December 13, 2012

Whooping Crane Update

Wade Harrell, U.S. Whooping Crane Recovery Coordinator

Whooping Crane News:
Nearly all of the radio-marked whooping cranes have migrated to their wintering grounds on the Texas coast. Visitors coming to the Aransas National Wildlife Refuge have a chance of seeing four adult whooping cranes that have been frequenting the observation tower. There are also several whooping cranes utilizing the Heron Flats area just south of Refuge Headquarters. The new observation deck at Heron Flats is now open for visitor use. Whooping cranes are being intermittently observed near Cavasso Creek, just off TX Hwy 35 North of Lamar. If you wish to view whooping cranes from a public highway, please use caution by making sure you are pulled completely off the highway and out of traffic flow. Keep in mind when viewing whooping cranes that they are sensitive to human disturbance and harassing them is a violation of federal law. Avoid approaching cranes and if they appear alarmed, increase your distance.
With the help of Texas Whooper Watch and other observers, several family groups and individuals have been confirmed outside the winter survey area, including:

  • A confirmed report of two unmarked birds sighted near Quivira National Wildlife Refuge in Kansas on November 29th. 
  • As of Dec. 1, a total of eight birds have been regularly spotted at Granger Lake east of the Austin area. Some of these birds are marked with satellite transmitters and we have confirmed that at least a portion of these birds are the same individuals that used this same area last year. 
  • A total of five birds, a family group with one chick and one pair, have been seen utilizing private lands north of El Campo. 
  • In Matagorda County, observers have noted two pairs of whooping cranes using coastal marsh. 

Continued observations of birds using habitat outside of the traditional wintering areas is an encouraging sign that whooping cranes are successfully exploiting resources and may be expanding their winter range. This would be a positive development for the continuing recovery of the wild flock. Expansion into new areas will provide additional security if a catastrophic event such as a late season hurricane were to impact the Aransas Refuge area. We will continue to monitor whooping cranes that are located outside of our regular aerial survey area.

Surveys & Monitoring:
We are conducting aerial surveys from Lamar to south of Port O’Conner as weather permits. Our survey goal is to fly at least five times before the end of December to obtain an accurate population estimate. To date, we have completed three flights (November 28th, 29th and December 5th ). We will provide a peak abundance estimate for our survey area once we have met our goal of at least five survey days. We are not able to capture 100% of the wintering flock within our aerial surveys. Our aerial survey focuses on the traditional high use areas on and around Aransas Refuge, but the continued expansion of the flock has resulted in birds spread out across a greater geographic area than we can effectively fly in a day. Hence, information on whooping crane locations from Texas Whooper Watch and other volunteer observers is invaluable In helping us document whooping crane use of areas outside of their traditional wintering grounds.

There has been considerable public interest in the changes to wintering whooping crane surveys over the past year. Staff members from Aransas Refuge have flown low-level aerial surveys to estimate the number of whooping cranes in and around Aransas Refuge since 1950. This long-term data set is key in understanding the only remaining wild whooping crane population and is paramount in helping us make effective decisions regarding whooping crane conservation. In the past, an attempt was made to conduct a complete census, counting every bird. Recently, the Service has established a protocol for the aerial surveys to ensure that our surveys are conducted in a systematic way. This protocol is repeatable, allowing any trained biologist to produce a consistent and reliable population estimate within the survey area. We fly predetermined transects at an altitude of 200 feet within the traditional winter coastal areas with two observers each looking for whooping cranes up to 500 m to the side of a small, single engine airplane. Realizing that it is unlikely that we are detecting every crane in the survey area, we have begun implementing a widely-used technique called distance sampling. Distance sampling allows us to account for missed birds and estimate the total number of birds within the survey area. This technique also provides a mechanism for estimating statistical error and produces a confidence interval for the estimate (i.e. +/-). Our agency policy directs us to use the best available science, and clarify uncertainty in our monitoring efforts. We are continuing to work with partners to refine our methodology, ensuring it is as scientifically sound and reliable as possible.

The US Geological Survey, International Crane Foundation and other partners are currently on Matagorda Island trapping, marking with satellite transmitters and releasing whooping cranes for an ongoing tracking study. Information from this study will provide us with valuable information on how whooping cranes utilize their entire range, from their nesting area around Wood Buffalo National Park, along the migratory corridor throughout the middle part of the US, and on their wintering grounds in Texas. This tracking effort also provides us estimates on whooping crane mortality throughout the range, an important piece of information for the recovery effort. As of December 10, six whooping cranes have been marked and released, with the winter 2012-2013 goal of marking 10 total birds. Currently around 35 marked birds in the flock that are being tracked.

Conditions on and around the Refuge have been drier than the long term forecast indicated, but the Refuge was fortunate to receive a total of 2” of rain from pre-frontal events in early December. Salinity levels for San Antonio Bay have ranged from 26 to 28 parts per thousand this past month. Recent rains should reduce salinity somewhat, which will help in maintaining blue crab abundance in the marsh.

Food Abundance:
Refuge staff continues to find whooping crane scat filled with wolfberry seeds. This year’s wolfberry crop on the refuge appears to be much improved from the previous few years. Tour boats have reported seeing whooping cranes regularly feeding on blue crabs in the marshes along the Refuge shoreline.  Refuge staff plan to prescribe burn a total of 7,000 -10,000 acres this winter to assist in providing food sources for the cranes.  To date, 1,657 acres have been burned since October.

Refuge Update:
We currently are developing plans to rehabilitate 2 existing water wells on Matagorda Island. This will provide consistent fresh water for whooping cranes to use during dry periods. The Friends of Aransas and Matagorda Island group has led the charge in raising funds for this effort and we are grateful for their assistance. We are also evaluating freshwater availability across the Refuge to ensure we are meeting the needs of whooping cranes and other wildlife. As mentioned earlier, the Heron Flats observation deck is now open for public use.