Life is tough for voles. Measuring just a few centimeters from head to tail, they’re vulnerable to a bunch of predators — especially predatory birds. But they have their ways of staying safe, or at least increasing the chance of staying safe. Whenever they hear calls from shrikes, birds that prey on them, voles cut the grass around them to better watch flying predators.
Voles are small rodents that look a lot like mice or gophers. They thrive on small plants, and are widely spread across the woodlands of Europe and Asia. Among the many different types of voles, Brandt’s vole (Lasiopodomys brandtii), also called the steppe vole, is found in parts of China, Russia, and Mongolia, especially in grassland areas. They live in small families and build a network of burrows with several entrances which they use for shelters.
Brandt’s voles are hunted by shrikes, relatively small but fierce predatory birds. Among other things, shrikes are known for impaling insects on plant spikes, saving them as a later snack.
Scientists led by Zhiwei Zhong, from Northeast Normal University in China wanted to see how voles try to protect themselves from shrikes, and came across something interesting: when shrike calls are heard, voles spend a lot of time cutting down tall bunchgrass. The voles don’t eat the bunchgrass, they just cut it down to have a better view of the sky and see if any shrikes are nearby.
“When shrikes were present, the voles dramatically decreased the volume of bunchgrass,” said Dirk Sanders, of the Environment and Sustainability Institute on Exeter’s Penryn Campus in Cornwall, and one of the study cu-authors.
It’s a fine example of ecosystem engineering — when an animal species modifies the ecosystem to its advantage. In this case, voles seem to modify their ecosystem and change the habitat structure in order to increase their chance of surviving predation. When there were no shrikes around, the voles stopped this behavior.
“This study provides a good example that animals can actively modify their habitat to reduce predation risk,” said Dr Zhibin Zhang, from the State Key Laboratory of Integrated Management of Pest Insects and Rodents, Institute of Zoology, Chinese Academy of Sciences.
The shrikes also take note of this and spend less time hunting around areas with a lot of cut bunchgrass.
“This led to fewer visits from shrikes – which apparently recognise cut-grass areas as poor hunting grounds,” Sanders adds.
“An activity like this is costly for the voles in terms of energy, so there must be high ‘selection pressure’ to do it – cutting the grass must significantly improve their chances of survival.”
The study could spell bad news for the voles: in some areas, voles are considered pests and researchers are now thinking that they could plant more bunchgrasses to attract shrikes in areas where rodent management is deemed necessary.
The study was published in Current Biology.