Browsing by Subject "Post-fledging"

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    Influence Of Habitat Type On Nest Success, Fledgling Survival, Predator Abundance, And Post-Fledging Habitat-Use Of The Golden-Winged Warbler In Northern Minnesota
    (2024-04) Howland, Brett
    The Golden-winged Warbler (Vermivora chrysoptera) is one of the most critically threatened birds in North America with a global population estimated at only 400,000 individuals of which 50% nest in Minnesota. The species relies on two distinct habitat types, shrub wetland and young forests, for breeding. Quantifying differences in demographic parameters, such as productivity and survival, between habitats is necessary to inform conservation efforts and ensure long-term population stability and growth. To better understand the breeding ecology of Golden-winged Warblers, we studied their nest success, post-fledging survival, and post-fledging habitat-use across 10 study sites in northern Minnesota, USA from 2020 to 2023. We monitored a total of 91 nests and tracked the post-fledging movements of 60 individuals from 52 broods. We used these data to determine the influence of vegetation characteristics, habitat, and landscape factors on nest success, fledgling survival, and post-fledging habitat-use. We assessed the effect of habitat type on nest and juvenile survival using a Markov likelihood framework to estimate daily survival rate as well as daily failure probabilities due to predation and weather events. Our results indicated that there was no difference in nest success and fledgling survival between young forests and shrub wetlands. Predation by sciurids, hawks, and mesocarnivores during the nesting period and the post- fledging period was the most common cause of mortality. Nest survival was lowest for nests that were close to forest edges and survival was lower for nests that were initiated later in the breeding season. Fledgling survival was also lower for birds near forest edges but increased as fledglings aged and became more mobile. Results from the habitat selection models indicated that Golden- winged Warbler fledglings used a variety of habitats including young forest stands that have retained trees and shrub wetland habitats; within stands, they select for areas with high shrub/sapling density, canopy cover, and coarse woody debris. Overall, our results showed that forest management activities that promote structural diversity in young forest stands and conservation of shrub wetland habitats is necessary to maintain stable breeding populations of Golden-winged Warblers in the 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.