NOTE: After evaluating this photo (among others of the same individual) again in comparison to other photos and specimens at The Field Museum I believe this is in fact A. castanilius. [Jan 2017]
A prime example a confusing West African bird is this presumed Chestnut-flanked Sparrowhawk in Parque Nacional Altos de Nsork, Equatorial Guinea. This bird did not exactly match any description or drawing in any field guide we possessed. It does, however, match other photographs of Chestnut-flanked Sparrowhawk that we have been able to locate. The bird is not so dissimilar from African Goshawks that inhabit nearby regions, and confusion with those birds is likely. If there are any comments regarding the identification of this bird they are welcome.