The numbers of Marabou at Naivasha was staggering. I saw well over 100 individuals over my boat trip around the lake (just under two hours).
Another interesting observation, and related to this picture, was the number of Grey Herons. I counted eight at Lake Naivasha, and only one Black-headed Heron. However, Grey Herons are supposed to be much rarer in Sub-Saharan Africa, with Black-headed being far more common (and this was reflected at eg. Lake Nakuru, where I saw several Black-headed Herons, and no Greys).