The Value of Objects to Satin Bowerbirds Ptilonorhynchus violaceus

Abstract

The mating success of male Satin Bowerbirds Ptilonorhynchus violaceus is known to correlate with the numbers of decoration objects present at their bowers. It was expected that the value of an object, in terms of fitness pay-offs to males, would be less in an area where the average number of objects at bowers was high than in an area where the average numbers of objects at bowers was low. We found (a) rates of visiting bowers by adult females and immature individuals were correlated with the number of marked objects at those bowers within but not between areas, (b) the rate of stealing objects was higher in the area at which the average number of objects at bowers was lowest and (c) bower destruction increased relative to stealing in the area where the average number of objects was highest. These findings suggest that the relative importance of behaviour associated with competition and sexual display in male Satin Bowerbirds is subject to variation in response to environmental conditions.