Vegetation type variation in marsh habitats: does it affect nest site selection, reproductive success, and maternal investment in Reed Warblers?

Abstract

Habitat choice may have an important impact on survival and fitness of an individual. Besides an individual’s intrinsic features, such as resource-holding potential, experience, age, and habitat characteristics like habitat heterogeneity may play a role. In line with this, we investigate the importance of vegetation type for habitat choice, reproductive investment, and success within one population of the Reed Warbler (Acrocephalus scirpaceus), a common Palearctic marsh bird that nests in reed (Phragmites australis) and reed mace (Typha spp.) stands. In particular, we want to know whether individuals differ in the use of the nesting habitat and whether choosing a different habitat, namely reed and reed mace, may have consequences for reproductive success and/or reproductive investment. Our results suggest clear differences in vegetation structure between reed and reed mace territories. Reed mace provided denser vegetation for nest sites, and, consequently, breeding density was higher and nest predation lower. Although reproductive success was significantly lower in reed nests, we did not find a directional habitat preference. We also found some indication for size-dependent habitat choice, as bigger males (with longer tarsi) settle in reed mace. Differences in vegetation type could also be observed in regard to maternal investment. Females reproducing in reed mace produced larger and heavier eggs. The results are further discussed in regard to the possibility of sympatric speciation.