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Hawk Migration

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					Hawk Migration
Why do they Migrate?
Hawk Migration

• Every fall hawks migrate south in
  spectacular migrations “rivers” of hawks
• 1000s passing particular locations at a
  time
• Spring migration is also observable but
  more spread out
Hawk Migration

• Migration is related to food availability
• Hawks that feed on cold blooded prey (insects)
    must winter in the tropics
•   Hawks that feed on small birds (who feed on
    insects) must follow the birds when they migrate
•   Hawks that feed on fish must follow the fish
    back down south and/or avoid frozen areas
Why don’t they stay down South?

• If they stayed in the southern areas they
 would deplete their food resources over
 time.
Hawks as Indicator Species
• An indicator species gives scientists information
    on the health of an ecosystem.
•   Hawks/Eagles/Falcons/Vultures are excellent
    indicator species because they are at the top of
    the food chain
•   Therefore; if there numbers are low, scientists
    can assume that something is going wrong in
    the ecosystem (affecting the raptors as well as
    lower animals on the food chain because they
    are the raptors food source)
Example of Raptors as Indicators

• In the 1960’s the number of many raptors
  went down due to DDT
• What Happened? Their food source had
  been contaminated by the DDT which
  then entered the birds body. In some
  instances this would kill the bird, but in
  others it would weaken their egg shells
  affecting the population.
• By seeing the number of raptors go down,
    scientists knew that something was wrong in the
    Ecosystem.
•   Often times you can see the effect on the larger
    predators before the smaller organisms due to
    their relatively smaller population size
•   And due to the fact that the pollutant will
    bioaccumulate through the food chain
    causing the greatest effect on the
    organisms at the TOP of the food chain

				
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posted:5/8/2013
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