Incubation behaviour and hatching synchrony differ in wild and captive populations of the zebra finch

Hatching asynchrony is widespread in birds laying clutches containing multiple eggs, yet is seemingly paradoxical as the age and size hierarchies result in asymmetric sibling competition and low survival prospects for late-hatched nestlings. We examined the causes of variation in hatching asynchrony between broods of zebra finch, Taeniopygia guttata, in three environments: domesticated, captive wild and wild free-living. We found that broods of both domesticated and wild birds taken into captivity hatched more asynchronously than wild free-living broods. This was directly attributable to both male and female parents of domesticated and captive wild broods initiating incubation as soon as the first egg was laid as opposed to when the clutch was virtually complete in wild free-living broods. Wild free-living birds that were transferred to captive environments immediately switched to the incubation onset behaviour seen in domesticated birds, thereby demonstrating a previously unsuspected level of intraspecific plasticity in incubation behaviour. This finding suggests that something about the captive environment is driving the early onset of incubation and contributing to an elevated level of hatching asynchrony in captive birds. Across all populations and environments males contributed almost equally to incubation, and the onset of incubation by males was highly coordinated with that of their partner.