For Eastern Meadowlarks, Grasshopper Sparrows, and Dickcissels, as the focal grassland songbirds, and
Brown-headed Cowbirds, their brood parasite, we estimated densities separately by species.
Brown-headed cowbird (Molothrus ater) parasitism on warbling vireos (Vireo gilvus) in southwest Colorado.
Nest parasitism by
brown-headed cowbirds represents a threat to the conservation of some bird species (Smith et al.
The increasing number of cleared areas (for roads, developments, powerlines, and the like) in these woodlands has increased the pressure on the birds, as populations of egg- and nestling-eating predators like opossums and blue jays have exploded, and the
brown-headed cowbird, an open-area blackbird that lays its eggs in other species' nests, has become much more abundant.
Proportion Bird status examined infested American goldfinch B, M 363 American redstartt B, M 38 0.03 American robin B, M 1,049 0.01 Baltimore oriole B, M 31 Barn swallow B, M 7 Black and white warbler NB, M 9 Black-capped chickadee B, NM 25 Blue jay B, M 22 0.09
Brown-headed cowbird B, M 65 Brown thrasher B, M 12 Cedar waxwing B, M 16 Chipping sparrow B, M 24 Common grackle B, M 105 0.03 Common yellowthroat B, M 8 Dark-eyed junco NB, M 8 Downy woodpecker B, M 50 Eastern wood-pewee B, M 5 Empidonax spp.
The narrowest observed elevational ranges were generally evident in a handful of species that are restricted to relatively low (for example, Belted Kingfisher, Willow Flycatcher, Red-eyed Vireo, Veery,
Brown-headed Cowbird) or relatively high (for example, Clark's Nutcracker, Horned Lark, Mountain Bluebird, American Pipit) habitats in the parks.
With a decline in the amount of suitable habitat paired with brood parasitism by the
brown-headed cowbird (Molothrus ater), the Kirthland's warbler population fell to a mere 201 pairs in 1971.
Among resident passerines, Tufted Titmouse, Northern Cardinal, American Goldfinch,
Brown-headed Cowbird, Eastern Towhee, Carolina Chickadee, White-breasted Nuthatch, Carolina Wren, and American Robin were abundant at all three sites.
Unfortunately,
Brown-headed Cowbird, a nest parasite native to American grasslands but invasive in fragmented forests, was found along all transects, as a possible (3 transects), probable (3 transects), or confirmed (2 transects) breeder.
Brown-headed Cowbird (Molothrus ater).--According to Butler (1898), M.
At each visit to the nest, we recorded the number of eggs and chicks, the age of chicks, the presence of adults near the nest, and any
Brown-headed Cowbird (Molothrus ater) parasitism.
In the Lower Rio Grande Valley (LRGV) of southern Texas, the 54-g bronzed cowbird (Molothrus aeneus) greatly outnumbers the 36-g
brown-headed cowbird (Molothrus ater, Gehlbach, 1987; Brush, 2005).