THE EFFECTS OF MOLT ON THE FLIGHT PERFORMANCE, BODY-MASS, AND BEHAVIOR OF EUROPEAN STARLINGS (STURNUS-VULGARIS) - AN EXPERIMENTAL APPROACH

The physiological and energy costs of avian molt are well documented, but indirect consequences such as changes in flight performance have r eceived less attention. Here, we report two experiments that investiga ted flight performance, body mass regulation, and behavior in captive starlings (Stumus vulgaris). In the first experiment, we found a U-sha ped change in take-off escape performance during natural molt: birds a scended at the shallowest trajectories during midmolt. Birds' body mas s was also reduced during molt. In the second experiment, we manipulat ed the plumage of starlings to simulate different stages of flight-fea ther molt. This allowed us to separate the aerodynamic costs of feathe r loss from the physiological costs of feather synthesis normally asso ciated with plumage growth. Through observations of flight (take-off, aerial maneuverability, and level flapping-flight speed) and behaviora l parameters, we demonstrated that birds in simulated molt have reduce d night performance and reduced body mass. These birds also decrease t he time spent performing energetically costly activities and seek area s of relative protection. In the longer term, some aspects of performa nce return to pretreatment levels, implying compensation for the pluma ge manipulations. Our results demonstrate. that molt incurs significan t functional costs that may play an important role in the adaptive rad iation of molt strategies and molt patterns observed in avian species.