The distances which birds cover when "migrating" are enormous. Some
American plovers are known to travel for 8000 miles, one part of the
journey being 2500 miles without resting as they pass over the sea.
The arctic tern goes even farther, it nests near the North Pole, and
then makes its way down to near the South Pole, a journey of 11,000
miles.
Perhaps you wonder how we know that the birds travel these long
distances. Well, a good many naturalists and stalkers catch birds when
young or tired and mark them by putting a small ring round their leg
with a number on it. Then other naturalists keep a look out in other
parts of the world, and when they kill or find a bird with such a
number on it they report it.
Aberdeen University marked a large number of birds in this way--with a
tiny aluminium ring round the bird's leg, with the words "Aberdeen
University" and a number on it.
A wild duck which they had marked in Scotland was caught in a net the
same year in Holland.
Of five lapwings marked in Aberdeenshire, four were shot in Ireland
the same year, and one in Portugal, 1250 miles away.
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