The whooping crane migration back north has started, however so slightly.

A survey Tuesday of the Aransas National Wildlife Refuge has accounted for all of the known whooping cranes in the only naturally migrating flock in the nation.

Whooping cranes are known to pass through the area. Last fall they sparked a massive birdwatching enclave to visit Cheyenne Bottoms Wildlife Area and the Quivira National Wildlife Refuge when birds set down for several days.

During Tuesday's survey, the count showed 263 birds, one of which has apparently left the refuge and is now resting on the Platte River in Nebraska, according to Tom Stehn, coordinator for the U.S. Fish and Wildlife Service program.

There are 242 adults and 21 juveniles at Aransas.

The report was issued the same day The Aransas Project, a public interest group, filed a federal lawsuit against the Texas Commission on Environmental Quality over reduced water inflows into the refuge.

A scarcity of blue crabs, brought on by low water conditions, has hit the cranes especially hard.

However, only one bird, a juvenile, died this winter.

Last year, 21 birds -- six adults and 15 juveniles -- died in the fall migration and winter season. Another 34 were unaccounted for and presumed to have died.

Only 247 birds made the flight back north last spring.

This year, only a single whooping crane has left the refuge, spotted at the Salt Plains National Wildlife Refuge in northern Oklahoma on Feb. 24 and 26. It has since moved on to the Platte River in Nebraska, where it was seen March 5.