Janice C. Daniel

The loss of anti-predator behaviour following isolation on islands.

When isolated from predators, costly and no longer functional anti-predator behaviour should be selected against. Predator naiveté is often pronounced on islands, where species are found with few or no predators. However, isolation on islands involves other processes, such as founder effects, that might be responsible for naiveté or reduced anti-predator behaviour. We report the first comparative evidence that, in macropodid marsupials, isolation on islands may lead to a systematic loss of ‘group size effects’—a behaviour whereby individuals reduce anti-predator vigilance and allocate more time to foraging as group size increases. Moreover, insular animals forage more, and are less vigilant, than mainland ones. However, we found no evidence that animals on the mainland are ‘flightier’ than those on islands. Remarkably, we also found no evidence that isolation from all predators per se is responsible for these effects. Together, these results demonstrate that anti-predator behaviour may indeed be lost or modified when animals are isolated on islands, but it is premature to assume that all such behaviour is affected.

Olfactory predator recognition: wallabies may have to learn to be wary

Many species modify their behaviour in response to the scents of their predators, but species or populations living without predators may lose such abilities. This loss has been suggested to be irreversible, and to constitute a significant hurdle in restoring historical ecosystems. Olfactory predator recognition was studied in two macropodid marsupials - the tammar wallaby ( Macropus eugenii ) and the red-necked pademelon ( Thylogale thetis ). Both species are in the ‘critical weight range’ of Australian native mammals that have been negatively affected by the introduction of novel predators since European settlement. Predator-naive animals were tested by exposing subjects simultaneously to two feeders with either a predator or a herbivore faecal or urine sample beneath the food tray. The presence of predator olfactory cues beneath the feeder did not affect foraging behaviour or feeder use when compared to control stimuli (herbivore faeces or urine). Previous studies have found that predator-experienced herbivorous marsupials modify their behaviour in the presence of predator scents. In contrast, our studies of predator-naive individuals found no evidence of such selectivity, suggesting that marsupial herbivores may have to learn to modify their behaviour in response to olfactory cues from predators. This implies that the loss of olfactory predator recognition may not be irreversible. Animals translocated from predator-free areas could potentially be trained to recognise the smells of their predators.

An experimental study of behavioural group size effects in tammar wallabies, Macropus eugenii

As animals aggregate with others, the time they allot to social and nonsocial activities changes. Antipredator models of vigilance and foraging group size effects both predict a nonlinear relationship between group size and the time allocated to behaviour. Group size effects were experimentally studied in captive adult female tammar wallabies, a small macropodid marsupial, by increasing group size from 1 to 10. Tammars foraged more, looked less, groomed more, engaged in more aggressive interactions and moved about less as group size increased. Nonlinear regression models explained more variation in the time allocated to foraging, looking, locomotion and affiliative behaviour than linear models. Variation in self-grooming and aggression was better explained by linear models. Wallabies lay down significantly more, and walked significantly less, as group size increased: these relationships were significantly nonlinear. Thus, changes in perceived predation risk, which are characterized by nonlinear relationships, explain tammar wallaby group size effects for most activities. These results support the assertion that predation has played an important role in macropodid social evolution. Moreover, the findings suggest that conservation biologists should pay particular attention to group size when translocating or reintroducing endangered macropodids. Copyright 1999 The Association for the Study of Animal Behaviour.

Do yellow-bellied marmots respond to predator vocalizations?

We conducted four experiments to determine whether yellow-bellied marmots, Marmota flaviventris, discriminate among predator vocalizations, and if so, whether the recognition mechanism is learned or experience-independent. First, we broadcast to marmots the social sounds of coyotes, Canis latrans, wolves, Canis lupus, and golden eagles, Aquila chrysaetos, as well as conspecific alarm calls. Coyotes and eagles are extant predators at our study site, while wolves have been absent since the mid-1930s. In three follow-up experiments, we reversed the eagle call and presented marmots with forward and reverse calls to control for response to general properties of call structure rather than those specifically associated with eagles, we tested for novelty by comparing responses to familiar and unfamiliar birds, and we tested for the duration of predator sounds by comparing a wolf howl (that was much longer than the coyote in the first experiment) with a long coyote howl of equal duration to the original wolf. Marmots suppressed foraging and increased looking most after presentation of the conspecific alarm call and least after that of the coyote in the first experiment, with moderate responses to wolf and eagle calls. Marmots responded more to the forward eagle call than the reverse call, a finding consistent with a recognition template. Marmots did not differentiate vocalizations from the novel and familiar birds, suggesting that novelty itself did not explain our results. Furthermore, marmots did not differentiate between a wolf howl and a coyote howl of equal duration, suggesting that the duration of the vocalizations played a role in the marmots’ response. Our results show that marmots may respond to predators based solely on acoustic stimuli. The response to currently novel wolf calls suggests that they have an experience-independent ability to identify certain predators acoustically. Marmots’ response to predator vocalizations is not unexpected because 25 of 30 species in which acoustic predator discrimination has been studied have a demonstrated ability to respond selectively to cues from their predators.

Group size effects in quokkas

The amount of time allocated to vigilance, foraging, and locomotion as a function of group size were studied in the quokka (Setonix brachyurus), a small, moderately social, macropodid marsupial, on Rottnest Island. Despite living in isolation from most predators for up to 7000 years, quokkas exhibited typical group size effects of aggregation: they foraged more and showed less visual vigilance as group size increased. Group size effects, therefore, may result from factors other than antipredator benefits. In groups larger than 10, quokkas, uniquely among macropodids, allocated virtually all of their time to foraging and none to looking. Given virtually no predation risk on Rottnest Island and no antipredator benefit from aggregation, competition for food or other resources may also be important factors influencing time allocation in quokkas. Quokkas seemingly retained some apparent antipredator behaviour: they remained sensitive to the distance they were from cover and to the time of day when allocating time to foraging and looking.

GROUP SIZE BUT NOT DISTANCE TO COVER INFLUENCES AGILE WALLABY (MACROPUS AGILIS) TIME ALLOCATION

Abstract Despite their widespread distribution and relative abundance, little is known about the antipredator behavior of agile wallabies (Macropus agilis). The ability to modify time allocation as a function of group size is an antipredator behavior that has been reported in some, but not all, previous studies of members of the genus Macropus. We studied group-size effects and space use for agile wallabies foraging in the open to develop a better understanding of behavior of mid-sized macropods. We found that agile wallabies modified time allocated to foraging and vigilance as a function of group size but were insensitive to distance from cover. We contrast the group size results from agile wallabies with those from other macropodids and speculate that predation by saltwater crocodiles (Crocodylus porosus) may have a profound effect on how agile wallabies perceive and manage predation risk.

Red kangaroos (Macropus rufus) receive an antipredator benefit from aggregation

Abstract For species that cannot seek cover to escape predators, aggregation becomes an important strategy to reduce predation risk. However, aggregation may not be entirely beneficial because aggregated animals may compete for access to limited resources and might even attract predators. Available evidence suggests that foraging competition influences time allocation in large-bodied macropodid marsupials, but previous studies have focused primarily on species in areas with protective cover. We studied red kangaroos, a species often found in open country without noticeable cover, to determine whether they experienced a net benefit by aggregation. Red kangaroos varied their time allocation as a function of group size and, importantly, more variation in time allocation to vigilance and foraging was explained by non-linear models than by linear models. This suggests red kangaroos directly translated the reduction of predation risk brought about by aggregation into greater time foraging and less time engaged in vigilance. We infer that red kangaroos received a net benefit by aggregation. Social species living in the open may be generally expected to rely on others to help manage predation risk.

Antipredator behaviour of red-necked pademelons: a factor contributing to species survival?

Australian mammals have one of the world’s worst records of recent extinctions. A number of studies have demonstrated that red foxes (Vulpes vulpes) have a profound effect on the population biology of some species. However, not all species exposed to fox predation have declined. We studied the antipredator behaviour of a species that has not declined ‐ the red-necked pademelon (Thylogale thetis), and contrasted it with previous studies on a species that has declined ‐ the tammar wallaby (Macropus eugenii), to try to understand behavioural factors associated with survival. We focused on two antipredator behaviours: predator recognition and the way in which antipredator vigilance is influenced by the presence of conspecifics. We found that predator-naive pademelons responded to the sight of certain predators, suggesting that they had some degree of innate recognition ability. However, pademelons responded similarly to a broad range of acoustic stimuli, including dingo howls, wedgetailed eagle calls, foot-thumps ‐ a predator-elicited sound ‐ and a control sound, suggesting that they did not specifically recognize predator vocalizations. Unlike a number of other macropodid marsupials, including tammars, pademelons did not modify time allocated to antipredator vigilance as group size increased. Taken together, these results suggest that red-necked pademelons independently assessed and managed their predation risk whereas tammars relied more on conspecifics to assess and manage risk. We suggest that these factors may have been important determinants of species survival. More generally, we suggest that a fundamental understanding of antipredator behaviour can enlighten conservation efforts.