Cane toads

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Local extinction of Northern Quolls – the effect of Cane Toad invasion.

Meri Oakwood & Amber Hooke

Envirotek: Ecological Research, Survey and Education

PO Box 25, Nana Glen NSW 2450 Ph: 02 6656 9079 Ph: 08 8979 2199


Cane toads (Bufo marinus) were introduced to coastal Queensland in 1935 and have been spreading south, north and north-west ever since. Cane toads possess toxic glands and consequently their consumption is fatal to many vertebrate predators. As cane toads colonized Cape York Qld between the mid 1980s to the mid 1990s, major crashes in populations of conspicuous native vertebrate predators were observed, in particular goannas and northern quolls (Burnett 1997). The northern quoll, Dasyurus hallucatus, a small marsupial carnivore, is a declining species now listed as “lower risk, near threatened” by the IUCN. The Northern Quoll was determined by the ERISS Risk Assessment of Cane Toads in Kakadu National Park (Van Dam et al. 2000) to be the single highest risk species in Kakadu.

In 2001, a project was established in Kakadu to monitor the short-term and long-term impacts of cane toads on individuals and populations of the northern quoll. Additionally, we monitored the abundance of toads during invasion and examined their prey. We examined two quoll populations: near Mary River Ranger Station and around East Alligator Ranger Station. Both sites had regular trapping sessions conducted from 2001 to 2004 to gather pre-invasion baseline population data and to monitor quoll population trends during and after cane toad invasion. Radio-tracking of northern quolls (n=40) was conducted at the Mary River site from January to June 2002. The toads arrived at this site in February 2002. After cane toad arrival, 31% of quoll deaths (total n = 16 deaths) were due to cane toad poisoning. The signs of cane toad poisoning are distinctive in quolls: there are no injuries or predator damage on the corpse and they have bright red lips and/or gums that is probably due to irritation from the cane toad toxins (photo in Oakwood 2004). Additionally, corpses often have a variety of other signs including bleeding from the nose and ears, bright purple teats and some abnormalities in the colour of internal organs. The Mary River population became extinct in February 2003. Eight subsequent trapping sessions in 2003 and 2004 failed to detect any quolls at this site.

Radio-tracking (n=41) occurred at the East Alligator site from March 2003 to January 2005. Cane toads arrived in November 2003. After cane toad arrival, 53% of quoll deaths (total n = 15) were due to cane toad poisoning. This population has dramatically declined from 45 individuals in January 2003 to 4 in January 2005. Radio-tracking and trapping ceased in January 2005 due to lack of funding, disallowing the completion of the study. Consequently we will be unable to determine the timing of extinction of this population, unless we can obtain funding for monthly trapping for March and April. The project to date has investigated the short-term effect of cane toads on northern quolls but at this stage, it looks as though we will be unable to complete the second main objective, to document the long-term impact. We are still hopeful that sufficient funding will be sourced to enable us to complete the project; to carry out annual post-extinction trapping to determine whether any re-colonisation occurs over the next few years.

This project has provided data that has been used for the recent nominations for the northern quoll to be listed as Threatened and the cane toad to be listed as a Threatening Process under the EPBC Act1999, as part of the basis for justification for the quoll translocation project to the English Company Islands by the NT DIPE in 2003 and for the establishment of a quoll captive breeding program near Darwin in 2004.

Further Reading:

* Burnett, S. 1997. Colonising cane toads cause population declines in native predators: reliable

anecdotal information and management implications. Pacific Conservation Biology 3, 65-72.

* Oakwood, M. 2004. Case of the Disappearing Spots. Nature Australia. 28, 26-35

* Van Dam, R., Walden, D., and Begg, G. 2000. A preliminary risk assessment of cane toads in

Kakadu National Park. Unpub. Report by ERISS, Jabiru.