January 2009 - Owl Pellets: Barn Owl (Tyto alba)

The upperparts of the barn owl are light grey with numerous fine dark lines and scattered pale spots on the feathers. There are buff markings on wings and on the back. The underparts are white with a few black spots, occasionally none. Feathering on the lower legs may be sparse. The heart-shaped facial disc is white with a brownish edge, with brown marks at the front of the eyes, which have a black iris. Its beak is off-white and the feet are yellowish-white to brownish. Males and females are similar in size and color, females and juveniles are generally more densely spotted.

The Barn Owl is one of the most wide-spread of all land birds. They are found on all continents (except Antarctica) and large islands and occur over the whole of Australia, including Tasmania. They occur throughout most of Britain and Europe and across many parts of Asia, Africa, and in much of North America. In South America they are found in areas of suitable grassland, as well as on oceanic islands such as the Galapagos. They were introduced to Hawaii in 1958.

Barn owls generally are nocturnal, although it is not uncommon to see them emerge at dusk or be active at dawn, occasionally being seen in flight during full daylight. Flight is noiseless, with wingbeats interrupted by gliding.

The Barn Owl calls infrequently, the usual call being a drawn-out rasping screech. The courtship call of male at nest is a shrill repetitive twittering. Adults returning to a nest may give a low, frog-like croak. When surprised in its roosting hollow or nest, it makes hissing and rasping noises and snapping sounds that are often called bill snapping, but possibly made by clicking the tongue.

Barn Owls specialize in hunting small ground mammals, and the vast majority of their food consists of small rodents. Voles (field mice) are an important food item, as well as pocket gophers, shrews, mice and rats. Barn Owls breed rapidly in response to mouse plagues. Other prey may include baby rabbits, bats, frogs, lizards, birds and insects. Prey are usually located by quartering up and down likely looking land - particularly open grassland. They also use low perches such as fence posts to seek quarry. Like many owls, it eats small prey whole and then regurgitates indigestible parts such as hair, feathers, and bones in the form of pellets.

So, what is an owl pellet and what does it tell us?

An owl pellet is the indigestible parts (fur, bones, teeth & feathers that are still in the gizzard) of its prey and are compressed into a pellet the same shape as the gizzard. This pellet travels up from the gizzard back to the stomach. It will remain there for up to 10 hours before being regurgitated. Because the stored pellet partially blocks the Owl's digestive system, new prey cannot be swallowed until the pellet is ejected. Regurgitation often signifies that an Owl is ready to eat again. When the Owl eats more than one prey item within several hours, the various remains are consolidated into one pellet.

The pellet cycle is regular, regurgitating the remains when the digestive system has finished extracting the nutrition from the food. This is often done at a favorite roost.