Both before and after they leave the nest, baby birds face a host of challenges. A new study in The Condor: Ornithological Applications examining songbird survival in the nestling and fledgling stages finds that even in the same habitat, different species face different risks and survive at different rates.
Ovenbirds and Acadian Flycatchers are migratory songbirds that nest in similar habitats, but they have very different nesting and foraging strategies. Julianna Jenkins of the University of Missouri and her colleagues tracked the survival of young birds of both species before and after they fledged. They found that flycatcher survival at both stages was related to mature forest, while Ovenbirds did best in mature forest as nestlings but sought areas with dense understories after fledging. Post-fledging survival was lower for Ovenbirds than for Acadian Flycatchers, with more than half of the tracked Ovenbird fledglings dying within ten days of leaving the nest.
Habitat information like this can be crucial for conservation biologists trying to address songbird population declines, because they can take action through land management to boost birds' survival at multiple life stages. "It is my hope that by investigating what affects both nesting and postfledging survival, we can make management decisions that are effective for the entire breeding season," says Jenkins.
Jenkins and her colleagues monitored nests at three sites in central Missouri, fitting nestlings with radio transmitters shortly before they fledged so they could continue to track their survival. From 90 Ovenbird and 264 Acadian Flycatcher nests, they tracked 50 Ovenbird fledglings and 45 flycatcher fledglings. "Tracking radio-tagged fledglings was the highlight of my day," says Jenkins. "Without transmitters, I doubt we could have relocated many fledglings, if any. I was amazed at how far from the nest newly fledged Ovenbirds could travel, even without the ability to fly."
In addition to the difference in survival between the two species, fledglings' success also varies between regions. According to the study's authors, this highlights the need for tracking postfledging survival for a variety of species and landscapes rather than assuming that birds nesting in similar habitat face similar risks. "Jenkins and her colleagues provide insight into factors related to post-fledging survival and how those factors might influence population trajectory," according to David Andersen of the University of Minnesota, an expert on bird population ecology who was not involved with the study. "Their results shed light on the complex interactions between fledgling songbirds, the landscapes in which they exist, and how this important life stage influences population dynamics."
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"Contrasting patterns of nest survival and postfledging survival in Ovenbirds and Acadian Flycatchers in Missouri forest fragments" www.aoucospubs.org/doi/full/10.1650/CONDOR-16-30.1