SONG SPARROWS VS. COWBIRD BROOD PARASITES - IMPACTS OF FOREST STRUCTURE AND NEST-SITE SELECTION

We studied Song Sparrow (Melospiza melodia) reproductive ecology in na tural and restored riparian forest to evaluate the influence of habita t structure and nest-site selection on parasitism by Brown-headed Cowb irds (Molothrus ater). Logistic regression revealed that habitat struc ture affected the probability of parasitism at two scales, BROAD (with in 11.3 m of the nest) and LOCAL (within 5 m of the nest). Nests with abundant lateral cover at a height of < 1 m (BROAD) were less likely t o be parasitized, suggesting that lateral cover at ground level may re duce parasitism by concealing host movements in the vicinity of the ne st. in contrast, nests with abundant foliage cover at a height of 2-3 m (LOCAL) were more likely to be parasitized, suggesting that foliage cover above the nest may increase parasitism by providing perches from which female cowbirds can watch host activities and find nests. Sparr ow nest-site selection varied among forest types, but lateral cover at ground level and foliage cover above the nest were similar for nests in each forest type. Results suggest that further research on the effe cts of habitat structure on nest-site selection and cowbird parasitism could lead to methods of reducing parasitism through appropriate habi tat management and restoration efforts.