Burrowing owls’ habit of bringing mammal dung to their burrows is an example of tool use, researchers say. The dung attracts beetles, an important part of owl diets, the scientists have found.
Owl watchers have long known that Athene cunicularia collects dung from mammals such as cows. They’ve also observed that if this dung disappears from the birds’ burrows during the early part of the breeding season, the birds replace it.
Douglas Levey of the University of Florida in Gainesville and his colleagues tested possible benefits of the dung, such as disguising the scent of eggs, in Florida owl populations. However, when the researchers made fake burrows, those furnished with dung succumbed to predators as rapidly as those without it.
Tests to determine if the dung was serving as bait were more telling. The dung, even in its dry state, attracted dung beetles. And when the researchers drenched the dung to simulate rainy conditions, its allure increased.
In 4-day tests with owls at 10 burrows, researchers found that taking the dung away from the burrows’ entrances left the owls with few beetles in their diet. Owls with a refurbished cow-dung decor, however, averaged ten times as many beetle meals during the test. The results appear in the Sept. 2 Nature
Scientists have proposed tool use by various animals, including birds (SN: 11/10/01, p. 295: Finches figure out solo how to use tools; 3/22/03, p. 182: Techno Crow: Do birds build up better tool designs?) and even insects. This study demonstrates something that has been hard to test in the wild: whether an animal manipulating a potential tool gets a clear advantage over an animal not using it.
Levey points out that dung collection may now offer the benefit of luring food, but there may have been another benefit behind its original evolution.