The latter description applies in this case. Browsing through bird books in the evening last week, I realised that I'd not seen Exclamatory Paradise-Whydah Vidua interjecta (yes, it is named thus because it looks like a flying exclamation mark!). This species is very similar to the Eastern Paradise-Whydah Vidua paradisea, but lacks the clear cut golden-buff area on the hind-collar of that species. The tail is also less tapering. The females are subtly different as well. V. paradisea parasitises Green-winged Pytilia and V. interjecta parasitises Red-winged Pytilia. Since I have only seen Red-winged Pytilia east of the Nile, I concluded that some of the birds I'd seen on that side of the river might be Exclamatory Paradise-Whydahs. Sure enough, looking through my photos I found several of a pair of Exclamatory Paradise-Whydahs. The photos below show the differences between the two species.
Pair of Exclamatory Paradise-Whydahs, male showing chestnut nape with no well-defined golden-buff patch
Close up of female Exclamatory Paradise-Whydah showing head pattern lacking crescent markings behind eye
Male Eastern Paradise-Whydah in advanced moult into breeding plumage - note golden-buff nape absent in Exclamatory Paradise-Whydah
Full breeding plumage male Eastern Paradise-Whydah
Female Eastern Paradise-Whydah showing two dark crescents behind eye, absent in female Exclamatory Paradise-Whydah.
This experience serves to demonstrate the advantages of digital photography, enabling thousands of images to be taken and stored at no cost beyond the initial investment.