Comparison of mechanically egg-triggered cameras and time-lapse video cameras in identifying predators at Dusky Flycatcher nests

Abstract

We compared the effectiveness and reliability of mechanically egg-triggered set-cameras and time-lapse video cameras in identifying nest predators at active Dusky Flycatcher (Empidonax oberholseri) nests in Siskiyou County, California. We monitored 72 active flycatcher nests using camera systems from 1998 to 2000. Nest abandonment, hatching success, and daily survival rate did not differ between camera systems. Set-cameras were less reliable than video systems in successfully recording predation events (45% versus 95%). The nest predator assemblage between camera types differed significantly with more avian predators (primarily raptors) recorded at video-monitored nests. This may have been due to the failure of hawks and owls to take the trigger egg at set-camera nests during the nestling stage. We did not find a strong association between the condition of the nest (disturbed or undisturbed) after the predation event and the identity of the predator (mammalian or avian). We also documented disruption of the nest by visitors other than the original predator. These observations suggest that identification of nest predators based on nest remains can be highly inaccurate. We recommend the use of videography for accurate identification of nest predators. Results from studies identifying predators with egg-triggered cameras should limit conclusions to the incubation stage.