Environmental and Geographic Conditions on the Breeding Grounds Drive Bergmannian Clines in Nightjars

ABSTRACT Aim To evaluate (1) whether three migratory nightjar species (Family Caprimulgidae) adhere to Bergmann's rule, (2) whether environmental factors on the breeding or wintering grounds determine body size, and (3) which mechanistic hypotheses best explain Bergmannian patterns in body size. Location North and South America; Europe and Africa. Taxon Eastern whip‐poor‐will ( Antrostomus vociferus ), Common nighthawk ( Chordeiles minor ) and European nightjar ( Caprimulgus europaeus ). Methods We used GPS tracking and morphometric data to assess competing hypotheses explaining variation in body size for each species, based on their breeding ( n = 3388) and wintering ( n = 189) locations. Results All three species exhibited Bergmannian patterns in body size, providing the first evidence that nightjars conform to Bergmann's rule despite adaptations to severe environmental conditions. Environmental and geographic variables at breeding sites were stronger predictors of body size than wintering‐site variables. Although we found partial support for Bergmann's temperature regulation hypothesis, geographic variables, rather than specific environmental factors, emerged as the strongest predictors of body size variation. Main Conclusions Latitude and longitude correlated strongly with environmental variables and migratory distance; thus, these geographical variables likely encompass many factors that influence body size in nightjars. The present study is among the first to use tracking data from individual birds to understand how environmental pressures across the annual cycle are related to body size. Our findings highlight the critical role of geographic breeding‐ground factors in shaping Bergmannian patterns, offering robust evidence to support nearly two centuries of research since Bergmann's rule was first described in 1847.

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Publication Details

Journal
Journal of Biogeography
Published
2025-07-12
DOI
https://doi.org/10.1111/jbi.15176
Citations
1
Primary Topic
Rangeland and Wildlife Management
Type
article
Field-Weighted Citation Impact
1.72

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article

Environmental and Geographic Conditions on the Breeding Grounds Drive Bergmannian Clines in Nightjars

R. Mark Brigham, Ian Henderson, Anders Hedenström, Autumn‐Lynn Harrison et al.
1 citations
Journal of Biogeography
Rangeland and Wildlife Management
1.72
article

Environmental and Geographic Conditions on the Breeding Grounds Drive Bergmannian Clines in Nightjars

R. Mark Brigham, Ian Henderson, Anders Hedenström, Autumn‐Lynn Harrison, Christopher M. Tonra, Kevin C. Fraser, Susanne Åkesson, Thomas J. Benson, Alicia M. Korpach, Peter P. Marra, Gabriel Norevik, Christina M. Davy, Marja H. Bakermans, Simon S. Christiansen, Michael P. Ward, Juha Honkala, Michiel Lathouwers, Andrew C. Vitz, Giovanni Boano, Aaron A. Skinner, Erin M. Bayne, Janet W. Ng, Steven L. Van Wilgenburg, Greg J. Conway, Elly C. Knight, Kasper Thorup, Ruben Evens, Amy L. Scarpignato, Lars Bo Jacobsen
article en
1 citations

Abstract

ABSTRACT Aim To evaluate (1) whether three migratory nightjar species (Family Caprimulgidae) adhere to Bergmann's rule, (2) whether environmental factors on the breeding or wintering grounds determine body size, and (3) which mechanistic hypotheses best explain Bergmannian patterns in body size. Location North and South America; Europe and Africa. Taxon Eastern whip‐poor‐will ( Antrostomus vociferus ), Common nighthawk ( Chordeiles minor ) and European nightjar ( Caprimulgus europaeus ). Methods We used GPS tracking and morphometric data to assess competing hypotheses explaining variation in body size for each species, based on their breeding ( n = 3388) and wintering ( n = 189) locations. Results All three species exhibited Bergmannian patterns in body size, providing the first evidence that nightjars conform to Bergmann's rule despite adaptations to severe environmental conditions. Environmental and geographic variables at breeding sites were stronger predictors of body size than wintering‐site variables. Although we found partial support for Bergmann's temperature regulation hypothesis, geographic variables, rather than specific environmental factors, emerged as the strongest predictors of body size variation. Main Conclusions Latitude and longitude correlated strongly with environmental variables and migratory distance; thus, these geographical variables likely encompass many factors that influence body size in nightjars. The present study is among the first to use tracking data from individual birds to understand how environmental pressures across the annual cycle are related to body size. Our findings highlight the critical role of geographic breeding‐ground factors in shaping Bergmannian patterns, offering robust evidence to support nearly two centuries of research since Bergmann's rule was first described in 1847.

Journal of BiogeographyVol. 52(10)
Worcester Polytechnic Institute (US), University of Copenhagen (DK), Public Policy Institute of California (US), Louisiana Department of Wildlife and Fisheries (US), Illinois Department of Natural Resources (US), Environment and Climate Change Canada (CA), University of British Columbia (CA), University of Antwerp (BE), University of Namur (BE), University of Alberta (CA), University of Illinois Urbana-Champaign (US), Georgetown University (US), Lund University (SE), University of Regina (CA), BirdLife Australia (AU), Smithsonian Conservation Biology Institute (US), Museo Civico di Zoologia (IT), National Zoological Park (US), Finnish Museum of Natural History (FI), Illinois Archaeological Survey (US), University of Manitoba (CA), The Ohio State University (US), Carleton University (CA), British Trust for Ornithology (GB), The University of Winnipeg (CA), Hasselt University (BE), UCLouvain (BE)
Smithsonian Institution, ConocoPhillips, Massachusetts MassWildlife Division of Fisheries and Wildlife, Illinois Department of Natural Resources, Ohio State University, Texas Tech University, Helsingin Yliopisto, Georgetown University, University of Manitoba, University of South Dakota, American Ornithological Society, Association of Field Ornithologists, Government of Ontario, Natural England, University of Alberta, Svenska Forskningsrådet Formas, Lunds Universitet, Vetenskapsrådet, Mitacs, Norges Forskningsråd, Environment and Climate Change Canada, Universiteit Hasselt, U.S. Fish and Wildlife Service, U.S. Geological Survey, University of Illinois at Urbana-Champaign, Smithsonian Conservation Biology Institute, Natural Sciences and Engineering Research Council of Canada, Center for Makroøkologi, Evolution og Klima, Université de Namur, Campus Research Board
Openalex Percentile: Top 16%
Rangeland and Wildlife Management
1.72
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