Study: Owls Use Dung As "Tool" To Lure Beetles

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An old adage says you can catch more flies with honey than vinegar. But the burrowing owl has come up with another alternative: manure.

University of Florida scientists have a new explanation for burrowing owls' odd habit of collecting and scattering animal feces within and around their shallow burrows. They believe the owls are simply using the feces as bait to attract a favorite insect meal - dung beetles.

The findings are significant because they are based on what the scientists say are the first controlled experiments of tool use - dung as bait, in this case - by wild animals, a hot issue because of the enormous difficulty of interpreting animal behavior.

"What makes this study unique is its experimental approach, documenting how effective tool use is. Tool use in general is a very controversial field because it's often difficult to know whether an animal is doing what you think it's doing," said Doug Levey, a UF professor of zoology and the lead author of a paper on the research in the journal Nature.

Burrowing owls, known scientifically as Athene cunicularia, range from Canada to Chile, with a handful of small populations in Florida. Observers throughout their range have long noted their curious habit of hoarding cow, horse, buffalo, dog and other dung in and around the entrance to their nesting burrows, shallow holes that may be up to 3 feet deep and 6 to 9 feet long.

Levey said a UF undergraduate ornithology class' routine outing to view a burrowing owl population in North Florida led to the beetle hypothesis. He and others noticed that the indigestible pellets the owls had regurgitated contained large numbers of dung beetle parts.

Unlike most other types of owls, burrowing owls are active during the day, when they often can be seen seemingly standing sentry outside their burrows. Many dung beetles also forage during the day.

"You can go out there and see these owls standing in front of their burrows and it looks like they're not doing anything," Levey said. "But I think it's pretty clear that they've got that old line in the water, fishing for these beetles."

To test the hypothesis, the researchers removed all the dung from the ground surrounding about a dozen of the owls' burrows at the sites of two separate North Florida populations. They then added similar amounts of cow manure to half the burrows, leaving the others without any. After four days, they collected all the pellets and prey remains near the burrows, then repeated the experiment by switching the control and experimental burrows, putting manure by those that had none in the prior test.

Examinations of the pellets and beetle parts around the burrows revealed that at those with dung, the owls "consumed 10 times more dung beetles and six times more beetle species than when dung was not present," according to the Nature paper.
The researchers do not believe the owls evolved their behavior solely to attract dung beetles, Levey said.

Levey also cautioned that the researchers make no claims the owls are consciously using the dung as bait, but rather that it has simply proved to be an effective and lasting behavior from an evolutionary standpoint.
The research was funded with a $500 grant from UF's University Scholars undergraduate research program. The paper's other authors are R. Scott Duncan, a faculty member at Birmingham-Southern College in Alabama who earned his doctorate at UF, and Carrie Levins, who earned her bachelor's degree in zoology at UF.

Doug Levey, dlevey@zoo.ufl.edu

by Aaron Hoover