Large‐scale longitudinal climate gradient across the Palearctic region affects passerine feather moult extent

Abstract

Large-scale spatial gradients of environmental conditions shape organisms, populations and ecosystems. Even though environmental gradients are a key research theme in macro-ecology and biogeography, the effects of large-scale, east-west, environmental gradients are largely overlooked compared with north-south gradients. Our study focused on feather moult, an important and energy demanding process in birds. By comparing Western and Eastern Palearctic populations of 21 species, we found that juvenile passerines in the Western and Eastern Palearctic differ in the number of feathers moulted as part of their post-juvenile moult. This difference is most likely the result of a large-scale climatic gradient in cold season duration and consequent differences in the time available for moulting. Eastern populations were characterized by a limited extent of feather moult that was additionally affected by migration distance and body mass. The longer migration distance in the Eastern Palearctic caused a generally less extensive moult while high body mass was correlated with a low difference in moult extent between the Western and Eastern Palearctic regions. These results highlight the importance of linking annual cycle processes at the organismal level to the specific environmental conditions within the distribution range of each species.

Which birds participate in mass concentrations of Bramblings Fringilla montifringilla?—Ring recoveries, biometry, age and sex composition

“…As shown in 21 Palaearctic passerine species, the extent of the partial post-juvenile moult was smaller east of the Ural mountains than in the western Palaearctic, probably because of a shorter vegetation season and hence less time available for moult in the east (Kiat et al 2021). Therefore, juvenile Bramblings which take part in mass concentrations in Switzerland are probably born later and hence possibly of more eastern and/or northern origin than autumn migrants.…”

Defining moults in migratory birds: a sequence‐based approach

“…Considering such moults on winter grounds as a single prebreeding moult compromises our ability to identify inserted moults and to discriminate and understand moulting strategies. Furthermore, recent analyses on factors influencing the extent of the postjuvenile and preaternate moults in migratory passerines have either confined this moult to the summer grounds (Guallar and Figuerola 2016, Delhey et al 2020, Pérez‐Granados et al 2020, Kiat et al 2021) or presumed that it can resume on winter grounds (Guallar et al 2021), which has lead to quite divergent interpretations of results.…”

Body mass and geographic distribution determined the evolution of the wing flight-feather molt strategy in the Neornithes lineage

“…As a result, the growth of poor quality feathers by juveniles takes place only if they are later replaced by durable, higher quality feathers after fledging 30,31 . Several internal and external factors, such as solar exposure, climate, migration distance, body size, plumage coloration and sexual dichromatism level (indicative of sexual selection level), hatching date and environmental conditions related to geographic distribution, are known to influence the extent of wing feather molt in the early stage of a bird's life 4,21,29,30,[50][51][52][53][54][55] . This is presumably due to their effects on the time available for this process to take place 30,51 , as well as their influence on the need to undertake an extensively molt 29 .…”