Erin J. Gott’s research while affiliated with The Peregrine Fund and other places

DEVOLVIENDO A FALCO FEMORALIS A LOS ESTADOS UNIDOS Se liberaron volantones de Falco femoralis criados en cautiverio a lo largo de las planicies costeras del sur de Texas (839 aves de 21 sitios durante 1993–2004) y en el desierto de Chihuahua del oeste de Texas (637 aves de 11 sitios durante 2002–2011) y del sur de Nuevo México (337 aves de 10 sitios durante 2006–2012). Las liberaciones en la costa de Texas produjeron dos poblaciones que anidaron: 15–18 pares cerca de Brownsville y 15 pares en dos islas cerca de Rockport. El hábitat de esta área se compone de una extensa sabana abierta, lo que representa la condición ancestral de casi toda la región. Actualmente se encuentra casi completamente dominada por tierras de labranza y matorrales; este último alberga a Bubo virginianus, uno de los mayores depredadores de halcones. Por el contrario, las liberaciones en el desierto de Chihuahua no fueron exitosas en el establecimiento de poblaciones silvestres. Aunque se encontraron 8–10 pares en el oeste de Texas en 2009, para el 2011 sólo se registró un par y no se encontró ninguno en 2012, como consecuencia aparente de una sequía severa. Una sola pareja documentada en Nuevo México en 2011 estuvo asociada con la alimentación artificial de aves de presa. Concluimos que la conservación y la expansión de poblaciones de F. femoralis en las planicies costeras de Texas requerirán de la protección y el manejo de los territorios de cría existentes, y de la creación y manejo de sabanas libres de matorrales. La sequía persistente, la reducción de las poblaciones de presas y las altas tasas de mortalidad debidas a la depredación por parte de rapaces parecen impedir el restablecimiento de poblaciones de F. femoralis en el oeste de Texas o Nuevo México.

Piracy (kleptoparasitism) accounted for 14% of observed foraging attempts on vertebrates (n = 125) by Aplomado Falcons (Falco femoralis) in southern Texas and northern Mexico, and was over twice as successful as hunting (82% versus 37%). Aplomado Falcons pirated prey cooperatively as well as individually. Eight bird species were targeted for piracy, six of which were as large or larger than the falcons. The majority of prey items stolen were mammals.

The northern aplomado falcon (Falco femoralis septentrionalis) has been the subject of a large-scale reintroduction effort conducted by The Peregrine Fund since 1993. Intensive monitoring during 2002–2004 revealed approximately 38 breeding pairs and numerous non-territorial individuals in two study areas centered on Matagorda Island National Wildlife Refuge (NWR) and Laguna Atascosa NWR. Continued releases (“hacking”) of captive-bred young after pair establishment and successful wild breeding provided an opportunity to compare survival and recruitment histories of wild-reared and hacked falcons hatched during 2001–2003. We used Program MARK to rank multi-state models of apparent survival and recruitment rates with Akaike’s Information Criterion scores, corrected for small samples. The top model candidate, with almost 3.5 times more support than the next best model, detected differences due to falcon origin (wild or captivity): although breeder survival was independent of origin, juvenile hacked falcons survived and recruited at lower rates than wild-reared falcons. Given the high density of territorial adult falcons in the study areas, the difference in apparent survival may reflect greater dispersal by hacked falcons, increased tolerance of wild falcons in territory margins due to prior socialization, or other factors effecting higher intrinsic fitness of wild falcons. However, natal dispersal did not differ between the two groups, strengthening the hypothesis of a difference in true survival. Disproportionately greater recruitment of wild falcons into the breeding population again suggests their higher intrinsic fitness. These findings show how close monitoring of population vital rates can efficiently guide adaptive management of recovering populations.