Assessment of Food Availability for Reintroduced Whooping Cranes
September 2007 - August 2011
- Louisiana Department of Wildlife and Fisheries
- Private Individual
The Whooping Crane was placed on the endangered species list in 1970 and was grandfathered into the Endangered Species Act in 1973. Since that time, the wild population has increased to about 235 birds (Tom Stehn, USFWS, personal communication). The Whooping Crane Recovery Plan, however, calls for the successful establishment of at least 3 breeding populations (including the wild flock) of at least 25 breeding pairs. Currently, efforts are underway to establish a migratory population that breeds in Wisconsin and winters in Florida. An experiment with a resident population in Florida has been deemed unsuccessful. In January 2007, the Whooping Crane Recovery Team formally endorsed intensive studies of habitat suitability, disease risk to the wild population, and socioeconomics to determine whether or not Louisiana would be a suitable site for reintroduction of Whooping Cranes (please see attached letter from Tom Stehn). Louisiana has a rich history in the story of the Whooping Crane as it historically supported both resident and wintering populations (Allen 1952). Allen (1952) indicated that Whooping Cranes used a variety of habitats in Louisiana, including tallgrass prairie, panicum marsh (paille-fine), prairie swale and prairie marsh, sawgrass and deep marsh, and sea-rim and brackish marsh (see Gomez (1992) for a more detailed summary). It has been surmised that the tallgrass prairie of Louisiana supported more Whooping Cranes than any other region in the country. Allen (1952) roughly estimated that as many as 2,500 Whooping Cranes could have wintered in this region. It has also been suggested that Whooping Cranes bred in the many potholes, or platains, in the prairie as well. E. A. McIllhenny reported that in the first half of 1880’s it was still abundant on prairies of Jeff Davis, Allen, Evangeline and Acadia Parishes (Allen 1952). As hunting pressure and rice agriculture increased throughout the late 1800s and early 1900s, however, the breeding birds (and wintering) were exterminated from the prairies. The last record of Whooping Cranes on Louisiana prairies occurred in 1918, when a farmer shot 12 of the birds that were feeding on rice near his thresher (Allen 1952). Whooping Cranes were also abundant in a variety of other Louisiana habitats. Whooping Cranes wintered in the marshes at the fringe of the coastal prairie and in marshes near the cheniers of southwestern Louisiana. Interestingly, this interspersion of upland oak habitats with abundant marshes mimics in many ways the habitat structure used by the wild population at Aransas National Wildlife Refuge. Clearly, the most infamous location in Louisiana was that located by John Lynch in 1939 near White Lake in southwestern Louisiana (Gomez et al. 2005). This large paille-finne marsh was nearly inaccessible until the development of the intracoastal canal in 1929-1930. On May 15, 1939, Lynch located 13 Whooping Cranes including 2 current year chicks. According to locals, this flock was at one time much larger and stretched nearly 19 km to Grand Lake, but over hunting and other human and natural causes led to a decline in the population (Allen 1952). On 7 August 1940, a major hurricane accompanied by massive rainfall scattered the cranes Lynch had observed. Normally occupied habitats were flooded up to 1 m deep until October and water levels did not return to normal until the summer of 1941 (Stevenson 1942). Only 6 of the 13 birds returned. The birds continued to decline and in March 1950 the last remaining Whooping Crane in the White Lake marshes was captured with the aid of a helicopter (Gomez 1992). This marked a temporary end of the Whooping Crane in Louisiana. Ironically, approximately 2 weeks before the WCRT meeting in January 2007, a Whooping Crane from the reintroduced migrant flock in Florida was located in southeast Louisiana, where it remained for nearly 2 months. This bird marked the first verified sighting of a Whooping Crane in Louisiana since 1950. Whooping Cranes are an important part of the cultural and natural heritage of our state. This charismatic species could serve as an ambassador to other areas in the United States of Louisiana’s coastal wetland issues. The reintroduction of this species would also bring signs of hope and recovery following the devastating hurricanes of 2005. Furthermore, the potential for tourism revenues from Whooping Cranes would provide important income to the state of Louisiana. It is estimated that Whooping Crane-related activities contribute about $6 million annually to the local economy near Aransas National Wildlife Refuge (Tom Stehn, Chair, Whooping Crane Recovery Team, personal communication) and Whooping Cranes would only add to a growing ecotourism economy in the region. Reintroduction of Whooping Cranes in Louisiana, if it is indeed deemed suitable, will be a long-term and expensive commitment. As such, detailed information is needed to assess the risks and maximize the possibility of success. An analysis of migration patterns of Sandhill Cranes wintering in Louisiana (funded by LDWF; led by Dr. Sammy King) is nearly completed and is providing important information related to the potential for interflock mixing and the identification of potential migration routes for Whooping Cranes to Louisiana (http://www.rnr.lsu.edu/King/Sandhill%20Crane%20Research.htm). An analysis of disease risk will be conducted by veterinarians to determine whether a reintroduction would put the wild flock at risk. Lastly, as habitats in coastal Louisiana have undergone significant changes in the last few decades (Barras et al. 2003), detailed habitat suitability studies must still be conducted prior to reintroduction; by identifying suitable habitat, the recovery team will be able to minimize risk and assure success to the extent it is possible for Whooping Crane re-introduction in Louisiana. The WCRT would like detailed evaluations of White Lake and Marsh Island as potential reintroduction sites for a resident and migrant flock of Whooping Cranes, respectively (see attached letter from Tom Stehn, Chair, Whooping Crane Recovery Team). Many changes in Louisiana’s coastal wetlands have occurred since the 1930’s when Whooping Cranes were last observed at White Lake. Extensive wetland loss, although much less severe in southwestern Louisiana, and the continued effects of the Intracoastal Waterway on White Lake are of concern. In spite of these concerns, however, several areas in the region were noted to be good to excellent Whooping Crane habitat in a WCRT commissioned study in the 1990s (Cannon 1998). Based on food availability, pond characteristics and vegetation structure, Marsh Island, Rockefeller Refuge, and Rainey Sanctuary (owned by Audubon) were all viewed favorably (Cannon 1998). A subsequent, low-intensity study was conducted at Marsh Island to evaluate crab densities during the winter period; Marsh Island received high scores for its food availability (Sherry and Chavez-Ramirez 1999). Food availability is unknown at White Lake. Whooping Cranes feed on a wide variety of plant and animal matter, but crustaceans (blue crabs and crawfish) are a staple of their diet (Allen 1952, Novakowski 1966, Bergeson et al. 2001). Fish, large invertebrates, frogs, snakes, and a variety of plants are also eaten. The density of prey is critical, but foraging efficiency is also important in determining habitat suitability. Foraging efficiency, or the ease at which prey is secured, can be affected by water depths, vegetation density, water clarity, and other factors. Too deep of water can prevent access to foods. Too muddy of water can reduce visibility and limit access to certain prey items, although Whooping Cranes are efficient foragers for crabs in muddy water. Too dense of submergent or emergent vegetation, however, may reduce foraging efficiency. Understanding how food availability varies temporally and spatially is also important. Chicks are flightless for several months and must be able to access ponds by walking. Similarly, Whooping Cranes undergo molt in August and are flightless during this period. Thus, food must be available in walking distance and across suitable terrain. Whooping Cranes prefer somewhat open grasslands for walking as they prefer to see over the existing vegetation to scan for predators and they must be able to walk relatively easily. Thus, too dense or too tall of vegetation outside of ponds can deem a site unsuitable. Pond characteristics, including their spatial distribution, are also important for nesting. Whooping Cranes build floating nests, usually inside a patch of bulrush (most frequently), cattail, or other robust emergent. The nest is concealed by the outer fringes of the patch of emergent vegetation. Water levels that prevent the development of emergent vegetation or that result in complete monocultures are not desirable. Whooping Cranes are territorial, thus enough suitable ponds must be distributed at the appropriate spatial scale to support a population of breeding Whooping Cranes. In Canada, nest territories average 4.1 km2 (2.5 miles2) but range from 1.3 km2 to 47.1 km2 (0.8 miles2 to 29 miles2); however, nests in Canada have been recorded as close as 400 m to each other (Kuyt 1976a, 1976b, 1981, 1993). The objectives of this study are to: 1) Assess food availability at White Lake; 2) Determine water depths and vegetation structure of ponds at White Lake; and 3) Assess vegetation structure and density in non-pond areas at White Lake.