Caterpillars that masquerade as twigs to avoid becoming a bird's dinner are actually using clever behavioural strategies to outwit their predators, according to a new study.
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PERTH: Caterpillars who mimic twigs know to select their hiding spots carefully in order to outwit looming predators, a new study has shown, researchers hoping the information will contribute to conservation efforts in the future.
Rather than trying to blend in with its surroundings, a masquerading animal attempts to look like an inedible or uninteresting object, and in the case of caterpillars, this means a simple twig. By understanding the type of environment required by these animals to hide themselves successfully, scientists are hoping to develop more effective conservation strategies.
“It is important to remember that the inedible objects these creatures resemble must remain abundant in order to protect them from predators,” said animal behaviour psychologist John Skelhorn from Exeter University in Britain.
A daytime masquerade
Camouflage involves the prey blending in with the environment to avoid being seen by predators. Masquerade, however, involves being detected by the predator but being mistaken for an inedible object.
The study, published this week in the Proceedings of the National Academy of Sciences, documents the complex habitat selection strategies the Early Thorn moth caterpillar (selenia dentaria) uses to outwit its predators. The study also looked at the behaviour of the predator, the domestic chick (gallus gallus domesticus).
In the first part of the study, caterpillars were given a choice between branches with a lot of twigs and branches with only a few twigs.
The caterpillars favoured branches with lots of twigs during times when predators that hunt by sight are active. At night when visual predators are rare the caterpillars favoured branches with more food, regardless of the number of twigs present.
Birds less willing to search
Caterpillars appeared to avoid areas where there were too many other masquerading caterpillars and favoured areas with more twigs.
In the second part of the study, the birds were split into two groups and exposed to a series of branches with caterpillars on them. Half of the birds were exposed to unrewarding situations with lots of twigs and few caterpillars. The other half was exposed to rewarding situations with lots of caterpillars and few twigs.
All of the birds then underwent a time trial to see how long it would take them to find one caterpillar amongst nine twigs. Birds that had previous experience with unrewarding situations were slower to find the caterpillar in the time trial.
“Birds were less willing to search for masquerading caterpillars when caterpillars were rare in comparison to the inedible items they mimicked,” said Skelhorn.
