Meeting Abstract
Smaller flight muscles and longer legs are characteristic of island birds, but the consequences of this morphology on performance are unknown. We tested how reduced flight muscles and longer legs affect take-off performance. We measured flight kinematics and leg thrust forces for take-offs of wild birds on the islands of Trinidad and Tobago using a custom-built perch and a high-speed video camera. The large island of Trinidad is continental in its avifauna and predators, while birds on smaller Tobago have reduced pectoral flight muscles and longer legs, and experience lower predation pressures. We found that birds on Tobago had slower maximum velocity (p=0.008) and maximum acceleration (p=0.01) during take-off relative to conspecifics on Trinidad. Initiation of wingbeats occurred later during take-off in populations on the island of Tobago in two species, the hummingbird Amazilia tobaci and flycatcher Mionectes oleagineus. Lower predation pressures on small, species-poor islands likely permit the slower take-off velocities that result from island birds’ reduced flight muscles. Our study produced a novel comparative dataset of take-off mechanics for 16 species from five orders, ranging in body size from 4.1g to 130g. Across this sample, maximum take-off velocity scaled with body mass to a power of 0.16 potentially offsetting adverse scaling of induced power requirements. Pectoral flight muscle mass ranged from 12% to 33% of total body mass. This relative flight muscle size correlated with the timing of wingbeat initiation (p<0.001), with larger-muscled birds beginning the first wingbeat earlier in take-off. Birds with larger flight muscles reached peak acceleration later in take-off (p=0.008), as expected if wings were more important contributors to take-off acceleration in species with large pectoral muscles.
