Biases in diet sampling methods in the Spanish Imperial Eagle Aquila adalberti

Abstract

This study quantifies for the first time the biases associated with different methods (direct observations, pellets, remains, and pellets plus remains referred to as pooled data) used to assess the diet of the Spanish Imperial Eagle Aquila adalberti. With respect to prey items delivered to the nest as a surrogate of the most objective method to assess the diet, pellets, remains and pooled data overestimated birds and underestimated mammals. With regards to the size of the prey, prey remains, pellets and pooled data underestimate larger prey (>601 g) but overestimated smaller and medium size preys (