Winter durability of pygmy bluetongue lizard burrows is higher for occupied than for unoccupied burrows and for those in less-grazed neighbourhoods

Abstract

Context Many ectothermic animals survive winter by hibernating, either buried or in burrows. During their hibernation these animals are vulnerable to changes in soil structure and temperature caused by the activity of grazing mammals. This may be a particular risk to ectotherms living in native grassland, as this habitat is often used for livestock grazing. The endangered pygmy bluetongue lizard lives in burrows, in fragments of native grassland in South Australia, and these burrows are likely to be affected by sheep grazing during the lizards’ hibernation. Aims The current study aimed to determine the following effects on the persistence of burrows suitable to the pygmy bluetongue lizard: different levels of grazing, winter vegetation cover, burrow entrance size and whether a lizard was overwintering in the burrow. Methods During two winters, we applied different grazing treatments to six experimental paddocks and determined whether suitable lizard burrows located in autumn were still suitable to lizards in the following spring. For each burrow, we recorded whether a lizard was overwintering, the burrow entrance diameter and the vegetation cover around the burrow during the winter. Key results Increased grazing pressure led to decreased persistence of lizard burrows. We also found that burrows with an overwintering lizard had a greater chance of persisting, but found no direct effect of winter vegetation cover or entrance diameter. Conclusions The results show that although pygmy bluetongue lizards may be able to stabilise their own burrows, the more intense the grazing the lower the chance of lizard burrow persistence. Implications Management of sheep grazing is an important component in future conservation of the endangered pygmy bluetongue lizard. Grazing on grassland with a lizard population should be kept at a moderate level and hard grazing should be avoided.