Reproductive Biology of the White-Throated Savanna Monitor, Varanus albigularis

Abstract

The reproductive biology of the white-throated savanna monitor lizard, Varanus albigularis, was examined in the arid savanna of Etosha National Park, Namibia. Both sexes were solitary during the the hot/wet season when prey were abundant, and during the hot/dry season when prey populations were declining. Male-male and male-female behavioral interactions were confined to a 2-3 week period at the transition from the cool/dry to the hot/dry seasons when prey populations were depleted. Interactions oc- curred at locations occupied by estrus females. Male-male interactions were restricted to resident males chasing intruding males after visual contact Males appeared to initially locate the general area occupied by females through scent cues. Once in visual contact with females, males exhibited a spasmodic body shudder, after which females responded by flattening their bodies. Mating generally occurred in trees. No aggression was noted between pairs during courtship or mating. At peak estrus, females had elevated (100 to 500-fold increase over non-reproductive period) plasma testosterone and total estrogen titers. Males showed similar dramatic increases in plasma testosterone levels during the mating period. Aspects of the reproductive biology of this species are discussed in the context of general patterns for the family Varanidae. As a group monitor lizards appear to be very conservative in the length of gestation, but highly variable in length of incubation. Length of incubation appears to be variably timed in order to place hatching during the period of greatest abundance of invertebrate prey.