Typically, both sexes of the black sparrowhawk have a predominantly black
plumage with a white throat, breast and belly. These white-breasted individuals are known as "white morphs" which are in the majority over most of the birds' range. The "black morph" variety is generally rare, (Black sparrowhawks do not occur more than about 200–300 km north of
Cape Town along the South African west coast, where there are almost no trees.) These "black (or dark) morphs", when seen perched, can be black all over, but more commonly have a few white spots on the breast or a white throat of variable size. In flight both morphs show white and black barring on the underside of the wings and tail (see picture). The black morphs are not
melanistic, as commonly alleged, as their plumage is not completely black, nor are they black as chicks or juveniles. There is no noticeable difference between the
plumage of mature females and males, which can only be distinguished by size. Young chicks have mid-grey eyes and white down, but when the feathers erupt they are predominantly brown. The full plumage of juveniles is a range of browns and
russets with dark streaks along the head and, more conspicuously, down the chest. Commonly there are white or light-colored spots and streaks as well, mainly on the wings. The typical total length is about and wingspan about . As in most hawks, the tails are long (about ), as are the
tarsi (about . Dark morph black sparrowhawks might be more common on the
Cape Peninsula due to
pleiotropic properties of the genes that code for dark colouration, meaning that they code for an apparently unrelated trait. In the dark morph black sparrowhawk, those genes are also responsible for an improved blood parasite resistance compared to the light morph. The species breeds during the dry season in most parts of South Africa, but during the wet season on the Cape Peninsula, where
blackflies and
biting midges which transmit the
haematozoan blood parasites (
Leucocytozoon toddi and
Haemoproteus nisi), may be more abundant. So, on the Cape Peninsula, black sparrowhawks gain a
selective advantage from a dark colouration. When it comes to breeding on the Cape Peninsula, the morph combination of the parents also influences their productivity. Mixed-pairs produce more offspring per year than pairs of the same morph, but this happens at the expense of the chicks' body condition. It has also been observed that dark morph black sparrowhawks have a higher hunting success in lower light conditions, while white morphs catch more prey in brighter conditions. This suggests, that the different morphs have a better
crypsis (so that prey cannot detect them) at different light levels. ==Distribution and habitat==