Do fledgling and pre‐breeding Common Swifts Apus apus take part in aerial roosting? An answer from a radiotracking experiment

This study has shown that fledgling Common Swifts Apus apus spend the first post‐fledging night of their life on the wing and that pre‐breeders also spend the full night on the wing. Even though this work was conducted during an unusually cold, wet period, the results show that fledglings do not return to their natal colony in the week after fledging. It also demonstrates that yearlings are only slightly more likely than fledglings to spend any time at a particular colony, but are more likely to move from colony to colony. Older pre‐breeders are more likely to spend more time at and revisit a particular colony more often than yearlings. It is our observation that only right at the end of the breeding duties will the parents participate in an evening ascent, and even then many of them return to their nest for the evening. Breeding adults displayed the greatest devotion to a particular colony. But even among such adults we detected some that ceased caring for their young a few days prior to their fledging. Adults roost in their nestbox if they meet with bad weather.