Vigilance and risk in sympatric marsupial carnivores

Animal Behaviour 56:1279-1284...

The Tasmanian devil Sarcophilus laniarius and the eastern quoll Dasturus viverrinus are marsupial carnivores that occur in the same areas of Tasmania. Both are nocturnal and tend to be solitary feeders although a number of animals may gather at a carcass.

However the Tasmanian devil is much larger with the average weight of 8.4 kg for a devil male and 5.4 kg for a female while an average eastern quoll male weighs 1.1 kg and the female 0.7 kg. 

Quolls are preyed on by large owls and while it is not known whether devils are also predators, the devils will eat quoll carcasses. In contrast to this, the devil has no predators.

These factors means that eastern quolls face greater risks when out and about than do Tasmanian devils. This study looked at how this difference in risk potential affected the behaviour of the two animals when feeding on carcasses and found that

• quolls were more vigilant in the presence of devils than they were when devils were absent suggesting that the devils pose a threat probably because of their greater size and hence the potential threat of injury to the quolls
• quolls used vigilance postures that gave then better visibility but disrupted their feeding
• smaller devils showed greater vigilance than did larger ones; larger devils displace the smaller ones from a carcass with the very real threat of injury
• vigilance behaviour of devils did not change when quolls were present suggesting that the quolls posed no threat to the devils