BREEDING BIOLOGY OF THE CHIPPING SPARROW IN PONDEROSA PINE FORESTS OF THE COLORADO FRONT RANGE

We present information on the breeding biology and nest-site characteristics of the western subspecies of the Chipping Sparrow (Spizella passerina arizonae) in montane ponderosa pine (Pinus ponderosa) forests of the Colorado Front Range. We located 83 nests during the summers of 1999–2002. The earliest egg date was 23 May and young fledged as late as 11 August. Nests were typically placed in needle clusters on outer branches of ponderosa pines. Mean canopy cover at nest sites was 50%. We observed no differences in nest placement or nest-site microhabitat between successful and unsuccessful nests. The nesting cycle lasted approximately 30 days, including 4 nest-building days, 3 egg-laying days, 14 incubation days, and 9 brooding days. Nests with known outcomes fledged a mean of 1.67 young from a mean clutch of 3.08 eggs. At least 27 nests (32.5%) were depredated, making predation the primary cause of nest failure. Of 42 successful nests, 5 (11.9%) were parasitized, although at least two Chipping Sparrows and one Brown-headed Cowbird (Molothrus ater) fledged from each parasitized nest. Both parasitism rates and nest success are highly variable among populations in this species.