RHODAMINE-INJECTED EGGS TO PHOTOGRAPHICALLY IDENTIFY SMALL NEST-PREDATORS

Abstract

Photographs that clearly disclose avian-nest predators are difficult to obtain, particularly when predators are small and exhibit subtle depredatory behavior. We exposed House Sparrow (Passer domesticus) eggs injected with Rhodamine B dye in camera-monitored ground nests for 12-d periods at 76 sites within mixed-hardwood forest stands in central Massachusetts, June–July 1997. Dye-injected eggs enabled us to recognize with certainty when eggs were breached at the nest because their contents were fluorescent pink and readily detected photographically. Eleven potential predator species were identified disturbing nests, of which eight were confirmed as predators. Eastern chipmunks (Tamias striatus) were the most frequent predators detected, along with fisher (Martes pennanti), raccoon (Procyon lotor), Blue Jays (Cyanocitta cristata), Black-capped Chickadees (Poecile atricapillus), red squirrels (Tamiasciurus hudsonicus), an Eastern Towhee (Pipilo erythrophthalmus), and a white-footed mouse (Peromyscus leucopus). White-footed mice were the most commonly detected species disturbing nests, but were photographed only once actually destroying an egg. The visual cue provided by dye-injected House Sparrow eggs confirmed depredatory behavior by eastern chipmunks, Black-capped Chickadees, an Eastern Towhee, and a white-footed mouse.