Owl Pellets
Imagine sitting down to a dinner of your favorite food and swallowing it in one big, indelicate gulp. No cutting anything into bite-sized pieces and no chewing; just swallowing your whole meal, bones and all.
This is exactly what many birds do. Their small prey are captured and killed, hurriedly swallowed, passing bones and all through the esophagus to the gizzard. The gizzard acts as a trap, separating the indigestible food items such as bones, teeth, nails, insect exoskeletons, fur, and feathers from the soft, nourishing parts. Parts that can’t be digested are formed into an elongated ball called a pellet. Once formed, this pellet of slimy, hard material is regurgitated when the bird leans forward, opens its mouth, and throws it up. Interestingly, the potentially harmful teeth, nails, and bones are neatly packaged towards the middle of the pellet. Softer fur or feathers form the outer layer, thus protecting the bird’s esophagus.
Pellet formation is typical of birds of prey such as hawks, eagles, and owls, but it also occurs occasionally in albatrosses, kingfishers, bee-eaters, swifts, goatsuckers, grouse, and gulls. Basically any bird that swallows whole prey or indigestible food fragments can cough up a pellet. In fact, there seems to be a need to produce pellets. Captive owls, for example, need the extra roughage in their diet to survive. Injured owls undergoing rehabilitation will thrive only if their food is rolled in fur or other hard fragments that require their gizzards to produce pellets.
Pellets are usually oval to round and gray to brown. Small owls, like Eastern Screech Owls, generally regurgitate pellets of only 1-1.5 inches. Great Horned Owl, Barred Owl, and Barn Owl pelletsare often 2 to 3 inches long. The size, shape, and color of pellets are sometimes diagnostic of the species of bird that produces them, but the food item also affects a pellet’s appearance. Soft, fuzzy yellow chicks fed to bald eagles become hard, dry yellow pellets.
A typical pellet takes from 12 to 20 hours to form in the bird’s gizzard. Generally, two or three pellets are produced per day. If the bird’s favorite roosting site or nest is in a dry and protected area such as a barn silo, pellets can accumulate in the nest or on the ground. Frequently, moth larvae, beetles, other decomposers, and the effects of weather reduce the pellets to piles of tiny, broken pieces.
The contents of owl pellets are quite valuable in determining what a bird has eaten and give excellent clues to members of the community food web. Pellets of a Great Horned Owl, for example, may contain bones of snakes, frogs, fish, crayfish, insects, scorpions, many birds, and many mammals including rates, mice, gophers, skunks, squirrels, rabbits, chipmunks, weasels, and even domestic cats.
PELLET FORMATION IN THE GIZZARD
Having no teeth, birds must either crunch their food with their beak, tear off chunks, or swallow it whole. A bird has as many as seven salivary glands in its mouth. These glands are well developed in seed eaters such as finches and sparrows. Saliva not only acts as a lubricant, but it also contains digestive enzymes which quickly begin to break down the food.
If a large quantity of food, such as corn or bird seed, is swallowed, the walls of the esophagus will enlarge and form a crop. The crop is used to temporarily store food before it passes into the stomach.
Many birds have astomach divided into two parts; the anterior proventriculus and the posterior portion called the gizzard. The proventriculus secretes acidic gastric juices that digest soft food. Most fruit and fish eating birds have a well-developed proventriculus.
The gizzard is very muscular, especially in birds that eat seeds and other rough vegetation. The inside lining of the gizzard is covered with a tough, pleated lining, or koilin layer, which helps in the grinding action of the gizzard. Some birds, such as pigeons, carry small stones or grit in their gizzards which help pulverize their food. Fish-eating birds, such as grebes, swallow feathers which protect their gizzard from injury from sharp bones.
Pellets are formed in the gizzard. The proventriculus, pancreas, and small intestine secrete enzymes into the gizzard during digestion. The nutrient effluent is pumped by muscular contraction into the small intestine for further digestion and absorption, while the indigestible solids collect to form the tight pellet. The pellet is forced from the gizzard and through the esophagus by muscular contractions of the gizzard, proventriculus and abdominal wall. It takes about five minutes to expel a pellet.
Where can you buy owl pellets?
Learn how to dissect an owl pellet.
Identify the bones from an owl pellet.
What owls live in my neighborhood?