BACKGROUND:
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.
PROCEDURE:
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.
- 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.
- Give each pair of students a pellet. Have them
disaggregate the material by using their hands, forceps, tweezers,
or toothpicks.
- 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.
- 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).
- Students should also be able to determine how many animals
there are by looking at the number of bones.
