Conclusions
Environmental conditions on Earth have specific spatial and temporal
attributes that can have immense influence on biological systems.
Understanding how environmental gradients shape various biological
processes on Earth can improve our understanding of organismal
life-history and annual-routine scheduling of different activities such
as migration, feather moult and breeding, as well as their evolutionary
development. Furthermore, this improved understanding can also help us
predict future responses to changes that may occur on the planet. In
this study, we focused on moult, an important process in the avian
yearly cycle, and how this process may be shaped by an environmental
longitudinal gradient, a seldom studied, large-scale environmental
factor. Our findings highlight the importance of linking the evolution
of annual cycle processes at the organismal level to the environmental
conditions to which the organism is exposed. We propose that moult
extent decreases as a response to the more extensive and colder winter
in the Eastern Palearctic compared with the Western Palearctic.
Consequently, this work exemplifies the importance of integrating
biogeography and climatology to enhance our understanding of biological
patterns and their causes over large spatial scales.