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Дата канвертавання27.04.2016
Памер15.61 Kb.
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Virtual Owl Pellet Dissection:

A Study of Food Chains & Food Webs 

 

INTRODUCTION

Owl pellets are the undigested remains of prey ingested by an owl.  The owl swallows its prey whole, and during the process of digestion, the soft parts of the prey are dissolved and passed on to the intestine for absorption.  The hard, non-digestible parts-bones, teeth, fur, feathers, and chitonous remains of insects are compressed in the gizzard and passed on to the proventriculus where the pellet remains until it is expelled.  These pellets are not eliminated as feces, but are regurgitated through the mouth.

 

Pellets are not found exclusively within the owl families.  There are many species of birds known to regurgitate pellets; hawks, eagles, kites, harriers, falcons, and even robins are some of the more familiar ones.  Out of all types of pellet ejectors, the efficiency of the process is probably as high in owls as in any other bird.



 

The Common Barn Owl feeds in early morning and early evening and will usually produce one to two pellets per day.  Glossy black when fresh, the pellet remains smooth and dark in color when dry.  These pellets can provide valuable information pertaining to the diet of owls.  By studying the contents of owl pellets, one may discover seasonal, regional, and habitat differences and even differences in individual tastes between owls.  Also, pellets can be used to effectively illustrate the nature of food chains, to demonstrate the role of avian predators within the ecosystem, and to provide information about the presence and relative abundance of animals in a particular area.  As an educational tool, pellets can also be used to introduce students to skeletal anatomy and to teach others how to identify and animal by its skull and jawbones.

 

The pellets in this Pak are from one of the two owl families, Tytonidae or Strigidae.  Each pellet has been fumigated to eliminate the presence of any insects and then individually wrapped for preservation.  Unless otherwise stated, the pellets in this Pak are from the family Tytonidae and more specifically, the Common Barn Owl (Tyto alba).



 

PURPOSE

Students will dissect owl pellets to collect and count the contents in order to create food webs.



 

PROCEDURE

  1. Open up Internet Explorer and go to this website http://www.kidwings.com/owlpellets/flash/v4/index.htm

  2. Click on the pellet to remove the fur.  Fur will automatically move to a pile in the corner.

  3. Click on the bones and drag them to the skeleton.  Match the bones correctly and they will snap in place. Note: Be sure to have your earphones so you can hear the name of the bones as you click on them.

  1. At any time you can click on the label button to turn the labels on or off.

  2. When you have correctly matched you will have a chance to download a certificate that you can print.

  3. In order to get credit for your dissection, you must save your certificate and email it to me.

Data, Observations, & Analysis:
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.

Rat

The rat's diet typically includes seeds, nuts, grains, vegetables, fruits, meats and invertebrates. They consume about one-third of their weight in food every 24 hours. Because of their inability to vomit, rats are very hesitant to try new foods that may be poisonous. They will take a small nibble and wait to see if they feel sick and, if so, will avoid that food in the future.

Bird

insects; terrestrial non-insect arthropods, seeds, grains, and nuts; fruit

Vole

Voles' diet includes many things, including grasses, sedges, seeds, flowers, leaves, roots of shrubs and small trees, bark, tubers, bulbs, and sometimes insects.

1. Use the information from Table 1 to construct a diagram of a food web (of at least 5 animals) with an owl at the uppermost trophic-level. The food web should be representative of your pellet. Be sure to include energy arrows in the proper direction.

 

Analysis Questions

1. What do we know about the digestive system of an owl based upon the pellets?

2. Owl pellets not only can give us information about the diet of the owl, 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 at the beginning)

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

4. Owls, hawks, and eagles are types of raptors, animals that have hooked beaks and sharp claws, and are therefore 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 that 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 the owls. Do you think an eagle pellet would be as useful as an owl pellet for dissection? Why or why not?

5. How would a crash in the shrew population affect the Barn Owl population?

6. How would a crash in the mole population affect the Barn Owl population?



7. Is the owl pellet the "end" or termination of a food chain? Explain. Is it the "end" or "termination" of a food web? Explain with details and/or examples.


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