Breeding behaviour and ecology of the grey fantail (Rhipidura albiscapa)

The grey fantail (Rhipidura albiscapa) is a common Australian flycatcher, yet no detailed reports have been made of its breeding ecology. A population of grey fantails was studied over four seasons in the Australian Capital Territory. Males had large testes and pronounced cloacal protuberances, morphology suggestive of sperm competition. Although two polyandrous trios were observed, most individuals bred as part of a season-long monogamous pair, suggesting that extra-pair copulation may be the principal cause of sperm competition. Indeed, behavioural observations revealed that males regularly intruded other territories, targeting those with building, rather than incubating, females. Intruding males were observed harassing, attempting to copulate and successfully copulating with resident females. Males did not mate guard, but regularly attacked their mates during each building attempt. Despite the probability that extra-pair paternity is common in this species, grey fantails were monomorphic and monochromatic, with a high level of paternal care. Nest depredation was common, with 83% of all clutches depredated before fledging. High levels of male care in care in this species may be better explained by an increase in fledging success associated with high male contribution to offspring care than confidence of paternity.

Repeatability of parental effort in male and female Pied Flycatchers as measured with doubly labeled water

Intensity of parental care is one of the critical factors affecting offspring growth and final size and thus is a key variable in life-history evolution. In the study population of Pied Flycatchers (Ficedula hypoleuca), it was previously shown that maternal daily energy expenditure was an important source of variance in offspring size and likelihood of infection by blood parasites. Thus, energy expenditure may be considered a parental-performance effect, and variation among females in the intensity of parental care they provide might itself be influenced by genetic differences, affording the opportunity for evolutionary change. To address whether parental work load is a consistent trait and thus may retain additive genetic variance, the same individuals were scored for mass-independent daily energy expenditure (DEE) across two consecutive breeding seasons, while feeding nestlings close to fledging. While DEE of females was significantly repeatable between years, this was not the case for males. DEE may retain additive genetic variance in females, although its expression may be obscured in males by their less constrained activity budgets and lower confidence of paternity.