Culling dingoes (Canis lupus dingo) – Australia’s native canines – through baiting has been common for decades, and in recent years researchers have studied its indirect impact on soils, plants, mammals and overall diversity.
Now they have looked at the physical effect on dingo populations, with interesting results.
Writing in the Biological Journal of the Linnean Society, a team led by Michael Letnic from UNSW reports that dingoes are up to 9% larger than they were 80 years ago in areas where baiting is used.
It is, they say, one of the first studies to show that vertebrates, as well as invertebrates, can be changed by pesticide use.
Letnic and colleagues measured the skull size – a marker of animal size – of nearly 600 dingoes that lived in one of three baited regions (Kalgoorlie, Pilbara and pastoral South Australia) or an unbaited region that stretches from Northern Territory to South Australia.
“Skulls from the baited regions grew by about four millimetres since poison baiting was introduced,” says Letnic. “This equates to roughly a kilogram in body mass.”
Females were more affected: their skulls increased by 4.5 millimetres, which is almost 9% body mass. Male skulls grew by 3.6 millimetres, or 6%.
The most likely reason for the growth, says co-author Mathew Crowther from the University of Sydney, is less competition for more food. Research has shown that kangaroos, the dingo’s primary prey, increase in numbers when dingo populations are suppressed.
Interbreeding is possible, but can probably be discounted, says Letnic. “We only tested dingoes in areas that have very low dog hybridisation rates, making it highly unlikely that dog genetics are contributing to the size growth.”
Similarly, climate change seems unlikely as a warming climate would decrease dingoes’ body size, as cooler conditions favour larger animals.
The bottom line, Letnic says, is that baiting is creating larger dingoes, which in turn means more poison is needed in culling programs.
The common poison is the pesticide sodium fluoroacetate – known as 10-80 – which is usually stuck into meat baits and left in dingo hotspots, often via helicopter drops. Baiting was rolled out in Kalgoorlie, Pilbara and pastoral South Australia during the 1960s and ‘70s.