Behavioral evidence of hunting and foraging techniques by a top predator suggests the importance of scavenging for preadults

Scavenging may be a regular feeding behavior for some facultative raptor species oc-cupying low quality habitats and/or with little experience in hunting techniques. However, its importance has been largely underestimated due to methodological limi-tations in identifying the real proportion in the diet. Here, through direct observations, we assessed the hunting and foraging success of the threatened Spanish imperial eagle Aquila adalberti determining the influence of age, sex, breeding status, habitat quality, prey type, and landscape characteristics. From 465 observations, Spanish im-perial eagles used hunting in flight (42%), scavenging (30%), hunting from a perch (16%) and kleptoparasitism (12%). Our model suggests that Prey size and Prey type best ex-plain hunting success, followed by Landscape and Sex. Our findings suggest that Spanish imperial eagles increase hunting success with age, with scavenging and klep-toparasitism regularly used as juveniles. The absence of relationships with any of the variables considered suggests that kleptoparasitism is an opportunistic behavior used sporadically. Scavenging is also independent of habitat quality and landscape charac-teristics. Accordingly, low prey density is not a driver of carrion use for preadult indi-viduals, suggesting that a lack of hunting ability obliges this age- class to use this alternative feeding technique regularly. As a result, the threatened Spanish imperial eagle population is also prone to mortality related to the illegal use of poison baits and, potentially, veterinary drugs (i.e., diclofenac).A.M. was supported by a Ramón y Cajal research contract by the Ministry of Economy and Competitiveness (RYC- 2012- 11867)