Aerobic capacity in wild satin bowerbirds: repeatability and effects of age, sex and condition

Individual variation in aerobic capacity has been extensively studied, especially with respect to condition, maturity or pathogen infection, and to gain insights into mechanistic foundations of performance. However, its relationship to mate competition is less well understood, particularly for animals in natural habitats. We examined aerobic capacity [maximum rate of O-2 consumption ((V) over dot(O2,max)) in forced exercise] in wild satin bowerbirds, an Australian passerine with a non-resource based mating system and strong intermale sexual competition. We tested for repeatability of mass and (V) over dot(O2,max), differences among age and sex classes, and effects of several condition indices. In adult males, we examined interactions between aerobic performance and bower ownership (required for male mating success). There was significant repeatability of mass and (V) over dot(O2,max) within and between years, but between-year repeatability was lower than within-year repeatability. (V) over dot(O2,max) varied with an overall scaling to mass(0.791), but most variance in (V) over dot(O2,max) was not explained by mass. Indicators of condition (tarsus and wing length asymmetry, the ratio of tarsus length to mass) were not correlated to (V) over dot(O2,max). Ectoparasite counts were weakly correlated to (V) over dot(O2,max) across all age-sex classes but not within any class. Adult males, the cohort with the most intense levels of mating competition, had higher (V) over dot(O2,max) than juvenile birds or adult females. However, there was no difference between the (V) over dot(O2,max) of bower-owning males and that of males not known to hold bowers. Thus one major factor determining male reproductive success was not correlated to aerobic performance.