Whooping Crane Census Flight
March 15, 2009
The ninth aerial census of the 2008-09 crane season at Aransas was conducted
March 15, 2009 with USFWS observer Tom Stehn in a Cessna 210 piloted by Gary
Ritchey of Air Transit Solutions of Castroville, Texas. Viewing conditions were
less than ideal with overcast skies and occasional light rain. Parts of the
crane range were not flown as rain and lightning ended the flight after 3.7
hours.
Whooping Crane Numbers
With estimated losses that has occurred at Aransas this winter, the
current flock size is estimated at 226 adults + 23 juveniles = 249. The
estimated peak winter flock size was 232 adults + 38 juveniles = 270 total.
Mortality
Today's flight provided evidence of 3 additional mortalities, with total
winter mortality now estimated for the winter at 6 adults and 15 chicks totaling
21 whooping cranes, a loss of 7.8% of the flock that was a record 270 in the
fall. In the last 20 years, the current winter ranks as the worst in terms of
mortality, ahead of 1990 when 7.5% of the whooping cranes (11 out of 146) died
at Aransas. The 3rd worst winter in 1993 showed a 4.9% loss at Aransas (7 out
of 143). Mortality in the 2008-09 winter (21 birds) can be added to the 34
whooping cranes that left Aransas in the spring of 2008 and failed to return in
the fall. Thus, 55 whooping cranes have died in the last 12 months, or 20.7% of
the flock of 266 present at Aransas in the spring, 2008.
Four dead whooping cranes have been picked up this winter; at least two were
emaciated, and the virus IBD (infectious bursal disease) has been isolated from
one of the juveniles by Dr. Hon Ip at the National Wildlife Health Center in
Madison, Wisconsin. It is not yet known if this strain of IBD is pathogenic to
whooping cranes, but it seems probable. The 4th carcass discovered this winter
was an old pile of white-plumaged feathers discovered March 2nd during a blue
crab count conducted by volunteer Katherine Cullen and two Chinese biologists.
The two Chinese that have cranes on their refuges in China expertly identified
the feathers. On today's flight, observations confirmed that one additional
adult is missing, leaving a one-adult family just south of Panther Point on
Matagorda. Also, the refuge's Pipeline and Matagorda's Airport juveniles are
missing and listed as dead. These last 3 mortalities had presumably all
occurred prior to the February 25th flight, with observations on today's flight
confirming the losses.
Migration
One juvenile whooping crane was confirmed on the Platte River in
Nebraska on February 20th. This is presumably the juvenile that had
over-wintered in Oklahoma and probably moved north with sandhill cranes. It was
still present on the Platte through March 9 and presumably is still there.
I have been asked how the current poor conditions of the cranes may affect the
migration. I have no idea how that may affect the timing of the migration which
seems to vary by only about one week from year to year. Low numbers of whooping
cranes start leaving Aransas the last week in March, with the majority of the
cranes departing the first 2 weeks in April. The last of the breeding pairs
have all gone by April 21st; a few subadults occasionally stay into May. I
expect the migration to proceed normally, with birds making it all the way to
Wood Buffalo National Park in Canada. However, mortality in the migration could
increase. My next census flight is scheduled for the week of April 6th to see
how the migration is progressing.
Sightings near Aransas
Three whooping crane subadults continue to use farm fields south of
Austwell. They were seen in a pond next to an agricultural field on March 12th,
but were not searched for on today's flight due to lack of time.
Habitat use
Management practices are aiding the cranes this winter. Crane locations
on the flight included 7 observed at man-made fresh water sources, 17 on burned
uplands, 33 on unburned uplands mostly foraging for tubers where feral hogs have
rooted up the earth, 4 at game feeders, 1 on a well pad, and 23 in open bay
habitat. Two cranes were on a recent burn on Matagorda Island conducted March
10th. Tides have risen somewhat since the previous flight on February 25th.
Salinities remain high, measured recently at 30 ppt in the refuge boat canal.
The drought rated as "exceptional" shows no sign of ending in central and south
Texas. Many counties have imposed prescribed burn bans due to the fire danger.
However, rain received in south Texas on March 14-15 has helped a little.
Blue crabs are still scarce due to the drought. These are the worst conditions
I have ever observed for the cranes at Aransas, with some birds looking thin and
with disheveled plumage. I wish I had better news to report. The refuge is
continuing its program of supplemental feeding with corn. A moderate response
by the whooping cranes has been observed with 76 photographs taken by remote
motion-activated cameras in the past week of whooping cranes at refuge feeders.
Other animals eating the corn include feral hogs, deer, raccoons, grackles and
just a few remaining wintering sandhill cranes.
The USFWS used 2 airboats the week of February 23rd to pick up 411 abandoned
crab traps in the crane area. This was done in conjunction with a program
organized by Texas Parks and Wildlife Department to pick up abandoned traps all
along the Texas coast. Waters within the boundary of Matagorda Island National
Wildlife Refuge have recently been closed permanently to commercial crabbing
with signs posted at most entrances into the marsh.
By Tom Stehn - Aransas National Wildlife Refuge
Tom Stehn, Whooping Crane Coordinator
U.S. Fish and Wildlife Service
Aransas NWR
P.O. Box 100
Austwell, TX 77950
(361) 286-3559 Ext. 221
fax (361) 286-3722
E:mail: tom_stehn@fws.gov
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Where applicable, CWS stands for Canadian Wildlife Service; USFWS is US Fish and
Wildlife Service. Crane monitoring involves cooperative efforts and support by
both countries, plus many volunteers and non-profit organizations along the way.