Feeding rates of raptors during autumn migration in the Central Appalachians 1987–2022

Migratory raptors can fuel their journeys by feeding along the way. To maximize migration success, raptors are suspected to time their movements with the availability of their prey. Feeding rates can vary among species depending on migration distance (long vs. short distance), flight strategies (flapping vs. soaring), and within species according to individual timing (early vs. late migrants). We assessed the feeding rate of four eastern North American migratory raptors over a period of 35 years. Using visual observations collected during autumn migration in the Central Appalachians, we assessed the presence/absence of distended crops of migrants. We quantified the feeding rates of species with different migration ecologies (migration distance, flight strategies), compared within-season (timing) species, and assessed if feeding rates varied over the last 35 years. We found a higher feeding rate in short-distance than in long-distance migrants and in power-flapping vs soaring migrants. We detected a long-term significant increase in feeding rate for most species, more evident in early migratory individuals coupled with a decrease in the feeding rate of late migrants. Understanding how feeding rates vary according to migratory behavior and how the migration ecology of raptors is changing under a scenario of global environmental change is important for their conservation

Cambios en las poblaciones de aves rapaces migratorias en Veracruz, México, 1995-2005.

Migration counts of raptors have been used as a valid technique to assess population levels. Counts from Veracruz, Mexico, have the potential of generating valuable information for regional- to continental-scale populations of some species and to provide coverage for others that are not monitored elsewhere. This paper evaluates the use of Veracruz migration counts to monitor populations, documents the adjustments made to a currently existing method to analyze migration count data and fit it to the specific properties of our dataset, and presents estimates of population change over a decade. We used long-term, effort-adjusted migration count data to generate annual indexes of abundance. The series of annual indexes is fitted to a polynomial regression to produce an estimate of the annual rate of change. The use of this methodology with Veracruz data shows its usefulness to datasets of many species, as well as limitations to datasets from species with high interannual variation in migration counts, and those recorded rarely. In seven species, the authors found significant population change. Six of them, Swallow-tailed Kite, Mississippi Kite, Cooper’s Hawk, Swainson’s Hawk, Zonetailed Hawk, and Peregrine Falcon show increases at an annual rate between 1.9-15.7% per year-1 in the period 1995-2005. One species, the Northern Harrier, is decreasing at a rate of -8.4% year-1 during the same period. Trends reported here reveal population increases in most cases, and concur with the pattern found in migration counts from surveys such as the Breeding Bird Survey and the Christmas Bird Count.Los censos durante la migración han sido utilizados como una herramienta válida para determinar estatus poblacionales de aves rapaces. En Veracruz, México, éstos tienen la posibilidad de generar valiosa información sobre poblaciones a escala regional y continental, y de proveer cobertura para aquellas que no son estudiadas en otros sitios. Los objetivos de este trabajo son evaluar el uso de los censos durante la migración en Veracruz para seguimiento de poblaciones, documentar los ajustes hechos a un método de análisis existente para hacerlo apropiado a las propiedades específicas de nuestros datos y presentar estimaciones de cambio poblacional de las especies a lo largo de una década. Esta metodología utiliza censos de la migración de rapaces a largo plazo ajustados a esfuerzo de muestreo para generar índices anuales de abundancia. La serie de índices anuales es ajustada a una regresión polinomial para producir una estimación de la tasa de cambio anual. El uso de esta metodología de análisis para los censos en Veracruz demostró su utilidad para determinar tendencias poblacionales en muchas especies, así como limitaciones en aquellas con gran variación interanual en los censos y en especies registradas raramente. Se encontraron cambios poblacionales significativos en siete especies. Seis especies, Elanoides forficatus, Ictinia mississippiensis, Accipiter cooperii, Buteo swainsoni, B. albonotatus y Falco peregrinus muestran incrementos a una tasa anual entre 1.9-15.7% por año-1 en el periodo 1995-2005. Una especie más, Circus cyaneus, registró descensos a una tasa de -8.4% por año-1 en el mismo periodo. Las tendencias poblacionales que se reportan aquí confirman en su mayoría incrementos poblacionales y coinciden con los datos de fuentes como los Censos de Aves Reproductoras o los Censos Navideños de Aves

Appendix A. A summary of composite concentrations of organochlorine pesticides and total PCBs detected in fish collected from five locations on the north Pacific coast of Mexico and eight locations along the southeastern Gulf of Mexico, 2000–2002.

A summary of composite concentrations of organochlorine pesticides and total PCBs detected in fish collected from five locations on the north Pacific coast of Mexico and eight locations along the southeastern Gulf of Mexico, 2000–2002