Stehn Reports from Aransas: April 30, 2004
Stehn and Survey Plane at Aransas NWR
On the April 28th census flight, the pilot and I both anticipated that
all the whooping cranes would be gone from Aransas. But during our survey,
it was hard to deny the sight of three 5-foot tall white birds standing
together around the same pond. Thus, three "stragglers" are
still here, while 190 whooping cranes (98% of the flock) have migrated.
I've had non-breeding cranes (and once a widowed adult) stay at Aransas
into the first week of May before departing, so I'm not concerned yet.
But I am ready for them to be gone and for me to get a break from monitoring
A Chick Left Behind?
of the three cranes yesterday was the chick from the one-parent family
group. The chick had some rusty brown feathers remaining on its head and
back, but mostly was all white. Was one of the two cranes with the chick
its parent, or had the parent started migration and left the chick behind?
I had no way to know. (I talked about what might happen in my April
Migration: the Most Perilous Time for Cranes
deaths of adult whooping cranes happen during the migration. What are
the main hazards the cranes face? When whooping cranes migrate, they fly
during the daytime and stop every night, often in unfamiliar territory.
This is because they fly on a slightly different migration pathway every
year as they get blown off course slightly to the east or west, depending
on the winds. The main hazard the cranes face and the number one cause
of death of fledged whooping cranes is collisions with power lines. The
cranes sometimes simply don't see the lines when flying, especially in
low light conditions or bad weather. Collisions are usually fatal, although
not always. This spring, one of the eastern whooping cranes was observed
bouncing off a power line and continuing on in flight with the group,
apparently shook up but not injured to any great extent. With the human
population growing in North America and more and more power lines being
built, the migration becomes more hazardous for whooping cranes every
year. Whooping cranes can also fly into fences that they don't see, especially
when a fence crosses a wetland that the cranes may be attracted to. Some
wetlands harbor diseases, such as fowl cholera or botulism in the water
and expose the whooping cranes to these diseases. Cranes have to avoid
predators such as bobcats and coyotes whenever they stop for the night.They
do this by standing all night long in shallow water. This allows them
to hear predators coming during the night. Cranes also can be attacked
in flight by eagles, especially golden eagles that are more common in
the western U.S. Hunters may occasionally shoot a whooping crane by mistake.
We have also documented one instance when an airplane struck and killed
a whooping crane.
A Question for You
Every year, after the cranes migrate 2,400 miles to Canada and then return
in the fall, I expect that about 10 of the cranes will have been killed.
With a population not quite at 200 cranes in the last natural migratory
flock, the loss of 10 is significant. We need to do everything we can
to enure the cranes can migrate safely. Do
you have any suggestions about how to do this?
Tom Stehn, Whooping Crane Coordinator
U.S. Fish and Wildlife Service
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