Aussie owls fall foul of rat poisons

December 6, 2017, Edith Cowan University
Aussie owls fall foul of rat poisons
Credit: Edith Cowan University

Lethal toxins from commercial rat poisons (rodenticides) have been found in more than 70 per cent of Australia's smallest and most common owl species, the Southern Boobook (Ninox novaeseelandiae).

PhD candidate Michael Lohr of Edith Cowan University's Centre for Ecosystem Management said the problem is linked to Australian use of poisons restricted in many other countries.

"Rodenticides such as the commonly-used Brodifacoum are anti-coagulants that are very strong and chemically stable, having a half-life of 200 days," Mr Lohr said.

"This means that when an owl or other predator consumes a rat or mouse that has fed on bait, they are consuming toxins that will stay in their system for a long time.

"The more they consume, the higher the toxic load in their liver, until they reach a fatal dose."

Half-life refers to the amount of time it takes for an animal to rid half of the toxin from its body.

While Mr Lohr's research is focussed on boobook owls, secondary poisoning also affects other animals, including cats, hawks and eagles.

Measuring between 23 and 36cm – about the length of an average dinner plate – the feisty boobook can be found in almost all Australian landscapes, including in and around urban areas.

In the United States, research has found that anti-coagulant poisoning reaches far up the food chain, with even mountain lions being found dead from rodenticide accumulation. Credit: Edith Cowan University

While this adaptability has increased its resilience in the face of habitat loss, it has also brought many into contact with human activities, including rat baiting.

"The first-generation version of anti-coagulant rodenticides weren't as damaging to secondary predators, as they only had a half-life of 16 days," Mr Lohr said.

"However, due to resistance, much stronger versions have been developed that are more chemically stable and last longer in the system."

Second-generation rodenticides also kills rats with a single ingestion, which increases the impact on secondary predators.

The poisons work by blocking a rodent's ability to produce vitamin K, however the animals have up to seven days of reserves in their bodies, which means they can keep feeding on bait, upping their toxicity.

The amount of time between ingestion and death also results in the rodents acting abnormally, including venturing out during the day, increasing the chances they will be attacked and eaten.

Mr Lohr's work will help inform a review of second-generation pesticides in Australia.

ECU has recently switched from Brodifacoum to Cholecalciferol, or activated vitamin D3, which has a half-life of only a few weeks and is less dangerous to secondary predators.

Explore further: What is killing Australia's smallest owls?

Related Stories

What is killing Australia's smallest owls?

September 12, 2016

When a rare bird is in decline, its rarity becomes part of the problem: how can you protect a species you poorly understand and seldom see? That's where the boobook—Australia's smallest and most common owl—comes in.

Toxic toll of rat poison on birds revealed

May 4, 2011

Rats might not be everyone's cup of tea, but you might want to think twice about reaching for the rat poison next time you come across one. While rat poison is brilliant at killing rats, it also spells danger for a whole ...

Poisons on public lands put wildlife at risk (w/ Video)

July 13, 2012

Rat poison used on illegal marijuana farms may be sickening and killing the fisher, a rare forest carnivore that makes its home in some of the most remote areas of California, according to a team of researchers led by University ...

'Super rats' develop genetic immunity to standard poisons

October 18, 2012

A University of Huddersfield scientist has alerted the UK to the mounting problem of destructive "super rats" immune to conventional poison. His research has created nationwide interest, especially in the West of England, ...

Recommended for you

Discovery of a simple mechanism for color detection

October 15, 2018

Color vision, consisting of ocular color detection, is achieved with complicated neural mechanisms in the eyes. Researchers from Osaka City University in Japan have found color detection with a simple mechanism in the fish ...

How beetle larvae thrive on carrion

October 15, 2018

The burying beetle Nicrophorus vespilloides buries the cadavers of small animals in soil to use them as a food source for its offspring. However, the carcass and thus the breeding site are highly susceptible to microbial ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.