Long‐term phenological shifts and intra‐specific differences in migratory change in the willow warblerPhylloscopus trochilus

Abstract

Climate change can influence many aspects of avian phenology and especially migratory shifts and changes in breeding onset receive much research interest in this context. However, changes in these different life‐cycle events in birds are often investigated separately and by means of ringing records of mixed populations. In this long‐term study on the willow warbler Phylloscopus trochilus, we investigated timing of spring and autumn migration in conjunction with timing of breeding. We made distinction among individuals with regard to age, sex, juvenile origin and migratory phase. The data set comprised 22‐yr of ringing records and two temporally separated data sets of egg‐laying dates and arrival of the breeding population close to the ringing site. The results reveal an overall advancement consistent in most, but not all, phenological events. During spring migration, early and median passage of males and females became earlier by between 4.4 to 6.3 d and median egg‐laying dates became earlier by 5 d. Male arrival advanced more, which may lead to an increase in the degree of protandry in the future. Among breeding individuals, only female arrival advanced in timing. In autumn, adults and locally hatched juvenile females did not advanced median passage, but locally hatched juvenile males appeared 4.2 d earlier. Migrating juvenile males and females advanced passage both in early and median migratory phase by between 8.4 to 10.1 d. The dissimilarities in the response between birds of different age, sex and migratory phase emphasize that environmental change may elicit intra‐specific selection pressures. The overall consistency of the phenological change in spring, autumn and egg‐laying, coupled with the unchanged number of days between median spring and autumn migration in adults, indicate that the breeding area residence has advanced seasonally but remained temporally constant.

Migratory response of polar bears to sea ice loss: to swim or not to swim

“…As a result, migration patterns are changing for many species (Cotton , Singh et al , Otero et al ). Studies on the impacts of climate change on migration have often focused on measuring the species‐wide response, with few studies comparing differential migration, in which migratory behaviour varies between age and sex classes (Rainio et al , Hedlund et al ). Ignoring individual and population variation may bias the estimates of the effect of climate change on migration, and fail to identify the ecological linkages that are sensitive to environmental change.…”

Early returning long‐distance migrant males do pay a survival cost

“…The indication of low survival on late dates that we find for both long-and short-distance migrants probably reflects individuals in poor body condition arriving late in the season (Hedlund et al, 2014;Kokko, 1999).…”

“…But it is also likely that they are better at adjusting timing of arrival to occurring weather condition because they winter closer to the breeding area as indicated in other studies where they found more flexible arrival dates and arrival over a larger time span in short‐distance than long‐distance migrants (Hagan et al., ; Mason, ). The indication of low survival on late dates that we find for both long‐ and short‐distance migrants probably reflects individuals in poor body condition arriving late in the season (Hedlund et al., ; Kokko, ).…”

“…However, especially for insectivorous species breeding at high latitudes, we expect a pronounced decrease in adult survival for very early returning individuals (Newton, ). In addition, we expect lower survival for late individuals, because they potentially reflect delayed individuals in poor condition (Hedlund, Jakobsson, Kullberg, & Fransson, ; Kokko, ). Furthermore, timing of migration often differs between sexes (reviewed by Morbey & Ydenberg, ).…”

The dependence of long-distance migration to North Norway on environmental conditions in the wintering area and en route

“…Similarly, at least one aspect of arrival distribution (first, mean or median arrival date) at locations in England, Germany, Finland and Russia advanced significantly during the last half of the 20th century ) whereas the same tendencies (but statistically insignificant trends) were found for both species arriving in W. Poland in 1983-2003(Tryjanowski et al 2005. Willow Warblers also advanced their first arrival dates in southern Sweden in 1989-2012 by 0.2 d yr -1 (Hedlund et al 2014). The arrival dates of Pied Flycatchers, on the other hand, seem to be less flexible.…”