PLUMAGE CONDITION AFFECTS FLIGHT PERFORMANCE IN COMMON-STARLINGS - IMPLICATIONS FOR DEVELOPMENTAL HOMEOSTASIS, ABRASION AND MOLT

Variation in length and asymmetry of wing primary feathers can arise f rom a breakdown of developmental homeostasis, feather abrasion and inc omplete growth during moult. Indirect predictions have been made conce rning the impact of primary length and asymmetry on the flight ability of birds, but they have not been explicitly rested. Here we provide e vidence from both natural variation in primary feather condition and e xperimental manipulations of primary feather length and asymmetry to i ndicate that these factors influence aspects of flight performance in the Common Starling Sturnus vulgaris. Damaged and incompletely grown p rimary feathers reduce escape flight performance. Experimentally reduc ed primary lengths reduce take-off speed; increased primary asymmetry decreases aerial manoeuvrability. A comparison of the experimental and natural plumage data indicates that birds may be able to adapt to a c hange in wing morphology, perhaps reducing the effects of feather loss or damage on flight. The results from this study indicate that primar y feathers are under strong stabilising selection to maximise developm ental homeostasis and reduce feather asymmetry. These findings are als o of ecological importance to the damage-avoidance and moult strategie s of these birds. This is the first experimental evidence to indicate a quantitative reduction in flight performance with feather lengths an d asymmetries typical of those observed during flight feather moult an d feather damage in any species.