The Comparison Of Diets Of Owl Essay

, Research Paper

Comparing the Feeding Habits of Barn Owls and Screech Owls

Background

Owls are comprised of two closely related families in the avian order Strigiformes-the barn owls, or Tytonidae, and the typical owls, or Strigidae. Owls are relatively large birds, with a big head and short neck, a hooked beak, talons adapted to seize prey, and soft, dense plumage adapted for swift yet almost silent flight. Owls have large eyes located on the front of their face. The eyes are almost fixed in their sockets, so that the entire head must be rotated or bobbed for the gaze to be shifted and for distance to be assessed.

Owls have excellent hearing and very large ears, although these are covered by feathers and are not readily seen. The ears are placed asymmetrically on the head to aid in detecting the location of distant, almost silent prey. Their sense of hearing is probably also aided by their facial disk, which helps to focus sound waves onto the ears. An owl’s sense of hearing is so acute that it can accurately strike its prey in total darkness, following the squeaks and rustling sounds created by a small mammal in motion.

The sex of an owl is not easy to distinguish, although typically, female owls are larger than males. Owls begin to incubate their eggs as they are laid. When hatching occurs it is sequential, and different-sized young are in the nest at the same time. During years when prey is relatively abundant, all of the young will have enough to eat and may survive. In leaner years, however, only the largest young may be fed adequately.

(Egan, T. (1994). Oregon, Foiling Forecasters, Thrives as it protects owls. New York Times, October 11, pg A1, A19)

Most owls are nocturnal predators, mostly feeding on small mammals and birds, and sometimes on small reptiles, frogs, larger insects, and earthworms. A few specialized owls feed on fish. Owls are known to change their food preference, depending on local or seasonal availability. Most owls do not digest the fur, feathers, or bones of their prey, and they regurgitate these items as pellets, which can be collected at roosts and examined to learn about the feeding habits of these birds.

Barn owls

The barn owls are a distinctive-looking group, with a characteristic like facial disk of stiff, white feathers, dark eyes, long legs that distinguish them from typical owls. All barn owls are nocturnal predators, and their prey consists mostly of small mammals. There are nine species of barn owls (genus Tyto) and two species of closely related grass owls (genus Phodilus).

The most familiar species is the barn owl ( Tyto alba). The barn owl is one of the most widely distributed species of birds, occurring on all continents except Antarctica. The barn owl is the only representative of this family in the Americas, occurring uncommonly through most of the United States and in much of Central and South America. The barn owl nests in cavities in trees and in barns and abandoned buildings, and it hunts at dusk and at night over marshes, prairies, fields, and farmyards.

Screech Owl

The screech-owl( Otus kennicotti) is a relatively familiar species in woodlands of temperate regions. This 8.5″(22 cm) long species occurs in several color phases-grey, red, and brown-and it nests in cavities and sometimes nestboxes.

Owl Pellets

The average owl pellet contains bones and other non-digestible items such as hair and feathers. After the bird has eaten its prey; the prey is digested into the gizzard where grinding occurs. After grinding the bird’s gizzard makes a ball of the indigestible material, is expelled by mouth. An average owl can produce an average of one to two pellets a day.

John Day, Oregon

The John Day area is considered a semi-arid desert region. John Day, Oregon is located at Latitude 44.418427 and Longitude -118.949399, which is 125 miles south of Pendleton, Oregon in Eastern Oregon. A desert is an arid land area, one that loses more water through evaporation, than it gains through precipitation-rain, sleet, or snow. These areas generally receive fewer than 10 in (250 mm) of water annually. Average annual precipitation in the worlds deserts ranges from about 0.4-1 in (10-25 mm) in the driest areas to 10 in (250 mm) in semiarid regions. The term desert can also be defined by comparing the solar energy an area receives with the its annual precipitation

Desert animals

The many animals that have adapted to harsh desert life include insects, arachnids, reptiles, birds, and mammals. Unlike plants, these animals can seek shelter from the scorching sun, burning cold, and strong winds by crawling into underground burrows. Reptiles, whose body temperature is controlled by the temperature of their environment, travel between sunlight and shade to stay cool. Birds, utilize metabolic water, behavioral adaptations, active at day or cool parts of the day, may be nomadic and they may migrate during the harsher seasons.

Just as the seeds of desert annuals can stay dormant for decades, so can those of egg-laying desert animals. Amphibians and freshwater shrimp hatch, mature, mate, and lay their own eggs rapid succession in desert pools created by infrequent storms.

Some small mammals, such as rodents, excrete only concentrated urine and dry feces, and perspire little as a way of conserving body fluids. Desert insects protect themselves from hot dry conditions with a waxy coating, long legs that keep them elevated above the hot ground, and virtually moistureless excretions. (Watkins, T.H. (1995). Desert Extraordinare. Audubon 97: 44-54.)

My question is how do the Western Screech-owls and the Barn-owls diets compare. Both live in John Day region of Eastern Oregon, which make the same variety and amount of prey available to both of the owls. I hypothesis that their diet will be very similar if not the same due to the same variety of prey that live in John Day Oregon. Both of the owls have similar feeding habits that include prey like Vole, mice, birds and occasional snakes. I will compare a study done by Hancock Field Station in John Day Oregon on the types of food that the Barn-owl eats in accordance to what they find in the owl pellets verses what I find in five Western Screech-owl pellets.

When I looked at the bones in the five different Screech owl pellets, I was able to see what kind of animals they were from and thus use these results against the results of the Barn owl test done at Hancock Field Station. Comparing these two sets of data will help me answer my question of how the diets of Screech owls and Barn owls compare.

Materials and Methods

To find out how the Barn owl and the Western Screech-owl’s diets compare I collected owl pellets to find out what the owls are eating. I located Western Screech-owl pellets, but was not able to obtain any Barn owl pellets from Eastern Oregon. In lieu of Barn owl pellets, I located a study done by the Hancock Field station in John Day concerning the eating habits of Barn owls. I then collected five Screech owl pellets to dissect. When I finish dissecting the Western Screech-owl pellets I will hopefully be able to find out the average diet of a Western Screech-owl.

To find out what the owls’ diet using the owl pellet, the pellet must be dissected and the different bones and skulls examined. I used a dental pick and a pair of tweezers to separate the hair and feathers from the bones and skulls. Once all bones were separated from the hair, I identified animals by using size of bone, color of teeth, size of skull, and what kind of material surrounds the bones (i.e. hair or feathers.) Once the bones were identified I determined what type of animal. Using this technique on all five Western Screech-owl pellets I was able to get an indication of what the Western Screech-owl’s.

Results

The results I got were similar to the results the Hancock Field Station found on their experiment with Barn owls. When my study of the owl pellets was complete I had two pellets that were mice, two pellets that were Vole and one pellet which was of a bird. When I studied the remains of the owl in the pellets I identified all the bones that were present and came up with a conclusion.

In pellet one I removed the following:

Number of Bones Type of Bones

1 Skull