Life Cycle - Natural Environment (5B)

  • Defining an organism's role in the food web. 
  • Exploring the eating habits of an owl.
  • food web
  • population biology
  • rulers 
  • owl pellets 
  • styrofoam meat trays
  • Swift-GH Microscope 
  • information charts on bones
  • toothpicks


Students determine the type and age of rodents from owl pellets. 

Great Horned Owl


One of the duties of the U.S. Fish and Wildlife Service is to estimate how many organisms there are in the United States.  One way to determine this is to watch wildlife or to develop an indirect way of observing them.  In order to find out more about the rodent population in an area, wildlife managers use owl pellets to develop a sense of the rodent population, both in number and in species.  One can also track the history of individual owls, and discover information about an owl population.  A common owl used is the barn owl pictured on the left. 

Wildlife managers collect information on the food that an owl eats by recording  the number, percentage, volume, and  weight of the ingested animals.  They can determine the frequency of what the owls eat since they collect data over time.  They look at the number of prey, how often it occurs, in what amount and what it is.


In this lab students will develop a food habit study of the owl.  In the post lab they will look at the information as a class to determine a rodent population.   

A wildlife biologist would collect owl pellets every day and record what they see.  Unless you have a local source of owl pellets which you can collect each day, you may have to artificially label the owl pellets as coming from successive days.  Remember you are trying to teach students the value of collecting data.  

Students need to prepare the sample, segregate the contents, identify the food items, record the day it was collected, and finally appraise the data to obtain results.

  1. Read the "Flight of the Raptors"  a story about the different raptors at a park with tall trees.  It emphasizes the owls, but shows other raptors in the area.
  2. Give each pair of students a pellet.  Have them disaggregate  the material by using their hands, forceps, tweezers, or toothpicks. 
  3. Students should determine the volume of the fur by stuffing the fur component into a graduated cylinder and reading how much volume it takes up. 
  4. Students will be able to determine if the bones are mature or not by looking at the growth.  When growth is complete, the cartilage is replaced by solid bone, so that the cap and shaft are fused firmly together.  The presence of a cartilaginous zone or lines representing its recent presence or its complete absence are criteria of use in aging many mammal bones. (See information on bones).  
  5. Students should also be able to determine how many animals there are by looking at the number of bones. 

  [Back to Life Cycle Grid]  [Back to Natural Environment (5)]