Effects of forest fragmentation on breeding and migrating birds in a midwestern landscape

Peter T Fauth, Purdue University

Abstract

I have investigated effects of forest fragmentation on breeding and migrating birds within the Indian-Pine Watershed, Tippecanoe and Warren Counties, IN. Specifically, I asked: (1) Do birds select migratory stopover habitats during migration and is the choice influenced by landscape pattern? (2) Is reproductive success of neotropical migrants adequate to maintain stable populations within the landscape? and (3) Can we develop statistical models that predict the location of "high-quality" breeding habitat? During fall migration, capture rates of Catharus thrushes within the large, mature Ross Biological Reserve were higher in a plot with a high density of flowering dogwood trees (Cornus florida) than an adjacent plot with a low density of dogwood. Capture rates of Catharus thrushes within the Ross Biological Reserve were similar to those in small, isolated woodlots. Surprisingly, other migratory birds were captured at higher rates in the small, isolated woodlots than in the larger forest tract. Food resources did not explain the high capture rates of migratory birds in the small, isolated woodlots, suggesting that birds were passively funneled from expansive agricultural areas into these woodlots. During three breeding seasons, I monitored 276 Wood Thrush (Hylocichla mustelina) nests within 15 forested study sites. Wood Thrush reproductive success (0.8 fledglings per nesting attempt) was reduced by Brown-headed Cowbirds (Molothrus ater) and nest predators: 90% of nests were parasitized with an average 2.4 cowbird eggs, and 58% of nests were depredated. Neither parasitism nor predation was related to forest area or distance to a forest edge. The relatively low productivity of Wood Thrush suggests that the landscape is part of a "regional sink", although some sites exceed the net replacement rate in some years. I produced models based on vegetation, fragment, and landscape characteristics that predicted the abundance of several neotropical migrants, but was unable to explain the pattern of Wood Thrush reproductive success. Because the location of "high-quality" habitat in fragmented midwestern landscapes will be difficult to predict, conservation efforts will require direct measurement of demographic parameters on a landscape scale, and should be directed at preserving and augmenting forested habitat in landscapes with low levels of parasitism and predation, as well as maintaining current forest patches for migration stopovers.

Degree

Ph.D.

Advisors

Rabenold, Purdue University.

Subject Area

Ecology|Zoology|Forestry

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