Browsing by Subject "Ovenbird"

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    Relations among invasions of non-native earthworms, forest floor habitat, and populations of ground-nesting songbirds in north temperate hardwood forests.
    (2011-07) Loss, Scott R.
    In north temperate and boreal North America, European earthworms Lumbricus have invaded previously earthworm-free forests, substantially changing soil structure, removing the litter layer, and reducing richness and cover of plants. Whether these changes affect ground-nesting and ground-foraging songbirds remains unknown. I sampled earthworm populations and surveyed for, monitored nests of, and measured attributes of habitat of Ovenbirds Seiurus aurocapillus and Hermit Thrushes Catharus guttatus, both ground-nesting songbirds, in the Chequamegon-Nicolet National Forest, Wisconsin. In another study at survey points scattered across 2 national forests, the Chequamegon-Nicolet and the Chippewa in north-central Minnesota, I investigated relations between Lumbricus biomass, point and landscape-scale habitat, and abundance of 4 ground-nesting songbird species. In the first study, bird surveys indicated significantly lower densities of Ovenbirds and Hermit Thrushes in relation to Lumbricus invasions. Moreover, Ovenbirds experienced greater nest predation rates - possibly due to reduced nest concealment - in association with increased sedge cover and decreased litter depth, habitat characteristics strongly related to Lumbricus invasions. In the second study, the Ovenbird was the only species to display significantly reduced density in relation to Lumbricus, with this relation evident only in sugar maple Acer saccharum-basswood Tilia americana forests. Lumbricus biomass was the variable most strongly related to Ovenbird density, displaying a significant inverse relation. These results provide strong evidence that earthworm invasions contribute to local - and potentially regional - population declines of ground-dwelling songbirds, and especially of Ovenbirds. Quantifying earthworm invasions is necessary for understanding earthworm impacts and for identifying earthworm-free areas for targeting prevention measures. Current earthworm sampling methods are effort intensive, making it economically impractical to quantify invasions across broad spatial scales. I developed a method for rapidly assessing earthworm invasion severity by testing how accurately a 5-stage system of visual classification, based on soil and forest floor characteristics, reflected true invasion stage. I found that the visual system successfully approximated previously proposed stages of earthworm invasion. Biomass of earthworm species differed as expected among the 5 categories. I conclude that the visual method provided an efficient and accurate approach for rapidly assessing severity of earthworm invasions in hardwood forests of the northern Midwest region.
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    Survival and habitat use by post-fledging forest-nesting songbirds in managed mixed northern hardwood-coniferous forests.
    (2010-10) Streby, Henry M.
    Until recently, studies of breeding migratory songbirds have been primarily limited to the nesting season. Therefore, there is very little information about songbird survival and habitat use during the post-fledging period (i.e. the time between nesting and fall migration) available to those making management decisions. I expanded on the traditional nest-monitoring study and used radio telemetry to monitor survival and habitat use of fledgling songbirds in managed northern hardwood-coniferous forests of northern-Minnesota. In addition, I used mist-nets to sample use of early-successional forest stands (regenerating clearcuts) and forested wetlands by mature forest-nesting birds during the post-fledging period. I found that many assumptions of songbird nesting studies are unreliable, including the common assumption that the presence of a family group is confirmation of a successful nest in an occupied territory. In addition, I found that annual fledgling survival can vary considerably, and does not vary consistently with nest productivity, a finding with broad implications for models of songbird population growth. Furthermore, I found that habitat used by birds during the post-fledging period can be considerably different than that used for nesting, and that post-fledging habitat use can affect fledgling survival. In addition, I found that factors commonly affecting nest productivity (e.g. edge effects) can affect fledgling survival differently. From mist-netting, I found that many mature-forest birds used non-nesting cover types during the post-fledgling period, but most of that use was by only a few species, and hatch-year birds rarely used non-nesting cover types before independence from adult care. Models of capture rates in non-nesting cover types indicated that use of non-nesting cover types by mature-forest birds was primarily related to food availability and secondarily to cover in the form of relatively dense vegetation. My results indicated that nearly every conclusion made about breeding population ecology of mature-forest birds based only on nesting data was contradicted by data from the post-fledging period. My results clearly demonstrate that data from the entire breeding season (nesting and post-fledging) are necessary to understand songbird seasonal productivity and habitat associations.