Identifying predators and fates of grassland passerine nests using miniature video cameras.

Nest fates, canses of nest failure, and idenfities of nest predators are difficult to determine for crassland passerines. We developed a miniature video-cainera system for use in grasslands and deployed it at (a) needs of 10 passerine species in North Dakota during 1996-97. Abandonment rates were higher at nests 1 day after camera deplov ment (23%) than 1 day or night (22-116 hr) at 6 nests 5 of which were depredaled by ground squirrels or tuice. For nests without cameras, estimated predation rates were lower for fround nests than aboveground nests (P = 0.055), but did not differ between open and covered nests P -74. Open and covered nests differed, however, when prodation risk (estimated by initial-predation rate was examined separately for day and night using camera-monitored nests; the frequency of initial predations that recurred during the day was higher for open uests than covered nests (P = 0.015). Thus, vulnerability of some test types may depend on the relative importance of nocturnal and dinrual predators. Predation risk increased with testhing age from 0 to S days (P = 0.07). Up to 15% of fates assigued to camera-monitored nests were strong when based solely on evidence that would have been available from periodic nest visits. There was ne evidence of disturbance at nearly half the depredated nests, including all 5 depredated by large mannuals. Oterlap to types of sign left by different predator species, and variability of sign within species, suggests that evidence at nests is unreliable for identifying predators of grassland passerines.