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Whooping Crane Census Flight

April 7, 2009

 

The tenth aerial census of the 2008-09 crane season at Aransas was conducted April 7, 2009 with USFWS observer Tom Stehn in a Cessna 210 piloted by Gary Ritchey of Air Transit Solutions of Castroville, Texas.  Viewing conditions were ideal with clear skies and light winds, although turbulence made the ride uncomfortable most of the time.  Nearly all parts of the crane range were flown.

Migration

Today’s flight tallied 103 adults + 6 juveniles = 109 total.  Thus, 56% of the flock has started the migration.  Whooping cranes have been confirmed on April 2nd as far north as Nebraska.  I expect a considerable number of cranes will start the migration in the next week.  Conditions should be ideal for departure with very strong southeast winds forecast for Aransas April 8-9.

Whooping Crane Numbers

With estimated losses that have occurred at Aransas this winter, the current flock size is estimated at 225 adults + 22 juveniles = 247.  The estimated peak winter flock size was 232 adults + 38 juveniles = 270 total.

Mortality

Today’s flight provided evidence of 2 additional mortalities, with total winter mortality now estimated for the winter at 7 adults and 16 chicks totaling 23 whooping cranes, a loss of 8.5% 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 (23 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, 57 whooping cranes have died in the last 12 months, or 21.4% of the flock of 266 present at Aransas in the spring, 2008.

The 2 additional mortalities confirmed on today’s flight that had been reported earlier by volunteers and staff are as follows: 

Tour Boat Naturalist Ray Kirkwood had seen March 19-29 the Rattlesnake Island juvenile with a very bad limp, using its wings when it moved to try to reduce the weight put on its injured leg.  The bird retained flight ability but was lethargic and may have stopped eating.  The chick was not observed on April 1st when I looked for it from a boat and had presumably died.  The pair believed to be its parents was observed on their territory on today’s flight with no sign of the juvenile. 

The second mortality involved a grouping of 1 adult with 1 chick observed twice about 4 hours apart on April 1st in the marsh west of the airstrip on the south end of Matagorda Island.  This same grouping of 1+1 was observed on their East Bray territory on today’s flight, providing confirmation that one adult has died.  

Sightings near Aransas

Three whooping crane subadults that used the farm fields south of Austwell for much of the winter were last reported present on March 14th.  They have either returned to the salt marsh or have started the migration.

Habitat use

For the first time all winter, nearly all the whooping cranes were found in the salt marsh on today’s flight.  The cranes are believed to be feeding on fiddler crabs since blue crabs in the marsh ponds are still scarce due to the continuing drought.  A blue crab count done on April 1st found zero crabs in the marsh.

Whooping crane locations on the flight included 2 observed at man-made fresh water sources, 2 at a game feeder, and 9 in open bay habitat.  No cranes were on burned or unburned uplands.  Tides were low caused by a very strong “norther” that had brought northwest winds on April 6th.  Salinities remain high, measured recently at 29 ppt in the refuge boat canal and 39 in the adjacent marsh.  One monitoring station in San Antonio Bay has a salinity of 25 ppt.  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.  Corpus Christi, Texas is 4.5 inches below normal rainfall starting January 1st.  

Overall, these continue to be some of the worst conditions I have ever observed for the cranes at Aransas, with some birds looking thin and with disheveled plumage.  The refuge is continuing its program of supplemental feeding with corn.  A moderate response by the whooping cranes has continued.  The cranes are getting somewhat of an energy boost by catching fiddler crabs just prior to migration.
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.