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The relative importance of cottonwood-willow riparian corridors and isolated oases to land birds migrating across southeastern Arizona was evaluated during four spring migrations, 1989 to 1994, based on patterns of species richness, relative abundance, density, and body condition of birds. We surveyed birds in 13 study sites ranging in size and connectivity from small isolated patches to extensive riparian forest, sampled vegetation and insects, and captured birds in mistnets. The continuous band of riparian vegetation along the San Pedro River does not appear to be functioning as a corridor for many migrating species, although it may for a few, namely Yellow-breasted Chats ( Icteria virens ), Summer Tanagers ( Piranga rubra ), and Northern Rough-winged Swallows ( Steldigopteryx serripennis ), which account for fewer than 10% of the individuals migrating through the area. Small, isolated oases hosted more avian species than the corridor sites, and the relative abundances of most migrating birds did not differ between sites relative to size-connectivity. There were few differences in between-year variability in the relative abundances of migrating birds between corridor and oasis sites. Between-year variability decreased with overall abundance of species and was greater for species with breeding ranges that centered north of 50 Њ N latitude. Body condition of birds did not differ relative to the size-connectivity of the capture site, but individuals of species with more northerly breeding ranges had more body fat than species that breed nearby. Peak migration densities of several bird species far exceeded breeding densities reported for the San Pedro River, suggesting that large components of these species were en route migrants. Peak densities of Yellow Warblers ( Dendroica petechia ) reached 48.0 birds/ha, of Wilson's Warblers ( Wilsonia pusilla ) 33.7 birds/ha, and of Yellow-rumped Warblers ( D. coronata ) 30.1 birds/ha. Riparian vegetation is limited in extent in the vicinity of our study sites, covering less than 1% of the landscape. We conclude that all riparian patches in southeastern Arizona are important as stopover sites to en route migrants regardless of their size and degree of isolation or connectivity. In light of potential habitat limitation, the protection of both small, disjunct riparian patches and extensive riverine tracts in western landscapes is imperative. Uso Comparativo de Corredores Riparios y Oasis por Aves Migratorias en el Sureste de ArizonaResumen: Se evaluó la importancia relativa de los corredores riparios de sauces y los oasis aislados para las aves que migran a través del sureste de Arizona durante cuatro migraciones de primavera, de 1989 a 1994, en base a patrones de riqueza de especies, abundancia relativa, densidades y condición corporal de las aves. Estudiamos aves en 13 sitios variando en tamaño y conectividad desde parches pequeños aislados hasta bosques riparios extensos. Muestreamos la vegetación e insectos y capturamos aves con redes. Las bandas continuas de vegetación rip...

Under the Bald and Golden Eagle Protection Act, the United States Fish and Wildlife Service (Service) can authorize take of golden eagles (Aquila chrysaetos), such as nest removal, disturbance, and lethal take, if the take is compatible with the preservation of the golden eagle. The Service needs baseline information on the current abundance and trend of subpopulations of the golden eagle to properly manage take of the species. Annually during late summer of 2006-2012, we used distance sampling on approximately 17,500 km of aerial line transects to estimate golden eagle abundance in 4 Bird Conservation Regions (BCRs; North American Bird Conservation Initiative Monitoring Subcommitte 2007) that collectively cover about 80% of the species' range in the coterminous western United States. We estimated study area abundances of 24,509 (90% CI: 19,406-31,947) in 2006 and 21,715 (90% CI: 18,165-27,624) in 2012, including all breeding and non-breeding individuals. We used a Bayesian hierarchical model to estimate trends in individual BCRs and the entire study area based on numbers of golden eagles counted along surveyed transects. We detected declines (90% credible intervals [CRIs] for trend coefficients <0.0) in numbers of golden eagles classified as juveniles in BCR 10 (Northern Rockies) and BCR 16 (Southern Rockies and Colorado Plateau) during 2006-2012. However, our results indicate the total abundance of golden eagles has not declined 2006-2012 in much of the western United States. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.

Increasing development across the western United States (USA) elevates concerns about effects on wildlife resources; the golden eagle (Aquila chrysaetos) is of special concern in this regard. Knowledge of golden eagle abundance and distribution across the western USA must be improved to help identify and conserve areas of major importance to the species. We used distance sampling and visual mark-recapture procedures to estimate golden eagle abundance from aerial line-transect surveys conducted across four Bird Conservation Regions in the western USA between 15 August and 15 September in 2006–2010, 2012, and 2013. To assess golden eagle-habitat relationships at this scale, we modeled counts of golden eagles seen during surveys in 2006–2010, adjusted for probability of detection, and used land cover and other environmental factors as predictor variables within 20-km2 sampling units randomly selected from survey transects. We found evidence of positive relationships between intensity of use by golden eagles and elevation, solar radiation, and mean wind speed, and of negative relationships with the proportion of landscape classified as forest or as developed. The model accurately predicted habitat use observed during surveys conducted in 2012 and 2013. We used the model to construct a map predicting intensity of use by golden eagles during late summer across our ~2 million-km2 study area. The map can be used to help prioritize landscapes for conservation efforts, identify areas where mitigation efforts may be most effective, and identify regions for additional research and monitoring. In addition, our map can be used to develop region-specific (e.g., state-level) density estimates based on the latest information on golden eagle abundance from a late-summer survey and aid designation of geographic management units for the species.