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Ecomorphology of Rufous Hummingbirds : an investigation of maneuverability and agility in four age-sex classes

University of British Columbia

Low and high velocity turning was investigated in four age-sex classes of rufous hummingbirds (Selasphorus rufus ). In the field, adult males outcompete all other age-sex classes for territories and it is assumed in the literature that adult males are more maneuverable (Feinsinger and Chaplin 1975, Kodric Brown and Brown 1978, Carpenter et al 1993 a,b). Using two experiments and a review of the flight literature, this thesis investigated high and low velocity turning in rufous hummingbirds. Rufous hummingbirds are sexually dimorphic in the length and shape of their wings. Adult males have short, narrow wings as compared to the females' long and broad wings. Juveniles of both sexes have longer wings than the adults. Wing disc loading is the ratio of mass to wing length and varies among classes as wing length varies. It has been assumed in the literature that birds with higher wing disc loading (adult males) are the most maneuverable. This assumption has led to numerous statements in the literature concerning the superior flight performance of adult male rufous hummingbirds. In a low velocity turning experiment, birds flew back and forth between two feeders 0.5 m apart. A computer recorded the elapsed time between feeders and a video camera recorded all flights from above. The average elapsed time recorded by the computer determined that juvenile females were the fastest of all four age-sex classes. The short-winged adult males were the slowest group and the adult female and juvenile males, which have similar wing lengths, had similar average elapsed times. The results were confirmed with the video data: adult males had the lowest maximum velocities and juvenile females the highest. These results clearly contradict those predicted in the current hummingbird literature. In a high velocity turning experiment, birds flew through a 4.8 m tunnel with 3 barriers that required the birds to alter their flight path en route to the feeder. The computer recorded the elapsed time between the perch and feeder and feeder and perch. Adult males flew faster flying from the feeder to the perch than all other age-sex classes. However, the classes did not differ significantly in elapsed time from perch to feeder. Adult males were the top performers in both angular and translational velocity during flights through the barriers towards the feeder. These results are predicted by current aerodynamic theory for bats and birds with non-hovering flight. An early chapter of this thesis examines the misuse of the terms maneuverability and agility throughout the hummingbird literature. Aerodynamic predictions concerning turning performance in hummingbirds have not been tested prior to this thesis. As these are the first measurements of maneuverability and agility in hummingbirds I feel that it is necessary for these terms to be operationilized for future use in hummingbird research.

Thesis/Dissertation

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2009-03-26

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http://hdl.handle.net/2429/6568

Zoology

University of British Columbia

UBCV

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