The breeding range of the white-breasted hawk and the sharp-shinned hawk is entirely allopatric, although the wintering range only partially overlaps. This allopatry combined with differences in plumage and, apparently, certain measurements, has been the background for the split, but hard scientific data is presently lacking. Disregarding field guides, most material published in recent years has therefore considered all to be members of a single widespread species – but not without equivocation: Ferguson-Lees et al. say that if they were to make a world list, they would include the three taxa as separate species, and the AOU's comment includes the note "split almost certainly good". Storer suggested that the southernmost populations of sharp-shinned hawk were paler below, thus approaching chionogaster. This has also been reflected in recent guides, where A. s. madrensis of southern Mexico is described as being relatively pale below, but if this is a sign of intergradation with chionogaster or a north-south cline which includes both the members of the nominate group and chionogaster remains unclear. The two syntype specimens of Nisus chionogaster Kaup are held in the collections of National Museums Liverpool at World Museum, with accession numbers D392 and D392a. The specimens were collected in Cobán, Guatemala in June 1843 by Adolphe Delattre and came to the Liverpool national collection via the 13th Earl of Derby’s collection which was bequeathed to the city of Liverpool.
Description
This is a small Accipiter hawk, with males long, with a wingspan of and weight from. As common in Accipiter hawks, females are distinctly larger in size, averaging some 30% longer, and with a weight advantage of more than 50% being common. The female measures in length, has a wingspan of and weighs. The wings measure each, the tail is long and the tarsus is. Measurements given here are for the northern group, but they are comparable for the remaining species in the group. Adults have short broad wings and a medium-length tail banded in blackish and gray with the tip varying among individuals from slightly notched through square to slightly rounded. The remiges are whitish barred blackish. The legs are long and very slender and yellow. The hooked bill is black and the cere is yellowish. The remaining plumage varies depending on group: The white-breasted hawk resembles the sharp-shinned hawk, but upperparts darker, thighs whitish-buff and underparts and cheeks entirely white. Juveniles have darker upperparts and distinctly finer streaking below than juveniles of the nominate group.
Distribution
It occurs in highlands from far southern Mexico, through Honduras, Guatemala and El Salvador, to Nicaragua. It is, as far as known, resident, but some local movements may occur.
Habitat
They are most commonly found in pine and pine-oak habitats, regularly visiting neighbouring cloud forest, tropical dry forest and farmland; mainly at altitudes of.
Diet
These birds surprise and capture most of their prey from cover or while flying quickly through dense vegetation. They are adept at navigating dense thickets, although this hunting method is often hazardous to the hawk. The great majority of this hawk's prey are small birds, especially various songbirds such as wood-warblers, wrens, and thrushes. Typically, males will target smaller birds, such as wood-warblers, and females will pursue larger prey, such as doves, leading to a lack of conflict between the sexes for prey. They often pluck the feathers off their prey on a post or other perch. Rarely, white-breasted hawks will also eat lizards, bats, and large insects.
Reproduction
White-breasted hawks construct a stick nest. Clutches of 2 to 4 eggs have been recorded. The eggs measure and weigh about. The incubation period is thought to average at about 30 days. After hatching, the young are brooded for 16 to 23 days by the female, while the male defends the territory and catches prey. The young fledge at the age of about a month and rely on their parents for feeding and protection another four weeks. The breeding behavior of the taxa are comparably poorly known, but based on the available knowledge they appear to differ little from that of the sharp-shinned hawk.
Conservation
The situation for white-breasted hawk is more problematic due to its limited range, although it, at least locally, remains fairly common.
