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. 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.