Near the habitat boundary, there is habitat choice, in which the snails preferentially move to the bushes for summer aestivation (Johnson, 1981). Thus, in the open area abundance can fall substantially due to high mortality in hot summers, with further reduction within 15–20 m of the adjacent Acacia thicket due to movement of the snails into the bushes.
Following autumn rains, however, there is a net movement from the bushes into the adjacent Open habitat, so that relative abundance in the area within 15–20 m of the ecotone varies seasonally (Johnson, 1981). Similar seasonal movements between habitats have been observed in T. pisana in pasture and adjacent roadside vegetation (Baker & Vogelzang, 1988) and in the land snail Cepaea nemoralis in a heterogeneous environment, in which open areas were favoured for feeding and sheltered areas favoured during hot summer periods (Chang & Emlen, 1993).