Aerial Census at Aransas

The first aerial census of the 2010-11 whooping crane season was conducted December 1, 2010 in a Cessna 210 piloted by Gary Ritchey of Air Transit Solutions, Castroville, Texas with USFWS observers Tom Stehn and Brad Strobel. Sighted on the flight were 199 adults and 38 juveniles = 237 total whooping cranes.

December 1 – Recap of whooping cranes (237) found at Aransas:

  Adults + Young
San Jose 51 + 11 = 62
Refuge 62 + 12 = 74
Lamar 10 + 3 = 13
Matagorda 54 + 8 = 62
Welder Flats 22 + 4 = 26
199 + 38 = 237

Flight conditions and visibility were excellent throughout the flight as a low pressure system that had brought howling north winds on November 30 had moved off the coast, followed by clear skies and light southeast winds. With nearly complete coverage of the crane area during the flight, the 237 cranes counted represent an accurate estimate of the number of cranes present.

To date, 38 of the 46 juveniles found in mid-August on the nesting grounds have made it safely to Aransas. The 38 chicks include three sets of “twin” chicks, (adult pairs that have brought two chicks each). Five pairs with two chicks each had been sighted in Canada in August. The third set of “twin” chicks to make it to Aransas had spent 21 days (October 29 – November 18) in Brown County, South Dakota observed nearly daily by Jay Peterson, USFWS District Manager of the Sand Lake Wetland Management District. Jay writes:

“What a treat it was for me to see the birds each time, but it was more rewarding for me to be associated with the folks I took with or gave directions to, who did not have whoopers on their life bird list.”

The last 3 of the 10 radioed whooping cranes completed the migration on November 26th, missing their Thanksgiving feast of blue crabs by one day. All 10 radioed cranes are now at Aransas. With no recent sightings reported north of Oklahoma (as of November 29th), it appears the migration is nearing completion. I have my fingers crossed that 50 more whooping cranes will still arrive since I’m hoping for a peak count greater than 285 this winter.

Crane habitat use observed on the census flight:

211 of the 237 cranes observed were in salt marsh habitat.

18 were in shallow open bay habitat.

5 were on uplands in areas rooted up by feral hogs on Matagorda Island.

3 were on grazed pasture oak savannah uplands at Welder Flats.

The cranes are feeding heavily on blue crabs and wolfberries this fall with both of those food items abundant in November. It is possible that the 18 whooping cranes observed in open bay habitat could also have been foraging on blue crab. The largest group size observed during the census was nine birds seen on refuge salt flats just north of the Pipeline. No cranes were observed at freshwater sources since salinities in San Antonio Bay are 14 parts per thousand, low enough for the cranes to drink water directly from the marsh. However, salinities have been rising (they were 9 ppt one week ago) and the area could use rain. Tides were high on today’s flight with all the tidal flats covered with water on San Jose Island. No commercial blue crab traps were found in the crane marshes or within 100 yards of shore. Only a few abandoned traps were seen in the crane marshes that will be targeted for removal during the annual crab trap pickup in February.

The observed proliferation of black mangrove in the crane marshes on Matagorda Island and at Welder Flats is very disturbing. The mangrove completely replaces the former salt marsh vegetation and excludes forage items used by the whooping cranes including Carolina wolfberry and fiddler crab populations. Many acres of marsh have become completely covered with this native species that is moving north as climate change reduces the number of hard freezes. In the past, hard freezes over multiple days limited the northward spread of mangrove since mangrove can only tolerate short spells of freezing temperatures. The last extended extremely hard freeze at Aransas occurred in 1989.

Happy Holidays

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