Effects of Prairie Fragmentation on the Nest Success of Breeding Birds in the Midcontinental United States

Abstract

Grassland fragmentation and habitat loss are hypothesized to be contributing to widespread grassland bird declines in North America due to the adverse effects of fragmentation on breeding bird abundance and reproductive success. To assess the effects of fragmentation on the reproductive success of grassland birds, we measured rates of nest predation and brood parasitism for four species of birds ( Grasshopper Sparrow [Ammodramus savannaru], Henslow's Sparrow[Ammodramus henslowii], Eastern Meadowlark [ Sturnella magna], and Dickcissel [ Spiza Americana] ) in 39 prairie fragments ranging from 24 to>40,000 ha in size in five states in the mid‐continental United States. Throughout the region, nest‐predation rates were significantly influenced by habitat fragmentation. Nest predation was highest in small (<100 ha ) and lowest in large ( >1000 ha ) prairie fragments. Rates of brood parasitism by Brown‐headed Cowbirds ( Molothrus ater ), however, were not consistently related to fragment size and instead were more strongly related to regional cowbird abundance, being significantly higher in regions with high cowbird abundance. Differences in nest‐predation rates between large fragments ( 54–68% of all nests lost to predators ) and small fragments ( 78–84% lost to predators ) suggest that fragmentation of prairie habitats may be contributing to regional declines of grassland birds. Maintaining grassland bird populations, therefore, may require protection and restoration of large prairie areas.

Conserving migratory land birds in the New World: Do we know enough?

“…This work suggested that for smaller grassland songbirds, the large core area of the BCA was not necessary, as reproductive success on the smaller grassland patches was not consistently different from that on larger patches (Winter et al 2006). This is not surprising, as other studies of grassland birds had suggested that these species responded positively to small tracts of habitat, requiring smaller areas of acceptable habitat within their landscape than forest birds might (McCoy et al 1999, Herkert et al 2003. Unfortunately, the validity of the BCA concept for species as large as prairie-chickens or Northern Harrier (Circus cyaneus) has not been tested; we not only lack a good idea of how large a landscape is needed to support smaller migratory grassland birds, but we also do not know if the BCA concept would work to save prairie grouse populations, many of which are declining.…”

Grassland Bird Productivity in Warm Season Grass Fields in Southwest Wisconsin

“…Rates of nest predation on grassland birds, including the Bobolink, decline only on large habitat fragments (≥ 1,000 ha; Herkert et al, 2003). Nest predation rates are generally higher near forest edges and decline as the distance from forest edges increases (Johnson and Temple, 1990;Bollinger and Gavin, 2004;Renfrew et al, 2005).…”

Nest Survival Relative to Patch Size in a Highly Fragmented Shortgrass Prairie Landscape

“…Habitat composition and configuration at scales greater than an individual breeding territory have been predictive of nest success for some grassland species (Greenwood et al 1995, Herkert et al 2003, Skagen et al 2005, but see Winter et al 2005). We defined an area~3 times the size of a large territory as a neighborhood.…”