State of The Whooping Crane Flock 2011-2012

by The Aransas Project

July 9, 2012: The Aransas Project (TAP) prepared this State of the Flock 2011-2012 report to provide critical information to our members and to the public regarding the well-being of the Wood Buffalo-Aransas Whooping Crane flock after the 2011-2012 wintering season.

Whooping Crane Flock Numbers Plunge during Winter 2011-2012

TAP Western Flock Graph 2011-2012

Figure 1: Whooping Crane Flock Numbers Plunge during Winter 2011-2012

A recent news release issued by the Southwestern Region of the United States Fish and Wildlife Service (USFWS) confirms that the winter of 2011-2012 was one of the worst winter seasons in Texas for the Wood Buffalo-Aransas flock, the last remaining natural flock of Whooping Cranes that winters at Aransas National Wildlife Refuge (see Figure 1).

USFWS official reports put the flock size at the end of the previous winter of 2010-2011 at 279 cranes. In the winter of 2011-2012, on the aerial surveys in late January 2012, USFWS counted only 193 birds and then used statistical methods to extrapolate from that number an estimated flock size of 245. This statistical estimate represents a decrease in flock size of 12.2% from the previous winter. This represents one of the largest declines in flock size ever recorded.

Despite these facts, USFWS officials have made several public statements, including “The flock is so large they can’t count individual birds,” that paint an overly optimistic, and ultimately misleading, portrait of the state of the Aransas-Wood Buffalo flock.

“The recent statements attributed to USFWS leave the public with the impression that the flock numbers are up,” says TAP legal counsel Jim Blackburn. “Yet, according to their own official reports, there are fewer birds. Any way you do the math, 245 is less than 279.”

Based on the aerial survey in late February 2012, USFWS reports that the flock size was estimated to be 196, notably less than the previous estimate of 245.

“Recent public statements by USFWS officials at the Refuge paint a rosy picture of the health of the flock when the scientific record says otherwise,” says Blackburn. “The facts are these—the size of the flock, even by USFWS’ own estimation, is lower than during the prior year, and the scientific record from electronically-monitored cranes in the flock suggests more cranes may have died than in the drought of 2008-2009, which was the highest mortality ever recorded. But we’ll never know what really happened, because USFWS has abandoned the methodology of counting individual cranes each month, as was done for 29 years, and instead has resorted to distance sampling of the birds, from which they then statistically extrapolate to provide an estimate of the flock size.”

USFWS Methodology Faulted

Beginning in the winter of 2011-2012, USFWS altered its methodology for tracking how many cranes are in the flock. “Every year but this year for 29 years, the former refuge biologist, Tom Stehn, did monthly flyovers during the wintering season and methodically counted every crane on the refuge, using both territories and defined transects to identify the birds,” says Blackburn. “This year the refuge didn’t do a census to count the cranes as they have every other year, but instead used a sampling method and also decreased the frequency of the flights.” Blackburn says TAP believes this methodology to be less reliable.

Stehn himself questioned the validity of the USFWS sampling methodology in a recent interview with the Corpus Christi Caller-Times. In the interview, Stehn noted that the current sampling methodology used by USFWS, known as “distance sampling,” has an error range of 15%, which Stehn believes is far too high when dealing with a population of fewer than 300 endangered cranes.

Stehn told the Caller-Times, “I’m really frustrated and disappointed with the changes in the census the refuge has made. It’s simply not accurate enough when you’re dealing with such a small population of endangered birds.”

Stehn noted that the aerial census methodology he employed for nearly 30 years used flyovers on a much tighter grid and allowed him more flexibility to conduct more thorough searches off the search grid.

USFWS has cited the growing number of cranes in the flock as its justification for resorting to a sampling and estimating approach, rather than actual counting. Blackburn comments, “We don’t really understand that, because Tom Stehn seemed to manage just fine with more cranes. Recent statements by USFWS would make you think that they were covered up in cranes down there, which even their estimates don’t support.”

Tracking Data Suggests Unprecedented Crane Mortality

Recent statements by USFWS also create the impression that the number of cranes that died this past winter was far less than during the drought of 2008-2009 because fewer crane carcasses were found. A recent sworn statement filed by Whooping Crane expert, Dr. Felipe Chavez-Ramirez, the principal investigator in an ongoing research project electronically tracking 31 cranes in the Aransas flock using GPS bands, suggests that crane mortality may actually be higher than USFWS reports indicate.

According to Dr. Chavez-Ramirez’ statement:

  • The carcasses of three juvenile cranes were recovered during the 2011-2012 wintering season
  • Out of the 31 banded cranes, this is a mortality rate of 9.6%
  • Out of the ten banded juvenile cranes, the mortality rate is 30%
  • The documented mortality rate of 9.6% in this monitored subgroup of birds is “unprecedented” and exceeds the previous high mortality rate of 8.5% during winter 2008-2009

Blackburn says this scientific evidence suggests that more cranes may have perished due to the drought in 2011-2012 than in the prior drought of 2008-2009. “It seems like USFWS is sticking their heads in the sand down there in terms of the health of the flock,” says Blackburn.


The Aransas Project continues to seek responsible water management of the Guadalupe River Basin to ensure adequate freshwater inflows to the bays and estuaries that provide the winter habitat for the endangered Whooping Cranes. Until this problem is addressed, the future health of the bays and estuaries and of the Whooping Cranes will not be secure. “What we need, and should expect from USFWS, is a clear-eyed, scientific view of the state of the flock,” says TAP Regional Director Ron Outen. “TAP feels that residents of the Coastal Bend and the broader public need to know what is happening down here. We hope that it contributes to a better understanding of this critical and ongoing issue for the state of Texas.”

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