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April 20, 2006
Dear Journey
North,
North winds delayed migration over much of the week. In the southeastern
portion of Saskatchewan several centimeters of snow and rain fell,
keeping birds on the ground. In the past week, only one new report
of migrating whoopers came in. This was of a pair of birds near the
town of Leask, Saskatchewan. These birds are within a 2-3 day flight
of the breeding grounds. The early migrants from a week ago should
be just arriving on the breeding grounds this week.
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What
makes a
good day for migrating?
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Today the
sky is clear, with a light southeast wind, a perfect day to be migrating
north. On a day like today, the whoopers will leave
the wetland that they roosted on overnight and move into a grain
field to feed for a couple of hours. At that time they may make a short
trip
back to the wetland for a drink before migrating or just leave straight
from the field . If cranes are going to migrate on
a particular day, they will usually leave before 10 am. The main
thing that the cranes are looking for are thermals of
warm air rising from the ground. The cranes will flap fly upwards until
they find a thermal;
once in the thermal they will use a spiraling flight, circling upwards
with the rising air column.
Cranes will pick up the thermals around 600 meters off the ground and
ride them up to an altitude of 1200 meters or more. Once at the top
of the thermal, they will enter a gliding flight until they reach the
next thermal, and
so on.
Glide
speeds average 58 km/hr while spiraling speeds are as slow as 20 km/hr.
With a tail wind, the cranes can fly as fast as 100 km/hr. In spring
the flight distances and duration are generally longer than during
fall migration. On a good day for migrating,n the cranes can stay aloft
for up 8 or 9 hours and cover distances of over 600 km.
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As
the cranes pass through the Canadian Prairies they will be performing
their courtship dance. In this photo, the male is jumping
in the air to display for the female. She seems indifferent
to
his gestures.
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Brian
Johns
Wildlife Biologist
Canadian Wildlife Service
Saskatoon, Saskatchewan, Canada
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1997-2006 Journey
North. All Rights Reserved.
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