The field study was carried out mainly from September 1996 to February 1999, with some data recorded even earlier, in some localities of southern Nigeria. These localities were situated in the territories of the Niger Delta (Delta, Edo, Bayelsa, and Rivers States), in Anambra State, Abia State, Akwa-Ibom State, Imo State, and Cross River State (Fig. 1). These territories are in general heavily populated, with patches of rainforest interspersed among wide plantations (yam, cassava, cocoa, pineapple, banana, plantain, oil palm, etc.). The forest patches may have dry soil, or may be permanently or seasonally inundated swamp-forests. Enormous extensions of mangrove formations (Avicennia marina, Rhizophora racemosa) are found in the brackish water tracts, mainly along the rivers Benin, Forcados, Ramos, Sangana, Nun, Brass, Saint Nicholas, Santa Barbara, San Bartholomew, Sambreiro, New Calabar, Bonny, Imo, Kwa-Ibo, and Cross. Much details of both study areas environmental characteristics and climate conditions are described elsewhere (Luiselli et al., 1998a, 1998b, 1998c).