Figure legends
Figure 1. Mean monthly temperature (°C) in ten polygons across
the longitudinal axis in the south (a) and north (b) of the Palearctic
biogeographic zone. Mean monthly temperature data (spatial resolution of
30 seconds) were based on WorldClim version 2.1 climate data for
1970-2000 (Fick & Hijmans 2017). Data processing and calculations were
performed using the R package ’raster’ (Hijmans & van Etten 2016) and
indicate a longer and colder winter in the Eastern Palearctic than in
the Western Palearctic.
Figure 2. The phylogenetic tree of the 21 examined species
included in the Phylogenetic Generalized Least Square (PGLS) analysis.
The tree is based on an analysis of global bird diversity (Jetz et
al. 2012) using 10,000 trees obtained from BirdTree.org (Ruboliniet al. 2015). The consensus tree was built using BEAST version
1.8.4. The tip colour represents the difference in (Δ) moult extent
between the Eastern and the Western Palearctic samples (black = maximum
Δ, white = minimum Δ). The scale (top left) represents 10 million years.
Figure 3. The difference in mean moult extent (number of
moulted feathers) between the Eastern and Western Palearctic (n = 21
passerine species). The results indicate that moult extent among western
populations is greater than among eastern populations of the same
species. The boxplots display the minimum, 1st and 3rd quartiles, median
and maximum of each tested region.
Figure 4. The effect of species-specific differences in (Δ)
migration distance on the difference in (Δ) moult extent between Eastern
and Western Palearctic passerines among the 21 examined species (± 95%
confidence intervals). The results indicate a strong relationship
between Δ migration distance and Δ moult extent: if an eastern
population migrates a longer distance than the western population of the
species, the extent of its moult decreases compared to the western
population. The circled insets depict examples of Δ moult extent between
Eastern and Western Palearctic regions in relation to the Δ migration
distance for two species (right: Coal Tit Periparus ater , left:
White Wagtail Motacilla alba ). The wing areas that are coloured
depict the wing’s moulted feathers while non-coloured areas represent
non-moulted feathers.
Figure 5. A schematic representation of major annual processes
in Eastern (inner circle) and Western Palearctic (outer circle)
passerines. The information is based on published data (Del Hoyoet al. 2019) and the authors’ field experience (Supplementary
Note 1) and demonstrates a delay of about one month in spring and summer
but not autumn events in Eastern Palearctic populations, causing a
shorter post-juvenile moult period compared to the Western Palearctic.
The overlap between migration, breeding and moult is represented by
colour combinations.