Rattus exulans (mammal)
A useful feature distinguishing them from other rats is the dark outer edge of the upper side of the hind foot near the ankle, the remainder of the foot being pale.
R. exulans is a major agricultural pest throughout Southeast Asia and the Pacific region. Crops damaged by this species include rice, maize, sugarcane, coconut, cacao, pineapple, and root crops.
Physical: Control on mainland sites predominantly consists of snap-trapping.
Chemical: Over the last fifteen years, Pacific rats (Rattus exulans) have been eradicated from increasingly larger New Zealand offshore islands. To date, the largest eradication has been from Raoul Island (2938 ha), although confirmation of eradication from the larger Little Barrier Island (3083 ha) is due this year. Eradication of R. exulans populations on islands is achieved using chemical poisons. In New Zealand compound 1080 has not proved effective against R. exulans, but they are susceptible to anticoagulant poisons such as brodifacoum and bromadialone. Recent successful eradication campaigns have all sown Talon 20 P baits aerially by helicopter. Talon 20 P is a cereal-based (pollard) pellet of approximately 0.8 g containing the anticoagulant toxin brodifacoum at 20 ppm. Currently this is applied at 15kg/ha at a cost of ~$75US/ha (Atkinson and Towns 2001).
Fisher et al. (2004) suggest that diphacinone especially, and also coumatetralyl and warfarin, should be evaluated in field studies as alternative rodenticides in New Zealand. Brodifacoum, the most widely used rodenticide in New Zealand currently, can acquire persistent residues in non-target wildlife. Mineau et al. (2004) presented a risk assessment of second generation rodenticides at the 2nd National Invasive Rodent Summit. O'Connor and Eason (2000) discusses the variety of baits which are available for use on offshore islands in New Zealand.
Biological: Monitor lizards and mongooses were introduced to Pacific islands in early attempts to control R. exulans.
Contraceptive methods of control are currently experimental, but the potential for effective control using contraceptive methods is promising. National Wildlife Research Center (USA) scientists are working on several possible formulations that may make effective oral immunisation possible (Nash and Miller, 2004).
Guidelines for the Eradication of Rats From Islands Within the Falklands Group offers guidelines for the eradication of rats from islands, based on the experiences in eradicating rats from the Falklands group.
Updates with support from the Overseas Territories Environmental Programme (OTEP) project XOT603, a joint project with the Cayman Islands Government - Department of Environment