An assessment of raptor hacking during a reintroduction

As part of a program to recover the peregrine falcon (Falco peregrinus,) in the southeastern United States, we assessed procedural and demographic influences on hacking success by evaluating inherent variation and incorporating controlled manipulation in hacking protocol. We examined release age and date, release cohort size and sex ratio, postfledging area occupancy, and feeding regimen. Fourteen peregrines dispersed successfully, 9 dispersed prematurely, and 5 died before dispersal. Generally, these variables were poor predictors of success with release age (t = -1.29, P = 0.25) and feeding regimen (χ ² = J.32, P = 0.25) showing only weak associations with success. Sex interacted predictably with release age and postfledging area occupancy to influence success; males were more successful when released younger (± SD days = 45.4 ±2.8 [successful] and 47.1 ±5.0 [unsuccessful]) onto a postfledging area occupied by few conspecifics (± SD number of peregrines = 0,3 ± 0.4 [successful] and 1.3 ± 1.3 [unsuccessful]), whereas females were more successful when released older (47.0 ± 1.8 [successful] and 44.5 ±0.7 [unsuccessful]) and were unaffected by postfledging area occupancy (0.9 ±0.8 [successful] and 1.0 ± 1.4 [unsuccessful]). These results added substantiation to the perception of hacking as a procedurally sound tool in the release of captive-reared peregrines and highlighted some alternate considerations on feeding regimen and release-cohort sex ratio in raptor hacking.