Grazing as a management tool: Effects of varying intensity of sheep grazing on the endangered pygmy bluetongue lizard.

Author: Torben Nielsen

Nielsen, Torben, 2017 Grazing as a management tool: Effects of varying intensity of sheep grazing on the endangered pygmy bluetongue lizard., Flinders University, School of Biological Sciences

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Abstract

The pygmy bluetongue lizard (Tiliqua adelaidensis) is an endangered scincid lizard only found in a few remaining patches of native grassland in the mid north region of South Australia. Pre-European settlement, these grasslands were a common habitat in the region and were grazed by native macropods. Today however, 98% have been converted into agricultural land and the remaining patches are primarily used for livestock grazing, which due to the high grazing intensity and the hard hooves of domestic ungulates can change both vegetation cover and composition in the grassland habitat. The lizards inhabit spider burrows dug by lycosid or mygalomorph spiders and previous experiments with simulated grazing have shown that they prefer burrows with surrounding vegetation and that grazing leads to increased basking. It has also been shown that lizard burrows in bare ground deteriorate faster than lizard burrows surrounded by vegetation. This thesis primarily investigated how different levels of sheep grazing affect the stability of lizard burrows and the availability of grasshoppers, the lizard's preferred prey. It also investigated how grazing affects the lizard's body condition and fecundity as well as their choice of burrows. The results show that while burrows inhabited by lizards are more stable than empty burrows, increased grazing intensity makes all burrows more likely to deteriorate. Based on the studies in this thesis it is not clear if lizards prefer burrows with a particular vegetation cover. Generally, lizard burrows were found in less vegetated areas than the average of the paddock, but in the spring, when lizards are more likely to move between burrows, they showed a tendency to prefer burrows with more vegetation than the average. This indicated that burrow choices could be dependent on the availability of burrows and may not necessarily reflect what lizards prefer. Grasshopper numbers were reduced by grazing, and lizard relative body mass also declined with increasing grazing intensity, although there did not seem to be a direct relationship between grasshopper numbers and relative body mass of the lizards, as the lizards were affected by grazing earlier in their activity season than the grasshoppers. Ultrasound scans of gravid female lizards showed a lower fecundity for lizards in hard grazed paddocks than for lizards in moderately grazed paddocks. This trend, which was not detected from observations of neonates in the burrows, is likely to be due to the neonates leaving their natal burrow before they were checked. These results show that grazing affects the pygmy bluetongue lizard, and that an understanding of these effects is essential for the future management of the species. Due to the lizard's cryptic lifestyle, finding their burrows in dense vegetation can be difficult and can cause large variations in monitoring surveys. A secondary aim of this thesis was to investigate the possible use of detection dogs in future surveys. It was found that one trained dog could detect pygmy bluetongue lizards in laboratory trials and during field training.

Keywords: Pygmy bluetongue lizard, Tilique adelaidensis, Management, Grazing, Body condition, Prey availability, Vegetation cover, Remote sensing, Fecundity, Detection dog, Sniffer dog
Subject: Biological Sciences thesis

Thesis type: Doctor of Philosophy
Completed: 2017
School: School of Biological Sciences
Supervisor: Michael Gardner