Age and Other Factors Influencing Mating Status in German Great Reed Warblers (Acrocephalus arundinaceus)

Abstract

We examined reproductive success of monogamous, primary and secondary females as well as factors influencing male mating status in a polygynous Great Reed Warbler population by analysing long term data. The analysis is based on 428 nests of which at least one parent was individually colour-ringed. The number of males studied over a 15 year period averaged 30/yr. of which 11.3% were polygynous and 13.9% unmated. Primary broods of polygynists started 10 days earlier than broods of secondary females. Average fledging success of secondary females was lower than that of monogamous females (relative success 0.79) but did not differ significantly from that of simultaneously monogamous females (relative success 0.85). The percentage of fledglings recruited to the breeding population overall was highest in primary broods, but did not differ significantly between monogamous and secondary broods. Mating status of males was influenced by age, with a higher proportion of older males becoming polygynous whereas correlations between age and mating status of females was not significant. We also investigated the relative importance of male and territory quality in female choice by analysing 3 territorial and 11 male characteristics (physical traits, age, repertoire size, aggressiveness, hormones) of 29 males (4 polygynous, 3 unmated, 22 monogamous) using a discriminant analysis. The best predictors for polygyny were a long reed edge against open water, lower aggressiveness, and a higher song repertoire size. We conclude (1) that it is not necessary to invoke female deception, which had been favoured in explaining polygyny in our population (2) that ecological conditions for polygyny are suboptimal in our study area but there seem to exist enough predictable differences in breeding situations to allow female choice and (3) that females base their mate choice on both male characteristics and territory quality, and that these factors are positively correlated.