Effects of grazing regime on the relative body mass of the endangered pygmy bluetongue lizard (Tiliqua adelaidensis)

Abstract

Many animals rely on fat reserves, to keep them alive through extended periods of food shortage, such as the winter, and to provide additional energy for reproduction. Fat reserves, measured relative to an animal's size, are often referred to as the animal's body condition. The present study investigated how different levels of grazing by domestic stock in native grassland habitat affect the body condition of the pygmy bluetongue lizard (Tiliqua adelaidensis), and if these effects are related to changes in the abundance and size of grasshoppers which are the lizards primary source of food. The initial hypothesis was that lizards would have the highest body condition in moderately grazed paddocks, because those paddocks would have more grasshoppers than heavily grazed paddocks, and better visual conditions for lizards to catch those grasshoppers than in ungrazed paddocks. The results, however, showed that both lizard body condition and the abundance of grasshoppers increased with decreasing grazing intensity. The connection between lizard body condition and abundance of grasshoppers was complex. Within an activity season, lizard body condition generally declined from spring to summer, while the number of grasshoppers grew. The mean size of grasshoppers seemed to be more important, as lizard body condition was higher in spring, the time of year with the largest grasshoppers. These results show that the intensity of grazing by domestic stock influences the body condition of pygmy bluetongue lizards, but that this effect is not entirely due to the reduction in the number of grasshoppers resulting from grazing.

Editorial for the Michael Bull special issue

“…Grazing is an important factor in this lizard’s ecology as all known populations are on sheep‐grazed properties. Nielsen and Bull (2020) looked at the effect of grazing regime on the lizard’s body mass concluding that body condition increased with decreased grazing intensity, but the presence and size of grasshoppers was also important in explaining body condition. Extending the conservation of this endangered lizard to captive breeding, Daniell et al .…”