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At least 91 records · Page 5Linked to original sources
USGS2019

Flexible timing of annual movements across consistently used sites by Marbled Godwits breeding in Alaska

The study of avian movement has detailed a spectrum of strategies for the timing and use of sites throughout the annual cycle, from near randomness to complete consistency. New tracking devices now permit the repeated tracking of individual animals throughout the annual cycle, detailing previously unappreciated levels of variation within migratory systems. Godwits (genus Limosa ) have featured prominently in studies of avian migration, but information derived from repeated tracking of individuals is limited. The Marbled Godwit subspecies Limosa fedoa beringiae breeds on the central Alaska Peninsula, and little is known about basic aspects of its migration ecology, including the repeatability with which this population times its annual migratory movements or uses migratory and nonbreeding sites. To address these questions, we equipped 9 Marbled Godwits breeding at a site near Ugashik, Alaska, with solar-powered satellite transmitters. We tracked individuals from July, 2008 to October, 2015 and obtained repeat migratory tracks from 5 of these birds. Individuals exhibited high fidelity to breeding, nonbreeding, and migratory stopover sites across years, but in contrast to congeners that conduct consistently timed, long, nonstop migrations, beringiae Marbled Godwits exhibited low levels of individual- or population-level repeatability in the timing of migratory movements. Their relatively short migrations may enable the integration of local environmental cues, potentially facilitating individual flexibility in the timing of annual migratory movements. Curiously, if local cues ultimately drive the timing of Marbled Godwit migratory movements, the population’s relatively constrained distribution during both the breeding and nonbreeding season should serve to synchronize birds if they are responding to similar cues. That our sample of Marbled Godwits nonetheless exhibited within- and between-year variation in the timing of their migratory movements suggests a complex integration of annually variable internal and external cues.

The Auk↗
USGS2019

Topographic drivers of flight altitude over large spatial and temporal scales

Bird movements vary spatially and temporally, but the primary drivers that explain such variation can be difficult to identify. For example, it is well known that the availability of updraft influences soaring flight and that topography interacts with weather to produce these updrafts. However, the influences of topography on flight are not well understood. We determined how topographic characteristics influenced flight altitude above ground level (AGL) of a large soaring bird, the Golden Eagle (Aquila chrysaetos), over several regions within the State of California, USA. Primary drivers of flight AGL, those to which eagles showed the same response at all spatial scales, were topographic roughness, ground elevation and the east-west component of aspect (eastness). Each of these is related to formation of thermal updrafts. Secondary drivers, those to which eagles showed region-specific patterns, included topographic position, percent slope, and the north-south component of aspect (northness). In contrast to primary drivers, these secondary drivers were related to formation of both thermal and orographic updrafts. Overall, drivers of flight altitudes that were related to thermal updrafts showed different levels of complexity due to spatial and temporal variation of those drivers than did flight altitudes related to orographic updrafts.

California↗
USGS2019

Biotic interactions are the dominant drivers of phylogenetic and functional structure in bird communities along a tropical elevational gradient

Understanding how biotic and abiotic interactions influence community assembly and composition is a fundamental goal in community ecology. Addressing this issue is particularly tractable along elevational gradients in tropical mountains that feature substantial abiotic gradients and rates of species turnover. We examined elevational patterns of avian community structure on 2 mountains in Malaysian Borneo to assess changes in the relative strength of biotic interactions and abiotic constraints. In particular, we used metrics based on (1) phylogenetic relatedness and (2) functional traits associated with both resource acquisition and tolerance of abiotic challenges to identify patterns and causes of elevational differences in community structure. High elevation communities were composed of more phylogenetically and functionally similar species than would be expected by chance. Resource acquisition traits, in particular, were clustered at high elevations, suggesting low resource and habitat diversity were important drivers of those communities. Traits typically associated with tolerance of cold temperatures and low atmospheric pressure showed no elevational patterns. All traits were neutral or overdispersed at low elevations suggesting an absence of strong abiotic filters or an increased influence of interspecific competition. However, relative bill size, which is important for thermoregulation, was larger in low elevation communities, suggesting abiotic factors were also influential there. Regardless of metric, clustered and neutral communities were more frequent than overdispersed communities overall, implying that interspecific competition among close relatives may not be a pervasive driver of elevational distribution and community structure of tropical birds. Overall, our analyses reveal that a diverse set of predominantly biotic factors underlie elevational variation in community structure on tropical mountains.

Kinabalu Park, Mt. Kinabalu, Mt. Tambuyukon↗
USGS2019

Does vegetation change over 28 years affect habitat use and reproductive success?

Individuals should prefer and use habitats that confer high fitness, but habitat use is not always adaptive. Vegetation in natural landscapes changes gradually and the ability of species to adaptively adjust their habitat use to long-term changes is largely unstudied. We studied nest patch and territory use over 28 yr in Orange-crowned Warblers ( Oreothlypis celata ) in a system that has undergone natural long-term changes in vegetation. Abundance of maple ( Acer grandidentatum ), its preferred nesting habitat, gradually declined from 1987 to 2015. We examined whether habitat use and its fitness consequences changed as the availability of preferred habitat decreased. We used resource selection function models to determine changes over time in the probability of using a nest patch given available patches, and the probability of using a territory given available territories. We estimated nest survival to evaluate changes over time in the fitness consequences of nest patch use. We also compared habitat use (nest patch and territory) and fitness (nest survival) between areas with naturally reduced abundance of maple and experimentally increased abundance of maple (fenced areas). Nest patch use depended on maple abundance and did not change drastically across 28 yr, even though the availability of preferred maple patches decreased over time. In contrast, nest survival tended to decrease over time. We did not see differences in nest patch use and nest survival between unfenced and fenced areas, unlike territory use, which increased with the abundance of maple in fenced areas and decreased in unfenced areas. Our study depicts one example of relatively unchanged habitat use in the face of decreased availability of preferred vegetation across years, with a resulting decrease in reproductive success. Investigating changes in habitat use and fitness consequences for animals exposed to long-term habitat change is necessary to understand adaptive behavioral responses.

Arizona↗
USGS2008

A multiscale analysis of nest predation on Least Bell's Vireos ( Vireo bellii pusillus )

We examined variables influencing nest predation on the endangered Least Bell's Vireo ( Vireo bellii pusillus ) at three spatial scales to determine what nest-site, habitat, or landscape characteristics affect the likelihood of nest predation and to determine the spatial distribution of predation risk and the variables influencing it. We used MARK to calculate daily survival rates of Least Bell's Vireo nests and applied an information-theoretic approach to evaluate support for logistic regression models of the effect of habitat variables on predation risk. Analysis of data for 195 nests collected during 1999 and 2000 at the San Luis Rey River and Pilgrim Creek in southern California revealed no effect of fine-scale factors, including nest height, supporting plant species, and three measures of nest concealment, on the likelihood of predation. At the intermediate scale, distances to the riparian-habitat edge and to internal gaps in the canopy were unrelated to nest survival. Surrounding land-use type was a poor predictor of predation risk, with the exception of proximity to golf course–park habitat and wetland. Nests within 400 m of golf course–park were only 20% as likely to avoid predation as nests >400 m from this habitat, and nests near wetland were more than twice as likely to survive as nests distant from wetland. Spatially, predation appeared to be random throughout the site, with localized clustering evident in the vicinity of golf course–park and wetland. Our results suggest that the landscape may be the most appropriate scale at which to manage nest predation in this system.

The Auk↗
USGS2008

Nutrient-reserve dynamics during egg production by female Greater Scaup (Aythya marila): Relationships with timing of reproduction

We studied nutrient-reserve dynamics of female Greater Scaup ( Aythya marila ) to quantify intraspecific strategies of nutrient acquisition for egg production, particularly in relation to the seasonal timing of reproduction (i.e., date of initiation of rapid follicle growth [RFG]). We collected female Greater Scaup on the Yukon-Kuskokwim Delta, Alaska, from arrival through clutch formation during the 2002 and 2003 breeding seasons, and we subsequently conducted standard proximate body-composition analysis. Endogenous lipid, protein, and mineral reserve levels did not decline during egg production. This result differs from most other nutrient-reserve studies of waterfowl, suggesting that female Greater Scaup rely on exogenous food resources, rather than endogenous nutrient reserves, to meet the energy and nutrient costs of clutch formation. Furthermore, endogenous nutrient-reserve levels did not decline with date of RFG initiation, which indicates that body condition at initiation of egg production was similar across the nesting season. We found evidence of nutrient-reserve thresholds for initiation of RFG, in that lipid, protein, and mineral reserves were smaller in nonreproductive than in reproductive females. In light of recent conservation concerns over declining North American scaup populations, our data contrast with nutrient-reserve dynamics described for Lesser Scaup ( A. affinis ).

The Auk↗
USGS2008

Endocrine effects of the herbicide linuron on the American Goldfinch ( Carduelis tristis )

Certain contaminants alter normal physiological function, morphology, and behavior of exposed organisms through an endocrine mechanism. We evaluated how the herbicide linuron, an endocrine-active compound, affects physiological parameters and secondary sex characteristics of the American Goldfinch ( Carduelis tristis ). When administered at relatively low doses (control, 1.0, 4.0, and 16.0 μg linuron per gram of body mass per day), linuron delayed prealternate molt progression in a dose-dependent manner. At the high dose level, linuron exposure lowered hematocrit and female plasma thyroxine concentrations and increased body mass. Neither plasma testosterone concentrations nor the color of plumage or integument of birds in the treatment groups were different from those of the control group. Overall, the physiological effects that were measured suggested disruption of thyroid function. These results highlight the importance of continual monitoring of avian populations for potential effects of exposure to pesticides and other chemicals at sublethal concentrations.

The Auk↗
USGS2008

Sources of variation in detection of wading birds from aerial surveys in the Florida Everglades

We conducted dual-observer trials to estimate detection probabilities (probability that a group that is present and available is detected) for fixed-wing aerial surveys of wading birds in the Everglades system, Florida. Detection probability ranged from <0.2 to similar to 0.75 and varied according to species, group size, observer, and the observer's position in the aircraft (front or rear seat). Aerial-survey simulations indicated that incomplete detection can have a substantial effect oil assessment of population trends, particularly river relatively short intervals (<= 3 years) and small annual changes in population size (<= 3%). We conclude that detection bias is an important consideration for interpreting observations from aerial surveys of wading birds, potentially limiting the use of these data for comparative purposes and trend analyses. We recommend that workers conducting aerial surveys for wading birds endeavor to reduce observer and other controllable sources of detection bias and account for uncontrollable sources through incorporation of dual-observer or other calibratior methods as part of survey design (e.g., using double sampling).

The Auk↗
USGS2008

On determining the significance of ephemeral continental wetlands to North American migratory shorebirds

Conservation challenges enhance the need for quantitative information on dispersed bird populations in extensive landscapes, for techniques to monitor populations and assess environmental effects, and for conservation strategies at appropriate temporal and spatial scales. By estimating population sizes of shorebirds in the U.S. portion of the prairie pothole landscape in central North America, where most migrating shorebirds exhibit a highly dispersed spatial pattern, we determined that the region may play a vital role in the conservation of shorebirds. During northward and southward migration, 7.3 million shorebirds (95% CI: 4.3–10.3 million) and 3.9 million shorebirds (95% CI: 1.7–6.0 million) stopped to rest and refuel in the study area; inclusion of locally breeding species increases the estimates by 0.1 million and 0.07 million shorebirds, respectively. Seven species of calidridine sandpipers, including Semipalmated Sandpipers ( Calidris pusilla ), White-rumped Sandpipers ( C. fuscicollis ), and Stilt Sandpipers ( C. himantopus ), constituted 50% of northbound migrants in our study area. We present an approach to population estimation and monitoring, based on stratified random selection of townships as sample units, that is well suited to 11 migratory shorebird species. For extensive and dynamic wetland systems, we strongly caution against a monitoring program based solely on repeated counts of known stopover sites with historically high numbers of shorebirds. We recommend refinements in methodology to address sample-size requirements and potential sources of bias so that our approach may form the basis of a rigorous migration monitoring program in this and other prairie wetland regions.

The Auk↗
USGS2008

[Obituary] In memoriam: Mortimer Brooke Meanley, Jr., 1915-2007

Mortimer Brooke Meanley, Jr., was born at Riderwood, Baltimore County, Maryland, on 19 January 1915, and died at home in Maine on 19 August 2007. He was always called “Brooke” as an adult. Much of his youth was spent in birding and other natural-history activities, interest he credits to the Boy Scouts and his teachers. These activities directed him toward a professional career in wildlife biology. He was educated at McDonogh High School in Owings Mill, Maryland – at the time a private, semimilitary school for boys – and graduated in 1934.

The Auk↗
USGS2009

What constitutes a nesting attempt? Variation in criteria causes bias and hinders comparisons across studies

Because reliable estimates of nesting success are very important to avian studies, the defnition of a “successful nest” and the use of different analytical methods to estimate success have received much attention. By contrast, variation in the criteria used to determine whether an occupied site that did not produce offspring contained a nesting attempt is a source of bias that has been largely ignored. This problem is especially severe in studies that deal with species whose nest contents are relatively inaccessible because observers cannot determine whether or not an egg was laid for a large proportion of occupied sites. Burrowing Owls ( Athene cunicularia ) often lay their eggs ≥3 m below ground, so past Burrowing Owl studies have used a variety of criteria to determine whether a nesting attempt was initiated. We searched the literature to document the extent of that variation and examined how that variation influenced estimates of daily nest survival. We found 13 different sets of criteria used by previous authors and applied each criterion to our data set of 1,300 occupied burrows. We found significant variation in estimates of daily nest survival depending on the criteria used. Moreover, differences in daily nest survival among populations were apparent using some sets of criteria but not others. These inconsistencies may lead to incorrect conclusions and invalidate comparisons of the productivity and relative site quality among populations. We encourage future authors working on cavity-, canopy-, or burrow-nesting birds to provide specific details on the criteria they used to identify a nesting attempt.

The Auk↗
USGS2009

Multistate models for estimation of survival and reproduction in the Grey-headed Albatross ( Thalassarche chrysostoma )

Reliable information on demography is necessary for conservation of albatrosses, the most threatened family of pelagic birds. Albatross survival has been estimated using mark-recapture data and the Cormack-Jolly-Seber (CJS) model. However, albatross exhibit skipped breeding, violating assumptions of the CJS model. Multistate modeling integrating unobservable states is a promising tool for such situations. We applied multistate models to data on Grey-headed Albatross ( Talassarche chrysostoma ) to evaluate model performance and describe demographic patterns. These included a multistate equivalent of the CJS model (MS-2), including successful and failed breeding states and ignoring temporary emigration, and three versions of a four-state multistate model that accounts for temporary emigration by integrating unobservable states: a model (MS-4) with one sample per breeding season, a robust design model (RDMS-4) with multiple samples per season and geographic closure within the season, and an open robust design model (ORDMS-4) with multiple samples per season and staggered entry and exit of animals within the season. Survival estimates from the MS-2 model were higher than those from the MS-4 model, which resulted in apparent percent relative bias averaging 2.2%. The ORDMS-4 model was more appropriate than the RDMS-4 model, given that staggered entry and exit occurred. Annual survival probability for Greyheaded Albatross at Marion Island was 0.951 ± 0.006 (SE), and the probability of skipped breeding in a subsequent year averaged 0.938 for successful and 0.163 for failed breeders. We recommend that multistate models with unobservable states, combined with robust-design sampling, be used in studies of species that exhibit temporary emigration.

The Auk↗
USGS2009

Effect of distance-related heterogeneity on population size estimates from point counts

Point counts are used widely to index bird populations. Variation in the proportion of birds counted is a known source of error, and for robust inference it has been advocated that counts be converted to estimates of absolute population size. We used simulation to assess nine methods for the conduct and analysis of point counts when the data included distance-related heterogeneity of individual detection probability. Distance from the observer is a ubiquitous source of heterogeneity, because nearby birds are more easily detected than distant ones. Several recent methods (dependent double-observer, time of first detection, time of detection, independent multiple-observer, and repeated counts) do not account for distance-related heterogeneity, at least in their simpler forms. We assessed bias in estimates of population size by simulating counts with fixed radius w over four time intervals (occasions). Detection probability per occasion was modeled as a half-normal function of distance with scale parameter sigma and intercept g(0) = 1.0. Bias varied with sigma/w; values of sigma inferred from published studies were often <25 m, which suggests a bias of >50% for a 100-m fixed-radius count. More critically, the bias of adjusted counts sometimes varied more than that of unadjusted counts, and inference from adjusted counts would be less robust. The problem was not solved by using mixture models or including distance as a covariate. Conventional distance sampling performed well in simulations, but its assumptions are difficult to meet in the field. We conclude that no existing method allows effective estimation of population size from point counts.

The Auk↗
USGS2009

Scrub-shrub bird habitat associations at multiple spatial scales in beaver meadows in Massachusetts

Most scrub-shrub bird species are declining in the northeastern United States, and these declines are largely attributed to regional declines in habitat availability. American Beaver ( Castor canadensis ; hereafter “beaver”) populations have been increasing in the Northeast in recent decades, and beavers create scrub-shrub habitat through their dam-building and foraging activities. Few systematic studies have been conducted on the value of beaver-modified habitats for scrub-shrub birds, and these data are important for understanding habitat selection of scrub-shrub birds as well as for assessing regional habitat availability for these species. We conducted surveys in 37 beaver meadows in a 2,800-km 2 study area in western Massachusetts during 2005 and 2006 to determine the extent to which these beaver-modified habitats are used by scrub-shrub birds, as well as the characteristics of beaver meadows most closely related to bird use. We modeled bird abundance in relation to microhabitat-, patch-, and landscape-context variables while adjusting for survey-specific covariates affecting detectability using N-mixture models. We found that scrub-shrub birds of regional conservation concern occupied these sites and that birds responded differently to microhabitat, patch, and landscape characteristics of beaver meadows. Generally, scrub-shrub birds increased in abundance along a gradient of increasing vegetation complexity, and three species were positively related to patch size. We conclude that these habitats can potentially play an important role in regional conservation of scrub-shrub birds and recommend that conservation priority be given to larger beaver meadows with diverse vegetation structure and composition.

Massachusetts↗
USGS2010

Polyphyly of Campylorhamphus , and description of a new genus for C. pucherani (Dendrocolaptinae)

We investigated the phylogenetic relationships of Campylorhamphus pucherani using DNA sequences from three mitochondrial genes and a nuclear intron, as well as 84 morphological characters from the skeleton, the integument, and the musculature. The molecular phylogeny indicated that C. pucherani is not part of Campylorhamphus ; instead, it is the sister species to Drymornis bridgesii , in a clade that also contains Lepidocolaptes . The morphological phylogeny also placed C. pucherani in a clade that contains Drymornis and Lepidocolaptes . Using a morphometric analysis of size and shape diversity, we demonstrated that the inclusion of C. pucherani in Drymornis would create an excessively heterogeneous genus compared with other dendrocolaptine genera. Because no generic name is available for C. pucherani , we describe the new genus Drymotoxeres for this species.

The Auk↗
USGS2010

Subspecies status and population genetic structure in Piping Plover ( Charadrius melodus )

Piping Plover (Charadrius melodus) is a migratory shorebird that is listed as endangered in Canada and the U.S. Great Lakes and as threatened throughout the rest of its breeding and winter range. We undertook a comprehensive molecular-genetic investigation to (1) address subspecific taxonomy, (2) characterize population genetic structure, and (3) infer past bottlenecks and demographic processes in this species. Analyses included individuals from 23 U.S. states and Canadian provinces and were based on mitochondrial DNA sequences (580 base pairs, n = 245) and 8 nuclear microsatellite loci (n = 229). Our findings provide support for separate Atlantic and Interior subspecies (C. m. melodus and C. m. circumcinctus, respectively). Birds from the Great Lakes region were allied with the Interior subspecies and should be referred to as C. m. circumcinctus. Population genetic analyses illustrated stronger genetic structure among Atlantic than among Interior birds, which may reflect reduced natal- and breeding-site fidelity of Interior individuals. Furthermore, analyses suggested that Interior birds previously experienced genetic bottlenecks, whereas there was no evidence of such patterns in the Atlantic subspecies. We interpret these results in light of 25 years of range-wide census data. Overall, differences between Interior and Atlantic Piping Plovers may reflect differences in spatiotemporal stability of nesting habitat between regions. ?? 2010 The American Ornithologists' Union.

The Auk↗
USGS2010

Traffic effects on bird counts on North American Breeding Bird Survey routes

The North American Breeding Bird Survey (BBS) is an annual roadside survey used to estimate population change in >420 species of birds that breed in North America. Roadside sampling has been criticized, in part because traffic noise can interfere with bird counts. Since 1997, data have been collected on the numbers of vehicles that pass during counts at each stop. We assessed the effect of traffic by modeling total vehicles as a covariate of counts in hierarchical Poisson regression models used to estimate population change. We selected species for analysis that represent birds detected at low and high abundance and birds with songs of low and high frequencies. Increases in vehicle counts were associated with decreases in bird counts in most of the species examined. The size and direction of these effects remained relatively constant between two alternative models that we analyzed. Although this analysis indicated only a small effect of incorporating traffic effects when modeling roadside counts of birds, we suggest that continued evaluation of changes in traffic at BBS stops should be a component of future BBS analyses.

The Auk↗