POLYGYNY IN GREAT REED WARBLERS: A LONG-TERM STUDY OF FACTORS CONTRIBUTING TO MALE FITNESS

Abstract

To study the relative importance of factors with direct and indirect effects on male fitness in the polygynous Great Reed Warbler, Acrocephalus arundinaceus, I investigated characteristics of both males and territories in relation to annual and lifetime breeding success. Male harem size and number of offspring recruits (i.e., young surviving to breeding age) were repeatable between years. I analyzed lifetime breeding success using stepwise multiple regressions and annual breeding success by testing for significant trends (over five years) in pairwise correlations with each male and territory characteristic. Male arrival order was the most important factor predicting pairing success, fledging success, and number of offspring recruits, and arrival order was also closely correlated with territory attractiveness rank. Thus females seemed to prefer early arriving males that occupied more attractive territories, and these females also gained direct benefits through increased production of fledglings and offspring recruits. Older males arrived earlier and were therefore able to occupy attractive territories. Male song repertoire size was positively correlated with annual harem size and annual and lifetime production of offspring recruits. Song repertoire size alone predicted male lifetime number of offspring recruits statistically adjusted for number of fledglings produced, i.e., the postfledging survival of offspring. These data suggest that males with large song repertoires sire offspring that have improved viability, and that females mating with these males can gain indirect (genetic) benefits for their young.