Moult, flight performance and wingbeat kinematics during take-off in European starlings Sturnus vulgaris

The effects of natural moult on avian flight performance have received relatively little attention, yet moult is an important part of the annual cycle. Quantification of flight costs will help to explain the diversity of moult patterns observed in avian taxa. Take-off from the ground requires a high power output from the flight muscles compared to other modes of flight, and is an important feature of foraging and predation escape. The present study was designed to quantify the effect of natural moult and new plumage on the take-off strategy, kinematics, and flight performance of European starlings Sturnus vulgaris. A high-speed (185 Hz) cine camera was used to film seven European starlings on three occasions: session 1, two weeks prior to the onset of moult; session 2, during mid-moult; and session 3, two weeks after full plumage had re-grown. From subsequent film analysis, we assessed take-off speed and angle, the energy gained per wingbeat, and wingtip kinematics. Take-off strategy (measured by angle and speed) altered through the course of the three experimental sessions, i.e. ascent angle decreased and take-off speed increased. Energy gained per wingbeat did not vary, suggesting there was no significant decrease in flight performance due to moult, but there was a significant improvement in take-off performance due to renewal of flight plumage. Wingbeat amplitude increased in association with moult and after flight plumage had been completely renewed. The European starlings incurred relatively minor flight costs due to moult, when comparing before-moult with during-moult take-off performance. The apparent absence of additional flight costs associated with moult may reflect a decreased mechanical performance of year-old feathers (which are replaced during the moult) and may also help to explain the relatively long duration of the moult in this species. This study also provides evidence of the benefits of plumage renewal, as take-off performance is improved after moult has been completed.