ROCKPORT PILOT

Whooper Mortality Rate Called Highest in 20 years

Mar 24, 2009 | Rockport Pilot by Editor | Related Press

The ninth aerial census of the 2008-09 crane season at Aransas was conducted March 15 with observer Tom Stehn of the United States Fish and Wildlife Service (USFWS). 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

The estimated flock size is 249 which includes 226 adults and 23 juveniles. The estimated peak winter flock size was 232 adults and 38 juveniles for a total of 270.

Mortality

The flight provided evidence of three additional mortalities, with total winter mortality now estimated at six adults and 15 chicks. That is a loss of 7.8 percent of the flock.

“In the past 20 years, the current winter ranks as the worst in terms of mortality, ahead of 1990 when 7.5 percent of the whooping cranes (11 of 146) died at Aransas,” said Stehn.

The third worst winter in 1993 showed a 4.9 percent loss at Aransas (7 of 143).

Mortality in the 2008-09 winter (21 birds) can be added to the 34 whooping cranes which 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. That’s 20.7 percent of the flock of 266 present at Aransas in the spring of 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. It is not yet known if this strain of IBD is pathogenic to whooping cranes, but it seems probable. The fourth carcass discovered this winter was an old pile of white-plumaged feathers discovered March 2 during a blue crab count conducted by volunteer Katherine Cullen, and two Chinese biologists. The two biologists who have cranes on their refuges in China expertly identified the feathers.

The March 15 flight confirmed 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.

Migration

One juvenile whooping crane was confirmed on the Platte River in Nebraska on Feb. 20. This is presumably the juvenile which 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,” said Stehn. “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 two weeks in April.  The last of the breeding pairs have all left by April 21. A few sub-adults 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,” said Stehn. “However, mortality in the migration could increase.  My next census flight is scheduled for the week of April 6 to see how the migration is progressing.”

Habitat use

Management practices are aiding the cranes this winter. Crane locations on the flight included seven observed at man-made freshwater sources, 17 on burned uplands, 33 on unburned uplands mostly foraging for tubers where feral hogs have rooted up the earth, four at game feeders, one on a well pad, and 23 in open bay habitat.  Two cranes were on a recent burn on Matagorda Island conducted March 10.

Tides have risen somewhat since the previous flight.  Salinities remain high. The drought rated as “exceptional” shows no sign of ending in central and south Texas. However, rain received in south Texas March 14-15 has helped a little, according to Stehn.

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,” said Stehn.

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 two airboats the week of Feb. 23 to pick up 411 abandoned crab traps in the crane area. This was done in conjunction with a program organized by the 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.

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