Migration of Birds (1979)Lincoln, Frederick Charles
Science
Migration of Birds (1979)
Lincoln, Frederick Charles
Birds; Birds -- Migration
The intensity of migration depends on circumstances including the
need for haste. In fall the flights are more likely to be performed
in a leisurely manner, so that after a flight of a few hours
the birds often pause to feed and rest for one or several days,
particularly if they find themselves in congenial surroundings.
Some indication of this is found in the recoveries of banded birds,
particularly waterfowl. If we consider only the shortest intervals
between banding in the North and subsequent recovery in the South, it
is found that usually a month or more is taken to cover straight-line
distance of a thousand miles. For example, a black duck banded
at Lake Scugog, Ontario, was killed 12 days later at Vicksburg,
Mississippi. If the bird was taken shortly after its arrival, the
record would indicate an average daily flight of 83 miles, a distance
that could have been covered in about 2 hours' flying time. Among
the thousands of banding records of ducks and geese, evidences of
rapid migrations are decidedly scarce, for with few exceptions, all
thousand-mile flights have required 2 to 4 weeks or more. Among
sportsmen, the blue-winged teal is well known as a fast-flying
duck and quite a few of these banded on Canadian breeding grounds
have covered 2,300 to 3,000 miles in a 30-day period. Nevertheless,
the majority of those that have traveled to South America were not
recovered in that region until 2 or 3 months after they were banded.
Probably the fastest flight over a long distance for one of these
little ducks was one made by a young male that traveled 3,800 miles
from the delta of the Athabaska River, northern Alberta, Canada,
to Maracaibo, Venezuela, in exactly 1 month. This flight was at an
average speed of 125 miles per day. A very rapid migration speed was
maintained by a lesser yellowlegs banded at North Eastham, Cape Cod,
Massachusetts, on 28 August 1935 and killed 6 days later, 1,900 miles
away, at Lamentin, Martinique, French West Indies. This bird traveled
an average daily distance of more than 316 miles.
It seems probable that most migratory journeys are performed at
little more than the normal, unforced rate of flight, as this would
best conserve the strength of the birds. Migrating birds passing
lightships and lighthouses or crossing the face of the moon have been
observed to fly without hurry or evidence of straining to attain high
speed. The speed or rate of migration would therefore depend chiefly
on the duration of flights and tail wind velocity.
Public-domain text, read in full here on John Shaqi.
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