European Starling ( Sturnus vulgaris ) parents call less often as their nestlings age

Contact calls made by a provisioning parent approaching the nest increase provisioning efficiency whether the calls are directed to offspring to elicit begging or to a brooding mate to coordinate parental care. Songbird nestlings are completely dependent on parents for care, as they hatch blind, helpless, and unable to thermoregulate. We studied how often parent European Starlings (Sturnus vulgaris) vocalized when approaching their nest boxes in Halifax, Nova Scotia, Canada. We recorded audio of seven early-season and four late-season broods across four nestling ages (days 2, 4, 11, and 13) to determine whether parents called when arriving at the nest box and whether the other parent was in the box. We predicted parents would call more often when nestlings were young (days 2 and 4) than when older (days 11 and 13), either to elicit begging by the blind nestlings or to alert their mate to exit the box. If calls were directed to nestlings, then we predicted that calling would be unrelated to whether the other parent was in the nest box. If calls were directed to their mate, we predicted that the provisioning parent would call more often when the other parent was in the nest box. As predicted, parents called significantly more often when nestlings were young (62% of visits on day 2, 36% on day 4) than when older (4% of visits on day 11, 4% of visits on day 13), although parents reduced their calling earlier (day 4) in late-season broods (50% of visits in early- and 17% in late-broods). Parents called on a higher proportion of visits when the other parent was in the nest (85% of 68 visits) than when they were not (17% of 877 visits). Our results suggest that the intended recipient of calls is the other parent rather than the nestlings. Flexible communication at the nest would be adaptive as parents can call when nestlings are young to increase parental coordination and provisioning efficiency, then stop calling when nestlings are older as it is no longer required and could be costly in terms of predation risk.