In the Grashopper Warbler Locustella naevia, males with better nutritional condition at the winter ground arrive earlier than other males at the breeding ground

Abstract

The aim of this study was to answer the question: Does grasshopper warbler Locustella naevia males with better physical condition in the winter quarter arrive earlier at the breeding ground than other males. This was accomplished by measuring growth bars in tail feathers and then correlate these measurements with different times of arrival at the study area of Björka lertag. The results strongly indicate that early arriving males had better physical fitness (nutritional condition) than later arriving males, at least when their feathers were growing on the wintering grounds in Africa.