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February 15, 2013

Whooping Crane Update

2012–2013 Winter Whooping Crane Survey:
U.S. Fish and Wildlife Service personnel conducted 7 surveys of the primary wintering grounds during December 2012. These efforts resulted in the training of 2 new observers and further refinement of the new survey protocol.

Preliminary analyses of the data indicated 257 (95% confidence interval (CI) = 178–362) whooping cranes inhabited the primary wintering grounds. Additional observations suggested that at least 22 whooping cranes were outside the primary wintering grounds during the survey period (see whooping cranes outside the primary survey area below). We estimated 105 (95% CI = 73–146) whooping crane pairs in the primary winter grounds and at least 33 (95% CI = 19–51) of those pairs arrived with at least one chick. We estimated the ratio of chicks to adults during the winter 2012–2013 was 14 chicks (95% CI = 9–21) to 100 adults. As our new observers gain experience and we work out methodological details, we anticipate precision in these estimates to increase.

Examination of the 60-year trend in whooping crane abundance reveals a slow, incremental increase with occasional declines. Such increase has been the rule rather than large year-to-year fluctuation. We do not expect to see wide swings in population growth from one year to the next unless there is a catastrophic event, like a hail storm or chemical spill. During winter 2010–2011, the traditional technique resulted in an estimate of 283 whooping cranes on the wintering grounds. We estimated 254 (95% CI = 198–324) whooping cranes in the primary wintering grounds plus approximately 13 were thought to occur in other areas (i.e., Bayside, Markham, and Granger Lake) during winter 2011–2012. Modeling of the historical time-series of whooping crane abundances predicted 272 (95% CI = 253–298) whooping cranes for winter 2011–2012 and 273 (95% CI = 250–301) for winter 2012–2013.

Measures of the uncertainty in our estimates are new to whooping crane monitoring. In the past, we did not include confidence intervals or other measures of precision because it was assumed that the traditional technique resulted in a complete count. The traditional technique assumed that 1) none of the birds were missed, 2) pairs consistently used a defined area throughout the winter, and 3) a single observer was able to see and account for every single bird over repeated survey effort. Previously, the traditional technique had no established protocol, there was not a survey area or flight pattern determined before each flight, and the observer flew wherever they thought birds might be seen. This made sense when the whooping crane population was small and occupied a relatively small geographic area. Now, we have a pre-established flight pattern that covers the primary wintering area, we used 2 observers on every flight, and accounted for missed birds. Because no statistical model was applied in the past, we had no way of knowing the uncertainty in our estimates. Now, with the application of a protocol-based survey design and statistical models, we can characterize our uncertainty and develop ways to reduce that uncertainty. A simple explanation of confidence intervals which are a measure of uncertainty can be found here.

Every year we do this survey we will learn something new and different and apply it to the next season. Our knowledge and precision will grow and we will have more solid information that leads to better management decisions. We expect this process will take several seasons before the obvious and not-so-obvious factors can be incorporated into the survey protocol and statistical models. This is how science progresses. It is a very typical process and ultimately helps us make the best decisions for the whooping cranes.

Whooping Cranes Outside the Primary Survey Area:
It is important to note that in addition to the estimate of 257 whooping cranes within the primary survey area, approximately 6% to 11% of the whooping crane population can now be found outside the survey area. This is not because the primary survey area is smaller than what was surveyed in the past; in fact, it is larger. This use of “nontraditional” wintering areas is great news and we are trying to get a better understanding of the expansion and use of whooping crane habitat. 

As many have stated, in the long-run, having whooping cranes winter in a variety of places across a broader geographic range gives us greater confidence that a catastrophic event will not wipe out the population. For decades there has been genuine concern that one catastrophic event near the refuge could lead to the extinction of whooping cranes. This is such an important part of the ongoing recovery of whooping cranes and cannot be understated. Between Texas Whooper Watch and the increasing number of birds marked with satellite transmitters via the tracking study, we are in a much better position to document birds using areas outside the primary survey area.

The tables below provide our best understanding of birds that were outside the primary survey areas during mid-December. These numbers are concurrent with our aerial surveys. Keep in mind some birds may have been missed. Also, we cannot ever be completely certain that the birds did not move between these locations and to/from the primary survey area while survey flights were being conducted.

These are three different data sources that help document the proportion of the whooping crane population using areas outside of the primary wintering area during mid-December.

Table 1: Texas Whooper Watch

Birds documented outside of the survey area in mid-December via Texas Whooper Watch 

General Area        Adults     Chicks     Total       Notes:   
Granger Lake             6  2  8  Includes 1 marked bird. 
N. of El Campo 2 1 3 Includes 1 marked bird. One more pair was documented in the area but we do not have mid-December records.
Total  8  3  11    

Table 2: Tracking Study
Birds documented outside of the survey area on December 17th via the tracking study  

General Area     Adults     Chicks     Total      Notes: 
Mission Bay (secondary survey area)   1     1  Marked as chick. 
North Matagorda Island (secondary) 2 1 3 Marked chick.
Holiday Beach (secondary)  2  1  3  Marked chick located on the edge of the primary survey area in early morning prior to the aerial survey & and in the secondary survey area twice in the afternoon. 
Total   5 2 7  

Table 3: U.S. fish and Wildlife Survey
Birds documented in the whooping cranes' secondary areas on December 13th via aerial survey 

General Area    Adults       Chicks      Total     Notes:  
Powderhorn Lake (secondary survey area)   2     2  Pair located on Myrtle-Whitmire Foster Unit of refuge. 
Guadalupe Delta (secondary)     Two pairs, total of 4 birds, were seen during the Christmas bird count on the 20th. 
Total       4   

* The data and results presented in this report are preliminary and subject to revision. This information is distributed solely for the purpose of providing the most recent information from aerial surveys. This information does not represent and should not be construed to represent any U.S. Fish and Wildlife Service determination or policy.

Last Updated: Feb 15, 2013
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