampshire, USA

Rusty Blackbird (Euphagus carolinus) populations have plummeted since the mid-20th century. Recent research in New England, USA, suggests that an ecological trap, created through timber harvesting on the breeding grounds, may be responsible. Red squirrels (Tamiasciurus hudsonicus) were hypothesized to be the primary nest predator, but definitive identification was lacking. The potential for mast cone crops to affect Rusty Blackbird nest predation via trophic interactions also remains unexamined. Our objectives were to identify the mechanisms by which an ecological trap may be operating in New England through a multiscale analysis of Rusty Blackbird habitat selection and nest survival, as well as predator identification and quantification. We located 72 Rusty Blackbird nests in Maine and New Hampshire in 2011 and 2012, and modeled habitat selection and nest survival as a function of habitat characteristics at the nest patch (5 m) and home range (500 m) scale. We placed camera traps at 29 nests to identify nest predators, and conducted ground surveys to obtain an index of squirrel abundance each year. We found that Rusty Blackbirds selected nest patches with a high basal area of small conifers and low canopy closure. Nest survival was not reduced in harvested stands, but increased with increasing basal area. Percent cover of wetlands and young softwood stands were the best predictors of Rusty Blackbird selection at the home range scale. At the home range scale, we found that nests that were closer to a road were less successful in 2011, but not in 2012. Red squirrels were the most frequent predator of Rusty Blackbird nests in 2012, when they were abundant following a mast year in 2011. These results suggest that dense cover of small softwoods is important for habitat selection and survival of Rusty Blackbird nests, and that precommercial thinning and possibly road-building could reduce habitat quality for this species.

Can interrupting parent–offspring cultural transmission be beneficial? The case of Whooping Crane reintroduction

Vladimir Dinets

Psychology Department, University of Tennessee, Austin Peay Building, University of Tennessee, Knoxville, Tennessee, USASchool of Renewable Natural Resources, Louisiana State University, Baton Rouge, Louisiana, USA
Inheriting behavioral patterns culturally (i.e. by learning from parents) rather than genetically is considered an integral part of individual development for many bird and mammal species. I discuss the possibility that in some cases, particularly when only heavily modified habitat remains available, such transmission might have a negative effect on the individual's adaptability and chances of survival. Instead, animals deprived of normal parental care may be better suited for survival in novel environments. I describe this possible scenario with captive-reared Whooping Cranes (Grus americana) released in southwestern Louisiana, primarily in the context of human-modified habitats used by this reintroduced population. Captive-rearing techniques based on this approach may be beneficial for other threatened species, particularly those that have little or no nonmodified habitat left and are amenable to alternative habitats if cultural transmission is interrupted.

Understanding the distribution of a threatened bird at multiple levels: A hierarchical analysis of the ecological niche of the Santa Marta Bush-Tyrant (Myiotheretes pernix)

Esteban Botero-Delgadillo, Nicholas J. Bayly, Sandra Escudero-Páez and María Isabel Moreno

Instituto de Ecología y Biodiversidad, Departamento de Ciencias Ecológicas, Facultad de Ciencias, Universidad de Chile, Santiago, ChileSELVA: Investigación para la Conservación en el Neotrópico, Bogotá D.C., Colombia
An understanding of the ecological factors determining bird species' distributions is essential for making informed conservation decisions. These data are especially important for range-restricted species, such as the Santa Marta Bush-Tyrant (Myiotheretes pernix), a threatened endemic of the Sierra Nevada de Santa Marta (SNSM) in Colombia. Here we adopt a novel hierarchical analysis to describe the bush-tyrant's ecological niche and infer the regional and local determinants of its limited distribution. We first describe habitat selection based on local habitat use and microhabitats used for foraging. We then use a geoprocessing modeling algorithm to combine habitat selection data with a climatic niche model. The resulting model produced an index of habitat suitability, which we converted into a predicted geographic distribution. Santa Marta Bush-Tyrants showed no clear habitat preferences, but favored forested and secondary growth habitats over open areas, at elevations between 2,100 and 3,300 m. The species' predicted distribution was restricted to the northern flanks of the SNSM, with an estimated extent of ~352 km2. This estimate is more restricted than previous estimates (570 km2), but does not alter the species' status as Endangered based on IUCN criteria. The model predicted that the presence of Santa Marta Bush-Tyrants was regionally dependent on cold and humid climates, with low annual variation in temperature and precipitation. Locally, the species' presence was determined by the availability of habitat edges between forests and open areas. Conservation actions should aim to reduce rates of forest loss, while maintaining the presence of areas with good light and exposed perches, microhabitat conditions typically found in habitat edges or areas of natural disturbance. An explicit integration of quantitative data on habitat use and foraging patterns into niche models would help to obtain more realistic and detailed projections of the occupied distribution of range-restricted birds.

Morphometrics of mid-Atlantic dabbling ducks for use in thermoregulation models

Mark C. Livolsi, Christopher K. Williams, John M. Coluccy and Matthew T. DiBona

Department of Entomology and Wildlife Ecology, University of Delaware, Newark, Delaware, USADucks Unlimited Inc., Ann Arbor, Michigan, USADelaware Department of Natural Resources and Environmental Control, Division of Fish & Wildlife, Dover, Delaware, USA
Bioenergetics modeling is a popular tool used by waterfowl biologists to estimate carrying capacity based on food energy availability and daily energy expenditure (DEE). For wintering waterfowl, estimates of DEE may incorporate a cost of thermoregulation (CT) component, which accounts for metabolic heat production when ambient temperatures fall below a species-specific Lower Critical Temperature (LCT). Typically, DEE estimates have utilized either a fixed CT component or a simple CT model based solely on the magnitude of the difference between ambient temperature and LCT. Using a more complex CT model that accounts for differential heat loss from individual body regions due to temperature, wind speed, and contact with air or water may provide more detailed estimates of CT and, in turn, carrying capacity. However, such models required detailed morphometrics as model inputs in addition to environmental data. We present morphometrics for 8 dabbling duck species for use in thermoregulation models, as well as regression equations that may substitute for measurements of unmeasured species. We compared CT values produced via simple and complex CT models for American Black Ducks (Anas rubripes) wintering on the Delaware Bayshore, 2011–2013. We found that the complex CT model produced significantly higher CT estimates (5.38 ± SE 0.38 kJ bird−1 hr−1) compared with the simple model (1.26 ± 0.04 kJ bird−1 hr−1). Applying these CT values to bioenergetics models for American Black Ducks wintering in southern New Jersey suggested that this disparity in CT could produce substantial differences in estimated carrying capacity. Thus, we recommend that researchers consider incorporating detailed CT models into their estimates of DEE to reduce bias in carrying capacity estimates.

Anthropogenic features influencing occurrence of Black Vultures (Coragyps atratus) and Turkey Vultures (Cathartes aura) in an urban area in central Amazonian Brazil

Weber G. Novaes and Renato Cintra

WGN Environmental Consulting, Lauro de Freitas, Bahia, BrazilGraduate Program in Ecology, Instituto Nacional de Pesquisas da Amazônia, Manaus, Amazonas, BrazilCoordenação de Biodiversidade, Instituto Nacional de Pesquisas da Amazônia, Manaus, Amazonas, Brazil
Recent increases in Black Vulture (Coragyps atratus) and Turkey Vulture (Cathartes aura) numbers, particularly in urban–suburban settings, have led to more frequent human–vulture interactions, including vulture–aircraft strikes. This problem highlights the need for vulture management strategies, including determining habitat use by these species in urban settings. We investigated the effects of structures and landscape features on habitat use by Black and Turkey vultures in and around the city of Manaus in central Amazonian Brazil. We repeatedly surveyed 80 sites (3–9 visits per site in 2009–2010) and used detection histories to derive maximum-likelihood estimates of (1) vulture occurrence and detection probabilities and (2) environmental covariate effects on occupancy. Hierarchical logistic models showed that Black Vultures were associated with urban features such as open garbage containers and streams, but Turkey Vultures were associated with forest fragments. These results suggest that Black Vultures select environments where the food supply is abundant, whereas Turkey Vultures may avoid sites that attract Black Vultures in favor of forest remnants, a habitat for which they have specific foraging adaptations. Black Vulture management should focus on reducing the amount of food waste available to the birds in urban open garbage containers and streams, but Turkey Vulture management could be improved through removal of animal carcasses, and perhaps also removal of nests and roosts from forest remnants, especially near airfields.

Genetic structure, diversity, and interisland dispersal in the endangered Mariana Common Moorhen (Gallinula chloropusguami)

Mark P. Miller, Thomas D. Mullins, Susan M. Haig, Leilani Takano and Karla García

U.S. Geological Survey, Forest and Rangeland Ecosystem Science Center, Corvallis, Oregon, USAU.S. Fish and Wildlife Service, Honolulu, Hawaii, USA
The Mariana Common Moorhen (Gallinula chloropus guami) is a highly endangered taxon, with fewer than 300 individuals estimated to occur in the wild. The subspecies is believed to have undergone population declines attributable to loss of wetland habitats on its native islands in the Mariana Islands. We analyzed mitochondrial DNA (mtDNA) sequences (control region and ND2 genes) and nuclear microsatellite loci in Mariana Common Moorhens from Guam and Saipan, the two most distal islands inhabited by the subspecies. Our analyses revealed similar nuclear genetic diversity and effective population size estimates on Saipan and Guam. Birds from Guam and Saipan were genetically differentiated (microsatellites: FST = 0.152; control region: FST = 0.736; ND2: FST = 0.390); however, assignment tests revealed the presence of first-generation dispersers from Guam onto Saipan (1 of 27 sampled birds) and from Saipan onto Guam (2 of 28 sampled birds), suggesting the capability for long-distance interpopulation movements within the subspecies. The observed dispersal rate was consistent with long-term estimates of effective numbers of migrants per generation between islands, indicating that movement between islands has been an ongoing process in this system. Despite known population declines, bottleneck tests revealed no signature of historical bottleneck events, suggesting that the magnitude of past population declines may have been comparatively small relative to the severity of declines that can be detected using genetic data.

Patterns of migratory connectivity in Vaux's Swifts at a northern migratory roost: A multi-isotope approach

Matthew W. Reudink, Steven L. Van Wilgenburg, Lauren S. Steele, Andrew G. Pillar, Peter P. Marra and Ann E. McKellar

Department of Biological Sciences, Thompson Rivers University, Kamloops, British Columbia, CanadaEnvironment Canada, Saskatoon, Saskatchewan, CanadaMigratory Bird Center, Smithsonian Conservation Biology Institute, Washington, D.C., USA

The strength of migratory connectivity between breeding, stopover, and wintering areas can have important implications for population dynamics, evolutionary processes, and conservation. For example, patterns of migratory connectivity may influence the vulnerability of species and populations to stochastic events. For many migratory songbirds, however, we are only beginning to understand patterns of migratory connectivity. We investigated the potential strength of migratory connectivity within a population of Vaux's Swifts (Chaetura vauxi). Like many aerial insectivores, this species is currently experiencing population declines. In 2012, a mass mortality event at a spring migratory roost on Vancouver Island, British Columbia, Canada, resulted in the deaths of >1,000 individuals (~2% of the British Columbia population). In these individuals, we examined variation in 3 stable isotopes (δ2H, δ13C, and δ15N) from claw samples to determine whether spring migrants showed inherent isotopic similarity in the habitats they used on their Mexican and Central American wintering grounds. Our results indicated the presence of 2 or 3 broad isotopic clusters, which suggests that Vaux's Swifts that migrated through Vancouver Island most likely originated from 2 or 3 overwintering locales or habitat types. We found no evidence of sex- or morphology-based segregation, which suggests that these groups likely share a similar overwintering ecology and, thus, may be equally vulnerable to stochastic events or habitat loss on the wintering grounds. Our results highlight the need for more studies on the nonbreeding-season ecology and migratory connectivity of this species.

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