Evaluation of trail-cameras for diet assessment of nesting raptors using the Northern Goshawk as a model

Abstract

Diet studies present numerous methodological challenges. We evaluated the usefulness ofcommercially available trail-cameras for analyzing the diet of Northern Goshawks (Accipitergentilis) as a model for nesting raptors during the period 2007&-2011. We compared diet estimatesobtained by direct camera monitoring of 80 nests with four indirect analyses of preyremains collected from the nests and surroundings (pellets, bones, feather-and-hair remains,and feather-hair-and-bone remains combined). In addition, we evaluated the performanceof the trail-cameras and whether camera monitoring affected Goshawk behavior.The sensitivity of each diet-analysis method depended on prey size and taxonomic group,with no method providing unbiased estimates for all prey sizes and types. The cameras registeredthe greatest number of prey items and were probably the least biased method for estimatingdiet composition. Nevertheless this direct method yielded the largest proportion ofprey unidentified to species level, and it underestimated small prey. Our trail-camera systemwas able to operate without maintenance for longer periods than what has been reported inprevious studies with other types of cameras. Initially Goshawks showed distrust toward thecameras but they usually became habituated to its presence within 1&-2 days. The habituation period was shorter for breeding pairs that had previous experience with cameras. Using trail-cameras to monitor prey provisioning to nests is an effective tool for studying the diet of nesting raptors. However, the technique is limited by technical failures and difficulties in identifying certain prey types. Our study also shows that cameras can alter adult Goshawk behavior, an aspect that must be controlled to minimize potential negative impacts.