Feral cats kill more native animals than expected

Conservation scientists from UNSW Sydney have used DNA technology to confirm that feral cats are the primary predators of reintroduced native animals in South Australia.

This research aligns with existing data showing that feral cats have caused more native animal deaths than any other predator in Australia. Experts believe feral cats are responsible for two-thirds of mammal extinctions since European settlement.

The recent study suggests that the impact of feral cats may be greater than previously estimated.

In collaboration with experts from the University of Adelaide, the researchers from UNSW found that conventional methods of determining the cause of death often underestimated the role of feral cats.

Pinpointing the cause of death

Professor Katherine Moseby, a co-author of the study, noted that pinpointing the exact cause of death for native animals has always been challenging.

“In past releases, we’d be radio tracking animals after release, and if we found dead animals, it would be difficult to determine what caused their death. We would use field evidence like animal spoor, carcass remains, or bite marks on collars to guess whether it was feral cats, birds of prey, fox, or if they just died a natural death,” said Professor Moseby.

“And because we’re working in really remote areas, it is difficult to access vets for necropsy. So taking a DNA swab of the dead animal was a really good way to identify if predation was the cause of death. And then we decided to compare the DNA outcomes with evidence in the field to determine if the latter was a reliable method of determining cause of death.”

The team concluded that field evidence alone was not a dependable way to confirm feral cat predation. DNA testing and necropsy were necessary to establish whether a cat had killed an animal.

Evidence from conservation sites

The scientists analyzed DNA evidence collected from radio tracking collars and wounds on the animals’ bodies. The team examined two conservation sites in South Australia where native species had been released.

At one location, 148 brush-tailed possums and 110 western quolls were introduced between 2014 and 2016. At another, 42 greater bilbies and 89 bettongs were released in 2017.

Of the 389 animals reintroduced, 74 were confirmed to have been killed by cats. DNA analysis identified 71 of these cases. Veterinary necropsy confirmed six cat-related deaths, while researchers witnessed three instances of feral cats killing prey.

Three of the four released species managed to survive in smaller numbers. However, bettongs failed to establish a stable population due to heavy predation.

Underestimated killings by feral cats

The research showed that even DNA analysis underestimated the number of animals killed by feral cats.

“The DNA is good, but it’s not infallible, and a lot of that is because we’re trying to get DNA from cat saliva found on the carcass, and that’s quite difficult because DNA degrades quickly in the environment,” said Professor Moseby.

“But ultimately it highlighted that there are a lot more cat killings than previously thought.”

This discovery reinforces concerns that current estimates of feral cat predation may not fully capture the extent of their impact on native wildlife.

Challenges in controlling feral cats

Senior author Ned Ryan-Schofield noted that one goal of the study was to assess whether conservationists could rely on field data for quicker assessments of cat predation.

“This could trigger prompt management action like increased cat control rather than waiting until DNA analysis occurred. However, we found that field evidence of cat predation are not obvious and even DNA testing is not infallible,” said Ryan-Schofield, a postgraduate researcher with the University of Adelaide.

Despite advances in research, controlling feral cat populations remains a difficult task. The researchers acknowledge that feral cats will continue to pose a significant threat to native animals for years to come.

Future conservation efforts

Professor Moseby emphasized the importance of continued research and improved management strategies.

“Until we develop genetic tools or other broad-scale methods targeted at feral cats, we can only rely on intensely managing them as best we can,” said Professor Moseby.

”We hope that this research might encourage more conservationists to use DNA and necropsy to identify the cause of death of animals in wildlife reintroductions, and to increase cat control even if no obvious evidence of cat predation are present.”

While eradicating feral cats from the Australian outback may not be possible in the near future, improving tracking and conservation techniques could help reduce their impact on endangered wildlife.

The study is published in the journal Australian Mammalogy.

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