NEST PREDATION IN THE MOUNTAIN WHITE-CROWNED SPARROW

Predation was the largest cause of failure in 1,132 Zonotrichia leucophrys oriantha nests, followed by desertion and inclement weather. Mean annual predation rate was 29.9% and did not vary significantly over the 19 years of the study. This was attributed to the presence of a large, stable population of Belding's ground squirrels, a known predator on Z. l. oriantha nests. Predation rate was highest during the nestling period, next highest during laying, and lowest during incubation. Mean daily predation rate for the whole nesting cycle was 2.0% per day. Investigator activities at nests frequently caused desertion during laying but seldom thereafter. These activities may have attracted predators on occasion but no convincing, pervasive effect could be demonstrated. Antipredator behaviors included several distraction displays and seasonal shifts in nest locations from above-ground to ground and from pines to willows. Predators at the nest were vigorously attacked but usually to no avail. Nest predation rates did not vary with parental age nor with clutch size.