If you’ve watched the news recently, you might have noticed that there has been a decline in the number of individuals in a variety of species. A small marsupial called a bettong is experiencing declining numbers, and scientists in southern Australia are looking for ways to mitigate this decline as well as increase their awareness of predators.

As species populations decline, groups of conservationists work to both increase the populations numbers as well as increase the survivorship of the organisms once they are reintroduced back into the wild. One of the biggest challenges to conservation efforts is predation, as it’s a major cause of mortality to prey. This is likely due to the fact that some prey have not experienced predators, and, as a result, they lack antipredator behavior. Such animals that have lost the ability to recognize predators and their cues are called naive-prey. Recent studies have examined the effect of predator exposure on the bettong (Bettongia lesueur), a marsupial native to Australia. The method used in the hopes of improving anti-predator behavior was to introduce low densities of cats to predator-naive bettongs so that the exposure might either lead to selection for individuals who are predator-savvy or learning. To study the effects of predator exposure, scientists compared the escape behavior of bettongs from both cat-naive and cat-exposed populations to identify possible differences in how they flee from a threat.

To study whether predator exposure altered escape patterns in prey, an experimental design was set up in a reserve in Southern Australia. In the reserve , efforts were made to keep out mammalian predators by using fences and netting. From this reserve, bettongs from two different paddocks were studied. Group one came from a completely predator free paddock, and group 2 came from a “predator paddock” in which a low density of feral cats were introduced to simulate the cat densities in arid Australia. Bettongs from each paddock were trapped and physical attributes including body mass, head length, and hind foot length were measured. From there, the scientists created a runway by using a cleared off road having cloth walls along the sides and cameras placed intermittently to film the bettongs response. Additionally, fluorescent powder was brushed on the bettongs feet to measure footfalls. Finally, the bettong, still in its capture bag, would be arranged at the start line. Once the bag was lifted, a chaser, from behind the bettong, would introduce a stimulus by loudly shaking a pole with a ball containing bells, following behind the bettong and matching its speed.

One of the first observations made was whether or not predator exposure impacted the size of the bettong. The data yielded results that indicated the only significant difference in terms of physical measurements between the groups of bettongs was the body mass. For the bettongs in this experiment, there was little to no evidence that the treatment impacted head or hind foot length. Due to the fact that cat exposed bettongs were heavier, significant interactions were discovered between treatment and initial gait of the bettongs, bound length, and average speed. These results indicate that larger bettongs would be more effective at escaping predators, but the scientists took other measurements to confirm this.

To determine whether predator exposure had an effect on escape behavior in these bettongs, scientists recorded various measures of reactivity. One such measure was the latency to leave, the time that it took between the removal of the bag from the bettong’s head and its exit. The results indicated that cat exposed bettongs not only had quicker reactions once the bag was removed, but they also had a faster escape speed. Cat naive bettongs paused, and occasionally even inspected the equipment before deciding to flee. Another measurement was whether the animal fled on all four legs or bipedally. For bettongs, quadrupedal gait is only used during slow activities such as foraging, and bipedal movement is the quicker, more maneuverable way to travel. The results showed that the cat-naive bettongs often opted for this quadrupedal gait in order to inspect the stimuli, and the predator exposed bettongs used the quicker, bipedal movement immediately after exiting the capture bag. Overall, the results indicate that cohabitating with predators appeared to change the bettongs perception of risk via selection as well as experiencing firsthand or observing encounters with predators.

 

References:

Natasha E. Tay, Patricia A. Fleming, Natalie M. Warburton, Katherine E. Moseby, Predator exposure enhances the escape behaviour of a small marsupial, the burrowing bettong, Animal Behaviour, Volume 175, 2021, Pages 45-56, ISSN 0003-3472, (https://doi.org/10.1016/j.anbehav.2021.02.013)

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