Owl Pellets Lab 08

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					                                                   Owl Pellet Lab
Name: _________________________

Background Information:
The predator prey relationship is important in an ecosystem. How can we measure that relationship? It would be
difficult to follow a predator, such as a wolf, for a day, a week, or longer to record exactly what and how much it ate.
Owls, however, provide a convenient means of studying the predator-prey relationship. They eat their entire prey,
including the fur and bones, digest the muscle and other soft tissues, and form the indigestible parts into a pellet, which
they regurgitate.

When you first see an owl pellet, you will think that it is its feces (solid waste, poop, doo-doo, whatever you call it!), but
this pellet has been ejected from the mouth. Owls are predators and basically they eat their prey whole. They eat
rodents, shrews, moles, and birds. In the owl’s stomach, the flesh is digested, but the fur and bones are passed back out
through the mouth. Still doesn’t sound like something you would want to touch, does it? These pellets were collected
and fumigated to kill all bacteria and parasites. They are perfectly safe to touch (with gloves, of course!)

Pellets are produced and regurgitated not only by owls, but by hawks, eagles, and other raptors that swallow their prey
whole or in small pieces. Owls feed early in the evening and regurgitate a single pellet approximately 20 hours after
eating. Unlike snakes, the protein enzymes and strong acids which 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, feathers, etc. into wet
slimy pellets. In this process, even the most fragile bones are usually preserved unbroken.

The owl pellets that you will be examining in this lab have been collected and fumigated from common barn owls. Owl
pellets themselves are ecosystems, providing food and shelter for communities which may include clothes moths, carpet
beetles and fungi. Clothes moth larvae are frequently found in pellets, because they feed 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.

In this investigation, you will work in groups of two to analyze the food consumed by an owl. From the data gathered,
you will determine common characteristics of owl prey and make inferences about predator-prey interactions in an

Pre-Lab Questions:
    1. If you were a zoologist doing a study of what wild horses eat, how would you collect your data?

    2. How might learning about an owl’s diet (what it eats) help us preserve the animal?

owl pellet, dissecting needle, forceps (tweezers), bone chart (attached), bone organization sheet (attached), ruler,
  1. Measure your owl pellet.

          a. Length of owl pellet       ___________ (cm)

          b. Width of owl pellet        ___________ (cm)

          c. Mass of owl pellet         ___________ (g)

  2. Carefully examine the exterior of the pellet. Do you see any signs of fur? Any signs of feathers? What color is
     the pellet? What does it feel like?

  3. Carefully use the dissecting needle and forceps to break apart the owl pellet and observe what is within. BE
     CAREFUL!! The bones are delicate and you could break them. Sort the bones into piles of similar size and shape
     on the Bone Organization Sheet. Use the attached bone diagram to help you identify your bones and then
     complete the chart below.

              Bone                           Type of Animal               Number Found




              Forelimb (arm bones)

              Hindlimb (leg bones)

              Pelvic bone (hip bones)


Analysis Questions:
   1. What do we know about the digestive system of an owl based on the pellets we observed?

   2. How would a sudden increase in a shrew population affect the barn owl population? What effect would a
      decrease in mole population do to the owl population?

   3. Owl pellets not only give us information about the diet of the owl, but owl pellets also provide a habitat for
      other animals. In fact, an owl pellet is a little ecosystem all on its own. What kinds of animals are found in the
      owl pellet ecosystem? (Hint: read the background on the first page!)

   4. Other types of birds form pellets. What would you expect to find in the pellet of a seagull?

   5. Owls, hawks and eagles are types of raptors, animals that have hooked beaks and sharp claws. They are
      adapted for seizing prey animals. Hawks and eagles differ from owls in that they eat their prey animals by
      tearing them into small pieces, picking out the flesh and avoiding most of the fur and bones. They also have
      strong stomachs which can digest most of the bone material which they might eat. The relatively small amount
      of indigestible bone and fur that remain will be compacted by their stomach muscles into a pellet similar to an
      owl’s. Do you think an eagle pellet would be as useful for dissecting as an owl pellet? Please explain your

   6. Construct a diagram ON A SEPARATE PIECE OF PAPER of a food web. The food web should include an owl at the
      highest trophic level and at least 6 other animals. You web should include at least 2 of the animals that were
      found in your owl pellet.
Bone Organization Chart:
      SKULL                JAW

      SCAPULA              FORELIMB (ARMS)


      RIBS                 VERTERBRAE

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