Ecology of cobras from southern Africa

Abstract

Large slender-bodied snakes that forage actively for a generalized array of small vertebrates are conspicuous elements of the terrestrial snake fauna of most continents; the venomous elapid species fill this role in much of Asia, Africa and Australia. Our dissections of eight species of cobras from southern Africa Aspidelaps, Hemachatus, Naja; Serpentes and Elapidae (total of 1290 specimens) provide extensive data on sexual dimorphism, reproductive biology and food habits. Females grow larger than males in Aspidelaps lubricus and Naja nigricincta, but (perhaps reflecting selection on male body size due to male-male combat) males grow as large as females in Naja anchietae, Naja melanoleuca, Naja mossambica, Naja nivea and Hemachatus haemachatus, and males grow larger than females in Naja annulifera. Overall, the degree of male size superiority is higher in species with a larger absolute mean adult body size. Male cobras typically have larger heads and longer tails than conspecific females. Fecundity increases with maternal body size, and is higher in the viviparous rhinkals H. haemachatus than in the oviparous Naja species studied. Diets are broad in all eight species, comprising a wide variety of amphibians, reptiles, mammals and (less often) birds. Ontogenetic (size-related) shifts in dietary composition (amphibian to reptile to mammal) are significant within some taxa (N. annulifera, N. nigricincta) but absent in others (notably N. nivea, the most arid-adapted species). Overall, despite substantial interspecific variation among the eight study species, strong parallels are evident between the cobras of southern Africa and their ecological counterparts in other continents.