Dear Journey North,
It’s happened, and right on schedule. As usual, the majority of
the flock began migration the second week in April. An estimated 127
whooping cranes (consisting of 103 adults and 20 young) or 59% of the
flock started the migration between April 6 and April 13. Since late
March, 89% of the flock (181 total cranes) has initiated migration. Present
on the April 13 census flight were 18 adults, 9 subadults, and 7 chicks.
All of the remaining cranes except possibly a few subadults are expected
to begin migration in the next week. Adult cranes always depart the
wintering grounds by April 20th since they have to travel north to Wood
National Park in Northwest Territories, Canada to nest. (Subadult
cranes, ages 1 to 3 or 4 years, are too young to breed; they
do not feel the same urgency to hurry back to Canada.) Our next census
flight is scheduled
for April 27. This allows us time to see if they have all departed
The best day in the past week for migration was April 9, a day when
presumably a lot of the cranes departed. This was on a Saturday.
I think the cranes
were busy all week working, doing their daily chores of catching
crabs and patrolling their territories to keep all other cranes out
protecting their food supply. With the work week over, many cranes
on April 9 left for a long weekend. But it’s far more than a weekend
trip, since it will be 6 or 7 months before they return to Aransas. They
will migrate 2,400 miles, a trip that takes 3 to 4 weeks. They will travel
anywhere from 200 to 400 miles per day. When conditions are favorable
(providing thermal currents and tail winds), the cranes will fly about
7 hours per day. If the winds are in their faces, they will stay put.
They will look for food to eat near wherever they have found a small
pond or wetland to roost in for the night where they are safe from predators.
They have to do about what I do when I travel: cover a lot of miles,
and then look for someplace to sleep and something to eat.
Why Do They Leave at Different Times?
The crane migration has been taking place for the past 3 weeks and
departures will continue for another 2 weeks. Thus, many of the
cranes are leaving
at different times. This is an advantage to the flock in case of
hazards the cranes encounter on the migration.Sometimes cranes
severe blizzards and actually be killed by freezing sleet. Or they
could stop in a wetland where they might be exposed to a disease
But the largest source of crane mortality is collision with power
lines that the birds don’t see when flying, especially late in the day
or early in the morning when making short flights from their stopover
locations. With cranes leaving at different times and stopping at different
places, not all the cranes are exposed to the same hazards. That ensures
that some cranes will survive and thus it’s an advantage for the
flock to migrate in small groups at different times.
Fueling Up on Crabs and Snakes
On today’s census flight, most cranes were in ponds that were drying
up with the cranes feeding on small blue crabs. One adult crane was observed
holding a large snake and its chick sprinted over to get the snake. Now
that’s a meal that will provide energy for the long migration.
Whooping Crane Coordinator
U.S. Fish and Wildlife Service
An aerial census on 13 April, 2005 of the Aransas National Wildlife
Refuge and surrounding areas estimated the number of whooping
at Aransas at 27 adults + 7 young = 34 total. The current
estimated size of the Aransas-Wood Buffalo population is 182 + 33
Recap of cranes observed on the flight: (34)
Refuge 11 adults + 3 young
San Jose 5 adults + 2 young
Matagorda 7 adults + 2 young
Welder Flats 4 adults + 0 young
Total 27 adults + 7 young = 34 cranes
Remarks: Excellent viewing conditions and light winds were
present throughout the day with a complete census flown.
can’t get any better.
An estimated 127 whooping cranes (103 adults and 20 young)
have started the migration since the last flight on April
6. The best
day in the past week
was April 9. The presence of the West Shell Reef family
group that had been overlooked last week indicated that 157
on the last flight
April 6. Present on today’s flight were 18 adults, 9 subadults, and 7 chicks.
The family group of cranes visible from the refuge observation tower has migrated.
The next census flight is scheduled for April 27.
On today’s flight, tides were at mid-range (2.5 mlt), higher than last
week. Most cranes were in ponds that were drying up with the cranes feeding on
small crabs. A few cranes were in dry vegetated marsh. One adult crane was observed
holding a large snake and its chick sprinted over to get the snake. No cranes
were in open bay habitat or on prescribed burns.
2005 Journey North. All Rights Reserved.
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