Age‐related reproductive success in dichromatic male Black Redstarts Phoenicurus ochruros: Why are yearlings handicapped?

Reproductive constraints on sexually mature, young birds may be the underlying cause for the evolution and maintenance of delayed plumage maturation in passerine birds. I examined whether yearling male Black Redstarts in non-definitive plumage are reproductively handicapped and explored possible reasons for it. Yearlings raised only half as many young per season as adults. Differential reproductive effort was excluded as a possible source for age-related reproductive success because yearlings and adults did not differ in the frequency of non-breeding or in paternal effort. The lower annual reproductive success of yearlings was attributed to their lower probability of obtaining (multiple) females and adult females. Males mated to adult females raised almost twice as many offspring as males mated to yearling females. I conclude that the proposed preconditions for the evolution and maintenance of delayed plumage maturation do still prevail in the Black Redstart.