NEST-BUILDING SIGNALS MALE CONDITION RATHER THAN AGE IN WRENS

An ornament used in mate choice may vary with male age for two reasons . It may be designed to signal age and females could use such an ornam ent to mate preferentially with older males that may be expected to be of higher quality. Alternatively, if an ornament is condition-depende nt it would be expected to vary with age because condition is expected to increase with age. These hypotheses make different predictions abo ut the variation of an ornament with male age between individuals with in a year and between years within an individual's lifetime. Female wr ens, Troglodytes troglodytes, have been shown to discriminate between males on the basis of the number of cock nests on their territories. A n analysis using information from males of known age showed that as ma les got older they built more nests per season, started building earli er in the year and built for longer. A previous analysis had demonstra ted that the number of nests on a territory was influenced by habitat structure and that male age failed to predict any of the inter-male va riation in number of nests constructed within a year. This was support ed by the present study: male age was not a good predictor of variatio n in the number of nests constructed between males within a year. As v ariation within a year between different males is much greater than th e variation between years within a male's lifetime it is effectively i mpossible for a female to mate selectively with older males; rather it suggests that nest construction in male wrens is a condition-dependen t trait and not a signal of male age. This analysis suggests that some males are more accomplished nest builders than others and that while males do improve with age, age cannot compensate for a lack of ability . (C) 1997 The Association for the Study of Animal Behaviour.