Owl Pellet Lab (Sample)

Lab. Examining Owl Pellets

I.  Problem?

If all the moles in an area died out due to drought, would all the owls also die out?

Hypothesis – If all the moles in an area were to die out due to drought, the owls also die out.

Skills

-       I learned how to dissect an owl pellet.

-       I also learned how to identify the different bones of small vertebrates through a bone chart.

II Materials and Methods

-       Forceps

-       News paper

-       Bone chart

-       Water

-       Lab sheet

-       One owl pellet

III Procedure

1.     Receive the forceps from the teacher.

2.     Slightly dampen the owl pellet.

3.     Begin to dissect the pellet, separating fur and feather from bone.

4.     Using the bone chart, sort the bones and determine what organisms the owl ate.

5.     Answer the questions and draw conclusions.

IV Data and Observations

1.    Owl pellets are a dense mass of bone, fur and feather; materials that are indigestible to the owl.

2.    Many skeletons are incomplete

3.    The owl eats more of the smallest animals than the larger ones.

Owl Pellet Data Table

Type of Prey	#S  found in sample	Prey Biomass in grams	Total biomass consumed
Rodent	1	150g	150g
Shrew	2	4g	8g
Mole	1	55g	55g
Bird	2	15g	30g

Total Biomass Eaten -  243 g

V Analyze and Apply

1.     Forming owl pellets help owls survive better by allowing them to expel materials that are harmful for them to digest.

2.     Our particular owl ate six animals at least.

3.     You can tell the difference between a vertebrate and an invertebrate because in the case of vertebrates, backbones or vertebrae would be present.

4.     If an owl eats 120g of food in a day, it would need to eat 30 shrews.

5.     If all the shrews in a forest died out, the owl would only be slightly affected at first. Shrews are not the owl’s only prey; an owl could work around this hole in the food chain. However, overall, whatever the shrews eat will overpopulate and what eats the shrews will have a limited food source. Also, the owl’s other food sources will diminish as a single owl must eat more rodents, birds and moles to satisfy his need for energy. At the end of the “day”, this eradication of the shrews would lead to a trophic cascade because the food web is interconnected and if one thing dies, there are serious repercussions for everything else.

6.     If all the rodents in the forest died our after the shrews, again there would be a trophic cascade in the long run because one organism cannot be eradicated in an ecosystem without there being repercussions.

7.     If an owl were to eat 100 one-gram insects and one 100 gram rat, the insects would offer more energy. Because they are lower down on the pyramid of energy, they have a higher concentration of energy for the owl. In addition, the owl would use less energy to hunt insects as opposed to rate=s because they have slower reflexes and are more plentiful in the ecosystem. The owl does not also have to exert as much energy to hunt.

8.     Quality over quantity is more important to the owl. If he eats lower down the food chain, he can eat less, consume more energy, and exert less energy during the hunt. Eating secondary and tertiary consumers will decrease his energy, force him to eat more, hunt more and for longer.

9.     From this lab, I can conclude that an owl could not possibly survive the death of all moles in his ecosystem. This is so because food webs are so intertwined no organism could survive the eradication of another species without a trophic cascade occurring.