Short-term effects of wildlife rehabilitation disappear over time in the wild: A case study on Spanish imperial eagles

Abstract

The efficiency and success of Wildlife Recovery Centers (WRC) is overall understudied contrasting with the great economic expense of rehabilitation programs. Studies on post-release monitoring of rehabilitated animals usually lack comparisons to wild counterparts. Here, we aimed to fill this gap by analyzing tracking data of a flagship species under conservation concern, the Spanish imperial eagle (Aquila adalberti). We focused our case-study on the dispersal movements of this species in the Iberian Peninsula. We GPS-tagged 17 eagles in Extremadura, consisting of five “injured” (required a physical recovery in a WRC), seven “healthy” (spent time in a WRC with no diagnosed injury), and five “control” (wild) individuals. We analyzed at a daily temporal scale the distance moved, the time spent across different behaviors, and the timing of maximum activity. We performed linear mixed models to study how these metrics were affected by WRC treatment, and how this effect changed over time. Sample size for observation units in our models was 8,596 daily tracking subsets. The timing of activity peak was not affected by any of our predictor variables of interest. Conversely, treatment affected daily distance moved, resting, and hunting behaviors. Particularly, we found widespread significant effects of the interaction between treatment and tracking day (i.e. day since release). Rehabilitated eagles (both healthy and injured) moved shorter distances, spent more time resting, and less time hunting than controls in the short term. However, such differences gradually declined over time and completely disappeared when pooling tracking data after 1 year (up to 2.3 years). These results highlight the long-term success of rehabilitation for dispersive Spanish imperial eagles.