The impact of sheep grazing on the fecundity and timing of reproduction in the endangered pygmy bluetongue lizard, Tiliqua adelaidensis

Abstract

The endangered pygmy bluetongue lizard (Tiliqua adelaidensis) is found only in a few remaining patches of South Australian native grassland, most of which are used for live stock grazing. The lizards occupy spider burrows, they mate in October-November and females produce litters of one to four live born neonates in mid-January-mid-March. In this study we use ultrasound scans of females and observations of neonates in their maternal burrows to investigate how grazing affects the fecundity of the pygmy bluetongue lizard. We predicted that lizards in moderately grazed paddocks would have a higher reproductive output than lizards in hard grazed paddocks. Ultrasound scans indicated that this hypothesis was correct by showing a higher mean number of yolk sacs in females from moderately than from hard grazed paddocks. Females from moderately grazed paddocks also gave birth significantly earlier than females in hard grazed paddocks. The higher number of yolk sacs did not result in a significantly higher number of neonates observed in the burrows, which indicates that the weekly burrow observations used in this study may underestimate true fecundity. Understanding how grazing affects the fecundity of the pygmy bluetongue lizard is essential to the future management of this endangered species. This is not only because grazing is used to manage the habitat of all currently known lizard populations, but also because successful reproduction will be needed in those populations to supply the “surplus” individuals predicted to be essential for relocation programs to ensure the survival of the species.

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

“…An alternative explanation is that any surplus energy stores accumulated during spring and shown by higher relative body masses in paddocks with lower grazing pressure in December are invested by the females in offspring that are born in January–February, and that females in each grazing treatment only retain enough energy reserves (as measured in March) to survive the following winter. This theory is supported by Nielsen and Bull () who shows that in year 2, female lizards in the paddocks grazed by 1.5 sheep/hectare/day produced more yolk sacks and therefore likely also more offspring than females in paddocks grazed by 2.7 sheep/hectare/day.…”