Nyungwe: the Albertine Rift
Nyungwe is the serious birding destination. Close to 300 species have been recorded, and around two dozen of them are Albertine Rift endemics found nowhere outside this narrow strip of mountains. The forest interior birding is hard work — dense canopy, poor light, mixed feeding flocks moving fast — and much better with a specialist guide than a general one. The trail network gives access to several distinct altitude bands, which is what makes the list possible; the Kamiranzovu marsh trail adds wetland species.
Akagera: water birds in volume
Akagera has over 500 recorded species and holds one of the largest concentrations of big water birds on the continent. This is easier, more visible birding than Nyungwe — storks, herons, jacanas, fish eagles, kingfishers and the papyrus specialists, all viewable from a vehicle or, better, from the Lake Ihema boat. Shoebill is the trophy and the reason serious birders come.
Volcanoes: montane and bamboo
Around 180 species in Volcanoes National Park, with the interest concentrated in the high-altitude specialists of the Hagenia and bamboo zones. Most visitors pick these up incidentally on a gorilla trek or a Bisoke climb rather than on a dedicated outing.
Building a birding itinerary
The efficient route is Nyungwe for endemics, Akagera for water birds, and whatever Volcanoes gives you alongside the primates. Lake Kivu and the wetlands around Bugesera fill the gaps in transit. Two nights minimum in each of Nyungwe and Akagera — one night in either is a wasted drive.