Most owls do not bother to tear small prey such as mice and voles apart but instead swallow them whole. After eight to sixteen hours, all the nutrients available in the eaten prey have been absorbed by the bird. Owls cannot digest the fur, feathers, bones, teeth and nails of their prey, so these parts remain in the bird’s gizzard (specialized organ that grinds up food in most birds but serves as a filter for holding indigestible parts in birds of prey). This accumulation of indigestible parts takes on its pellet form (which is the shape of the gizzard) about eight hours after ingestion, but is sometimes retained by the owl for another six hours or so before being coughed up. As a rule, bones are on the inside of the pellet, and the fur and feathers form a soft coating on the outside.
The stored pellet partially blocks the entrance to the digestive system so it must be ejected before the owl can eat again. This process takes anywhere from a few seconds to several minutes. The owl appears to “yawn” several times before regurgitating the pellet. Note that the pictured Barred Owl has prey (a Deer or White-footed Mouse) in its talons, but out of necessity is getting rid of a pellet before devouring it.
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