Morphometrics and Flight Performance of Southern African Peregrine and Lanner Falcons

Abstract

Twenty-four morphometric parameters were measured from samples of live southern African Peregrine Falcons Falco peregrinus minor and Lanner Falcons F. biarmicus biarmicus. The two species were different in most measurements, especially those relevant to prey capture and handling techniques, and flight performance (bill size, foot size, wing span, wing area, tail length and wing loading). Flight performance parameters calculated from mensural data predicted significant differences in the flying abilities of the two species, notably that Peregrines should fly faster in level powered and gliding flight, but incur greater fuel costs in terms of both time and distance flown. Peregrines should glide less efficiently and be restricted in their ability to soar in thermals. These predictions were compared with observations of Peregrines and Lanners under uniform environmental conditions, and mostly were confirmed. Peregrines flew faster but for less time, flapped more and soared in thermals less than Lanners. Theoretically, Peregrines should tend more towards sedentary perch hunting than Lanners, and be more habitat selective as a result. Observations and distributional data from South Africa corroborate this. Form and functional differences in these two falcons are relatable to differences in foraging mode, distribution and abundance. I suggest that similar inferences may be drawn from morphological comparisons of other large falcons to provide proximal explanations for broad-scale patterns of distribution.