Owl Pellet Dissection-Trophic Levels and Energy Loss

Owl pellet dissection is used to teach ecology topics such as food webs, biomass pyramids and energy loss.

Buying Pellets and Materials.

Both small and large pellets work with this lab. I’ve used small when my funds are more limited and large when they’re not. Large pellets give more prey per pellet which is fun for the kids.  If you don’t have enough science funds, here’s some suggestions on where to find additional money for your science classroom.

I buy one pellet per team of 4 students due to cost. This is not ideal, but they are only dissecting to count the prey–not to identify all the bones or do anything else with them.

The pellets are sterilized, but I provide gloves for kids who prefer gloves. My pictures show dissection trays, but they’re not necessary. A paper plate or a paper towel works just as well.

Pre-Lab

Since I try to teach inquiry-style with the 5E learning cycle, I don’t want to pre-load information into the kids’ brains. I do, however, want them to see where owl pellets come from and basic dissecting techniques. I assign these videos the night before on Edpuzzle, but these can also be shown in class prior to the lab.

Phenomena-based video of baby owl regurgitating a pellet.

Basic information and dissection techniques.

Dissecting pellets

There are many variations of the owl pellet lab which are wonderful.  My copy is a 5E learning cycle which was adapted from the original creator.

Kids can use their fingers or tweezers to take the pellet apart. Provide reference sheets. Many can be found for free online.

Bone sorting chart found on Pinterest. I added some more info (like the size of mouse vs. rat skull or “2 per animal”) before copying.

I altered this reference sheet to help kids correctly identify a mouse vs. a rat. I make kids measure as they don’t readily know how large 1 cm is.

Mice skulls are usually 1 cm. Many students tell me they have a mouse and I say “have you measured it?”. When they do, they find out its a small rat.

I combine ecocolumn data along with owl pellets at the same time so 4 kids have more tasks to do. Two kids take ecocolumn data while the other 2 kids in the group dissect the pellet.

After about 20 minutes both pairs are finish and all 4 of them will do calculations and answer questions on their owl pellet papers together.

Calculations and Analysis Questions

(I want to give a shout-out to the original creator of this lab–the famous Dr. E)

Students take their data and fill in a chart. The entire chart is NOT filled in.  Most of the prey will be a rat or mouse. Students always think they found something else like a mole or shrew, because it sounds more interesting, but unless they can ID a skull, it  probably isn’t. (I have some kids who think they have a shrew, because the ribs they find are so skinny….)

Sample data. Point out to students that they will have zeros for some rows animals.

Next, the students create a numbers pyramid and a food web. I draw a pic on the lab white board to help them.

This is in the lab to help them with the numbers pyramid and food web. The food web is partially complete.

For the food web, you can choose to have students create a food web from just the prey found in their pellet or from all the prey the owl could eat.  I choose the first option (but am thinking of switching to the second for next year to give them more practice with a more complicated food web).

Next comes a biomass pyramid which is the crux of this lab in terms of calculating energy loss.  Students need to complete the biomass chart and then draw a pyramid. I have detailed instructions on the lab paper on how to do that since it confuses them.  

Sample paper with biomass chart, biomass pyramid and energy loss calculations.

Working in groups for the questions is helpful so they can hash out what the correct answers should be and learn better. I flipped my class last year so I have the luxury of time to allow an extra day to do this.  Students are often confused that the energy “loss” from the prey to the owl is over 99%. They need to understand that 90% energy “loss” is an average and they will hypothesize why the loss is this lab is so much higher (the owl doesn’t weigh very much for being a top predator).  Its good for them to question their numbers, however, if they seem “off” as that is a good skill for the math is this course.  But, in this case, its correct.

The questions also discuss that energy is not really “lost”, but becomes heat and an unusable form for food in ecosystems–1st and 2nd laws of thermodynamics.

Normally, I have the kids write a conclusion and submit through Turnitin.com, but this year, I had them do an oral conclusion on Flipgrid. The results were much stronger in terms of understanding energy loss than if they did the conclusions by themselves.  Much of the AP® Exam is higher level thinking and students can help build these skills by working together.

 

 

 

 

 

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