Debate about counting Whooping Cranes continues

by Friends of the Wild Whoopers

Not all Whooping Cranes counted

Whooping Cranes

Whooping Cranes over Aransas NWR.  Photo by Kevin Sims ©2105

 

Aransas Wildlife Refuge biologist Tom Stehn conducted Whooping Crane census flights for 29 years at Aransas during which he tried to find every crane.  When Tom Stehn retired from U.S. Fish and Wildlife Service (USFWS) in 2011, the agency changed from doing a weekly Whooping Crane census to conducting a survey that takes place for roughly one week every December.  The change to a survey incorporated a technique called distance sampling where not every crane is counted but estimates of the cranes not seen are based on how far observed cranes were from the aircraft when sighted.  This statistically-derived method provides 95% confidence limits for an estimated Whooping Crane population.  Unfortunately, those confidence limits are quite large, equaling plus or minus 39 cranes out of an estimated flock of 338 during the winter of 2016.

Monitoring Whooping Cranes, Comparison article published

Dr. Bruce Pugesek and Tom Stehn, in January, 2017 published an article in the Proceedings of the 13th North American Crane Workshop entitled “THE UTILITY OF CENSUS OR SURVEY FOR MONITORING WHOOPING CRANES IN WINTER”.  The article compares the survey and census methods of counting Whooping Cranes.  An abstract for this paper is provided below, along with a link to download the entire 10-page article.

Tom Stehn commented to Friends of the Wild Whoopers about the article as follows:

“The article is not an easy read, but that’s the way science sometimes works.  It is a rebuttal of some of the things that USFWS wrote regarding their crane survey method.  In the article, Dr. Pugesek and I point out problems with the survey, including statistics, as well as what we consider as some of the “falsehoods” contained in what was written trying to justify the survey instituted after I retired.  I feel the USFWS was overly critical with unfair and overstated criticism of the census method that USFWS had done for 60 years.  And I firmly believe that with very thorough coverage of the crane area combined with the knowledge I had of individual cranes and their territories accumulated over 29 years of work and over 400 census flights, I could estimate the size of the whooping crane population in a manner much more accurately, and with a justifiable estimate of winter mortality, than what is being done on the current survey method.  The bottom line is that a census is usually stronger scientifically than a survey if the species’ biological parameters allow a census to be conducted.”

Tom continues: “If current USFWS policy requires that a survey with confidence limits be continued, I recommend that after the annual survey is completed, that additional funds be spent doing a census in a manner similar to what I used to do.  Doing some additional flying will allow comparison of the former census method with the current survey results which will provide more information about the crane population as well as better assess the survey methodology currently being employed.  A census would involve thorough coverage of the crane range with transects no more than 500 meters apart.  If there are now more cranes and a bigger area to cover, do the census over 1.5 days if need be.  Also, territories of all family groups should be determined, with a follow-up flight or two in early March to show which juveniles have died during the winter.  This estimate of annual winter mortality is very important, given what is known about drought and reduced inflows related to increased whooper mortality.”

ABSTRACT:

THE UTILITY OF CENSUS OR SURVEY FOR MONITORING WHOOPING CRANES IN WINTER
BRUCE H. PUGESEK,
1 Department of Ecology, Montana State University, Bozeman, MT 59717, USA
THOMAS V. STEHN, 1613 South Saunders Street, Aransas Pass, TX 78336, USA

Abstract: We discuss recent changes in the monitoring program for endangered whooping cranes (Grus americana) on their winter habitat in Texas. A 61-year annual census was replaced in the winter of 2011-2012 with a distance sampling procedure. Justification for the change was, in part, based on criticism of the previous methods of counting cranes and the assessment of crane mortality on the wintering grounds. We argue here that the arguments, methods, and analyses employed to discount the census procedure and mortality estimates were applied incorrectly or with flawed logic and assertions. We provide analysis and logical arguments to show that the census and mortality counts were scientifically valid estimates. The distance sampling protocol currently employed does not provide the accuracy needed to show small annual changes in population size, nor does it provide any estimate of winter mortality. Implications of the relative merit of census and mortality counts versus distance sampling surveys are discussed in the context of management of the whooping crane.

Link to article

***** FOTWW’s mission is to help preserve and protect the Aransas/Wood Buffalo
population of wild whooping cranes and their habitat. *****

Friends of the Wild Whoopers is a nonprofit 501(c)3 organization.

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Wintering Whooping Crane Update, December 15, 2016

Wintering Whooping Crane Update

Wade Harrell, U.S. Whooping Crane Recovery Coordinator

Whooping crane at Aransas National WIldlife Refuge. Photo courtesy of Kevin Sims.

Whooping crane family at Aransas National WIldlife Refuge. Photo courtesy of Kevin Sims.

We completed our annual whooping crane abundance survey this week, flying nearly six surveys. Unfortunately, we were plagued with poor flying conditions throughout the survey period. Of the nine days we had pilots and planes available, only five days (Dec. 9, 10, 11, 13, 14) offered safe enough conditions to fly. Of those five days, only two days (Dec. 9 and 13) had good flying weather most of the day, allowing for complete surveys. Fog, rain, low ceilings and high winds all contributed to poor flying conditions. Fortunately, we had two pilots and planes from our Migratory Birds program and four observers available, allowing us to fly more than one survey a day.

Prep for Whooping Crane survey

Aransas NWR biologist Diana Iriarte and Migratory Birds Program pilot biologist Terry Liddick preparing for the first whooping crane survey of the season

Once again, Terry Liddick, pilot/biologist from our Migratory Birds program, served as a pilot, flying a U.S. Fish and Wildlife Service Cessna 206. This year Phil Thorpe also served as a pilot, flying a U.S. Fish and Wildlife Service wheeled Kodiak. Observers were Wade Harrell, Jena Moon (Refuges Inventory and Monitoring biologist), Doug Head(Refuges Inventory and Monitoring biologist) and Stephen LeJeune (Chenier Plains Refuge Complex Fire Program). Doug Head (Refuge Inventory and Management biologist) served as survey coordinator.

Whooping Crane abundance survey results to be released in a few months

Data management and analysis once the actual survey is complete is a significant effort conducted by multiple staff members, so we won’t have the final results to present for a few months. But, I will share some general post-survey observations:
We observed whooping cranes using four units of Aransas National Wildlife Refuge (Blackjack, Matagorda, Tatton and Lamar) and 3 Texas coastal counties (Aransas, Calhoun and Matagorda).

  • Overall, habitat appeared to be in good condition with adequate freshwater resources. Northern portions of the primary survey area (Welder Flats, Matagorda Island Central) appeared to have much more standing freshwater than southern portions of the primary survey area (Blackjack, Lamar-Tatton), presumably due to higher rainfall totals over the last couple months. Coastal marshes had higher than normal water levels due to high tides in the early part of the survey; however tides fell to normal levels this week.
  • We observed significant amounts of water hyacinth, an invasive freshwater plant, floating in San Antonio Bay, presumably having been flushed out of the Guadalupe River after the last flood event in November. Rainfall in November and December has provided positive freshwater inflows into local estuaries.
  • This year we did not have as many large group sizes (>8) of whooping cranes in our primary survey blocks, so it is possible that many of the subadult groups we observed in the past few years have successfully paired.We observed at least one family group that included two juveniles (i.e. commonly referred to as “twins”).
  • Due to poor flying conditions, most of our secondary areas did not get surveyed, but we did have one survey over the Mad Island and Matagorda Peninsula secondary areas. The Mad Island secondary survey area had one family group and two additional adult whooping cranes detected.
  • A family group of whooping cranes was reported in a rice field near Garwood, TX on December 8th. This area has had whooping crane use the last several years and is well outside (north) of our survey area.
  • While coastal salt marsh was the most common habitat type that we observed whooping cranes using during the survey, we observed whooping cranes using a wide variety of other habitat types as well, including freshwater wetlands, upland prairies and shrublands, agricultural fields and open-water bay edges.

There are several opportunities for visitors to Aransas National Wildlife Refuge to view whooping cranes in publically accessible areas this winter. Whooping cranes have been consistently sighted from the Heron Flats viewing deck, the observation tower and the tour loop near Mustang Slough. We consistently observed a family group of whooping crane in the Mustang Lake salt marsh in front of the observation tower, so you have an excellent opportunity to view whooping crane behavior with a juvenile in tow in their natural habitat.

Whooping Crane abundance survey a collective effort

I want to note that the annual whooping crane abundance survey is a collective effort, with the pilot and observers in the plane only serving one small role within the overall survey. I want to personally thank Joe Saenz, Aransas NWR project leader, for serving as overall manager of the effort; Doug Head, Refuge Inventory & Monitoring biologist as survey coordinator; Josie Farias, administrative staff at Aransas NWR, for assisting with logistics and dispatch; and Grant Harris and Matthew Butler from our Refuge Regional Office Inventory & Monitoring Team for survey protocol development and data analysis.

We will be flying some additional surveys in February in order to complete our survey of secondary areas and train new observers.

Habitat Management on Aransas NWR:
No prescribed burns have taken place yet this winter; however, we are planning for prescribed burns on the Blackjack
Unit, Tatton Unit and Matagorda Unit of Aransas NWR this winter.

Current refuge conditions

Recent Precipitation/Salinity around Aransas NWR:
November precipitation: 2.57” @ Aransas HQ

December precipitation (as of 12/15): 2.62” @ Aransas HQ

Salinity at GBRA 1: averaging around 13 parts per thousand

 

***** FOTWW’s mission is to help preserve and protect the Aransas/Wood Buffalo
population of wild whooping cranes and their habitat. *****

Friends of the Wild Whoopers is a nonprofit 501(c)3 organization.

wind farm

friendsofthewildwhoopers.org