Male Satin Bowerbirds Research Articles

Flower choice and bower decoration in the satin bowerbird Ptilonorhynchus violaceus: a test of hypotheses for the evolution of male display

Flowers are a common decoration used on the bowers of male satin bowerbirds. The characteristics of flowers that promote their use as decorations by males are evaluated. Out of a total of 70 species recorded along transects, inflorescences from 29 species were found on bowers. Seven flower species accounted for 93% of the inflorescences used on bowers. Blue and purple species occurred on bowers at a greater frequency than they occurred in the habitat. White and yellow species appeared on bowers proportionately less often, and orange, pink and red not at all. Male satin bowerbirds used a wider range of colours of flowers than has been previously reported, and preferred blue and purple over yellow and white flowers. Flower choice experiments showed that males may discriminate between flowers only on the basis of colour, and that males favour flowers that appear infrequently on bowers. The results suggest several conclusions about how flowers are used on bowers. (1) Male flower preferences and male ability to collect inflorescences affect how flowers are used on bowers. The common use of flowers shown to be less preferred in choice tests implies that there are constraints on the gathering of more preferred flowers and this causes males to produce suboptimal displays. (2) Male preference for novel flowers suggests that flower choice by males is due to a set of general selection criteria and does not result from preferences for specific flower species. (3) The strong male preference for, and the high rate of use of, rare blue flowers supports the hypothesis that the rarity of colours may influence the evolution of male flower references. This strong preference for scarce flowers offers some support for models that suggest that male displays are not arbitrary, but may serve as indicators of male quality as sires.

Satin bowerbird parasites: a test of the bright male hypothesis

The number of a common parasite (Cuclotogaster sp.) on male satin bowerbirds was related to male mating success in a test of Hamilton and Zuk's (1982) bright male hypothesis. The data do not show the expected inverse correlation between female mating preferences and the level of parasitic infection of males predicted by that model. Nearly all matings are accomplished by bower-holding males (Borgia 1985a), but the vast majority of these males were uninfected. There were large differences in mating success among the uninfected bower holders, but this could not be explained by between male differences in the level of parasitic infection. From this I conclude that levels of parasitic infection are not now an important direct cause of intermale variation in mating success. The results are, however, consistent with a hypothesis that a low level of infection is indicative of the overall healthy condition of a male. If this is true, it supports the hypothesis that the ability to hold a bower may be an indicator of male condition to females.

Feather stealing in the satin bowerbird ( Ptilonorhynchus violaceus): male competition and the quality of display

Male satin bowerbirds use feathers to decorate their bowers and often steal feathers and other decorations from the bowers of other males. Decorations are a key element in sexual display and tracking their movement between bowers provides the first detailed information about this unique pattern of sexual competition. For two field seasons the movement of marked feathers was followed. Males varied greatly in stealing activity. The most active feather thieves were often from areas where bowers were close together and they were involved in reciprocal stealing with males at adjacent bowers. The rate of stealing by males was significantly correlated with the number of feathers on their bowers. This suggests that stealing is important in determining the level of bower decoration and mating success. Patterns of stealing behaviour support models of sexual selection which suggest that male interactions are important in influencing female choice through their effect on the quality of male display.

Bower destruction and sexual competition in the satin bowerbird (Ptilonorhynchus violaceus)

Male satin bowerbirds often destroy the bowers of other males. Bowers are a key element in male sexual display and their destruction represents a unique pattern of sexual competition. For two mating seasons bowers of displaying males were continously monitored to produce a complete record of bower destructions. The number of destructions at bowers and the amount of destruction of bowers were invesely correlated with bower quality. The best predictor of male bower destroying behaviour is male aggressiveness at feeding sites. Males directed most destructions at adjacent bower sites. These results show that male interactions are important in determining differences in the quality of display among male satin bower-birds, and are consistent with the view that females use bowers as indicators of male quality in mate choice.

Bower quality, number of decorations and mating success of male satin bowerbirds ( Ptilonorhynchus violaceus): an experimental analysis

Bowerbirds build large bowers of twigs decorated with brightly coloured objects at display sites where males court females. The bower and its decorations are hypothesized to influence female choice in these birds. However, there have been no empirical tests of this hypothesis. Data from two years of field research on the satin bowerbird ( Ptilonorhynchus violaceus) show: (1) an extremely skewed distribution of matings among males, and (2) a consistent pattern of female preference for particular males, especially those with well-constructed, highly-decorated bowers. These results support the hypothesis that bower quality is important in influencing female mating preferences. In particular, they support the ‘marker’ hypothesis, which suggests that the construction of bowers evolved to provide females with information about the relative quality of males.

Distribution of Bowers of the Satin Bowerbird at Leura, NSW, with Notes on Parental Care, Development and Independence of the Young

SUMMARYVellenga. R. E. 1980. Distribution of bowers of the Satin Bowerbird at Leura, NSW, with notes on parental care, development and independence of young. Emu 80: 97–102.Three primary territories owned by old dominant male Satin Bowerbirds were known in the neighbourhood of Leura, NSW. Male 85, which we observed most, disappeared (? died) in 1970, probably after fifteen years' occupation of his bower. Several changes in ownership of bowers occurred at about the time of his disappearance and another male from six kilometres away eventually replaced him and was dominant at his bower. Males take no part in nesting activities. The nestling period was about nineteen days in one nest. The female at that nest fed nestlings about six times an hour when the young were about a week old but only three times an hour six days later. On fledging, the young were conducted to a nursery area where they were attended by the female for at least fifty-nine days after fledging. The characteristics of this species seem to agree with those postulated by Gilliard (1963) for arena species.