Burrow choice by individuals of different sizes in the endangered pygmy blue tongue lizard Tiliqua adelaidensis

Abstract

The pygmy blue tongue lizard Tiliqua adelaidensis had been considered extinct until its recent rediscovery near Burra in the mid-north of South Australia. The lizards apparently rely on spider burrows as refuge sites. In this paper we describe the dimensions of burrows occupied by lizards. Larger lizards occupy deeper burrows with wider entrance diameters than do smaller juvenile lizards. When offered a choice of artificial burrows in the field, all lizards preferred vertical over angled burrows, while adult lizards preferred deeper burrows than did juveniles. In laboratory trials with artificial burrows of equal depth, lizards tended to prefer the narrowest burrow they could fit into. We suggest that lizards are constrained by a preference for a deep burrow to reduce the risk of being dug out, and to avoid climatic extremes, and a preference for a narrow burrow in which they can block predator access. The result is that smaller lizards have different optimal burrow dimensions than larger lizards. To maintain a viable population of lizards a variety of burrow sizes is needed. Conservation strategies for this species may include maintaining a diverse community of hole digging spiders, or providing a variety of sizes of artificial burrows.