ARANSAS NATIONAL WILDLIFE REFUGE

The sixth aerial census of the 2010-11 whooping crane season

Mar 2, 2011 | Aransas National Wildlife Refuge by Tom Stehn | Related Press

The sixth aerial census of the 2010-11 whooping crane season was conducted March 1, 2011 in a Cessna 210 piloted by Gary Ritchey of Air Transit Solutions, Castroville, Texas with USFWS observers Tom Stehn and Brad Strobel.  All portions of the crane range were covered in the 6-hour census.  Flight conditions were excellent, though late afternoon sun made it difficult to find cranes when flying towards the sun.

Sighted on the flight were 216 adults and 41 juveniles = 257 total whooping cranes.  The expanded range of the cranes on upland areas and movements to fresh water made it harder to find all the cranes.  At least five additional family groups and pairs (14 cranes) and 7 subadults were estimated to have been overlooked.

Adults + Young
San Jose 48 +   8  =    56
Refuge 80 + 13  =    93
Lamar 17 +   5  =    22
Matagorda 51 + 10  =    61
Welder Flats 20 +   5  =    25
Total 216 + 41  =  257

Observations on today’s flight confirmed the loss of two additional whooping cranes so that winter mortality in 2010-11 has totaled 4 cranes (3 adults and 1 juvenile).  No carcasses have been found, and cause of the deaths is unknown.  On today’s flight, one group of 1 adult with 1 chick was observed on the G1 prescribed burn on Matagorda Island with no other cranes around.  Also, for the third flight in a row, the East Spalding Lake juvenile was not found, with just the adult pair seen on the territory.  With this mortality, the current flock size is estimated at 279.  The peak size of the Aransas flock this winter was 283.

On March 1st, one whooping crane was confirmed present in a flock of > 10,000 sandhills cranes near Pampa, (north of Abilene) in the Texas Panhandle.  It’s likely that what might have been the same crane seen in January and February in Texas near Electra and Anson never wintered at Aransas, but instead elected to remain with sandhill cranes in north Texas and has started its migration north with sandhills.

Crane habitat use observed on the census flight (n=257):

160 of the cranes observed were in salt marsh habitat

40 were in shallow open bay habitat

21 were on prescribed burns

20 were at fresh water sources

9 were on uplands areas

7 were at game feeders

The continuing moderate use of prescribed burns and heavy use of open bay habitat is notable, although cranes are finding low numbers of blue crabs in the marsh.  Low tides are continuing with over 70% of San Jose Island consisting of dry mudflats.  Cranes are continuing to seek out freshwater to drink because of high marsh salinities.

Burn Location Unit Number # of Cranes Observed

Matagorda Island        G1                              6

Matagorda Island        G4                              2

Aransas Refuge          C4/C5                         8

Aransas Refuge          C8/C9                         0

Aransas Refuge          C12                             5

This flight at Aransas may have been my final census.  For the past 29 winters, I’ve done aerial observations on 544 flights totaling 3,448 hours.  It’s time to step aside and let younger staff get experienced in finding the cranes.  So hopefully for the rest of the spring, Brad Strobel will be in the front observer’s seat, and I’ll stay on the ground.

Tom Stehn, Aransas National Wildlife Refuge

Read the entire article »