Owl Pellet Investigation
Learning Target
Understand that that changes to physical or biological components of an ecosystem affect populations.
Success Criteria
I can recognize the different changes that can happen within an ecosystem.
I can recognize how the different changes could have an impact on specific organisms within an ecosystem.
Questions to Ponder
What are three things you know about owls?
Do you know your owl facts?
Take this short survey to see what you know about owls
Owl Adaptations
Owls are a type of carnivorous bird called raptors. Other raptors include hawks, eagles, falcons, and ospreys. Most raptors hunt small mammals, birds, amphibians, reptiles, and larger invertebrates. All raptors possess similar adaptations that allow them to hunt: they are strong and agile fliers, they have keen eyesight to locate prey, strong legs and talons for capturing prey, and hooked bills to tear flesh. Although owls share these characteristics, they have adapted to their nocturnal lifestyle. Other species of raptors are active primarily during the day so they have not evolved these specialized adaptations to be active at night.
Owl Traits
As a Team...
Your team will be assigned one of the following owl adaptations. Adaptations can either be structural or behavioral. Explain the unique structural and behavioral adaptations that allow owls to survive in darkness.
Eyesight
Hearing
Silent Flight
Talons and Beak
Behavior
Diet
Owl-natomy
Owls have two stomachs; the proventriculus and the ventriculus. Owls cannot chew so they swallow their food whole and use muscular contractions in the proventriculus to separate the meat from the bones and fur.
Owl Pellet Investigation
Learning Target
Understand that that changes to physical or biological components of an ecosystem affect populations.
Success Criteria
I can collect and analyze data from observations.
I can compare and contrast human skeletons to other skeletons.
I understand the term "indicator species."
Questions to Ponder
What types of animals do Barn Owls eat?
What ecosystem did those animals most likely come from?
How do animal (such as rodents) skeletons compare to human skeletons?
Why do we dissect Owl Pellets?
Owl pellets provide important information to ornithologists about owl adaptations and habits. Scientists can determine what owls are eating at various times and places by finding and dissecting owl pellets. Owl pellets also provide information about the approximate numbers of prey animals in the owl's feeding area, which is valuable information to scientists studying animal populations. Pellets are often found at the base of a perching tree.
Materials
1 owl pellet
bone sorting charts #1 and #2
gloves
dissection picks
tweezers
scale
Procedures
Observe - Carefully unwrap your owl pellet from the aluminum foil and observe it.
Are there any bones sticking out or other features that may indicate what organism may be inside?
Measure - Use the scale to find the mass of your owl pellet. Record this in your notebook.
Categorize - Pull the owl pellet apart and start separating the fur from the bones. Discard the fur. Place the bones in separate piles and begin trying to identify them using the bone sorting charts.
Bones you may find: Skull, Jaws, Scapulas, Forelimbs, Hindlimbs, Pelvic Bones, Ribs
Based on your observations, is there more than one skeleton in your owl pellet? How can you explain this?
Can you identify the skeleton in your owl pellet?
Measure - Use the scale to find the mass of the bones from your owl pellet. Record this in your notebook. Calculate the percentage of bones that comprise your owl pellet.
Reconstruct - Using white glue and a piece of construction paper, use your knowledge of the human skeletal system to try to assemble the bones into a complete skeleton.
Compare - Compare the skeleton diagrams below.
How are they similar and different?
Back to Teams...
What types of animals do Barn Owls eat?
Did you identify anything else in your owl pellet?
How do animal skeletons compare to human skeletons?
How does this activity demonstrate that owls are indicator species? What does their presence indicate?
Extend: Owl Food Web
Design a food web with the Barn Owl as the top consumer.
Your web should have at least 4 trophic levels.
Arrows must show the transfer of energy from prey to predator.
Use the following list of common owl prey and their eating habits*:
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. Deer mice sometimes eat their own feces (this is called coprophagy).
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, ichneumonid 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.
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 - Birds eat insects; terrestrial non-insect arthropods, seeds, grains, and nuts; fruit.
* you do not need to include every organism listed
Owl Food Web Checklist:
at least 4 trophic levels
owl is the apex predator (top of the food web)
arrows showing transfer of energy from producer to consumer
More Owl Facts
There are nearly 150 species of owls worldwide.
Nineteen species of owls are found in North America, north of Mexico.
Owls live everywhere except Antarctica and a few remote islands.
The Elf Owl of the southwestern desert is the smallest owl, standing only 6 inches tall and weighing two ounces.
Snowy Owls can stand about 2 feet tall and have a wingspan of over 5 feet.
Although most owls only eat small mammals and birds, the Great Horned Owl will eat skunks, groundhogs, and porcupines.
A single owl may catch up to 2000 rodents a year. That’s 5 or 6 a night.
One study of 200 Barn Owl Pellets found 454 mammal skulls, among which were 225 voles, 179 house mice, 20 rats, and 20 shrews.
Pellets are not exclusive to owls. Kites, hawks, falcons, eagles, harriers, and even some robins also regurgitate undigested remains.
Some Great Horned Owls in the wild have lived up to 27 ½ years.
A captive Common Barn Owl has lived up to 51 years.
