Lesson 1.2 - Population Change 

Only rarely does a population stay constant for an extended length of time.  Some populations can explode if the conditions are right.  Other populations can collapse if conditions turn very bad.  If a population reaches a critically low level, that species may become extinct. 

Read Find Out Activity: Population Change on page 256 in your textbook. 

Then, go to the following Internet site to learn more about the burrowing owl: http://esrd.alberta.ca/fish-wildlife/species-at-risk/species-at-risk-publications-web-resources/birds/documents/SAR-BurrowingOwlAlberta-RecoveryPlan-Oct2012.pdf

Then, answer the following questions.

Question 1. Where do burrowing owls live?

Question 2. The common view of owls is that they sleep in the day and hunt at night.  When do burrowing owls hunt?

Question 3. What kind of food do burrowing owls eat?

Question 4. How many eggs does a female burrowing owl lay?

Question 5. How long must she sit on the eggs before they hatch?

Question 6. After the eggs hatch, how long is it before the young burrowing owls can hunt for themselves?

Question 7. How many breeding pairs of burrowing owls were in Canada in 1979?

Question 8. How many breeding pairs of burrowing owls were in Canada in 1987?

Question 9. How many breeding pairs of burrowing owls were in Canada in 1979?

Question 10. What is the average annual rate of change in the burrowing owl population?

Question 11. Answer questions 1, 2, and 3 of What Did You Find Out.

Check your answers with those that follow.

 

 

 

 

 

 

 

 

 

 

 

 

Answers to Questions:

Question 1. Where do burrowing owls live?

Burrowing owls live in burrows underground, usually in unused gopher holes.

Question 2. The common view of owls is that they sleep in the day and hunt at night.  When do burrowing owls hunt?

Burrowing owls hunt in the daytime.

Question 3. What kind of food do burrowing owls eat?

Burrowing owls catch and eat insects and mice.

Question 4. How many eggs does a female burrowing owl lay?

A female burrowing owl lays six to twelve eggs.

Question 5. How long must she sit on the eggs before they hatch?

A female burrowing owl will sit on the eggs for about four weeks before they hatch.

Question 6. After the eggs hatch, how long is it before the young burrowing owls can hunt for themselves.

It takes about two months after they hatch before the young burrowing owls can hunt for themselves.

Question 7. How many breeding pairs of burrowing owls were in Canada in 1979?

In 1979 there were about 2100 pairs of breeding burrowing owls. (4200 owls)

Question 8. How many breeding pairs of burrowing owls were in Canada in 1987?

In 1987 there were about 700 pairs of breeding burrowing owls. (1400 owls)

Question 9. What was the change in population of the burrowing owls from 1979 to 1987?

The change in population of burrowing owls from 1979 to 1987 was 1400 breeding pairs. (2800 owls)  The calculations are 2100 - 700 = 1400 breeding pairs or 4200 - 1400 = 2800 owls.

Question 10. What is the average annual rate of change in the burrowing owl population?

The average annual rate of change in the population is calculated by dividing the change in the number of owls divided by the number of years the change occurred over. The change in the number of owls was -2800 owls.  The number of years the change occurred over was 1987 - 1979 = 8 years.  The average annual rate of change in the population was, therefore, (2800 owls)/(8 years) = 350 owls/year.
You could write this as a negative number (-350 owls/year) or write the decrease in words (a decrease of 350 owls/year).

Question 11. Answer questions 1, 2, and 3 of What Did You Find Out.

        1. If you were a naturalist, you would have to be concerned about the burrowing owls.  The population is very small and decreasing rapidly.  There is a danger they will be extinct in only a few more years.
        2. The decrease in burrowing owl population could be due to several factors.  One is the loss of habitat (where they live) due to farming practices, urban sprawl, or other human use of land.  Another possibility is fewer unused gopher holes to nest in because gophers are considered pests that farmers eliminate.  Another is that the food supply is decreasing as more mice and insects are eliminated by the use of chemical pesticides.  Also, the predator population that is killing burrowing owls might be increasing.
        3. Obviously, the population of the burrowing owls is decreasing rapidly.  The burrowing owl was placed on the endangered species list in 1995.

 


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