White-breasted Hawk

Accipiter chionogaster

Please send me photos and information on this species so that I can build up a more detailed database.

The taxonomy of the White-breasted Hawk has never been fully sorted out. The AOU currently lump it (and the rest of the superspecies) as Sharp-shinned Hawk Accipiter striatus, though acknowledge that this is based on the lack of research done on most of these forms. All of the field guides that cover Northern Central America consider the White-breasted hawk to be a separate species Accipiter chionogaster. Some authors in the past, eg Dickey and van Rossem (1938) lumped the three Neotropical forms as Rufous-thighed Hawk Accipiter erythronemius, but as a separate species distinct from Sharp-shinned Hawk of North America. This was based on the fact that all of the Neotropical forms have paler unstreaked underparts (at least in some variants) and buff to red coloured, unbarred thighs. Storer (1952) studied skins from Mexico and described a cline in the paleness of the underparts from north to south Mexico, with the form madrensis being almost as pale as chionogaster. I have never seen this form, but a friend of mine, Jesse Fagan, recently saw one in Oaxaca (southern Mexico) and stated that it was very similar to chionogaster. I have studied the skins in the British Museum’s collection at Tring (see attached photo), where they have many specimens of sharp-shin from Mexico. None of them show the pale underparts described by Storer, but the dates (where they exist) indicate that most were taken in the winter months and so could represent migrant sharp-shins from further north, rather than resident birds.

Food
The main food of White-breasted Hawks is small to medium sized birds, though larger species (up to the size of Band-tailed Pigeon) are also taken. Species identified to date include: Band-tailed Pigeon, Barred Ant-Shrike; Brown-backed Solitaire, White-winged Dove, Black-throated Green Warbler, Rufous-naped Wren, Swainson’s Thrush, Magnolia Warbler and Cley-coloured Thrush. It has been hard to identify many of the kills directly, so most of these identifications were made from feathers found at plucking posts near the nest. I have also seen them eat a lizard and a bat. This is clearly not atypical as a friend, Oliver Komar, also observed one trying to catch a lizard.

Breeding
I have seen birds displaying from the end of December until early February, though it may well extend beyond these times. The display flight is similar to that seen in other Accipiters, with the birds diving downwards on closed wings and then swooping back up, before diving down again. On April 20th, and therefore well into the nesting season, I saw a bird circling up very high then making a slow gliding flight and rocking from side to side, which had the effect of flashing the white underparts. I have only seen this once, but it is interesting because it showed off the one feature that distinguishes the White-breasted Hawk from the Sharp-shinned Hawk. The individual followed this flight with a long dive towards a steep ridge, where it pulled up then circled back up high and flew off into the distance.

The earliest observed nest building was on Feb 7th, when the nest was already well under construction. This nest was still a fair way from completion by 20th March. Most nest-building takes place in the mornings, with both the male and the female bringing material, but the female doing most of the actual construction and bringing the larger branches.
The two nest sites, with two nest trees at each site, were both located on the brow of a steep pine covered ridge. All four nests were in pine trees (Probably all Pinus oocarpa) between 20 and 28m from the ground. The nests were constructed of pine and deciduous twigs (eg Quercus), the latter of which being taken from small bushes in the open forest under-storey. The nests were variable in shape; the two in Honduras were flat platforms on small branching side branches. The other two were a deeper cone shape located in a fork with the nest up against the truck. They were all just over 30cm in diameter and between about 20 to 30 cm in depth. They have a shallow depression with a loose lining of bark, though this depression is less evident after the growing chicks have trampled into more of a flat platform. The nest trees were never the largest in the vicinity and the nests were located between two-thirds and three-quarters of the way up the trees.

The four nests studied to date had 2 or 3 eggs. The eggs are subelliptical in shape; the ground colouration was very pale bluish white, marked with mostly rusty brown, but sometimes dark brown, spots and blotches. The markings vary in extent, even within a clutch, from a few small specs to large blotches covering around 25% of the surface. The markings are randomly distributed about the egg. Of five eggs that have been measured, the wieght averaged 20.8g, the length averaged 38.5mm and the width averaged 31.3mm

Moult
The molt follows a similar pattern to other Accipiters, such as Sharp-shinned Hawk. Very young chicks had thin white down. As with other Accipiters, older chicks have a second growth of down. This was evident in H03 where both chicks had white down when only a few days old, but two weeks later one had white down and the other mostly grey coloured down. The bird with white down was slightly the larger of the two, but they could not be sexed at this age so it is not evident if this is a difference between the sexes, or just individual variation.
Females do a suspended moult during incubation; the amount varying between individuals. They tend to lose most of their tail feathers and inner primaries, leaving around 4 outer primaries unmoulted. They also seem to lose most of their body feathers and tertials, though the extent has been hard to determine from field observations. No males have been observed to moult during the nesting time. A couple of skins of males in the British Museum were showing some moult in August and September, suggesting that they wait until the chicks have fully fledged before starting. Presumably, the females complete their moult at this time as well.

Known sites

Guatemala
Rubbish dump site with Jason
Known from Biotopo del Quetzal

Honduras
Celaque
La Muralla
La Tigra
Also seen at Campamento in Olancho

El Salvador
El Pital
Perkin
Known also from La Montañona

Storer, R. W. (1952) Variation in the resident Sharp-shinned Hawks of Mexico. Condor, 54, 283-9.

Webber, T. and Brown, J. L. (1994) Natural history of the Unicolored Jay in Chiapas, Mexico. Proc. West. Found. Vert. Zool. 5(2):135-160.