Effect of Sex and Age at Release on the Independence of Hacked Harpy Eagles

Release methods used in species restoration can affect the success of establishment and survival of released animals. We evaluated the effect of age at release and sex on the length of the dependence period of hacked captive-bred juvenile Harpy Eagles (Harpia harpyja). Between 2002 and 2007, we released 34 (19 males and 15 females) young eagles in Panama and Belize. To test the effect of age, these eagles were divided into two age classes: younger age class 1 (5–7 mo old) and older age class 2 (18–22 mo old). Survival (hacking success) was lower for the younger release age (70%) compared to the older release age (100%; Z = −2.05, P = 0.040). This difference in hacking success was attributed to the extended period of dependence on provisioned food by the younger (18.9 ± 1.3 mo [SE]) compared to older eagles (1.5 ± 0.8 mo). Between-sex comparisons showed that the average length of the dependence period was longer for males of age class 1 (males = 21.8 mo vs. females = 14.3 mo) and for females of age class 2 (females = 2.7 mo vs. males = 0 mo). Cox regression models indicated that the interaction of age at release and sex had a significant effect on the dependence period, and that age at release was the most influential variable. Eagles released at 18 mo or older showed increased survival and shorter dependence periods. Hacking can be used to successfully release captive-bred Harpy Eagles into the wild, but this technique was more efficient when delayed from fledging age (when falconers traditionally hack falcons) to nearer the Harpy Eagle's age of independence.