Each year I attend a conference in Niamey and stay at the SIL center which is near the American and French Embassies. This is very close to the river, and there is a path that runs along the gardens next to the river. This is a good birding area and very accessible by taxi: my starting point was the Club Equestre of Niamey. Going along that path downstream you reach the barrage. I rented a pirogue canoe at the barrage and we went to the islands upstream and the reedbeds across from the Nigerian embassy. Mamadou Tinni operated the pirogue, and knows the areas with birds and stops whenever asked. I would recommend him to other birders, he can be found at the barrage.
I also went by vehicle to the village of Gourou Kirey 15 km from downtown. In the late afternoon we went to this area which is a near-dry river bed next to a large sand dune. If you want a truly beautiful spot that is also uniquely "Niger", I would highly recommend it. There were many good birds in the vegetable gardens between the river and the sand dune, including a pair of Black-eared Wheatears and a Redstart. Many expats picnic in this area, and the local name for the spot is "Pillule" because it used to be a drug hangout.
I was able to see Sedge Warbler in the thick brush next to the barrage. It was noisy but a real challenge to find hidden in thick leaves. Plus I had a crowd of children bothering me as I tried to follow the it through the bushes. That was the only time I had problems being bothered by people. Those working in the gardens were curious but few spoke French. When I showed them the illustrations in my bird book, they understood I was not a photographer.
There are very many Palearctic warblers in Niamey during January-February, as can be seen from the list below.