Owl Pellet - Food Web Activity

Owl Pellet - Food Web Activity

**Owl Pellet - Food Web Activity:

(Any part of the lab marked with ** and underlined must be included in your activity write up.)

  1. Pre Lab Discussion

Owl pellets are masses of bones, teeth, hair, feathers, scales, and insect skeletons. They are produced and regurgitated, not only by owls, but also by hawks, eagles, and other predatory birds which swallow their prey whole or in large pieces. Because owls swallow their prey whole, each pellet contains virtually complete skeletons of the animals which the owl ate the day before the pellet was formed. By examining the bones of the animals which were eaten, the types of animals that are eaten and the number of each species in the diet of an owl can be determined.

  1. **Purpose: Dissect and identify the components of an owl pellet. Determine the transfer of energy through the trophic pyramid by studying all parts of a food web.
  2. Materials

Barn owl pellet

Magnifying glass

Dissecting tools

Newspaper and white piece of paper

Identification key

  1. Safety

The barn owl pellet has been sterilized and does not contain any harmful or disease-carrying organisms. The pellet can be dissected with bare hands but wash your hands when the laboratory exercise has been completed.

  1. Procedure
  2. Place an owl pellet on a sheet of white paper.
  3. Using dissecting tools, separate the bones of the animals in the pellets from the fur and feathers. Bones are extremely fragile. (Don’t sneeze or cough on the specimen as it is laid out on the paper, if you do you’ll understand why.)
  4. Remove all fur and debris from the bones and sort them according to their types (example: skulls, vertebrae, femurs, etc).
  5. Using diagrams of the skeletons of owl prey animals and the magnifying glass identify the prey species whose skulls you have found in the pellet. Examine the teeth, especially the incisors and molars, to assist you in the identification.
  6. Separate the skull bones using the following criteria:
  7. Shape and size
  8. Shape of eye socket
  9. Length of snout compared to the rest of the skull
  1. **OBSERVATIONS & DATA:
  1. Individual Data

Total number of prey species found in owl pellet = ______

Name(s) of species found in owl pellet = ______

  1. **CLASS DATA (TOTAL # OF PELLETS DISSECTED ______)

Prey Species / Numbers Present / Percent of Total Prey
Mouse
Mole
Shrew
Vole
Bird
Total #
Average number of prey animals per pellet:

Table 1. Owl prey and their respective diet

Prey / Diet
Mouse / It eats a wide variety of plant and animal matter depending on what is available, including insects and other invertebrates, seeds, fruits, flowers, nuts, and other plant
products.
Mole / A mole's diet is mostly insects and other invertebrates, including earthworms, centipedes, millipedes, snails, slugs, grubs, ants, sowbugs, termites, beetles, and crickets
Shrew / Food habit studies have revealed that shrews eat beetles, grasshoppers, butterfly and moth larvae, wasps, crickets, spiders, snails, earthworms, slugs, centipedes, and
millipedes. Shrews also eat small birds, mice, small snakes, and even other shrews when the opportunity presents itself. Seeds, roots, and other vegetable matter are also eaten by
some species of shrews.
Vole / Voles are found in habitats ranging from meadows, to marshy areas, forests, dry plains, prairies, and even ocean beaches. They eat chiefly green vegetation but seeds, nuts, bark fungi, and some insects..
Bird / Eat insects; terrestrial non-insect arthropods, seeds, grains, and nuts; fruit.

VII. **Analysis and Conclusion

1. Use Table 1 (above) to draw and label a Food Web that is representative of the bone specimens from the pellet. Remember all arrows go from “food to feeder” to show the movement of energy.

•Draw and label the owl as the top consumer.

•Draw and label all prey found in the pellet as the next level of consumer.

•Draw and label any consumers eaten by the prey.

•Draw and label any producers eaten by prey or consumers.

•Draw ‘energy’ arrows from victim towards consumer (head of the arrow points towards consumer) - From each producer towards each primary consumer that eats that producer.

•Repeat for each level towards the owl. Note: some arrows may be drawn sideways.

**Post Lab Questions: (answer in complete thought/sentences)

  1. What happens to the number of producers if there is an overabundance of rain in one season?
  2. What therefore happens to the number of consumers if there is plenty of rain?
  3. What would happen to the number of prey if the owl was removed due to something such ashabitat destruction? Why?
  4. How would question #4 change the shape of a trophic pyramid? Explain, sketch if needed.
  5. If the owl population increases over the next 5 years, what would that do to the food web you created from question 1? Specifically mention organisms found in the food web.
  6. If the “rodent” or bird was removed from the food web because of a rodenticide (pesticide). How would this affect the rest of the organisms in the web? Be specific and mention trophic levels.
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