A bait efficacy trial for the control of feral cats on Dirk Hartog Island

Johnston,M. D. Algar, M. Onus, N. Hamilton, S. Hilmer, B. Withnell and K. Koch. 2010. A bait efficacy trial for the management of feral cats on Dirk Hartog Island. Arthur Rylah Institute for Environmental Research, Department of Sustainability and Environment, 2010.

A field efficacy trial of a novel feral cat baiting technology was undertaken on Dirk Hartog Island, Western Australia. The objectives of the study were to investigate; 

• the attractiveness and palatability of the Eradicat® bait,

• the acceptance of an encapsulated pellet that was implanted into the bait, and

• home range and activity patterns of feral cats.

This trial was initially planned to utilise an encapsulated pellet containing the toxicant araaminopropiophenone

(PAPP) and provide a direct assessment of baiting efficacy of the Curiosity^® Feral Cat Bait in the semi-arid zone. However, supply of sufficient PAPP pellets was not received in time. Instead, an alternative method utilising similar pellets that contained non-toxic Rhodamine B dye (RB) was utilised to ‘mark’ animals that were expected to have died had PAPP pellets been available.

The processed meat baits, implanted with the RB pellet, were poisoned with 4.5 mg sodium fluoroacetate (1080) to enable collection of data on bait consumption by feral cats. All cat carcasses located after baiting were investigated to determine presence of dye marking indicating that the animal had consumed a RB pellet.

Baits were laid from an aircraft over the study site on 19 April 2009. Sixteen feral cats had been trapped within the study site, fitted with VHF transmitter / GPS data-logger collars and released three weeks before baiting. Activity plots were established and monitored for feral cat presence before and after baiting. Follow-up baiting was undertaken using hand distributed baits around feral cats that were still alive eight days after the aerial application of baits. 

Monitoring and retrieval of carcasses of the radio-collared feral cats indicated that one animal died before baiting and that twelve died after eating a poison bait. Post mortem examination indicated that nine cats had consumed the RB pellet. Three cats were found to have died following consumption of a bait but had not consumed Rhodamine dye. The remaining three cats were shot at the conclusion of the trial, having failed to consume baits. Two additional uncollared feral cats were located following baiting and were also found to have died as a result of bait consumption indicated by the presence of RB dye. 

Feral cat activity at the monitor plots indicated a twelve-fold reduction following baiting. 

Monitoring of non-target species did not detect any negative impact on populations of resident raptor species. Our data suggests a decrease in goanna activity following baiting, but (given the high tolerance to 1080 exhibited by these reptiles) it is more likely that the apparent decrease was a result of a fault in the monitoring technique.

The results indicate that a pellet-delivered toxicant in Eradicat baits is appropriate for managing feral cat populations in the semi-arid zone. A proposed plan to eradicate feral cats from Dirk Hartog Island should include this bait type within the techniques considered for use. 

Data from the GPS dataloggers is to be reviewed to determine whether the bait frequency, application rate and pattern used in this study will provide for optimum bait encounter rates for feral cats on Dirk Hartog Island.

See more on Dirk Hartog Island feral cat eradication proposal