12.2. Asio otus: Long-eared Owl http://www.ck12.org
Theory #1:Some scientists believe that the wings of birds evolved from an ancestor that would leap into the air to
either capture prey or avoid predators. Based on this hypothesis, scientists conclude that wing were once modified
arms that helped these bird ancestors to leap higher.
Theory #2:Scientists have also introduced the theory that wings evolved from an ancient bird ancestor that lived in
trees. Based on this, these scientist believe that the wings were simply modified arms that helped these ancestors to
glide from tree to tree with much more speed and ease.
Even though there are many theories on how birds took flight, it is a topic that scientists continue the search for
answers, examining fossils of ancient bird ancestors to find out exactly how birds developed wings.
Ecology
Long-eared owls are the hosts of many internal and external parasites.They mainly hunt animals weighing under
100g. Their key prey includes, but is not limited to, voles and deer mice. Additional prey includes kangaroo rats,
pocket gophers, shrews, juvenile rabbits, and other types of rats. They will also occasionally eat small birds, small
snakes, and insects. They also relate to hawks, crows, and magpies, as they have been known to settle in the old
nests of these animals that have been deserted.
Anatomy and Physiology
Long-eared owl pairs will begin to breed anywhere from the beginning of February to mid-July. Females will lay
eggs, generally around 2-10, on 2-day intervals, and will raise 1 brood per season. The eggs have a glossy, smooth
texture and generally have a whitish-grayish coloration. These fledglings generally become independent around 11
months, and the average male and female long-eared owl are sexually mature around the age of 1 year old.
The average lifespan for long-eared owls living in the wild is high, around 27.8 years. Long-eared owls have
excellent low-light eye site and especially great hearing, both helping them capture concealed prey during nighttime.
The flight sounds of long-eared owls are muffled by special wing feathers that allow them to use stealth to sneak up
on prey. Like all owls, long-eared owls are unable to chew their food. Instead, they will swallow their smaller prey
whole, while tearing larger prey to pieces before consumption. Unlike most birds, owls have no crop. The crop is
a loose sac located in the throat that helps most bird species store excess food that will be consumed later. Because
owls lack this special feature, all food is passed directly into the digestive system for immediate consumption.
The long-eared owl, along with all birds, have stomachs that consist of two major parts.The first vital organ is the
proventriculus. This is part of the anterior glandular stomach that produces gastric acids and digestive enzymes,
helping to start the digestive process. The second major part of birds stomachs are the ventriculus or gizzard, which
is located in the posterior muscular stomach.The gizzard is the site of chemical digestion and is designed to grind
food. It serves a filter to long-eared owls, keeping down indigestible items such as bones, teeth, feathers, and fur.
Before it passes through the rest of the digestive system, muscular contractions will grind down the softer parts of
foods. The ground food then passes through the small intestine, where digestive enzymes are released to by the
pancreas and liver.
Several hours after eating, the insoluble materials still in the gizzard (bones, feathers, fur, teeth) are compressed into
a pellet in the same shape as the gizzard. This pellet is then transferred back up to the proventriculus, where it can
remain for up to 10 hours before the regurgitation process begins. Once the regurgitation process is complete, the
long-eared owl is allowed to eat once more, due to the fact that the stored pellet partially block the digestive system,
which prevents the digestion of new prey before the pellet is ejected. However, if various prey are eaten within a one
hour period, the myriad of remains are collected into one large pellet.
Owl pellets differ from the pellets of other birds of prey because they contain more material residue, due to less
acidic digestive juices. Owl pellets are released on a regular cycle, regurgitating them once all nutrients have been
extracted from the pellet by the digestive system.