Surprisingly picky: Most Tasmanian devils have a favorite prey whose carcass they prefer to eat. They are therefore unusually picky for a scavenger, as a study reveals. This unique behavior likely stems from the low level of competition from other predators on the Australian island. The findings could help in the care of captive Tasmanian devils and the rescue of the critically endangered animal species.
Scavengers excel at one thing in particular: they eat carrion. This usually also means that they cannot choose what or when they eat. When they find a carcass lying around, they have to strike. Otherwise they could get nothing. The opportunistic decision about what to put on the table can be stronger or weaker depending on the season and whether there is a smaller or larger supply of food. However, animals of one species or at least one group of scavengers usually behave in the same way when choosing their food.
Food is reflected in whiskers
Tasmanian devils also feed mainly on carrion. To what extent and on what basis these predatory marsupials decide between different animal carcasses was not known until now. Anna Lewis from the University of New South Wales and her team investigated whether special patterns can be recognized in Tasmanian devils.
In the survey, the research team examined a total of 71 wild Tasmanian devils for their eating habits. To do this, they caught the animals and removed a few whiskers from each before releasing them back into the wild. Carbon and nitrogen isotopes can be detected in the bristly hairs, the ratio of which differs slightly depending on the organism.
The scientists compared the isotopic ratios in the whiskers with those of potential Tasmanian devil food. In this way they were able to get an impression of what the individual animals had been feeding on recently. Depending on which isotopes showed a conspicuous accumulation, they divided the predators into carbon or nitrogen specialists. Animals in which no particular isotope distribution and thus no fussy food intake could be identified were referred to as generalists.
“Most of them have a favorite food”
The result of the investigation surprised the researchers: “Scavengers are actually generalists, they take everything they can find. But we found that most Tasmanian devils are picky and selective eaters – they broke the laws of scavenging,” said senior author Tracey Rogers, also of the University of New South Wales.
Just over three quarters of the animals examined turned out to be specialists when they were classified using the carbon isotopes. When calculating on the basis of the nitrogen isotopes, it was still a good 53 percent of the Tasmanian devils who specialized in certain prey animals. According to the results, only about ten animals can be described as generalists.
Heavy devils are pickier
Also unusual: there were individual differences even within the species. “We were surprised that the devils didn’t all want to eat the same thing. Most have chosen a favorite food,” adds Lewis. “That definitely seems to be a devil-specific habit. There is no other scavenger in the world that we know of that behavior.”
The scientists found another unusual feature in the fact that the weight of the animals seems to be related to their diet. The heavier the individual Tasmanian devil, the choosier it is in its diet. However, the reason for this is unclear. The research team suspects that heavier animals are either more likely to allow themselves to be more picky about what they eat, or that the food they choose has made it easier for them to gain weight.
Why? Because it works
The researchers’ explanation for why Tasmanian devils are so picky about their favorite carcasses in the first place is due to the lack of competition from predatory marsupials on the Australian island. “Put simply, they do it because they can,” says Rogers. “If you’re a scavenger in Africa, you’re competing for food with all the other predators. But in Tasmania there are no other predators and no competition for carcasses. They mainly compete with each other.”
And even this is not the case everywhere: Among the areas from which the Tasmanian devils studied were captured, the scientists classified two areas as having reduced intraspecific competitive pressure. They established this by the fact that the highly contagious and usually fatal facial cancer DFTD (Devil Face Tumor Desease) has already broken out in these areas. The disease occurs specifically in Tasmanian devils and reduces an area’s population by 77 percent within five years.
In the areas contaminated with DFTD, the scientists found an even higher proportion of Tasmanian devils, which have specialized in certain carcasses. According to them, this underscores the theory that less competition leads to greater specialization, since there is also less intraspecific competition in these areas.
Better care for isolated devils
To prevent the Tasmanian devil from dying out completely from DFTD, there are now a few uninfected populations that are being kept isolated. The scientists hope to be able to provide them with better care on the basis of their research results. “The results help us feed devils in captivity the right way. Right now there’s a long list of foods that devils can eat, but it’s not specified how often they eat all of those foods or if they just focus on a few different types of food,” Lewis explains.
In the next step, the scientists want to investigate the basis on which a Tasmanian devil chooses its favorite food. In addition, the results also prompt possible research on the eating habits of other scavengers. “It’s still hard to believe that scavengers can be specialists,” says Lewis. “One has to wonder if other scavengers like hyenas or wolverines would behave like devils if they didn’t have to compete with other species.” (Ecology and Evolution, 2022; doi: 10.1002 / ECE3.8338)
Quelle: University of New South Wales