Neotropical Migratory Songbird Research Articles

Individual timing consistency across long-distance songbird migrations.

Migration timing in long-distance migratory birds plays an essential role in individual survival and fitness and is thought to be driven by circannual routines cued by photoperiod with some plasticity to environmental conditions. We examined the individual order of migration timing in purple martins (Progne subis), a neotropical migratory songbird that travels between breeding sites throughout eastern North America and nonbreeding sites in Brazil. Migration timing data were collected for 295 different individual purple martins over 9 years using light-level geolocators deployed at breeding sites across the range. We used linear mixed-effect models to examine the influence of the rank order of individual departure dates in one season on the rank order of four subsequent migration events while controlling for the effects of breeding latitude, sex, and age. Overall, we found evidence for consistent individual timing that can extend across 8 months and 12,000-24,000 km of migration. Individual rank order of migration timing in purple martins was generally conserved across migrations with consistent timings between fall departure dates from, and spring arrival dates to the breeding site the following year (0.28 ± 0.03, 95% CI 0.22-0.34), as well as at a finer scale across fall migration (0.33 ± 0.05, 95% CI 0.23-0.43), over the stationary nonbreeding period (0.39 ± 0.04, 95% CI 0.31-0.47), and across spring migration (0.03 ± 0.001, 95% CI 0.028-0.032). These results demonstrate that purple martins exhibit consistency in individual migration timing throughout the annual cycle that is likely driven by inherent individual circannual schedules. We additionally found that migration distance played a significant role, as the consistency of individual timing lessened over longer distances. Understanding how individual birds time migrations and if individuals are consistent between events can provide insight into how birds respond to shifts in their environment with climate change.

Correction to: An overview of the drivers of performance in nonbreeding Nearctic–Neotropical migratory songbirds

Correction to: An overview of the drivers of performance in nonbreeding Nearctic–Neotropical migratory songbirds

An overview of the drivers of performance in nonbreeding Nearctic–Neotropical migratory songbirds

ABSTRACT Developing conservation and recovery strategies for Nearctic–Neotropical migratory songbirds requires key research because population-limiting factors remain unknown for many species. In particular, the stationary nonbreeding period (sometimes referred to as overwintering) encompasses 6–8 months of the full annual cycle. We conducted a systematic review to assess what is known about the factors that influence individual-level performance (i.e., fitness proxies or indicators of self-maintenance) of Nearctic–Neotropical migratory songbirds during the stationary nonbreeding period. We focused on the metrics of apparent survival, persistence, and body condition (mass-related) indices. We found that 51 of 125 migratory Passeriformes species’ performance has been studied in 57 studies during the nonbreeding period. However, most species appear in only one study; thus, knowledge is skewed toward 3 species appearing in ≥ 10 studies. Body condition indices were the most studied group of metrics and apparent survival was the least studied. Habitat type, food availability, and precipitation were studied much more than other drivers, such as disease and predation. The most studied driver of nonbreeding performance was habitat type. Evidence was found among these studies that suggest that natural habitat types, wetter habitats or precipitation, and high availability of food may positively influence body condition, apparent survival, and persistence. Significant knowledge gaps remain that, if filled, could inform conservation strategies, especially for 59.2% of Passeriformes that are Nearctic–Neotropical migratory species and for areas of the nonbreeding range.

Advancing Our Understanding of Cerulean Warbler Space Use Through Radio Telemetry

Abstract Space use information can be integral in the creation of effective conservation and management strategies. However, avian territories (defended areas) are studied far more frequently than home ranges (entire use areas), and few studies have compared the two. This is the case for the cerulean warbler Setophaga cerulea, a declining Neotropical migrant songbird. There is an extensive record of cerulean warbler territory estimates, while the home range has only recently been explored. Studies of these space use areas differ in their sampling and estimation techniques and location. Consequently, comparison of both space use areas is difficult. We used radio telemetry to delineate cerulean warbler diurnal space use areas in southern Indiana. Our primary objective was to describe the relationship between the home range and territory. Kernel density home range estimates of sampled adult male cerulean warblers (n = 14, mean ± SE = 2.33 ± 0.29 ha) were significantly larger (0.54 ± 0.18 ha, P = 0.006) than territory estimates of the same group of individuals (n = 14, mean ± SE = 1.79 ± 0.39 ha; P = 0.006). Minimum convex polygon home range estimates of the same group of birds (n = 14, mean ± SE = 3.45 ± 0.55 ha) were also significantly larger (1.38 ± 0.19 ha, P < 0.001) than territory estimates (n = 14, mean ± SE = 2.07 ± 0.58 ha). Additionally, the territory estimates that we report are considerably larger than other published estimates for this species, which were delineated using spot mapping methods. Cerulean warbler home ranges contain territorial and extraterritorial space, and the latter has not been studied in detail. Area and habitat requirements likely vary throughout this species' range, and regional conservation management might benefit from study in peripheral space use areas.

Cerulean Warblers exhibit parallel migration patterns and multiple migratory stopovers within the Central American Isthmus

Abstract The Cerulean Warbler (Setophaga cerulea) is a declining Nearctic–Neotropical migratory songbird of conservation concern. Implementing full annual cycle conservation strategies to facilitate recovery has been difficult because we know little about the migratory period or strength of migratory connectivity between North American breeding and South American nonbreeding regions. Between 2014 and 2017, we deployed geolocators on 282 males at 14 study sites throughout the species’ range to (1) evaluate the strength and pattern of connectivity between breeding and nonbreeding regions, (2) identify approximate routes and stopover regions, and (3) document migration phenology. We obtained data from 26 birds and observed moderate migratory connectivity overall but documented strong parallel migration for birds breeding in two longitudinally disparate regions. Most (14 of 15; 93%) Appalachian breeders spent the stationary nonbreeding period in the Colombian/Venezuelan Andes, whereas most (5 of 7; 71%) Ozark-breeders spent the stationary nonbreeding period in Peru/Ecuador. The majority of spring migration (62%) was spent in Central America at multiple stopover locations between Panama and southern Mexico. The 2 migratory periods were approximately equal in duration: 38 ± 2 days (SE) in fall and 42 ± 2 days (SE) in spring. Based on the observed connectivity pattern, conservation of Appalachian-breeding populations during the stationary nonbreeding period should focus on forest conservation and restoration in pre-montane/lower montane forests of Colombia and Venezuela, whereas Ozark-breeding population conservation should focus on forest conservation and restoration efforts in Ecuador and Peru. Further conservation efforts are also needed on the breeding grounds, especially for the most sharply declining populations. And finally, conservation of forests used by Cerulean Warblers during stopover periods throughout Central America and southern Mexico, in southeastern United States coastal areas, and in the Mississippi Alluvial Valley will benefit individuals from multiple breeding locations and populations.

Arrival condition and refueling performance of long-distance migratory songbirds at a spring stopover site in the eastern Gulf of Mexico

Barrier islands along the northern Gulf coast provide critical stopover habitats for Nearctic–Neotropical migratory songbirds using a spring trans-Gulf migration strategy. Islands bordering Apalachicola Bay, Florida, project southward into the Gulf of Mexico providing an opportunity for first landfall. In 2013 and 2014, we studied spring stopover ecology on St. George Island, Florida. We provide a detailed description of the arrival body condition and fuel deposition rates of 8 species of migratory birds. We used 3 approaches to measure fuel deposition rate: (1) estimated an hourly rate of mass change by regressing body mass or scaled body mass by time of day, (2) estimated a daily rate of mass change by examining body mass of recaptured individuals, and (3) for 4 species, measured plasma triglyceride concentrations as a proxy of individual refueling rate. The majority of migratory birds in the eastern Gulf of Mexico arrived in poor body condition with depleted fat and muscle stores. We found no significant changes in body mass or scaled body mass as the day progressed, except for Indigo Bunting (Passerina cyanea), which gained mass throughout the day. Recapture rate was low on St. George Island (<5%), but most recaptured individuals tended to lose mass. Using plasma triglyceride concentration, we found that refueling rate for Gray Catbird (Dumetella carolinensis) declined throughout the day. We found no relationship between body condition and refueling rate in Gray Catbird or Catharus thrushes. Our results suggests that long-distance migratory birds arriving on St. George Island after a nonstop migratory flight may be physiologically challenged due to poor body condition. Our results provide the first quantitative assessment of songbird refueling performance on Florida panhandle barrier islands and reinforce the importance of Gulf of Mexico barrier islands as critical stopover sites for long-distance migrants in poor body condition.

Vulnerable Neotropical migratory songbird demonstrates flexibility in space use in response to rainfall change

Abstract Behavioral flexibility of individuals is essential if organisms are to ultimately adapt to climate change. As environmental conditions, such as precipitation patterns become increasingly variable, fine-scale spatiotemporal flexibility in space use may allow for individuals to track resources during periods of adverse or atypical conditions. Individual behavioral flexibility is observable over short timeframes and can therefore be used to assess resilience of a species to projected shifts in climate. The goal of our study was to determine if and how individuals modified their space and habitat use in response to rainfall-driven changes in resources throughout a period of atypical seasonal rainfall patterns. We used radio telemetry to estimate home ranges of nonbreeding Swainson’s Warblers (Limnothlypis swainsonii) in 2 time frames (bi-seasonally and bi-weekly) in Jamaica during dry and wet periods. We measured habitat structure and food (leaf litter arthropod) availability within each home range to determine possible predictors of space use change. Individuals modified the area and/or location of their home ranges with changes in precipitation, and those occupying more open habitats had greater changes in home range area as seasonal rainfall increased. As food increased following rain, individuals constricted their home ranges (bi-weekly) or shifted spatially (bi-seasonally) to a novel area with greater food availability. This suggests individuals are able to rapidly respond to how their environment changes, presumably adjusting to trade-offs between home range size and resource availability. This flexibility may be a key behavioral component in enduring long-term increasingly unpredictable environmental variability and may have population-level consequences. These responses are, however, mediated by habitat, suggesting the ability to respond to variable or poor conditions is not homogeneous across a population.

Canada Warbler response to vegetation structure on regenerating seismic lines

Seismic lines have an extensive footprint in Canada's western boreal forest that alter habitat conditions for many species. Seismic lines exist within a range of seral states due to changing practices and regulations related to operational needs. Forest regeneration is often hindered on seismic lines as they are frequently repurposed for recreational or alternative industrial uses. The Canada Warbler (<em>Cardellina canadensis</em>) is a Neotropical migrant songbird that relies on Canada's boreal region for breeding habitat. As a species at risk both federally (Threatened) and provincially within Alberta (Sensitive), their response to seismic lines has been a significant gap in our understanding of human impacts on the boreal breeding grounds. We used playback surveys along seismic lines within Canada Warbler habitat to identify individual territories. Arrays of autonomous recording units (ARU) were deployed to conduct acoustic source localization (ASL) and map the locations of territorial singing events. Canada Warblers avoided seismic lines with little to no woody vegetation but were more likely to be observed near seismic lines when shrub cover on the line increased. Canada Warblers used the seismic line and the edge environment but did not select for the line when compared to its availability. Use was more evenly distributed across the seismic line as shrub density on the line increased. However, even the most overgrown seismic lines were still perceived as a feature and influenced Canada Warbler space use and behavior. For Canada Warblers, ensuring that seismic lines in old-growth deciduous forests are allowed to recover by reducing reuse of lines should mitigate population level impacts, but more work is needed to assess how population dynamics are influenced by seismic lines and other energy sector disturbances.

Migratory behavior and connectivity revealed in a secretive Neotropical migratory songbird, the Swainson’s Warbler

Improving our understanding of migratory behaviors and connectivity is fundamental for identifying limiting factors and drivers of population decline. With advances in miniaturized tracking technology, we are now able to study these critical aspects of avian ecology, which, for secretive species, was once an exceptional challenge. Here, we identify several unknown aspects of the migratory behavior and connectivity of the elusive Swainson’s Warbler (<em>Limnothlypis swainsonii</em>), by tracking individuals from populations breeding in Louisiana, U.S., and wintering in Jamaica. We identified a migratory divide between the western and eastern portions of the species’ distribution, showing that most Louisiana breeders overwintered in southern Mexico and the Yucatan peninsula, whereas the Jamaica individuals migrated to the eastern portion of the Swainson’s Warbler breeding range. Geolocator data documented that a portion of migratory flights in both populations were sustained well into the day, suggesting that birds migrated over large bodies of water (i.e., Gulf of Mexico and Caribbean Sea) during both spring and fall migration. Furthermore, the phenology and rate of migration differed between populations. Additional research efforts across a broader portion of the range are necessary to better understand the demographic consequences of high migratory connectivity and the implications for the conservation of the species.

Shade coffee or native forest? Indicators of winter habitat quality for a long-distance migratory bird in the Colombian Andes

Neotropical migratory songbirds overwintering at mid elevations in the Andes of northern South America depend on remnants of native forest and shade-grown coffee plantations. The quality of such habitats is one of the primary ecological factors limiting survival of migratory birds during the non-breeding season. We assessed the relative quality of shade-grown coffee plantations vs. forest in the Colombian Andes as winter habitat for Swainson’s Thrush (Catharus ustulatus). We hypothesized that native forest has a higher intrinsic value (i.e., food abundance) than shade-coffee plantations, as native forest was the original habitat for Swainsońs Thrush. We compared thrush physical condition, density, feather corticosterone values, and apparent annual survival as indicators of habitat quality in these two habitats. Measures of body condition and density were higher in forest than in shade-grown coffee, while survival was similar between habitats. This implies that forest had a higher carrying capacity than shade coffee and therefore had higher intrinsic value. Seasonal trends in body condition revealed a decline in the quality of forest with the onset of the dry season in early winter and an increase during late winter in line with increasing rainfall, suggesting that the timing of the rainy season likely offsets the negative effects of seasonal drought. Feather corticosterone levels were higher in forest, possibly as a result of a density-dependent stress response, however, we cannot rule out the effects of food availability or its distribution in space on stress levels. Our indicators suggested that native forest is a higher-quality winter habitat than shade-grown coffee. Our findings highlight how individual indicators of habitat quality can be misleading and emphasize the value of using multiple measures. While shade coffee is a critical habitat in the absence of native forest and its importance for the conservation of migratory birds is widely accepted, our results indicate that the conservation of native forest must be a conservation priority wherever possible.

Habitat loss on the breeding grounds is a major contributor to population declines in a long-distance migratory songbird.

Many migratory species are declining and for most, the proximate causes of their declines remain unknown. For many long-distance Neotropical migratory songbirds, it is assumed that habitat loss on breeding or non-breeding grounds is a primary driver of population declines. We integrated data collected from tracking technology, community science and remote sensing data to quantify migratory connectivity (MC), population trends and habitat loss. We quantified the correlation between forest change throughout the annual cycle and population declines of a long-distance migratory songbird, the Connecticut warbler (Oporornis agilis, observed decline: -8.99% yr-1). MC, the geographic link between populations during two or more phases of the annual cycle, was stronger between breeding and autumn migration routes (MC = 0.24 ± 0.23) than between breeding and non-breeding locations (MC = -0.2 ± 0.14). Different Connecticut warbler populations tended to have population-specific fall migration routes but overlapped almost completely within the northern Gran Chaco ecoregion in South America. Cumulative forest loss within 50 km of breeding locations and the resulting decline in the largest forested patch index was correlated more strongly with population declines than forest loss on migratory stopover regions or on wintering locations in South America, suggesting that habitat loss during the breeding season is a driver of observed population declines for the Connecticut warbler. Land-use practices that retain large, forested patches within landscapes will likely benefit breeding populations of this declining songbird, but further research is needed to help inform land-use practices across the full annual cycle to minimize the impacts to migratory songbirds and abate ongoing population declines.

Seasonal variation in habitat selection for a Neotropical migratory songbird using high‐resolution GPS tracking

AbstractDeciphering how environmental heterogeneity affects population dynamics in migratory species is complicated by the redistribution of individuals in time and space across the annual cycle. Approaches that tackle this problem require information about how migratory species respond to ecological factors across time and space, and how they are linked across migratory periods. Using high spatial resolution (10 m) GPS tracking of individual male songbirds, we quantified for the first time (1) local‐ and landscape‐scale habitat selection across the annual cycle and (2) patterns indicative of regional habitat selection for individuals within five populations of wood thrush (Hylocichla mustelina) throughout their breeding range. Wood thrush exhibited seasonal variation in local‐ and landscape‐scale habitat selection. Within stationary periods, wood thrush occupied forested habitats and proximity to forest edge was an important predictor of habitat selection at the local scale. In contrast, during migratory periods wood thrush exhibited greater behavioral flexibility indicative of a more generalist approach to habitat selection. Landscape habitat selection was only identified during the breeding season (average patch size) and could be a response to the extensive forest fragmentation in the North American breeding grounds. We also identified individual population distribution patterns indicative of regional habitat selection during fall migration and winter period, but not spring migration. Seasonal changes in habitat selection at multiple spatial scales suggest the factors driving habitat selection patterns are aligned with life‐history stage and may be dependent on regional differences in landscape composition. These results highlight the importance of a full annual cycle approach to ecological studies that address how migratory species respond to spatial and temporal environmental heterogeneity.

Fuel loads of Neotropical migrant songbirds on autumn passage through the Darién region of Colombia: Influence of migratory distance, route, ENSO, age and body size

AbstractAvailable energy stores determine stopover length, migration speed and likely survival in migrating birds. We measured energy stores by estimating fuel load in 11 species of Neotropical migrant songbirds in the Darién of Colombia over five years. We evaluated 1) whether individuals flying further from breeding origin arrived with smaller fuel loads, 2) if the ENSO (El Niño-Southern Oscillation) cycle affected fuel load and 3) if species known to migrate mostly overwater arrived with less fuel relative to those migrating overland. Breeding origin, inferred from feather δ2H values, only had a significant positive effect on fuel load in Swainson’s Thrush (Catharus ustulatus). Veery (Catharus fuscescens) and Swainson’s thrush had higher and lower fuel loads, respectively, in El Niño years. Multi-species mixed-effects models revealed support for larger fuel loads in larger-bodied species and in species taking overwater routes, contrary to our prediction. Across species, we found no support for common effects of breeding origin or ENSO on fuel loads, in contrast to community-wide effects of migration route and body-size. In general, the variables considered here explained little of the variance in fuel loads, suggesting that inter-individual differences likely have a greater impact than broad-scale factors in our study system.

Warmer April Temperatures on Breeding Grounds Promote Earlier Nesting in a Long-Distance Migratory Bird, the Prothonotary Warbler

Global climate change and warming are altering hemispheric and local weather patterns. Altered weather patterns have great potential to affect the phenology of life history events, such as the initiation of breeding in organisms that reproduce seasonally. Long-distance migratory birds may be particularly challenged by changes in local weather on breeding grounds because they arrive from distant locations and must commence breeding when conditions are appropriate. Here we explore the effects of local temperature on first egg dates and annual productivity in a long-distance Neotropical migratory songbird, the prothonotary warblerProtonotaria citrea. We present results from a 20-year (1994 to 2013) study documenting the detailed nesting activities of a color-marked population (average of 155 individual females each year) of warblers in southern Illinois, United States. The warblers typically arrive in April and start breeding in late April and May in our study system. We tested for an effect of local average April daily temperature and female age on first egg dates, total number of offspring produced per female, and the probability of fledging two broods. We found that warmer April temperatures promoted earlier first egg dates and higher average annual productivity in the warblers. On average, older females had earlier first egg dates than 1-year-old females, but both age groups responded similarly to local April temperatures. The reproductive gains associated with earlier first egg dates in warmer years stemmed from an increased probability of successfully fledging two broods, suggesting that earlier first egg dates do not currently create a mismatch with food (insect) resources. Earliest arrival dates of warblers to the region of our study system were not affected by local April temperatures, suggesting that females vary their first egg date based on conditions they experience/assess after their arrival. Whereas these birds currently adjust the timing of their breeding and actually produce more offspring in warmer years, continued global warming may eventually upset the current balance between arrival dates, food resources, and the commencement of nesting.

Earlier and slower or later and faster: Spring migration pace linked to departure time in a Neotropical migrant songbird.

Migratory birds travel vast distances and the timing of migratory flights can affect survival and the ability to reproduce. For Neotropical migrant songbirds, early spring departure from wintering sites, early arrival to the breeding grounds and higher reproductive success have been related to the use of suitable habitats and environmental conditions during the non-breeding season. However, how migratory strategies are shaped by winter habitat choice is largely unknown due to the general inability to track birds from specific wintering habitats to stopovers or breeding destinations. We assessed how winter habitat (native forest vs. shade-grown coffee plantations) relates to spring departure date and migration pace in Swainson's Thrush Catharus ustulatus. We also determined the effect of departure date and total migration duration on the arrival date of birds detected near or within their breeding range. We used a novel application of Motus radiotelemetry arrays to track individuals from their wintering grounds in the Andes of South America along their migratory journey to North America. We found variation in migratory strategies between habitats, with birds wintering in native forest departing later than birds in coffee. We present isotopic evidence for native forest being of higher quality than shade-coffee for Swainson's Thrush and hypothesize that moister conditions in forest, as shown by stable isotope (δ13 C) analysis of thrush whole blood, provides favourable pre-migratory conditions allowing birds to delay departure from wintering grounds. Habitat, between-site and -year variation in departure date, suggests that birds made facultative adjustments to winter habitat quality and environmental conditions. Independent of habitat, birds that departed later migrated faster and this pattern was maintained along the migration route (n=44). Migrating earlier and slower or later and faster was unlikely to result in significant differences in arrival time to breeding destinations. Our findings reveal underappreciated complexity in migratory decisions by long-distance migrants that contrast with the current paradigm of earlier departures and arrival from optimal habitats. The next step is to understand the relative fitness benefits of early versus late schedules or whether each strategy is an equally good response to experienced conditions.

Ground-Nesting Warblers on the Eastern Shore of Maryland: Declining Population Trends and the Effects of Forest Composition and Structure

Changes in forest size and composition can affect Neotropical migratory songbirds breeding in Eastern North America, leading to population fluctuations and declines. In 2012–2014, we conducted point counts at locations previously surveyed in 1981–1983 and analysed Breeding Bird Atlas data from 1980–2013 to estimate long-term population trends of two declining ground-nesting warblers on the Eastern Shore of Maryland within the Atlantic Coastal Plain: the Ovenbird Seiurus aurocapilla and the Worm-eating Warbler Helmitheros vermivorum. We detected significant declines for Ovenbirds in both datasets, but we found conflicting data for Worm-eating Warblers. During 2012–2015, we investigated the effects of forest characteristics, such as vegetative composition and ground cover, on occupancy and nest success. Ovenbirds were found more where there were more and larger trees but were negatively affected by the proportion of pines, whereas Worm-eating Warblers were more abundant when there were higher numbers of trees and more pines. Nest success was not affected by vegetation other than the proportion of pine trees or leaf litter depth, both of which increased nest success. Worm-eating Warblers with more pine needles in their nests also had increased nest success. This study presents a nuanced view of how forest composition (proportion of pine trees) of the Atlantic Coastal Plain in Maryland influenced ground-nesting warblers differently, and suggests that effectively managing ground-nesting warblers in this area may differ from other regions of Eastern North America due to its unique vegetative composition, structure, and history.

Climate change and land management implications for a declining Neotropical migratory songbird breeding in the North American Great Plains

Climate change and land management implications for a declining Neotropical migratory songbird breeding in the North American Great Plains

Space Use by Prairie Warblers in Regenerating Mixed-oak Forests of Central Pennsylvania

Setophaga discolor (Prairie Warbler) is a Nearctic–Neotropical migratory songbird that is experiencing long-term population declines. A potentially important driver behind these decreases is the loss of shrubland and early successional forest communities in the eastern United States. Central to conservation for species like the Prairie Warbler is an understanding of breeding habitat requirements at the scale of the home range. Despite the Prairie Warbler being identified as a species of continental conservation concern, few studies have explicitly quantified habitat conditions within its home ranges. We used radio telemetry to quantify Prairie Warbler use of space during the breeding season as well as associated vegetation data across 3 study sites in north-central Pennsylvania from May to June 2016. We radio-tracked 11 adult male Prairie Warblers. Using the telemetry locations, we estimated kernel densities and classified minimum convex polygons around kernel densities to define males' home ranges and core-use areas. The average home range (95% kernel) was 6.4 ha, and the average core-use area (50% kernel) was 0.73 ha. Prairie Warbler core-use areas contained more shrubs and lower tree count than peripheral portions of home ranges. To this end, management activities that promote a dense shrub layer across early successional communities should benefit Prairie Warblers. Results from this study serve as baseline data that can be used to help direct future studies at the home-range scale of Prairie Warbler breeding-season ecology.

Post-fledging habitat use in a declining songbird.

BackgroundFledglings 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.MethodsSince 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.ResultsFledgling 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.ConclusionsOur 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.

Influence of climate change and postdelisting management on long-term population viability of the conservation-reliant Kirtland's Warbler.

Rapid global climate change is resulting in novel abiotic and biotic conditions and interactions. Identifying management strategies that maximize probability of long‐term persistence requires an understanding of the vulnerability of species to environmental changes. We sought to quantify the vulnerability of Kirtland's Warbler (Setophaga kirtlandii), a rare Neotropical migratory songbird that breeds almost exclusively in the Lower Peninsula of Michigan and winters in the Bahamian Archipelago, to projected environmental changes on the breeding and wintering grounds. We developed a population‐level simulation model that incorporates the influence of annual environmental conditions on the breeding and wintering grounds, and parameterized the model using empirical relationships. We simulated independent and additive effects of reduced breeding grounds habitat quantity and quality, and wintering grounds habitat quality, on population viability. Our results indicated the Kirtland's Warbler population is stable under current environmental and management conditions. Reduced breeding grounds habitat quantity resulted in reductions of the stable population size, but did not cause extinction under the scenarios we examined. In contrast, projected large reductions in wintering grounds precipitation caused the population to decline, with risk of extinction magnified when breeding habitat quantity or quality also decreased. Our study indicates that probability of long‐term persistence for Kirtland's Warbler will depend on climate change impacts to wintering grounds habitat quality and contributes to the growing literature documenting the importance of considering the full annual cycle for understanding population dynamics of migratory species.