The Ecology of Some of Hartley's Less Common Birds

MAP 1: Areas safe from Cowbird Parasitism
Brown-headed Cowbird reduce the populations of many forest birds because they lay their eggs in other birds nests when the parents are singing and feeding away from the nest. This behavior of cowbirds allowed them to follow wide ranging Bison herds previous to European immigration; they depended on other species of birds to raise their young.
Cowbirds were feeding on insects that the Bison were shaking up in their movements, and abundant grassland seeds.
Today, cowbirds will also use bird species that nest in large continuous areas of forest, like some of the ones we have in Hartley Park : Red-eyed Vireo, Ovenbird, Least Flycatcher, Black-throated Green Warbler, and Eastern Wood Pewee. 
But it’s been shown that cowbirds will not penetrate far into the forest (no further than about 250 feet into the forest, MAP 1 above) to find nests; they still are birds that utilized narrow forest  along grassland water courses. 

Map 1, above shows the areas in the park that should be safe from cowbirds and that so far, cowbirds have not been observed in. The fortunate fact that cowbirds don’t have much grassland and farm around here to feed in, is probably the reason for their low numbers in the park, even though they occasionally come to our bird feeders! In North America, cowbirds are another reason why some birds are decreasing. As forests that would otherwise support deep forest birds become fragmented into smaller pieces, each one has a large edge that exposes the birds within to cowbirds.

MAP 2 Although it may appear that the map shows that Eastern Wood-Pewee are trying to keep away from cowbird problems, in truth its more likely just showing their preferred nesting vegetation. The boundaries of areas safe from cowbirds are based on a 2004 aerial photo as well as mapped vegetation land cover and ground observations of the vegetation cover.  Some of the boundaries were determined by the distance a NRRI breeding bird surveyor will hear and map birds in the park, others are guesses as how pewees interpret more or less small rural housed properties. In some areas of the park, they don’t seem to interpret them as non-forest area but as small openings within a surrounding contiguous forest.

MAP 3 Take a moment to observe. Most Indigo Bunting were observed over the years in what kind of habitats?  The locations just north of the NE part of the park are mostly Tansy fields adjacent to trees and forest. What do these habitats have in common? Where would you go in the park in spring and summer to look for these birds? These observations were from NRRI surveys and other observations. Indigo Buntings are also known elsewhere to be very subject to Brown-headed Cowbird nest parasitism.