Arrival dates of male and female willow warblers (Phylloscopus trochilus) to their breeding site in Sweden 1979-2016

Protandry is a widespread life-history phenomenon describing how males precede females at the site or state of reproduction. In migratory birds, protandry has important influence on individual fitness, the migratory syndrome and phenological response to climate change. Despite its significance, accurate analyses on the dynamics of protandry using data sets collected at the breeding site, are lacking. Basing our study on records collected daily, spanning a period of 38 years, we aim to investigate protandry dynamics over time in a breeding population of willow warblers (Phylloscopus trochilus). Temporal change in the timing of arrival was analysed in males and females, and protandry (number of days between male and female arrival) was investigate both at population level and within breeding pairs. Our results show advancement in the arrival time to the breeding site in both sexes, but male arrival has advanced to a greater extent, leading to an increase in protandry both at the populatio...