The Effect of Simulated Flight Feather Moult on Escape Take-Off Performance in Starlings

Abstract

We investigated the effects of the plumage changes associated with moult on the anti-predator take-off performance of European Starlings Sturnus vulgaris. By altering the plumage to simulate moult, we have isolated the biomechanical consequences of changes in wingform from the underlying physiological and metabolic changes that may occur during natural moult. Previous analyses 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 of overall take-off performance. The advantages of this measure compared with previous approaches are that it summarises the potential trade-off between height gain and speed gain, and can be related directly to lift on the wings. Analysis of high speed (100 Hz) video tapes indicated that birds in simulated 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 pattern of movement of the wingtip during flight; moult-manipulated birds appear 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 able to regain, in part, their flight performance within 6 days of the manipulations, as take-off speeds returned to pre-manipulation levels. This partial return to pre-manipulation flight performance was associated with an alteration in pattern of movement of the wingtip during take-off. The relevance of this adaptation to birds in natural moult is discussed. Any reduction in 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 moult in wild birds.