Predation by introduced cats Felis catus on Australian frogs: compilation of species records and estimation of numbers killed

Date: 20, Apr, 2020
Author(s):   Woinarski J. C. Z., Legge S. M., Woolley L. A., Palmer R., Dickman C. R., Augusteyn J., Doherty T. S., Edwards G., Geyle H., McGregor H., Riley J., Turpin J., Murphy B.P.
Publisher: Wildlife Research

Context: We recently estimated the numbers of reptiles, birds and mammals killed by cats (Felis catus) in Australia, with these assessments providing further evidence that cats have significant impacts on Australian wildlife. No previous studies have estimated the numbers of frogs killed by cats in Australia and there is limited comparable information from elsewhere in the world.

Aims: We sought to (1) estimate the numbers of frogs killed by cats in Australia and (2) compile a list of Australian frog species known to be killed by cats.

Methods: For feral cats, we estimated the number of frogs killed from information on their frequency of occurrence in 53 cat dietary studies (that examined stomach contents), the mean number of frogs in dietary samples that contained frogs, and the numbers of cats in Australia. We collated comparable information for take of frogs by pet cats, but the information base was far sparser.

Key results: Frogs were far more likely to be reported in studies that sampled cat stomachs than cat scats. The mean frequency of occurrence of frogs in cat stomachs was 1.5%. The estimated annual per capita consumption by feral cats in Australia’s natural environments is 44 frogs, and, hence, the annual total take is estimated at 92 million frogs. The estimated annual per capita consumption by pet cats is 0.26 frogs, for a total annual kill of one million frogs by pet cats. Thirty native frog species (13% of the Australian frog fauna) are known to be killed by cats: this tally does not include any of the 51 threatened frog species, but this may simply be because no cat dietary studies have occurred within the small ranges typical of threatened frog species.

Conclusions: The present study indicated that cats in Australia kill nearly 100 million frogs annually, but further research is required to understand the conservation significance of such predation rates. Implications: The present study completed a set of reviews of the impacts of cats on Australian terrestrial vertebrates. Cat predation on Australian frogs is substantial, but is likely to be markedly less than that on Australian reptiles, birds and mammals.