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Give a hoot.

In "Vanishing Forest" (p. 18), you learned that the boreal forest is disappearing at a rapid rate. This robs many bird species--including owls--of their food source and breeding ground, affecting their ability to survive. How do scientists know if the populations of certain owl species in the boreal forest are increasing or decreasing? They count the number of the different types of owl hoots they hear. That's because owls are nocturnal (active at night)--and it's very difficult to spot them.

Every year in late March through early April, scientists walk along marked routes within a section of the boreal forest in Manitoba, Canada. They stop at several different spots along each route to count the number of the different types of owl hoots they hear during a set period of time. If the number of hoots for a particular owl species increases over the years, the population in the area exhibits an upward (growing) trend. If fewer hoots are heard, the population in the area shows a downward (decreasing) trend. Study the data table below to answer the questions that follow.</p> <pre> Total Counts of Hoots from Various Owl Species in a Selected Forest Area in Manitoba Year Barred Owl

Boreal Owl Great Gray Owl Great Horned Owl 1991 14

38 44 45 1993 32 46 18 68 1995 22 41

14 80 1997 20 100

28 172 1999 22 81 29

111 2001 7 54 14

47 2003 8 34 13

89 2005 12 15 9 38 SOURCE: DR. JAMES R. DUNCAN, MANITOBA CONSERVATION </pre> <p>PART 1: Graph It!

Directions: On a separate piece of paper, construct a graph showing each owl species and their hooting trends for the years featured in the data table above.

(Hint: Which type of graph best displays continuous changes in data over time?)

PART 2: Analyze It!

Directions: Use the data table and your graph to answer the following questions in complete sentences.

1. According to your graph, which owl species had the largest population increase between 1995 and 1997? For that owl species, how many more owl hoots were recorded in 1997 compared with 1995?

2. According to the data table, which two owl species showed only a downward trend in its population from 1999 through 2005?

3. What is the average number of barred owl hoots for the years shown on the data table.

4. Which year had the lowest total number of owl hoots? What does this fact suggest about the owl populations in this area of Manitoba?

1. The great horned owl had the largest increase in population between 1995 and 1997 The scientists heard 92 more hoots in 1997 compared with 1995.

2. Both the boreal owl and the great gray owl showed completely downward trends in their populations from 1999 through 2005.

3. The average number of barred owl hoots for the years shown on the data table is 17.

4. The lowest number of owl hoots was heard in 2005 Since the total is lowest in the most recent year the owl populations must be declining
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Publication:Science World
Date:Mar 27, 2006
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