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Do Not Disturb
A new study suggests that eagle owls use a natural sort of “paint” to mark their territory. 

A breeding eagle owl perches next to a rock is has marked with its white feces.

Keeping tabs on where birds do their business sounds like a dirty chore, but it can offer insight into the way some species communicate—at least where eagle owls (Bubo bubo) are concerned. These European birds use vocalization to attract one another’s attention, but recent studies have shown that they also respond to visual forms of communication. For example, young eagle owls develop a bright patch of feathers at the edge of their mouth just before fledging. The brighter the patch, it seems, the more fit the bird; the more fit the bird, the worthier it is of receiving food from its parents.

A recent study appearing in the Public Library of Science has now identified another method of visual signaling that adds to the bird’s repertoire. Vicenzo Penteriani and Maria del Mar Delgado, researchers from Spain’s Department of Conservation (part of the Estación Biológica de Doñana, which is affiliated with the Consejo Superior de Investigaciones Científicas) found that eagle owls selectively defecate on dark rocks and other prominent structures near the nests—which are actually holes made in the ground—before they lay eggs and throughout the nestling period.

Eagle owls mark posts that are very close to their nests, which are holes in the ground.

Among the methods it used to gather proof, the research team painted over rocks and posts that the eagle owls had christened and found that the birds refreshed the same areas soon thereafter. The team also found piles of brightly colored feathers—plucked from other birds—in similar spots as the eagle owls’ white feces. Given that eagle owls’ diet consists mainly of rabbits, the discovery of plumes from prey such as short-eared owls, wood pigeons, azure-winged magpies, and little egrets suggested that the birds were trying to say something.

Eagle owls go on marking sprees during the breeding season, mainly from the courtship to the fledgling period.  

That “something” is probably “keep out,” according to Penteriani. Eagle owls are aggressive, and confrontations generally end in the death of one of a squared-off pair. Squirting feces and flinging feathers could be a strategy to avoid direct confrontation by signaling that an area is occupied. It also lasts longer than a warning call. After an eagle owl demarcates its terrain, it can take off hunting while the poop and plumes do the work of a no-trespassing sign. “This is a very economic way to mark a territory,” says Penteriani.


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