The Common Black-Hawk usually scans for prey from a perch and, when a potential quarry is identified, will drop from its perch to make the kill. The hunt follows a step down approach with the location of a general foraging area the first decision. The hawk will typically alight on a high perch within the foraging zone and scan the area. If a possible target is detected, the hawk will move to a closer perch, and continue to do this until it is in striking distance. From this vantage point the hawk will mount its final attack in swift fashion. If the kill is made in water, the hawk will extend its talons only the length of the legs and will not risk getting its feathers wet. Other hunting strategies are employed, such as standing in water and "herding" fish into the shallower reaches, and catching birds in mid-flight.
It is not clear if pair formation has occurred before arrival at a nest site. In one instance a male was observed performing courtship displays for one week before a female arrived. Once paired, the hawks will perform a number of ritualized flights above the nest stand. These range from circling at high elevations with wings held in a dihedral, to a daring close encounter as one bird stoops (reportedly the male) with legs dangling and narrowly missing the other bird. In one thrilling observation, the male was observed soaring high above the nest stand when it folded its wings and dropped in full stoop, just breaking its fall before a branch, which it broke off with its feet. Whether this was a symbolic act or just the gathering of nest materials is not known. Noisy, raspy calls reminiscent of night herons is often heard during the nesting season. Copulation occurs within 50 to 300 feet (15.5 to 93 meters) of the nest with the male swooping down directly on the female or landing beside the female and then mounting. Copulation rate increases as egg laying nears.
The Common Black-Hawk vigorously defends the nest site from others of their kind. The conflicts are usually most severe at the onset of the nesting season. Aerial combat consisting of calling, chasing, and locking up of talons has been observed.
Like other raptors, the Common Black-Hawk will aggressively defend its nest site from other raptors such as Golden Eagles, Red-tailed Hawks, Peregrine Falcons, vultures, and ravens. Great Horned Owls are implicated in deaths to nestlings.
The oldest age known for the Common Black-Hawk is 13 years six months.
ADAPTATIONS
As with other Falconiformes, the Common Black-Hawk exhibits reversed size dimorphism where the female tends to be larger than the male. There are many benefits to this adaptation, but the underlying cause is not known. Reversed size dimorphism is most pronounced in species which pursue fast moving prey. For example, in the Sharp-shinned Hawk, a specialist of small songbirds, the males are 40 percent smaller in body size and can be 50 percent smaller in body weight than females. The Common Black Hawk, which pursues slow moving prey, is only weakly dimorphic, a probable reflection of their slow moving prey.
Their exceptionally broad wings, relative to other broad winged hawks like the buteos, is interesting. A high wing surface area to volume ratio suggests that this bird would be a superior soarer, being able to obtain good lift, but since it does not hunt from the wing this benefit is not obviously employed.
