The birds cage was placed under and artificial star-filled sky at migration time
the bird tried to fly in the same direction as that taken by his outdoor cousins
Any change in the position of the make-believe stars caused a change in the direction of his flight.
Scientists think that warblers
when flying in daylight, use the sun for guidance.
But the stars are apparently their principal means of navigation.
What do they do when the stars are hidden by clouds.
Apparently, they find their way by such landmarks as mountain ranges,
coast lines, and river courses.
But when its too dark to see these
the warblers circle help-lessly, unable to get their bearings.
17. What do we learn form the experiment with the warbler?
18. How do warblers migrate according to the passage?
19. How do warblers find their way when the stars are hidden by clouds?
20. How do warblers find their way in total darkness
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