Arrival timing in subadult and adult Black Redstart males: competition-dependent behaviour?

Abstract

The different arrival times of 1-year-old and older males is a widely recognised phenomenon in most migrating passerines. The converse pattern, i.e. the yearlings arriving at the breeding grounds at the same time as adults, has been reported only exceptionally. Two hypotheses have been formulated to explain the delayed arrival of yearling males: investment reduction, and energetic constraint hypotheses, respectively. However, which of these is the more appropriate to explain the phenomenon remains unclear. We studied arrival timing in two distinct urban populations of Black Redstart (Phoenicurus ochruros), a small passerine exhibiting delayed plumage maturation, whereby dull-coloured yearlings are easily distinguishable from black adults. The birds inhabiting South Moravian villages did not show differential timing of arrivals between yearlings and older birds in the resource-rich environment. On the other hand, under suboptimal conditions in Prague the yearlings were delayed by three days on average compared to the adult males. We discuss the possibility that the young birds of this species sample the situation on a potential breeding site during the autumnal singing period and flexibly adapt their migrating behaviour according to the circumstances. In such a case the investment reduction hypothesis is the best explanation for different arrival timing of yearling and adult males in Black Redstart.

Key Words:

• arrival timing
• Phoenicurus ochruros
• DPM
• intraspecific competition

ACKNOWLEDGEMENTS

We thank Alice Exnerová for initial encouragement and useful discussions. The research was supported by FRVŠ Grants No. 1689/1999 and No. 1770/2001.