Why don t owls completely digest food like other birds and animals

A. Owls have several digestive features that mean they have to regurgitate the remains of indigestible food in the form of pellets rather than pass them out through their digestive system.

However digestible parts are passed right through the bird in the normal way.

Q. Why are some foodstuffs indigestible

A. Like other bids, owls cannot chew their food. Owls are birds of prey and so often catch relatively large mammals, which they tear to pieces before eating. But, because smaller prey is often swallowed whole and because owls have relatively weak beaks, something has to happen to the indigestible bits like the skeleton and fur.

Q. Why can't owls stomachs digest these things, I thought stomach acid could break down all kinds of things

A. Owls have relatively weak stomach acid, with a ph of around 2, similar to vinegar. Consequently only the prey's soft tissue is digested leaving fur and bones, often intact, to be regurgitated. This, and the fact that other bids of prey tend to pluck their meal before eating, means that owl pellets contain a greater proportion of food residue.

Enthusiasts are therefore given a graphic insight into the owls dining preferences.

Q. What happens to the food once it's been torn up and swallowed

A. Because owls don't have a 'crop' food is passed straight into the owl's digestive system. First of all anything that can be broken down is taken care of by the owls stomach acids. Then anything indigestible is filtered out.

Q. What's a crop

A. It's a loose sac, located in the throat, where other birds store food for later.

Q. What happens to the indigestible parts

A. Several hours after eating, the owl's stomach compresses everything into a pellet that is then pushed back up into the throat where it remains for up to 10 hours.

Q. Doesn't this prevent the owl from eating

A. Yes, until the pellet is regurgitated nothing else sizeable can be swallowed. When the owl finally expels the pellet it often signifies that it's ready for its next meal.

Q. Do only owls regurgitate undigested food

A. No, more than 300 bird species do it.

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by Lisa Cardy