Cuckoo-Finch

The cuckoo-finch, also known as the parasitic weaver and cuckoo weaver is the last of the four species of Viduidae I encountered in Uganda. We were in Kidepo Valley NP with our guide William and ranger Zachary, near the small Apoka airfield when Zachary called our attention to a small yellow-bird ahead of us standing in the weeds. He said it was an important bird and I should remember it. So I took lots of photos. The cuckoo-finch lays its eggs in the nests of cisticolas and prinias. The young cuckoo-finch is raised by its host and the host's own young usually disappear but have been known to survive. 

The cuckoo-finch has a short tail and short stubby bill. The upper mandible is laterally compressed, the culmen (the dorsal ridge of the upper mandible) is ridged and straight, the lower mandible is bulbous and deeper than the upper mandible. The male in breeding plumage, which is what I saw, has streaked black above, bright yellow with fine dark streaks below, and a black bill. I won't go into the female or male in non-breeding plumage, as I did not see them.  

Illustration of a female cuckoo-finch from Birds of the World. I did not see a female, but the male/female contrast needs to be shown. 

Range of the cuckoo-finch from Birds of the World. 

There are two subspecies listed in Birds of the World with no information about the differences between them. The given ranges of the two subspecies do not mention Uganda, but ssp. butleri lists South Sudan which is very close to Kidepo Valley NP and probably the ssp. I saw. It is widespread, but uncommon and local. The patchy distribution prevents making reasonable population estimates.