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April 13, 2006
Dear Journey
North,
The big push-off that I’ve been anticipating occurred right on
schedule. Nearly half of the whooping crane flock left Aransas this past
week, with an estimated 102 birds starting migration April 5-12. Some
of the flock is already well on their way, with sightings received from
as far north as North Dakota. The whooping cranes travel though Texas, Oklahoma,
Kansas, Nebraska, South Dakota, North Dakota, and the easternmost portions
of Montana. I bet some of you forgot to list Montana as a state
the whooping cranes migrate through. Now name the 3 Canadian provinces
the whooping
cranes have to fly across. Here is a hint – the easternmost of
these 3
provinces only gets a few whooping crane sightings.
A Big Week
For Migration
During April 5 - 12, an estimated 102 whooping cranes (47.7% of the
flock)
eft Aransas. During that period, most days provided suitable weather
for migration except when a low pressure system brought strong northwest
winds to Aransas on April 8th. That front crossed the coast quickly,
with groups of whooping cranes reported starting the migration on April
9 and 10 with the winds turning around and blowing from the southeast.
Sunshine and warm temperatures in Texas currently in the 80’s heats
up the land and creates thermal currents to aid the migration of birds
with large wing spans such as cranes and pelicans, and hawks. Thermal
currents come from the hot air rising due to temperature differences
between the earth’s surface
and the sky. Birds with smaller wings don’t have a large enough
wing span to
“ride” thermal currents. Thus, small birds such as songbirds and
shorebirds flap their wings at a rapid pace and fly in a straight line. I think
I’d want to be a large bird and simply spread my wings and
ride the thermal currents up a mile high in the sky and then glide
down
4,000 feet at 60 miles per hour as I traveled north, catching the next thermal
when I got down close to the ground. In the late afternoon when the
thermals were dying out, I would look for a place to stop, eat a little bit, and
spend
the night.
Only an estimated 35 whooping cranes (32 adults + 3 chicks) are currently still at Aransas. Thus, 83.6% of the flock has migrated. Remaining at Aransas are 2 family groups, 28 subadults, and 1 chick all by itself.
One
Lone Chick?
Why do you think so many subadults are still at Aransas? Whooping
crane juveniles normally separate from their parents either shortly
after
arrival on
the nesting grounds, en route in the northern parts of the migration,
or occasionally separate at Aransas. Presumably the parents started
the migration and the juvenile had no idea what was going on or
perhaps just wasn’t quite ready to migrate, so it stayed behind.
Based on other instances of this happening, I fully expect this juvenile
will head north in the next 2-4 weeks and successfully return
to
the Canadian nesting grounds. It will presumably even show up
on its parent’s nesting territory, but will be driven off by
the parents who will not tolerate last year’s chick.
Whooping cranes are usually quite vocal as they start a migration flight. Can anybody think about what the chick and its parents were saying to each other as the adults started migration and the chick stayed behind? I bet the chick was saying: “Where the heck are you off to? No way am I going to migrate 2,500 miles just to eat berries and insects!”
Crane
Look-alikes
I also observed
on my census flight that the numbers of white pelicans at Aransas has
also greatly
decreased
in the last couple of weeks. The migration of whooping cranes and
white pelicans at approximately the same time across North America
leads several people to report large flocks (20+ birds) of whooping
cranes. What they really are seeing, however, are white pelicans. The
two species look amazingly
alike at a distance, both large white birds with black wing tips
and an identical spiral flight pattern in migration. However, whooping
cranes
usually migrate in small groups
of up to 8 birds, and frequently migrate as singles, pairs,
or family groups.
Tom Stehn
Whooping Crane Coordinator
USFWS
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1997-2006 Journey
North. All Rights Reserved.
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