Owl Pellets

Owl Pellets


Background

Owl pellets are masses of bone, teeth, hair, feathers and exoskeletons of various animals preyed upon by raptors, or birds of prey. Pellets are produced and regurgitated not only by owls, but by hawks, eagles and other raptors that swallow their prey whole of in small pieces. Owls feed 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, feather 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 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.

Materials

  • Owl pellets
  • Dissecting Needle
  • Paper

Procedures

  1. Unwrap your owl pellet
  2. Measure the approximate length and width of your owl pellet in cm
  3. Weight your owl pellet in grams to the nearest tenth (one place after the decimal point)
  4. Make observations about the surface of your owl pellet
  5. Carefully tease apart your owl pellet, being careful not to break or lose any small bones.
  6. Choose a skeleton and use the attached identification sheets to reconstruct the skeleton of the prey.
  7. After obtaining all of your data, dispose of the fur and feathers from your pellet and place any bones in a labeled petrie dish.

    Data and Observations

    1.      Length of your owl pellet_______        Average length_______
            Width of your owl pellet_______         Average width_______
            Mass of your owl pellet_______          Average mass_______
    
    2.      Total number of prey animals found_______
                    Birds_______
                    Rodents_______
                    Insects_______
                    Other_______
            Average number of prey per pellet_______
    

    Questions and Conclusions

    1.If a barn owl produces one pellet each day, estimate how much food the
    owl would eat in a year.  (Show your work.)
    
    
    
    
    
    
    2.The average adult barn owl requires 80 to 100 grams of food daily.  Find
    out how much a typical adult barn owl weights, and calculate the percentage
    of its weight that it must consume daily to survive.
    
    weight of prey / weight of owl=  % of weight
    
    
    
    
    
    
    
    3.Do you think an herbivore would consume a larger or smaller % of its
    weight that a carnivore? Why or why not?
    
    
    
    
    
    
    
    
    4.Environmentalist are concerned about the accumulation of certain poisons
    in the body systems of predators.  Why do you think owls, eagles,
    swordfish, lions and humans are often the most threatened organisms in a
    community that is exposed to DDT or mercury? (Both DDT and mercury are
    stored, not broken down in animals)
    
    
    
    
    
    
    
    
    
    
    5.On the other side of this paper, construct a diagram of a food web (of at
    least 15 animals) with an owl at the uppermost trophic level.  Use an arrow
    to show which organism in the consumer or predator.
    
    
    
    
    
    
    
    
    
    
    
    6.Use the following diagram to reconstruct the skeleton of one of the prey
    items consumed by your owl.