Name______Period______

Owl Pellet Dissection Lab

Background: Predatory mammals such as bobcats and wolves have teeth to grind up the bones and claws of their prey, 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. Instead, these materials form a pellet that is surrounded with the hair or feathers of the prey consumed.

Barn Owls swallow small rodents and birds whole, and the resulting pellets generally contain the complete skeletons of their prey. Pellets begin forming within the digestive tract of an owl as soon as the prey is swallowed. Enzymatic juices break down the body tissues in the prey but leave the bony materials and hair or feathers undigested. Depending upon the prey eaten, the undigested portions may include beaks, claws, scales, or insect exoskeletons. This type of material has little nutritional value and must be orally expelled, or “gagged,” before the owl feeds again.

Pre-Lab:

  1. Based on its diet, would a Barn Owl be considered an herbivore, carnivore, or omnivore? Why?

Before you dissect the pellet, examine the outside of the pellet for clues to where it was gathered. Pellets are collected from a variety of places around the country. Use the information below to see if you can determine where the Barn Owl might have gagged your pellet.

What you might find / Where the owl gagged the pellet
milo seeds (small seeds) / open sheds
grain / grain elevator
dirt / under trees
hay or straw / barns and hay sheds
feathers / man-made nesting boxes
pine needles / under evergreen trees

Based on the outside of the pellet and the chart above, where do you think the pellet was found? ______

Procedure:

  1. Dip your pellet in a beaker of water for approximately 20 seconds to make it easier for you to pull apart.
  2. SLOWLY and CAREFULLY pull your pellet in half to expose the inside.
  3. Using dissecting needles and forceps, carefully separate the bones of the animals from the fur and/or feathers.
  4. Clean the bones of debris and sort them according to type (e.g. skulls, vertebrae, etc). Clean the skulls as thoroughly as possible since these are the best bones for identifying the prey.
  5. Use the skull key to identify your owl’s prey.
  6. Record the numbers of each type of prey you find on your data sheet. Once you have completed your data table, add your information to the class data table on the board.
  7. Answer the analysis questions about what was in your owl pellet.
  8. If you have extra time, try your best to make a complete skeleton for one species of prey.

Individual Data:

Type of Prey / Number of Skulls
Rodent
Shrew
Mole
Bird

Total number of skulls (or pairs of jaw bones) found in your owl pellet: ______

Class Data:

Type of Prey / Number of Skulls (class total)
Rodent
Shrew
Mole
Bird

Analysis:

  1. How many different animals (total) did you find in your pellet? ______
  1. Assume that an owl forms one pellet each day. Based on your answer from Question 1, how many animals would your owl eat… in a week? ______in a month? ______in a year? ______

Conclusion:

  1. Draw a food chain that includes a Barn Owl. Don’t forget the sun!
  1. On which trophic level is the Barn Owl found? (hint: Look at the pyramid at the bottom of the page)
  1. Why do you think farmers and ranchers want owls in their barn?
  1. Predict what would happen if the Barn Owl population was removed from the ecosystem.