Female age and breeding performance in a cyclic population of black grouse Tetrao tetrix

Abstract

The breeding performance in yearling and adult female black grouse Tetrao tetrix was studied in a 6–7 year cyclic population during 1989–93 in central Finland. Eighty yearlings and 108 adults, radio‐marked in late winter, survived until the breeding season. Adults were larger, had more body mass at capture, initiated laying earlier and had larger eggs and clutches than yearlings. Yearlings and adults lost 11.8 and 20.9%, respectively, of their first nests to egg predators. Hatching dates and success of eggs were similar for both age classes. The proportion of females losing the entire brood was 32% for yearlings and 27.1% for adults. Brood size in late summer and number of chicks produced per female initiating breeding did not differ between age classes.