An experimental analysis of mate choice in the wren: A monomorphic, polygynous passerine

Abstract

Male wrens (Troglodytes troglodytes) construct nests that are used in their display to females. Previous work has suggested that the number of vacant nests may be used as a mate choice cue. Correlational data from 1992 confirmed that females appeared to be assessing the number of vacant nests on a male's territory and preferentially mating with males with more nests. Male tail length was also correlated with mating success. In 1993 the numbers of nests on territories was experimentally manipulated, the female settlement patterns confirmed that the number of vacant nests did mediate mate choice. Male tail length failed to explain additional variance in mating success when the variance explained by the experimental manipulation was removed, suggesting that the original correlation arose because both tail length and mating success were correlated with a confounding variable. The structure of the vegetation in a male's territory influenced mating success. This appeared to be due to nests surviving better in territories with dense vegetation. Males on territories in which nests survive well had longer tails. Male-male competition for good territories may explain the observed effects of male morphology on mating success. Further analysis of the nest choice data showed that all nests had an equal chance of being used by a female. The fact that all nests had an equal probability of being chosen by a female means that each additional nest built by a male wren results in the same increase in mating success. This suggests that the benefits to males of nest building increase linearly. The number of nests on a territory will be affected by various factors such as predation pressure, nest building rate, and vegetation structure. The information that females are getting by assessing such a signal is discussed.