Abstract
Disentangling individual- and population-level variation in migratory movements is necessary for understanding migration at the species level. However, very few studies have analyzed these patterns across large portions of species’ distributions. We compiled a large telemetry dataset on the globally endangered Egyptian Vulture Neophron percnopterus (94 individuals, 188 completed migratory journeys), tracked across ~70% of the species’ global range, to analyze spatial and temporal variability of migratory movements within and among individuals and populations. We found high migratory connectivity at large spatial scales (i.e. different subpopulations showed little overlap in wintering areas), but very diffuse migratory connectivity within subpopulations, with wintering ranges up to 4000 km apart for birds breeding in the same region and each subpopulation visiting up to 28 countries (44 in total). Additionally, Egyptian Vultures exhibited a high level of variability at the subpopulation level and flexibility at the individual level in basic migration parameters. Subpopulations differed significantly in travel distance and straightness of migratory movements, while differences in migration speed and duration differed as much between seasons and among individuals within subpopulations as between subpopulations. The total distances of the migrations completed by individuals from the Balkans and Caucasus were up to twice as long and less direct than those in Western Europe, and consequently were longer in duration, despite faster migration speeds. These differences appear to be largely attributable to more numerous and wider geographic barriers (water bodies) along the eastern flyway. We also found that adult spring migrations to Western Europe and the Balkans were longer and slower than fall migrations. We encourage further research to assess the underlying mechanisms for these differences and the extent to which environmental change could affect Egyptian Vulture movement ecology and population trends.
Highlights
Many migratory bird populations have undergone substantial declines, mainly as a consequence of widespread expansion of human infrastructures and activities, habitat alteration, direct persecution, and climate change (Bauer et al, 2018)
Generalized Linear Mixed Model (GLMM) were fitted with Gaussian distribution and identity link using the lme4 package in R (Bates et al, 2015), and we considered the model with the lowest Akaike Information Criterion (AIC) as the most parsimonious and present parameter estimates from that model
Complete fall migrations finished in four countries for the Balkans (Chad = 16/30; Ethiopia = 7/30; Sudan = 5/30; Yemen = 2/30 migrations) and Western Europe (Mauritania = 39/54; Mali = 11/54; Senegal = 3/54; The Gambia = 1/54 migrations), with Caucasus fall migrations mainly finishing in Ethiopia (23/30 migrations) and the three fall migrations from the Middle East ending in Chad (1) and Sudan (2), with spring departures following similar patterns (Figure 2)
Summary
Many migratory bird populations have undergone substantial declines, mainly as a consequence of widespread expansion of human infrastructures and activities, habitat alteration, direct persecution, and climate change (Bauer et al, 2018). Disentangling individual- and population-level variation in migratory movements is essential to understand what factors influence migrations and to predict how different species and subpopulations might respond to environmental changes (Trierweiler et al, 2014; Bauer et al, 2018). To gain a more complete understanding of migratory systems it is valuable to evaluate variation in migratory patterns within and among individuals and subpopulations and to produce continental-scale maps of flyways and migratory networks (Trierweiler et al, 2014; Bauer et al, 2018). While migratory patterns have been assessed for individuals from the same or proximate populations (Sergio et al, 2014; Vardanis et al, 2016; Schlaich et al, 2017; Vansteelant et al, 2017), and migratory connectivity has been evaluated for some raptor species (Martell et al, 2014; Trierweiler et al, 2014; Finch et al, 2017), relatively few studies have analyzed these patterns across large portions of a species’ distribution (Mandel et al, 2011; Dodge et al, 2014; Monti et al, 2018)
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