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.

The underappreciated extent of cannibalism and ophiophagy in African cobras

“…Discrepancies between our findings and those of Shine et al. () likely arise as a result of differences in sampling effort and the number of methods employed: method‐specific biases in the detection of different prey items in animal diets can severely limit studies of prey diversity when only one method is used (Glaudas et al. ).…”

“…This result was somewhat surprising given that Shine et al. (), in an excellent empirical review of southern African cobra diets, found no evidence of ophiophagy in N . nivea or N. subfulva whereas our assessment suggests snakes account for about 32% and 24% of their diets, respectively.…”

“…Additionally, this male bias in our observations raises the question of whether cannibalism evolved from a male–male combat behavioral precursor, especially given that male–male combat in cobras is known to include biting (Shine et al. ). Luckily, frequent cannibalism raises important, testable hypotheses regarding age‐structured utilization of point resources which might provide fruitful avenues of enquiry.…”

“…nigricincta ) whereas Shine et al. () found no evidence of cannibalism at all. Our review suggests that conspecifics represent at least 4% of all prey items consumed by cape cobras, and 12.5% of all snake prey items ( N = 148).…”

No evidence for proteolytic venom resistance in southern African ground squirrels

“…We focused on two species of venomous snakes that prey on rodents and live sympatrically with X. inauris, the puff adder (Bitis arietans) and the snouted cobra (Naja annulifera) (Broadley, 1990;Phelps, 1989;Shine et al, 2007). The venom of B. Arietans causes severe local and systemic effects to tissue including swelling, haemorrhage, and necrosis (Rippey et al, 1976;Warrell et al, 1975;Mallow et al, 2003).…”