Migratory connectivity and population-specific migration routes in a long-distance migratory bird

Abstract

Knowledge about migratory connectivity, the degree to which individuals from the same breeding site migrate to the same wintering site, is essential to understand processes affecting populations of migrants throughout the annual cycle. Here, we study the migration system of a long-distance migratory bird, the Montagu's harrier Circus pygargus, by tracking individuals from different breeding populations throughout northern Europe. We identified three main migration routes towards wintering areas in subSaharan Africa. Wintering areas and migration routes of different breeding populations overlapped, a pattern best described by 'weak (diffuse) connectivity'. Migratory performance, i.e. timing, duration, distance and speed of migration, was surprisingly similar for the three routes despite differences in habitat characteristics. This study provides, to our knowledge, a first comprehensive overview of the migration system of a Palaearctic-African long-distance migrant. We emphasize the importance of spatial scale (e.g. distances between breeding populations) in defining patterns of connectivity and suggest that knowledge about fundamental aspects determining distribution patterns, such as the among-individual variation in mean migration directions, is required to ultimately understand migratory connectivity. Furthermore, we stress that for conservation purposes it is pivotal to consider wintering areas as well as migration routes and in particular stopover sites.

Migratory routes and wintering locations of declining inland North American Common Terns

“…Birds from the western breeding colonies (lakes Winnipeg and Superior) followed a pattern similar to a clockwise loop migration (e.g., Berthold 2001, Trierweiler et al 2014, with many birds traveling southeast during autumn migration but using a route farther west during spring migration. By contrast, individuals from Lake Huron used migratory routes that followed a more direct north-south route, and Common Terns from Oneida Lake showed a pattern of counterclockwise loop migration.…”

“…Furthermore, identifying the strength of migratory connectivity-the geographic linking of individuals and populations between one lifecycle stage and another-may help in evaluating the vulnerability of populations to local environmental hazards and human influences (Webster et al 2002, Trierweiler et al 2014, Bauer et al 2016) and explaining differences in population trends among populations. Determining how connected migratory individuals and populations are throughout the year requires knowledge of the seasonal distribution of a species and a corresponding measure of strength of co-occurrence between seasons .…”

Settling down of seasonal migrants promotes bird diversification

“…Seasonal migration can potentially enhance speciation, because different populations within the same species may have different migratory flyways or strategies which can lead to genetic divergence between populations [9][10][11][12][13]. Furthermore, vagrancy, i.e.…”

Methods in field chronobiology

“…As Montagu's Harriers are long-distance migrants, daily activity patterns could be compared across different ecological contexts, i.e. the breeding site in Europe, their main migratory stopover site in Northwest Africa, and the wintering site in the Sahel in Africa [55]. Within individuals, daily activity patterns differed between the breeding, stopover and wintering site.…”