Morphological Adaptations to Migration in Birds
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Migratory flight performance has direct or carry-over effects on fitness. Therefore, selection is expected to act on minimizing the costs of migratory flight, which increases with the distance covered. Aerodynamic theory predicts how morphological adaptations improve flight performance. These predictions have rarely been tested in comparative analyses that account for scaling and phylogenetic effects. We amassed a unique dataset of 149 European bird species and 10 morphological traits. Mass-adjusted aspect ratio increased, while mass-adjusted heart weight and wing loading decreased with increasing migration distance. These results were robust to whether the analyses were based on the entire species pool or limited to passerines or migrants. Our findings indicate that selection due to migration acts on wing traits that reduce the energetic cost of transportation to increase the flight range. Consequently, the demands for high ‘exercise organ’ performance might be low, and hence such energetically expensive tissues are not associated (pectoral muscle) or are inversely associated (heart) with migration distance.
KeywordsAerodynamics Functional morphology ‘Migratory syndrome’ Organ size Phylogenetic comparative analysis Wing morphology
We appreciate the help during fieldwork by Lőrinc Bărbos, Attila Marton, Krisztina Sándor and Judit Veres-Szászka, the numerous bird carcasses provided by the members of the ‘Milvus Group’ Bird and Nature Protection Association, the Museum of Zoology of Babeş-Bolyai University and Costică Adam. László Zsolt Garamszegi kindly aided with statistical analyses and Jácint Tökölyi with the calculation of migration distances. We thank the administration of the ‘Alexandru Borza’ Botanical Garden of Cluj Napoca for the permission to capture birds. Two anonymous reviewers provided constructive criticism. This work was licensed by the Romanian Academy of Sciences and adhered to recommended practices for the ringing, measuring, and sampling of wild birds for research purposes. Logistics and data collection between 2010 and 2013 was financed by a CNCSIS Grant (PN II. RU TE 291/2010) of the Romanian Ministry of Education and Research. CIV and OV were supported by the European Union and the State of Hungary, co-financed by the European Social Fund in the framework of TÁMOP 4.2.4.A/2-11-1-2012-0001 ‘National Excellence Program’. During writing, CIV was financed by the Postdoctoral Fellowship Programme and PLP by the János Bolyai Research Scholarship of the Hungarian Academy of Sciences.
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Conflict of interest
The authors declare that they have no conflict of interest.
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