ArticlePublisher preview available

Exposure to risk factors experienced during migration is not associated with recent Vermivora warbler population trends

June 2023
Landscape Ecology 38(9):1-24

DOI:10.1007/s10980-023-01701-2

Authors:

Gunnar Kramer

Iowa State University

David E. Andersen

United States Geological Survey

David A. Buehler

University of Tennessee at Knoxville

Petra Bohall Wood

US Geological Survey at West Virginia University

Show all 14 authorsHide

Context Understanding the factors limiting populations of animals is critical for effective conservation. Determining which factors limit populations of migratory species can be especially challenging because of their reliance on multiple, often geographically distant regions during their annual cycles. Objectives We investigated whether distribution-wide variation in recent breeding population trends was more strongly associated with exposure to risk factors experienced during migration (i.e., natural and anthropogenic threats often associated with increased mortality or carry-over effects) or factors associated with breeding and nonbreeding areas in golden-winged warblers (Vermivora chrysoptera) and blue-winged warblers (V. cyanoptera), two Nearctic-Neotropical migrants experiencing regionally variable population trends. Methods We used geolocator data from 85 Vermivora warblers (n = 90 geolocator tracks) tracked from North American breeding locations and Central American nonbreeding locations from 2013 to 2017 to determine variation in space use among populations. We assessed whether differences in space use among populations of Vermivora warblers during migration were associated with exposure to migration risk-factors and whether increased relative exposure to migration risk factors was associated with population declines at regional and subregional scales. Results Regional and subregional populations of Vermivora warblers exhibited variation in space use and exposure to anthropogenic and natural risk-factors. However, we found no evidence that recent variation in population trends of Vermivora warblers was associated with risk-factors experienced by different populations during migration. Instead, factors associated with land cover-types in breeding and nonbreeding areas were more strongly associated with recent population trends. Conclusions Understanding how populations of migratory birds are affected by factors experienced during migration is critical for their conservation. We did not find evidence that variation in exposure to migration risk-factors is associated with recent regional or subregional variation in Vermivora warbler population trends. Consequently, our results suggest that efforts to reverse ongoing population declines of Vermivora warblers may be more effective if directed toward conservation actions targeting limiting factors within the breeding and nonbreeding periods versus those directed at conditions encountered during migration. We caution that geographic variation in projected land-use change may differentially affect areas used by different populations of Vermivora warblers during migration, posing a potential threat to these species in the future.

Breeding (light gray) and nonbreeding (dark gray) distributions of blue-winged warblers (Vermivora cyanoptera; left) and golden-winged warblers (V. chrysoptera; right). Sites where geolocators were deployed and recovered from Vermivora warblers are denoted by colored circles. The size of circles corresponds to the number of individuals tracked from that site. The color of circles indicates the state- or province-level population trend from 2000 to 2015 at breeding distribution sites or the average state- or province-level breeding population trend from 2000 to 2015 of individuals marked at nonbreeding distribution sites based on Breeding Bird Survey data (BBS; BBS Regional Trend Analysis Form). Shaded polygons delineate Bird Conservation Regions (BCRs) that we used to aggregate sites into regional populations. Shaded areas linking breeding and nonbreeding regions indicate the general migratory connectivity of populations but do not represent migratory routes. Geolocators from deployment sites in Central America are from Bennett et al. (2019b). Geolocators from deployment sites in the US and Canada are from Kramer et al. (2018b)

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Average probability density functions for blue-winged warbler and golden-winged warbler populations (based on Bird Conservation Regions [BCRs]) during autumn and spring migrations. Darker purple cells represent areas of greater relative importance during migration (i.e., higher probability of use for greater durations by more individuals). We averaged the probability density functions of individual warblers derived from geolocator data spanning the duration of each warbler’s seasonal migration period. Geolocator deployment sites are represented by circles and colors of circles correspond with Bird Conservation Regions (BCRs) of breeding sites. A solid gray line delineates the breeding distribution whereas a dashed line identifies the nonbreeding distribution (including a 100-km buffer)

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A Regional population-specific core-use areas (25th percentile) of Vermivora warblers during autumn and spring migration. Blue-winged warblers and golden-winged warblers from breeding sites (triangles) associated with different Bird Conservation Regions (BCRs) are represented by different colors. Geolocator-derived nonbreeding and breeding location estimates are identified by × ’s and + ’s, respectively and colored according to breeding population (i.e., BCR). B The spatial distribution of the mean-adjusted cumulative exposure to migration risk-factors represents the sum of standardized rasters of eight migration risk-factors considered in our analyses. Red cells indicate areas with above-average exposure to migration risk-factors whereas blue cells are associated with below-average exposure. Boxplot shows the scaled exposure of different regional populations (based on the exposure of individuals tracked within each population; colors correspond with the A) of Vermivora warblers to the mean-adjusted cumulative exposure to migration risk factors. Populations that experienced different levels of exposure (based on one-way ANOVA and Tukey HSD; P < 0.05) are denoted with letters. Values inside boxes indicate regional population trend estimates from the Breeding Bird Survey (BBS) for 2000–2015 (BBS Regional Trend Analysis Form). Asterisks specify population trends with 95% confidence intervals that do not overlap zero. Regional populations are defined by BCR and species (blue-winged warbler [BW] or golden-winged warbler [GW]) in boxplot legend: Prairie Hardwood Transition BCR (BW PHT, teal), Central Hardwoods BCR (BW CH, pink), Appalachian Mountains BCR (BW AM, light orange; GW AM, dark orange), and Boreal Hardwood Transition (GW BHT; maroon) BCR

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Comparison plot of the absolute value of regression coefficients and variable importance for the projection (VIP) of explanatory variables included in a partial least squares (PLS) regression model relating explanatory variables to variation in recent state- and province-level population trends of Vermivora warblers (i.e., 2000–2015). Explanatory variables comprise factors relevant to individual fitness that warblers may be exposed to in different periods of the annual cycle: migration (migration risk-factor terms; yellow circles), the breeding period (breeding factors; green circles), and the sedentary nonbreeding period (nonbreeding factors; purple circles). Gray dashed lines denote regression coefficients with absolute values > 1 and VIP > 0.8, which correspond with terms that are important in the PLS model

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Boxplots displaying potential future exposure of currently stationary and increasing, or declining populations of Vermivora warblers to different types of anthropogenic land-use change. Asterisks indicate differences in averages that are significant at ⍺ = 0.05. Spatially explicit data describing the suitability of land for potential future (i.e., 2030) anthropogenic development come from NASA Socioeconomic Data and Applications Center (SEDAC; Oakleaf et al. 2015, 2019)

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Landsc Ecol (2023) 38:2357–2380

https://doi.org/10.1007/s10980-023-01701-2

RESEARCH ARTICLE

Exposure torisk factors experienced duringmigration

isnotassociated withrecent Vermivora warbler population

trends

GunnarR.Kramer· DavidE.Andersen· DavidA.Buehler· PetraB.Wood· SeanM.Peterson·

JustinA.Lehman· KyleR.Aldinger· LesleyP.Bulluck· SergioHarding· JohnA.Jones·

JohnP.Loegering· CurtisSmalling· RachelVallender· HenryM.Streby

Received: 25 October 2022 / Accepted: 4 June 2023 / Published online: 21 June 2023

Abstract

Context Understanding the factors limiting popu-

lations of animals is critical for eﬀective conserva-

tion. Determining which factors limit populations

of migratory species can be especially challenging

because of their reliance on multiple, often geograph-

ically distant regions during their annual cycles.

Objectives We investigated whether distribution-

wide variation in recent breeding population trends

was more strongly associated with exposure to risk

factors experienced during migration (i.e., natu-

ral and anthropogenic threats often associated with

increased mortality or carry-over eﬀects) or fac-

tors associated with breeding and nonbreeding areas

in golden-winged warblers (Vermivora chrysop-

tera) and blue-winged warblers (V. cyanoptera), two

Supplementary Information The online version

contains supplementary material available at https:// doi.

org/ 10. 1007/ s10980- 023- 01701-2.

G.R.Kramer(*)· H.M.Streby

Department ofEnvironmental Sciences, University

ofToledo, Toledo, OH43606, USA

e-mail: gunnarrkramer@gmail.com

Present Address:

G.R.Kramer

Department ofOrganismic andEvolutionary Biology,

Harvard University, 26 Oxford Street, Cambridge,

MA02138, USA

D.E.Andersen

U.S. Geological Survey, Minnesota Cooperative Fish

andWildlife Research Unit, University ofMinnesota,

St.Paul, MN55108, USA

D.A.Buehler· J.A.Lehman

Department ofForestry, Wildlife andFisheries, University

ofTennessee, Knoxville, TN37996, USA

P.B.Wood

U.S. Geological Survey, West Virginia Cooperative Fish

andWildlife Research Unit, West Virginia University,

Morgantown, WV26506, USA

S.M.Peterson

Department ofEnvironmental Science, Policy,

andManagement, University ofCalifornia, Berkeley,

CA94720, USA

K.R.Aldinger

West Virginia Cooperative Fish andWildlife Research

Unit, West Virginia University, Morgantown, WV26506,

USA

L.P.Bulluck

Center forEnvironmental Studies, Virginia

Commonwealth University, Richmond, VA23284, USA

S.Harding

Virginia Department ofWildlife Resources, Henrico,

VA23228, USA

J.A.Jones

Department ofEcology andEvolutionary Biology, Tulane

University, NewOrleans, LA70118, USA

Content courtesy of Springer Nature, terms of use apply. Rights reserved.

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Exposure to risk factors experienced during migration is not associated with recent Vermivora warbler population trends

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