Ask Tom Stehn

Tom Stehn

friendsofthewildwhoopers.org

Friends of the Wild Whoopers has created this question and answer section, “Ask Tom Stehn” in an effort to provide scientifically accurate information to the public regarding the Aransas-Wood Buffalo Whooping Crane flock, the only self-sustaining wild population on earth.

Tom Stehn will answer questions concerning conservation, management and future needs of the Aransas-Wood Buffalo population of wild Whooping Cranes and they will be posted on this page.

If you have a question about the wild flock send us an email at admin@FOTWW.org.

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Dear Mr. Stehn,

I understand that Whooping Cranes have run out of space on their winter habitat on Aransas National Wildlife Refuge (ANWR) and that about 50% are wintering off the refuge. Is suitable wintering habitat available for purchase in the vicinity of ANWR? What is being done to acquire more wintering habitat if available?   Thank you, Elizabeth P.
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In 1941 when there were only 15 whooping cranes remaining in the flock, they wintered on the Aransas National Wildlife Refuge in the area of Sundown Bay, which I’ve always considered as hallowed ground for the species.

The use of salt marshes on Matagorda Island across from the refuge  was documented in the early 1900’s when there were more whooping cranes in the flock, and also occurred sporadically in the 1940’s and 1950’s.  By 1960, one pair of cranes had established a territory on Matagorda Island, and there have been cranes there every winter since.
Using aerial census data starting in the 1950s through 2006, colleague Felipe Prieto and I looked at the expansion of the flock.  What we found was that “Crane pairs have opted to establish territories in or close to the traditional winter area rather than moving long distances along the coast. This distribution seems based on the preference of the male crane to establish a territory as close as possible to its parents.”  The flock has slowly expanded out to available habitat in all directions, but mainly to the north and south along the coast due to habitat availability.  Since a whooping crane territory must contain enough food to support a pair or family group throughout the winter, territories must have a minimum size, calculated to average about 425 acres, roughly 2/3’s of a square mile.  The refuge is basically at capacity, so for the flock to reach a down-listing goal of 1,000 birds, it is important that sufficient habitat be provided for them.  Back to my work with Felipe Prieto.   “The current winter range and contiguous areas can support up to 576 whooping cranes.  Additional salt marsh habitat was measured in a 111-km radius from Aransas National Wildlife Refuge. If suitable, this noncontiguous area could support an additional 580 whooping cranes to reach a total flock size of 1,156. However, with the Texas coast undergoing rapid development and sea level rise, there is insufficient protected habitat for whooping cranes to reach recovery targets.” 
 
Fortunately, Matagorda Island is part of the national wildlife refuge system, and the extensive marshes on San Jose Island have been privately owned by a family that has fully protected the cranes along with large landowners at Welder Flats.  But other marshes in the area that are privately owned are subject to development.  Organizations including the Texas Nature Conservancy, Coastal Bend Bays and Estuaries Program, and U.S. Fish and Wildlife Service are trying to protect crane marshes as they become available through conservation easement or purchase.  The Whooping Crane Conservation Association has also provided some funding to help meet matching grant targets.  In 2016, one bloc of marsh was purchased for over 1 million dollars.
Conservation laws prevent the salt marsh from being drained or developed unless mitigation measures are carried out.  But developers either want to turn the marshes into marinas, or build right up to the edge of the marsh that would lead to an unacceptable level of disturbance to the cranes.  Ongoing sea level rise may make much of the crane habitat too deep for the species to use by the next century.  Also, with warmer winters due to climate change, black mangrove is invading the crane area do to the lack of prolonged freezing weather that in the past killed the mangrove.  Invading mangrove will crowd out many of the salt marsh plants including Carolina wolfberry that the cranes rely heavily upon for food.  So with the quadruple threat of human development, sea level rise, reduced freshwater inflows that depress blue crab numbers, and mangrove invasion, the winter habitat and thus the species remains in jeopardy.
To read the full article referred to above by Stehn and Prieto, click on the 11th Proceedings of the North American Crane Workshop and look starting on p. 40 found on the following link:      https://www.savingcranes.org/proceedings-of-the-eleventh-north-american-crane-workshop/
Tom Stehn