This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Should I stay or should I go? What determines whether birds migrate for the winter?
This is one of the questions explored in a new doctoral thesis by Cassandra Ugland from NTNU's Department of Biology. The work is published in the Journal of Animal Ecology. This is leading to greater seasonal variation, which in turn may cause birds to adopt new strategies.
"Climate change is affecting the behavior of bird species, causing some individuals to migrate away from their breeding grounds while others remain resident throughout the year," says Ugland. One such species is the European shag (Gulosus aristotelis), found from Northern Norway to Southern Europe. Ugland studied a population that breeds on the Isle of May in Scotland.
Around half of the population remains in roughly the same area throughout the winter, while the rest may migrate some distance northward along the coast. Why do different shags adopt different strategies? "To understand how individuals and populations adapt, we need to look at the interplay between several factors," says Ugland.
These factors are natural selection, genetic variation and behavioral flexibility, often referred to as "plasticity." "I investigated how these factors shape early-life expression of migration during the winter versus residence in the same area throughout the year," explains Ugland. To do this, Ugland examined large amounts of bird-banding data (information collected when wild birds are safely caught, fitted with a uniquely coded, colored leg band, and then recorded and released). She used advanced models to analyze variation, selection and genetics during the birds' first years of life.
"The results show considerable variation between individuals and from year to year. But we can see that early experiences are very important," says Ugland. The choice each individual bird makes during its first winter appears to matter most.
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