Post-fledging habitat use in a declining songbird

Abstract

Background Fledglings of many mature forest-dependent Neotropical songbirds move from mature forest habitats into areas of thick vegetation such as regenerating clearcuts. The Cerulean Warbler (Setophaga cerulea), a Neotropical migratory songbird, is a species of conservation concern across its range and it is listed as endangered in Indiana. This species has declined faster than any other species of wood-warbler in North America. Most prior research on Cerulean Warblers has examined the breeding biology, but there are no data on habitat use by fledgling Cerulean Warblers. Our research aimed to determine where fledgling Cerulean Warblers dispersed after they left their nest, but before they migrated to their wintering grounds. Methods Since 2007, Cerulean Warbler breeding populations have been monitored in Yellowwood and Morgan–Monroe state forests in southern Indiana as part of a 100-year study called the Hardwood Ecosystem Experiment. To identify habitats used by fledgling Cerulean Warblers, we captured by hand or mist-nets, adult and juvenile Cerulean Warblers once young had fledged from a nest. We attached radio-transmitters to individuals and tracked each bird daily using radio-telemetry. Radio-telemetry data were collected from May to July 2015–2017, and microhabitat data on fledgling locations and random locations were collected during the same years in the month of July. Results Fledgling presence, when compared to random non-use sites, was positively correlated to presence of grapevines, greater vertical vegetation density, and greater ground and canopy cover. Fledgling presence was negatively correlated with white oak abundance, aspect, basal area, and the abundance of mature trees that Cerulean Warbler adults use for nesting. Conclusions Our study is the first to demonstrate that Cerulean Warbler fledglings occupy habitats that are characterized by specific habitat components. Fledgling sites were located in areas with high vegetation density, such as clusters of grapevine, which provided cover from predators. Identifying Cerulean Warbler habitats throughout the breeding season can better inform natural resource personnel on how to manage forests to meet the habitat needs of this rapidly declining migratory songbird.

Rusty Blackbird Habitat Selection and Survivorship during Nesting and Post-Fledging

“…Differences in food requirements and vulnerability to predators between the nesting and post-fledging periods may lead to differences in habitat selection between these stages of the breeding season [7,10,11]. For example, ovenbird, worm-eating warbler, hooded warbler, Acadian flycatcher (Empidonax virescens), cerulean warbler, red-eyed vireos (Vireo olivaceus), and Swainson's thrush (Catharus ustulatus) families all move to stands with greater structural complexity following fledging [1,2,[11][12][13][14][15]. High mortality rates are associated with this movement as young birds seek better-suited post-fledging habitat [6,7].…”

Analysis of microhabitat characteristics at roost sites of Cerulean Warblers

“…The presence or absence of canopy cover and ground cover from the center point were recorded from 0 to 10 m at 2 m intervals in each cardinal direction. A densitometer was used to identify canopy cover, while ground cover was determined by visually examining the ground where the survey flag entered the soil at every 2 m intervals [35][36][37]. Shrubs were counted and grouped into 2 categories (< 3 cm diameter at breast height [DBH] and 3-10 cm DBH); shrubs were only counted within a 5 m radius of the center point.…”

Post-fledging survival, movements, and habitat associations of Gray Vireos in New Mexico

“…Traditionally, due in part to technological limitations, many studies that quantify habitat associations of breeding songbirds only consider the nesting period, thereby neglecting the post-fledging period (Streby et al 2014). However, habitat associations and relationships with survival can differ between the nesting and post-fledging periods (e.g., Anders et al 1998, Marshall et al 2003, Delancey and Islam 2019; but see also Fisher and Davis 2011, Vormwald et al 2011, Jones et al 2017, Goguen 2019, and annual population growth (ƛ) in songbirds can be particularly sensitive to fledgling survival (Anders and Marshall 2005, Cox et al 2014.…”