Comparative biology of the forest-inhabiting hawks Accipiter spp. in the Democratic Republic of Congo

Abstract

The four Accipiter species in the equatorial forest of the Democratic Republic of Congo (from small to large: Red-thighed Sparrowhawk A. erythropus, Chestnut-flanked Sparrowhawk A. castanilius, African Goshawk A. (tachiro) toussenelii and Black Sparrowhawk A. melanoleucus) were studied in the field, as to crop and stomach contents, fat storage, and behaviour. Museum specimens (in the Royal Museum for Central Africa, Belgium) were also examined for the purpose of studying morphometry, sex- and age ratios, and moult. Insects, amphibians, reptiles and mammals were found in the crops and stomachs of the three smallest species, but no birds were found, which is surprising and perhaps due to poor identification prospects. The variation in prey demonstrates the large diet; ecological separation between species must be based mainly on behavioural differences. Storage of fat in adult females (perhaps in the pre-breeding phase) and in immature birds was discovered, an unexplained event in a resident tropical species. Because photographs of the Chestnut-flanked Sparrowhawk show its relatively large eyes, suggesting an adaptation to living in dense forest, morphometry of the skull was done, showing that it is proportionally broader in this species than in the African Goshawk. Males of Black Sparrowhawk, females of African Goshawk, adult males of Red-thighed Sparrowhawk, and juvenile females of Chestnut flanked Sparrowhawk are more common in the collection than the opposite sex (in each case). These unequal sex ratios between species, some statistically significant, could be due to behavioural differences. Although annual primary moult is descendant in most specimens, it is demonstrated here for the first time in the genus Accipiter (in the African Goshawk) that it does not always follow a strict descendant mode. Some serial descendant primary moult cases are illustrated. They could indicate breeding in rapid sequence, which is not unexpected in tropical regions without marked seasons. But the cases of asymmetrical moult are less easily explained; perhaps these involve replacement of feathers after accidental loss.

Ostrich 2007, 78(1): 21–28