Ecological relationships in two Afrotropical cobra species (Naja melanoleuca and Naja nigricollis)

Aspects of comparative ecology were studied in the spitting cobra, Naja nig ricollis, and the black forest cobra, Naja melanoleuca, from southeastern N igeria. Both species were common and widely distributed in the study region . Naja melanoleuca inhabited mainly primary and secondary forest patches, b ut also plantations and suburbia. The two species differed significantly in terms of habitat types frequented. A logistic regression model showed that the presence of N. melanoleuca was significantly influenced by the presenc e of a unique macrohabitat category (primary swamp-forest), whereas the pre sence or absence of N. nigricollis did not correlate with any macrohabitat categories. Aboveground activity of both species was lowest during the hott est months of the dry season (December to February) and peaked during the w ettest months of the wet season (June and July). Sexual size dimorphism was minor in both species, but N. melanoleuca attained a significantly greater body size than N. nigricollis. The adult sex ratio was approximately 1:1 i n both species. Both species preyed on a wide variety of small to medium-si zed vertebrates; adult N. melanoleuca fed with similar frequency upon mamma ls, frogs, and fish, whereas the young fed mainly upon fish. Adult N. nigri collis preyed mainly on lizards and to a lesser degree on mammals and frogs , whereas the young preyed with similar frequency upon lizards, frogs, and fish. Many of the prey of both these cobra species were terrestrial (rodent s and shrews), but semiaquatic (frogs) and aquatic (fish) prey were also fr equently taken. In both N. melanoleuca and N. nigricollis, egg laying proba bly occurred over a broad time-span, there was a positive relationship betw een maternal size and litter size, and reproduction first occurred when ind ividuals attained a low proportion of their maximum size.