Australian dingoes are getting bigger and poison-baits might be to blame, a new scientific study has found.
Researchers measured more than 500 of the indigenous dogs' skulls and found they had increased by six to nine per cent over the past 80 years.
But the growth is only happening in areas where the ubiquitous pesticide sodium fluoroacetate - known as 1080 - has been used.
"Our interventions have consequences," University of NSW biologist Michael Letnic says.
"Whatever pressures we put on animal populations - be it pesticides or not - there will be side effects."
Scientists compared dingo skulls found in areas where baiting occurred to those located in places where it had not.
They found skulls from the baited regions grew by about four millimetres since pesticide use started.
"This equates to roughly a kilogram in body mass," Professor Letnic said.
Researchers think the baits reduced dingo numbers to such an extent that surviving animals had less competition for food, such as kangaroos.
"With more food in abundance, dingoes' physical growth is less restricted," University of Sydney biologist Mathew Crowther said.
Pesticides are also likely to be favouring the survival of bigger dingoes.
"Smaller dingoes need less poison for a lethal dose, so are more likely to be killed by baiting," Prof Crowther said.
"This leaves the larger dingoes to survive and breed."
Both male and female dingoes were found to have increased in size, however, female dingoes had the biggest growth spurt.
Their skulls grew by 4.5 millimetres, which is about a 9 per cent body mass increase, while male skulls grew by 3.6 millimetres or 6 per cent of their body mass.
Sodium fluoroacetate, a flavourless white powder, was usually hidden in meat baits and left in dingo hotspots during the 1960s and 70s.
Targeted areas included mining and pastoral areas in Western and South Australia.
Dingoes from the unbaited regions - which included Indigenous-owned lands and conservation reserves - saw no change in body size.
The joint study by the University of NSW and the University of Sydney was published in the Biological Journal of the Linnean Society.
Australian Associated Press