Sensory cues and foraging decisions in a large carnivorous lizard, Varanus albigularis

The white-throated savanna monitor, Varanus albigularis, is a large (>5 kg) carnivorous lizard that inhabits the arid savanna in southern Africa. In the natural environment, feeding occurs only during the 4-month wet season when invertebrate and small vertebrate prey are abundant. Seven experiments were conducted to examine the foraging, feeding and sensory discrimination behaviour of these lizards towards land snails, a favoured natural prey. Subjects were 16 subadult, captive-hatched lizards. Each lizard received several trials in choice discrimination tests with two or three types of snail stimuli differing in visual, chemical or tactile cues. Lizards differentiated between land snails using both visual and chemical cues. Large snails and those requiring short handling times were chosen over small snails and those requiring greater handling time. Neither snail movement nor snail weight were significant cues in choice of individual prey. Lizards preferred empty shells with fresh snail odour to empty snail shells without odour. The results suggest that these monitor lizards discriminate between prey items using visual and chemical cues. A result of their selectivity is obtaining a high caloric reward at a minimum energetic cost.