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White-tailed Deer (Odocoileus virginianus) Predation
on Grassland Songbird Nestlings

Study Areas and Methods

We used miniature black-and-white cameras (4 × 4 × 4 cm) to videotape predation and other activities at grassland passerine nests (Pietz and Granfors, 2000) in Stutsman and Barnes (1996-1997) and McHenry and Bottineau (1998-1999) counties in southeastern and northcentral North Dakota. Each year we searched for nests in different fields of grassland vegetation. We placed cameras at nests of 12 passerine species. Average distance between the nest and camera was 21 cm; the camera field of view included the nest and a small surrounding area. Infrared light-emitting diodes (LEDs) mounted around the camera lens provided cryptic illumination at night. Each camera was connected by a 50-m cable to a time-lapse videocassette recorder which recorded continuously at 4-5 images/sec. When the nesting attempt was completed we removed the camera and examined the nest area for signs of fledging and predation.

Recorded videotapes were reviewed to determine fates of all eggs and nestlings and to identify nest predators. Identifying deer on videotapes was sometimes difficult because usually only a portion of the deer's head was in camera view. We used head shape and size and the presence of a black spot on the side of the lower lip (Fig. 1C; Fig. 2E in Pietz and Granfors, 2000) to identify images of deer. Our assessments were confirmed by comparisons to reference images of known mammals videotaped with our miniature cameras. We assumed that deer at nests were white-tailed deer because mule deer (Odocoileus hemionus) are very rare east of the Missouri River in North Dakota.

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