Competition for territories in red-winged blackbirds: Is resource-holding potential realized?

Abstract

In resource-defence mating systems we intutively expect that the most competitive males should win the best resources so that, in territorial species, male quality and territory quality will be highly correlated. In the “polygyny threshold model” (PTM) of mate choice this expectation has become an assumption. We performed a removal experiment using red-winged blackbirds to test the validity of this assumption. On the basis of two morphological and two behavioral indices of competitive ability we found only weak correlation between male competitive ability and territory quality. Factors potentially contributing to this result include habitat quality perception, site dominance, and site fidelity. However, both our experimental design and measurement of male competitive ability may have caused us to underestimate the real correlation between male quality and territory quality. Nevertheless, our results suggest that male quality is not perfectly correlated with territory quality as is assumed in the PTM. Therefore, male quality and territory quality should be treated independently when modelling mate choice in this and other territorial species.