Nest‐dwelling ectoparasites influence the start and duration of the first pre‐basic moult in the European starling Sturnus vulgaris

Nest‐dwelling ectoparasites represent an early stressor for birds as they impair the development of nestlings, which can adaptively respond by adjusting their growth rate to current conditions. While nest ectoparasites have long‐term effects on nesting adults, no study has examined if they also have an impact on the moult patterns of juveniles. Herein, we investigated whether the presence of ectoparasites in the nest influences the start and duration of the first pre‐basic moult in the European starling. To do so, we experimentally removed nest‐dwelling ectoparasites from a group of nests and used another group of unmanipulated (i.e. naturally infested) nests as the control. The moult began at an earlier age and lasted longer in birds from the ectoparasite‐free nests compared to their control counterparts. The timing of the moult was also affected by the hatching date (i.e. birds that fledged later had shorter moults) and the brood size (i.e. birds in larger broods started their moult at an older age). We also found evidence that the removal of nest ectoparasites influenced the condition of individuals during the course of the moult. In the control birds, we observed a decrease in hematocrit levels, but these were unaltered in the birds fledged from the ectoparasite‐free nests. Our study shows that nest‐dwelling ectoparasites adversely affected the timing of the moult and the individual condition of juvenile starlings, with possible major consequences for their subsequent life‐history events.