Sex-specific difference in migration schedule as a precursor of protandry in a long-distance migratory bird

• Published in: Die Naturwissenschaften Vol. 106; no. 7-8; pp. 45 - 10
• Main Authors: Pedersen, Lykke, Jakobsen, Nina Munkholt, Strandberg, Roine, Thorup, Kasper, Tøttrup, Anders P.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.08.2019; Springer Nature B.V
• Subjects: Airspeed; Animal breeding; Animal Migration - physiology; Animals; Autumn; Behavioral Sciences Biology; Biologi; Biological Sciences; Biomedical and Life Sciences; Bird migration; Birds; Breeding grounds; Divergence; Environment; Etologi; Female; Females; Geolocator; Life Sciences; Male; Males; Migratory birds; Natural Sciences; Naturvetenskap; Original Paper; Passeriformes - physiology; Precursors; Protandry; Proximate causes; Red-backed shrike; Schedules; Sex; Sex Determination Processes - physiology; Sex differences; Sex Factors; Songbird migration; Spring; Spring (season); Red-backed shrike; Geolocator; Protandry; Songbird migration
• ISSN: 0028-1042; 1432-1904
• DOI: 10.1007/s00114-019-1637-6

Protandry, the earlier arrival of males at the breeding grounds relative to females, is common in migratory birds. However, due to difficulties in following individual birds on migration, we still lack knowledge about the spatiotemporal origin of protandry during the annual cycle, impeding our understanding of the proximate drivers of this phenomenon. Here, we use full annual cycle tracking data of red-backed shrikes Lanius collurio to investigate the occurrence of sex-related differences in migratory pattern, which could be viewed as precursors (proximate causes) to protandry. We find protandry with males arriving an estimated 8.3 days (SE = 4.1) earlier at the breeding area than females. Furthermore, we find that, averaged across all departure and arrival events throughout the annual cycle, males migrate an estimated 5.3 days earlier than females during spring compared to 0.01 days in autumn. Event-wise estimates suggest that a divergence between male and female migratory schedules is initiated at departure from the main non-breeding area, thousands of kilometres from-, and several months prior to arrival at the breeding area. Duration of migration, flight speed during migration and spatial locations of stationary sites were similar between sexes. Our results reveal that protandry might arise from sex-differential migratory schedules emerging at the departure from the main non-breeding area in southern Africa and retained throughout spring migration, supporting the view that sex-differential selection pressure operates during spring migration rather than autumn migration.