First evidence of aggressive interactions by native rakali towards invasive black rats

Jenna P. Bytheway; Margarita Goumas; Peter B. Banks

doi:10.1071/AM25009

RESEARCH ARTICLE (Open Access)

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First evidence of aggressive interactions by native rakali towards invasive black rats

Jenna P. Bytheway

^A ^* , Margarita Goumas

^B and Peter B. Banks ^A ^B ^*

+ Author Affiliations

- Author Affiliations

^A School of Life and Environmental Sciences, The University of Sydney, Sydney, NSW 2006, Australia.

^B School of Biological Earth and Environmental Sciences, University of New South Wales, Sydney, NSW 2052, Australia.

^* Correspondence to: jenna.bytheway@sydney.edu.au, peter.banks@sydney.edu.au

Handling Editor: Graeme Coulson

Australian Mammalogy 47, AM25009 https://doi.org/10.1071/AM25009

Submitted: 26 February 2025 Accepted: 9 July 2025 Published: 25 July 2025

© 2025 The Author(s) (or their employer(s)). Published by CSIRO Publishing on behalf of the Australian Mammal Society. This is an open access article distributed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND)

Abstract

The mechanisms by which native species might compete with invasive alien species are poorly understood, especially for competing cryptic small mammals. We document the first evidence of an aggressive interaction between a rakali (water rat, Hydromys chrysogaster) and a black rat (Rattus rattus) in the natural environment in Australia. Our camera trap recorded a rakali ambush a black rat in bushland on the Sydney Harbour foreshore. This finding suggests there is potential for rakali to play a positive role in biotic resistance against invasive black rats, additionally providing ecological justification for the conservation and promotion of rakali especially in urban environments where introduced rats are common.

Keywords: biological control, biotic resistance, interference competition, intraguild predation, invasive species, mesopredator, native rodent, urban ecology.

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