The effect of simulated flight feather moult on escape take-off performance in starlings

We investigated the effects of the plumage changes associated with moult on the anti-predator take-off performance of European Starlings Sturnus vulga ris. By altering the plumage to simulate moult, we have isolated the biomec hanical consequences of changes in wingform from the underlying physiologic al and metabolic changes that may occur during natural moult. Previous anal yses of avian take-off performance have relied on descriptive observations of wingtip kinematics or dual measures of take-off speed and angle. We have developed a novel method using the energy gain per wingbeat as a measure o f overall take-off performance. The advantages of this measure compared wit h previous approaches are that it summarises the potential trade-off betwee n height gain and speed gain, and can be related directly to lift on the wi ngs. Analysis of high speed (100 Hz) video tapes indicated that birds in si mulated moult suffer a reduction in total energy produced during the second wingbeat of take-off, resulting in a slower take-off speed. This reduction in take-off performance is also associated with a marked change to the pat tern of movement of the wingtip during Eight; moult-manipulated birds appea r to reverse the wingtip at the top of the downstroke although there is no associated change in wingbeat amplitude or duration. Birds appeared to be a ble to regain, in part, their Eight performance within 6 days of the manipu lations, as take-off speeds returned to pre-manipulation levels. This parti al return to pre-manipulation Eight performance was associated with an alte ration in pattern of movement of the wingtip during take-off. The relevance of this adaptation to birds in natural moult is discussed. Any reduction i n take-off performance is likely to influence directly individual behaviour and survival; hence the ability to quantify take-off in different species under a common currency is of general ecological importance and will enable predictions to be generated and tested concerning the effects of natural m oult in wild birds.