Relationship between nest success and concealment in two ground-nesting passerines

We examined vegetation characteristics around nest sites of the Hermit Thru sh (Catharus guttatus) and Ovenbird (Seiurus aurocapillus) for three summer s in the northern- and mixed-hardwood forests of northern Wisconsin and the Upper Peninsula of Michigan to test the hypothesis that nests with greater concealment are less vulnerable to depredation. Because these two ground-n esting passerines differ in terms of nest structure and behavior near the n est, they present an opportunity to examine how these two factors influence reproductive success in sympatric species. Depredation was the most common source of nest failure for both species, with Ovenbirds having higher nest success for data pooled across years. Side (but not overhead) concealment was correlated positively with nest success for the Hermit Thrush but not f or the Ovenbird. Side and overhead concealment did not differ between the H ermit Thrush and Ovenbird. We found a substantial proportion of nests in gr ound pine (Lycopodium obscurum). Hermit Thrush, but not Ovenbird nests in g round pine were significantly more concealed than nests in other sites both from the side and overhead. Vegetative concealment at the nest microsite m ay be more important to the open-cup nest of the Hermit Thrush than to the domed nest of the Ovenbird. Because flushed Ovenbirds perform a distraction display and Hermit Thrushes do not, Ovenbirds may have an incentive to cho ose nest sites that offer less than maximum concealment.