Search

The American Kestrel (Falco sparverius) has been steadily declining throughout most of its eastern North American range, and the cause of this decline is still relatively unknown. As a cavity nesting species, the American Kestrel often competes with other cavity nesters such as the invasive and abundant European Starling (Sturnus vulgaris) over nest boxes. The relationship between European Starling presence at nesting sites and American Kestrel occupancy and nesting success is understudied. We analyzed data from nest boxes monitored in eastern Pennsylvania, USA, from 1992 to 2021 to identify changes in occupancy of American Kestrels and competitors, and to examine the relationship between competition at nest boxes and American Kestrel nesting parameters. We found that American Kestrel occupancy decreased while European Starling occupancy increased over the study period. All other species occupying nest boxes (small mammals, passerines, owls, and snakes) showed no significant occupancy trends. On average 21% of nest boxes remained unoccupied annually, and 7% of occupied nest boxes were used by both American Kestrels and competitors in the same breeding season. The presence of these competitors had negative associations with American Kestrel occupancy, clutch size, number of fledglings produced, and overall nesting success. Specifically, the rate of nesting success decreased by 26% when European Starlings used the same nest box within the same breeding season. In recent years, nesting productivity of American Kestrels has decreased, with the average number of nestlings, fledglings, and nesting success rate all declining, while the average clutch size remained constant. Our results suggest that American Kestrel nesting parameters in eastern Pennsylvania are negatively associated with competition for nest boxes during the breeding season. The opposing trends in occupancy for the European Starling and the American Kestrel in this study area coupled with the declining productivity of American Kestrel nests raise concerns over the future of this raptor species in eastern Pennsylvania. Falco sparverius ha estado disminuyendo constantemente en la mayor parte de su área de distribución oriental en América del Norte, y la causa de esta disminución aún es relativamente desconocida. Como especie que anida en cavidades, F. sparverius a menudo compite por las cajas nido con otras que también anidan en cavidades, como Sturnus vulgaris, una especie invasora y abundante. La relación entre la presencia de S. vulgaris en los lugares de cría y la ocupación y el éxito de cría de F. sparverius está poco estudiada. Analizamos los datos de cajas nido monitoreadas en el este de Pensilvania, EEUU, desde 1992 hasta 2021, para identificar cambios en la ocupación de F. sparverius y competidores, y para examinar la relación entre la competencia en las cajas nido y los parámetros de anidación de F. sparverius. Encontramos que la ocupación de F. sparverius disminuyó mientras que la ocupación de S. vulgaris aumentó durante el período de estudio. Todas las demás especies que ocupan cajas nido (mamíferos pequeños, paseriformes, búhos y serpientes) no mostraron tendencias significativas en la ocupación. En promedio, el 21% de las cajas nido permanecieron desocupadas anualmente, y el 7% de las cajas ocupadas fueron utilizadas por F. sparverius y competidores en la misma estación reproductiva. La presencia de estos competidores tuvo asociaciones negativas con la ocupación, el tamaño de la puesta, el número de volantones producidos y el éxito general de cría de F. sparverius. Específicamente, la tasa del éxito de cría disminuyó en un 26% cuando S. vulgaris utilizó la misma caja nido dentro de la misma estación reproductiva. En los últimos años, la productividad de F. sparverius ha disminuido, con una caída en el número promedio de polluelos, volantones y en la tasa de éxito de cría, mientras que el tamaño promedio de la puesta se mantuvo constante. Nuestros resultados sugieren que los parámetros reproductivos de F. sparverius en el este de Pensilvania están negativamente asociados con la competencia por las cajas nido durante la estación reproductiva. Las tendencias opuestas en la ocupación para S. vulgaris y F. sparverius en esta área de estudio, junto con la disminución de la productividad de los nidos de F. sparverius, plantean preocupaciones sobre el futuro de esta rapaz en el este de Pensilvania. [Traducción del equipo editorial] [ABSTRACT FROM AUTHOR]

Dispersal is the process by which individuals move through different sites away from their natal place during their life. Many factors can regulate dispersal movements of individuals, from intrinsic characteristics of the individuals to environmental conditions. Here, we report American Kestrel (Falco sparverius) natal dispersal in central Argentina and analyse some of the factors that can modulate it. We also report information on breeding dispersal, and nest box fidelity, using banding data from 2011 to 2019. The number of kestrels banded was high, but only 5.59% of birds were recaptured or re-sighted. Part of the American Kestrel population is philopatric, and most kestrels were detected breeding at 1 year of age for the first time (41.38%). Kestrels bred from one (mostly) to 6 years in the same nest box. Natal dispersal ranged from 2 to 36.9 km, and females dispersed longer distances than males. We did not record kestrels dispersing between the different sampling sites, but we recovered two dead dispersing juveniles more than 200 km from their natal nest, suggesting some long-distance dispersal may occur in our studied population. Further banding studies or better, studies based on the tagging of American Kestrels with GPS tracking devices will certainly be needed to better understand dispersal movements and factors that modulate these dispersal patterns in South America. [ABSTRACT FROM AUTHOR]

Land-use changes due to agricultural intensification and climatic factors can affect avian reproduction. We use a top predator of agroecosystems, the American kestrel (Falco sparverius) breeding in nest boxes in Central Argentina as a study subject to identify if these two drivers interact to affect birds breeding. We analyzed their breeding performance across a gradient of agricultural intensification from native forest, traditional farmland to intensive farmland. The surface devoted to soybean was used as a proxy of agriculture intensification; however, it did not affect the breeding performance of American kestrels. Even though the presence of pastures was important to determine the probability of breeding successfully. Climatic variables had strong effects on the species breeding timing, on the number of nestlings raised by breeding pairs and on the probability of those pairs to breed successfully (raising at least one fledgling). Our results highlight the relevance of pastures and grasslands for American kestrel reproduction. These environments are the most affected by land-use change to intensive agriculture, being transformed into fully agricultural lands mostly devoted to soybean production. Therefore, future expansion of intensive agriculture may negatively affect the average reproductive parameters of American Kestrels, at least at a regional scale. Further research will be needed to disentangle the mechanisms by which weather variables affect kestrel breeding parameters. [ABSTRACT FROM AUTHOR]