The Short-tailed Hawk is unique within the genus Buteo in that its prey selection is primarily birds. Most buteos, with their broad wings, typically forage on small mammals, such as rodents and rabbits, as their aerodynamic design is not suited for the aerial pursuit of birds as is typical of falcons and accipiters. Although the Short-tailed Hawk has the overall body design of a Buteo, it has a behavioral adaptation unique to itself. By riding wind currents, which are deflected upwards at the interface between open areas and woodland, it is able to hang motionless in the air waiting for a bird to alight atop one of the trees. When this happens, the hawk will dive on the prey. If it misses, it will not pursue, probably because the buteo body design is not suited to give chase in woodlands like the accipiter.
The Short-tailed Hawk flies actively with strong, stiff wingbeats. It soars with wings held in a slight dihedral and glides on flat wings. In the "hanging" position the hawks' head is pointed down, the wings appear stiff and flat, and the tips of the primary feathers are upturned.
The selection factor for the light and dark phases is not understood. In terms of sexual selection, there does not appear to be any assortative mating based on color of the bird, with numerous observations of like-morph and between-morph pairing. There is some evidence which might suggest that there is a heritable trait related to sex which determines color phase. Of 12 specimens known to be male, all were dark and of 11 known to be female, eight were light. More observations are needed to confirm this trend.
This species is present year-round within Florida, although there is movement for at least a portion of the population off their breeding grounds to nonbreeding grounds. Fall migration occurs in mid October and involves populations from central to north peninsula. Correspondingly, the number of Short-tailed Hawks increases in southern Florida in winter. Spring movements back to breeding grounds occurs in February and March.
There is little information pertaining to the breeding behavior of this species. As in other hawks, there is an elaborate flight pattern often called the "sky dance" where both members of the pair perform aerial acrobatics which signify ownership of a territory. The male in this species has been observed flying in an undulating fashion suggesting a roller coaster. This flight is interspersed with steep dives of rolling spirals accomplished by opening and closing the wings. The male has also been observed carrying nesting material or prey which has been interpreted as symbolic for the female, because copulation occurred after the male landed beside the female. The male calls out during copulation.
ADAPTATIONS
The Short-tailed Hawk has two adaptations unique to its buteo body design which probably allows it greater advantage for capturing birds. The first is that it is small, only about crow size. A small body size allows greater mobility and maneuverability when chasing agile birds. The other adaptation is a relatively large foot which, when one considers that it makes only one attempt on any one prey item, is probably beneficial to have as great as possible surface area to increase the probability of successful capture.
