Medium term control methods for cane toads: Olfactory and acoustic attractants

About the document

Large populations of cane toads (Bufo marinus) occur in Queensland, the Northern Territory and New South Wales, and toad populations are still expanding west and south. In states where toads occur, and states toads will reach soon (i.e., Western Australia), there is significant public concern about toads and their impacts on natural ecosystem values, native wildlife and domestic pests. Methods of toad control involving gene technology or introduced or genetically engineered diseases are in the early development stage, and are not likely to be available in the short to medium term (5-10 years). Thus, low technology approaches to control, such as trapping, provide a temporary solution that may allow control of toads in localised areas, and empower the public to “do something”. Recent mathematical modelling suggests that if traps are very efficient, cane toad control is possible using traps, or that traps might be useful as part of an integrated pest management scheme, incorporating several methods. Wire cage traps have been designed that trap toads with little by-catch.

The purpose of this study was to examine attractants that may enhance the effectiveness of trapping. We examined the possible effectiveness of scents as attractants using two techniques. We used a Y-maze to determine whether toads are attracted to the odours of other toads, food, and pond water, and performed cafeteria trials of food preferences to screen a variety of foods that seemed likely to attract toads. In Y-mazes, we exposed focal toads to the odours of male toads, female toads, dog food (MasterfoodsTM My DogTM Lamb Classic) and pond water. In the cafeteria trials we allowed toads to choose between minced beef, minced chicken, cat food and dog food. We also examined the effectiveness of acoustic cues, in the form of male toad mating calls, for attracting toads. We initially performed tests in a large circular arena to determine whether male and female toads were attracted to a toad mating call when they were not reproducing. We placed toads in the centre of the arena and exposed them to loud (67dB at 1 m) and soft (47 dB at 1 m) cane toad calls, and to ‘pink’ noise at the same volumes. We recorded the distance and direction the toads moved after 5 minutes of exposure to sound.

The results of the Y maze experiments indicated that toads do respond behaviourally to the scents of conspecifics and the single type of food we used in these trials, but their responses were not simple strong attraction of the sort that would have allowed us to design improved trapping methods. In the Y-maze, male toads were more likely to approach male toads than female toads when given a choice between males and females, but avoided male toads when given the choice between males and nothing. Female toads approached other females when given a choice between males and females, showed no preference when choosing between other toads of either sex and no stimulus, and avoided the dog food. Neither sex showed any response, positive or negative, to the scent of pond water. If the data for both sexes were considered together, both approached their own sex when given the choice between conspecifics of the same sex and the opposite sex, both avoided the dog food, and neither responded to water. Examining data only for trials in which responding toads (and stimulus toads, where applicable) were in reproductive condition as determined by dissection following trials, led to the same Schwarzkopf and Alford. Medium term control methods for Cane Toads: Olfactory and Acoustic Attractants. 2006. 3 conclusions, indicating that reproductive condition of toads did not affect their responses to odours.

Further information

• More about cane toads