Interactive effects of arrival date, territory quality and male polyterritorial behaviour on the mating system of the sedge warbler Acrocephalus schoenobaenus – a path analysis

Classical models predict that male fitness is based on resources monopolized and invested in reproduction, and/or on individual quality providing offspring with sexually attractive traits or viable genes. However, these factors are frequently correlated, making their relative influence on male fitness difficult to describe and quantify. We analysed the relative influence of the main features of the sedge warbler's (Acrocephalus schoenobaenus) breeding system, i.e. age, arrival date, territory quality, male sexual activity (song and polyterritorial behaviour), on males' mating success, fledging success and local recruitment. Results show that this species’ breeding system involves three main paths: (1) earlier-arriving males have higher mating success, regardless of territory quality, (2) the quality of territories pre-empted by earlier males directly influences recruitment, and (3) mating success is influenced by male sexual activity (polyterritorial behaviour), but an additional territory also affects recruitment directly. As arrival date plays a significant role in all the paths, the whole system seems to depend on male quality; although the benefits accruing to male fitness are obtained not only through sexual selection but also through resource monopolization.