NEST SITE CHARACTERISTICS OF AMERICAN ROBINS BREEDING IN DESERT-RIPARIAN HABITAT
We describe the nest site characteristics, and report on the association between site characteristics and reproductive success (brood size at day 8), for a population of American Robins (Turdus migratorius) breeding in the Toiyabe Mountains of central Nevada. Based on data from 132 nests, the immediate vicinity (a 10-m radius) around robin nests was sparsely vegetated with limited cover at any vegetation height. Nest tree diameters at breast height were not significantly different from those of
... erent from those of nearby trees. Based on tree availability in the immediate vicinity, robins chose to nest in single-leaf pinyon (Pinus monophylla) more often (49.6% of nests used versus 39.3% availability), and quaking aspen (Populus tremuloides) less often (24.8% of nests used versus 52.1% availability), than expected by chance. Contrary to predictions based on previous studies, there was no change from coniferous to deciduous trees for nesting as the breeding season progressed, nor did robins build their nests higher in trees later in the season. Nest orientation was significantly directional in the 90Њ arc between east and south, but was unrelated to the amount of concealment conferred by shrub and bush cover in the four quadrants around the nest. Solar insolation resulting from nest placement was not related to brood size at day 8 and there were no discernable relationships between either solar insolation or orientation and clutch initiation date. Brood size on day 8 was inversely related to mean dbh of the surrounding trees, while canopy cover and height were associated positively with larger broods at day 8.