Dingoes have grown and pesticides might be to blame
Dingo skull from central Australia. Photo: Dr Melanie Fillios
Dingoes getting bigger
Dingoes have grown around 6-9 percent bigger over the past 80 years, new research from University of Sydney and UNSW shows 鈥� but the growth is only happening in areas where poison baiting is used.
The findings, published in the , compared the sizes of dingoes that lived in three baited regions (Kalgoorlie, Pilbara and pastoral South Australia), with those from an unbaited region that stretched from the Northern Territory to South Australia.
The scientists measured the skull size 鈥� which is a marker of animal size 鈥� of nearly 600 dingo specimens originating from the sites. The skulls from the baited regions grew by about four millimetres since poison baiting was introduced. This equates to roughly a kilogram in body mass.
While both male and female dingoes grew, female dingoes had the biggest growth spurt: their skulls increased by 4.5 millimetres, which is almost 9 percent body mass. Male skulls grew by 3.6 millimetres, or 6 percent body mass.
The question is: why are dingoes in poison-baited areas growing?
鈥淭he most likely theory is that dingoes who survive baiting campaigns have less competition for food,鈥� says co-author Associate Professor Mathew Crowther from the School of Life and Environmental Sciences.
He explains that dingoes鈥� primary prey, kangaroos, have been shown to increase in numbers when dingo populations are suppressed.
鈥淲ith more food in abundance, dingoes鈥� physical growth is less restricted.鈥�
1080 baits are commonly used across Australia to control dingo and other pest populations. Photo: Shutterstock
Pesticides
The pesticide sodium fluoroacetate 鈥� known as 1080 (pronounced 鈥榯en eighty鈥�) 鈥� is commonly used across Australia to control dingo and other pest populations.
A flavourless white powder, 1080 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 over the 1960s and 70s.
Dingoes from the unbaited region 鈥� which included Indigenous-owned lands and conservation reserves 鈥� saw no change in body size.
The 1080 poison is usually stuck into meat baits and dropped from helicopters or planted in dingo hotspots. Photo: Michael Letnic
A predictable cycle
This is not the first time a pesticide has been linked to changes in animal bodies.
鈥淥ur interventions have consequences 鈥� and they're actually quite predictable consequences,鈥� says聽, co-author of the paper and professor in conservation biology and ecosystem restoration at聽.
鈥淲hatever pressures we put on animal populations 鈥� be it pesticides or not 鈥� there will be side effects.鈥�
Scientists usually observe these impacts in invertebrate pests: for example, some insects 鈥� like cockroaches 鈥� are becoming more resistant to the insecticides used on them.
However, this study is one of the first to show that vertebrates, like dingoes, also change from pesticide use.
鈥淧oison baiting campaigns could be favouring the survival of larger dingoes,鈥� says Associate Professor Crowther, from the University of Sydney鈥檚 Faculty of Science.
鈥淪maller dingoes need less poison for a lethal dose, so are more likely to be killed by baiting. This leaves the larger dingoes to survive and breed.鈥�
As a result of their growing size, the 1080 dose required to kill a dingo in the baited regions has increased since the toxin was introduced.
鈥淭he reaction to this finding may be to add more poison to the baits, or to find a new poison,鈥� says Professor Letnic. 鈥淏ut, eventually, the cycle will start again.鈥�
Dingo bodies are changing over time. Photo: Mathew Crowther
Baiting is changing dingoes
The exact mechanisms at play are still unclear 鈥� but a greater abundance of food post-baiting and dingoes adapting to the poison are likely the most influential factors.
Other factors that could have potentially led to the dingoes鈥� growth, like climate change or interbreeding with dogs, seem unlikely.
鈥淲e 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,鈥� says Professor Letnic. Most dingo-dog hybridisation, he explains, occurs on the east coast of Australia.
The researchers also suggest that 鈥� if anything 鈥� a warming climate would decrease dingoes鈥� body size, as cooler conditions favour larger animals.
Further studies that use a broader sample of dingoes from across Australia could help better understand the cause of the dingo body change.
In the meantime, the researchers hope to explore other ecological impacts of 1080 baiting.
鈥淏aiting is changing dingoes, so it could be changing other animal populations,鈥� says Professor Letnic.
鈥淎nimals respond to human interventions, whether directly or indirectly. The changes could well be adaptive, and we must think about that.鈥�
Declaration: This research was funded by the Australia Pacific Science Foundation.聽This story is also . Top image of a dingo in the wild by Peter Contos.