Owl Pellet Dissection

Owls of Maryland

• Five species of owls live in or pass through Maryland.

1. Barn owls

2. Great Horned owl

3. Barred owls

4. Eastern Screech owl

5. Northern Saw-whet owl

Barred Owl

Adaptations as predators

• Owls have special adaptations that enable them to hunt at night.

1. Their eyes are large and fixed, with binocular vision and good depth perception.

2. Because owls are unable to move their eyes, they have developed an incredibly flexible neck that allows them to turn their head 270 degrees in both directions.

3. Their eyes are also extremely light sensitive, allowing them to see well at night.

Barred Owl

4. Owls rely on silent flight to surprise their prey.

5. The shape of the owl’s flight feathers muffles the sound wind makes as it flows past them.

6. These are all perfect adaptations for finding and catching prey at night, and explain why owls have become the most efficient “hunters of the night”.

Owls as predators

Saw-Whet Owl

An idealized food pyramid

Owl Pellets

• Predatory mammals such as bobcats and wolves have teeth to grind up bones and claws, and, a digestive tract adapted to pass these ground parts.

• Owls, on the other hand, do not have teeth for grinding and cannot pass whole bone and claws through their digestive tract safely.

• The protein enzymes and strong acids that occur in the digestive tract of raptors do not digest the entire meal.

• The relatively weak stomach muscles of the bird form the undigested fur, bones, feather etc. into a bolus (or wet slimy pellets).

• The undigested portions may include beaks, claws, scales, or insect exoskeletons. This type of material has little nutritional value and must be passed from the body.

• The owl pellets that you will be examining in this lab have been collected and fumigated from common barn owls (Tyto alba).

• Owl pellets themselves are ecosystems, providing food and shelter for communities that may include moths, carpet beetles and fungi.

• Moth larvae are frequently abundant in pellets, feeding on fur and feathers. The black spheres about the size of periods (.) that are found in the pellets are the droppings of the caterpillars. The larvae metamorphose near the surface of a pellet in cocoons made of fur.

Owl Pellets• Ecologist examine owl pellets to estimate the diversity of prey species

• The contents are a direct indicator on – What the owl has fed

upon.– Species richness– Species abundance

• Important information for species management and protection

Species diversity has two components:

1. Species richness: how many different species are present in a habitat

2. Relative abundance: total number of individuals of each species present given in % of total.

Species diversity has two components:

4%

6%

8%

14%

17%

18%

33%

7. American Beech

6. Loblolly Pine

5. American Holly

4. Oaks

3. Sweet Gum

2. Black Gum

1. Red Maple2003 1. Species richness:

how many different species are present in a habitat

2. Relative abundance: total number of individuals of each species present given in %

Common Name

Genus Freq Found

Vole Microtus 70%

Shrew Sorex 20%

Mole Scapanus 5%

Deer Mouse

Peromyscus 2%

House mouse

Mus 2%

Rat Rattus 1%

(small bird)

Hirundo rare

Type and # of bones

Vole Shrew Mole Rat Mice Bird

Skulls

Jaws

Shoulder blade

Front legs

Hips

Hind legs

Assorted ribs

Assorted vertebrae

# of animals