Diet composition in the Tengmalm's Owl Aegolius funereus: A comparison of camera surveillance and pellet analysis

Abstract

During a two-year study in Central Europe, we used a combination of pellet analysis and camera recordings to assess the diet composition of Tengmalm's Owls during the breeding season, with regards to availability of the main prey components in the field. The diet of the owls consisted mainly of voles (Arvicolidae), mice (Muridae) and shrews (Soricidae), and their proportion in the diet reflected their local abundances in the field. Pellet analysis allowed us to determine 40.2 (± 6.9 SD)% in 2004 and 46.4 (± 14.7 SD)% in 2006 of all delivered prey items recorded by cameras. We determined 77.1 (± 17.1 SD)% in 2004 and 80.2 (±12.5 SD)% in 2006 of the prey items recorded by camera monitoring. Pellet analysis underestimated the proportions of all main diet components, but the , differences were significant only for the proportion of voles and birds. The underestimation of voles may have been a consequence of their decapitation before delivery to the nest. We regularly recorded decapitated voles and mice in the nest boxes of Tengmalm's Owl, while whole shrews were found more often. Our study highlights that a combination of both methods allows for a more accurate assessment of diet composition in nocturnal raptor species.