THE ENDANGERED MISSISSIPPI SANDHILL CRANE
AND WET PINE SAVANNA
Scott G. Hereford
With their large size, graceful form, piercing calls, and elaborate courtship displays, cranes (Gruidae) are among the most spectacular of birds. Rare and beautiful as well as being one of the oldest, few bird families have such a large percentage of species on the brink of extinction. Seven of the world's fifteen species are endangered and others, though numerous, are declining. Because of their large size they have been targets of human persecution, but the major cause of their decline is destruction of their habitats of wetlands, savannas and grasslands, which are rapidly shrinking throughout the world. The Mississippi sandhill crane (Grus canadensis pulla), an endangered subspecies and one of the world's smallest crane populations, is found in the wild only in Jackson County in southeastern Mississippi in a unique and interesting savanna habitat.
Scattered colonies of non-migratory sandhill cranes were once found along the Gulf Coastal Plain from Louisiana into the western Florida panhandle. The most important plant community in the ecology of the cranes is the wet pine savanna, also called moist pine barrens, flatwoods, wet prairie, grass-sedge bog, or pitcher plant bog. They are best characterized as wet grasslands with scattered longleaf pine, cypress, and slash pine. These savannas occur on the Lower Gulf Coast Plain stretching 100 km inland and range from the Apalachicola River in Florida into Louisiana. Before alteration by human activity, these communities were abundant and Folkerts (1982) believes that the western edge of Florida into Mississippi was almost "continuous bog until the late 1800s". The unique flora characteristic of this habitat includes Aristida spp., Ctenium aromaticum, Calopogon spp., Pogonia spp., Rhexia spp., Polygala spp., Xyris spp., Eriocaulon spp., and most notably, carnivorous plants such as Drosera spp, Sarracenia spp, Utricularia spp. Folkerts (1982) estimates that Gulf Coast pitcher plant bogs, "one of the continent's most unusual assemblages of organisms" have a diversity of carnivorous plants equaled in few other places. The savannas are largely Rains soils, highly acidic, and very poorly drained. The characteristic heliophytes are dependent on1) soil acidity and infertility to inhibit invasion of competing species; 2) anaerobic soil conditions from frequent soil saturation to inhibit invasion of moisture-intolerant species; and 3) frequent fire to eliminate fire-intolerant species. Fire is probably the most important factor in maintaining these systems. In a comparative study of Mississippi savannas, Norquist (1984) found species richness among the highest in temperate North America averaging 25 species/0.25m2 on wet-mesic frequently burned sites and 21 species/0.25m2 on mesic infrequently burned sites.
With gradual alteration to their unique habitat, cranes disappeared from nearly all of this range. The last known nesting of sandhill cranes in Louisiana was in 1919 and in Alabama in 1960. In Mississippi, resident sandhills were not reported until 1929 when Aldo Leopold noted them during a state game survey. The crane colony in Jackson County, Mississippi was fairly secure due to its relative isolation and the poor soil unsuited for agriculture. By the 1950's a number of threats arose for the crane and its habitat. These included silviculture, fire suppression with the repeal of open grazing, and residential and commercial development. The most important was the ditching, plowing, and planting of slash pine in thousands of acres of open meadows. Smith and Valentine (1987) looked at changes in habitat types in ten nesting areas from the 1940s to 1981, and found open savanna dropped from 74% to 14% and woodland had increased from 18 to 70%. Called on to investigate the effects of an interstate highway construction project through the crane range, the Fish and Wildlife Service began the first important study of the crane and its habitat (Valentine and Noble 1970). This effort resulted in a recommendation for the establishment of a refuge. In 1972, the Mississippi sandhill crane (G.c. pulla) was described as a separate subspecies based primarily on size and plumage color. In 1973, it was added to the federal Endangered Species List. The Mississippi Sandhill Crane National Wildlife Refuge was established in 1975.
Cranes are long-lived (20+ years) but their potential for reproduction is limited. Breeding doesn't begin until 4 years or older. They are perennially monogamous (Tacha et al. 1992) and lay their two egg clutches in large ground nests. Mated cranes defend large often variable nesting territories. Over 50 current and potential nesting areas have been identified. Eggs hatch in about 30 days and the precocial young are able to fly at 75-80 days. Rarely is more than one young raised to fledging. Both sexes incubate and provide parental care and young stay with them for nine to ten months. In Mississippi, nesting begins in late March, peaks in April, and extends into May. Nesting is predominantly in savanna and swamp edges. The nest materials are those found growing at the site. Sedges and grasses (Scleria, Carex, Panicum, Andropogon spp.) are the most common but Lophiola, Lachnanthes, Sarracenia, sphagnum bits, and twigs may also be included. Nut-rush (Scleria baldwinii) is so common at nest sites that it may be considered an indicator species.
Besides nesting, savannas are used for other stages of the life history. Cranes roost in shallow water. In Mississippi, cranes have historically roosted in the Bluff Creek marshes in the fall and winter and in the savannas during the long nesting and rearing season. They historically fed in corn fields and pastures and pecan orchards in fall and winter. In spring and summer they feed in the same savannas they nest in and along the edges of swamps. Cranes eat seeds, tubers, shoots and a number of worms, arthropods, crustaceans, and other invertebrates.
The restoration of crane habitat is a long term and on-going project. The refuge has returned to fire as an important tool in restoring and maintaining savanna. Approximately 2,430 hectares are burned annually. Smoke management is an important issue as the refuge is now an island surrounded by roads and residential development and bisected by a major interstate highway. A number of techniques are used to remove trees. In rare areas with a good site index timber sales are used to remove merchantable lumber. Most of the trees are non-commercial. In drier areas, bull-dozing or drum-chopping is used for savanna rehabilitation. Approximately 2,100 hectares of savanna were restored by bulldozing and drum-chopping pine plantations. If possible a prescribed burn is conducted in the area within weeks of the chopping. Hot growing season prescribed burns are used to kill small pines. Much of the area is so wet and/or soil so sensitive to disturbance that the only method employed is hand clearing. Approximately 640 hectares of potential or active nesting territories were hand-cleared.
Efforts have been made to manage water as well. Five water control structures were built into refuge roads intersecting major drains. Four two-hectare impoundments were created by raising road elevations and using culverts to regulate the water depth. Three wetland cells, impounding five hectares, were created by a sewage wastewater treatment facility. Four other small (< 2 ha) ponds were constructed as roost ponds. A number of drainage ditches were plugged. A new initiative is underway to accomplish additional hydrological restoration, particularly on the western refuge unit, by mapping water flow, plugging ditches, cross-culverting beneath roads, and replacing water control structures.
By the time the refuge was established there were only 30-40 cranes remaining and no fast way to increase their numbers. An augmentation effort to bolster the small wild population was needed. Extra eggs had been taken from selected nests since the mid-1960's. The resulting young have formed the basis of a captive flock at Patuxent Wildlife Research Center and are to be a genetic reservoir, in case of a catastrophe. Juveniles from Patuxent were shipped to the refuge in 1980 and have been annually since then in a gentle release effort. To date, 220 captive-reared cranes have been released onto the refuge. They now comprise 85 percent of the entire free-flying population of 120-130. Captive-reared birds have joined the breeding population and now make up one or both members of most of the 8-10 breeding pairs.
Increasing recruitment, decreasing juvenile and adult mortality, and continuing habitat restoration and maintenance were among the strongest recommendations of a 1992 population viability workshop. After the remaining 2000-3000 hectacres of pineland are restored to savanna, there should be sufficient habitat available for the 25-30 breeding pairs and 130-170 total cranes necessary for a sustainable population. Recovery of this endangered subspecies is dependent on restoration of the its unique species rich savanna habitat.
The Mississippi sandhill crane population may be expanded by releases at other sites including the new Grand Bay National Wildlife Refuge, east of the current refuge on the Alabama-Mississippi border. The savanna in the Grand Bay area is one of the largest remaining tracts of that habitat in the Gulf Coastal Plain and accounts for a third of the 5,000 hectares recommended for acquisition.
Folkerts, G. W. 1982. The Gulf Coast pitcher plant bogs. American Scientist 70:260-267.
Norquist, H. C. 1984. A comparative study of the soils and vegetation of savannas in Mississippi. Unpublished M.S. thesis. Miss. State Univ., Miss. State, Miss. 110 p.
Smith, E. B. and J. M. Valentine. 1987. Habitat changes within the Mississippi sandhill crane range in Jackson County, Mississippi (1942-1984). Pages 341-354. In J. C. Lewis ed. Proceedings 1985 Crane Workshop. Platte River Whooping Crane Maintenance Trust and U.S Fish and Wildlife Service, Grand Island, Nebraska.
Tacha, T. C., S. A. Nesbitt, and P. A. Vohs. 1992. Sandhill Crane. In: A. Poole, P. Stettenheim, and F. Gill, eds. The Birds of North America, No. 31 Philadelphia: The Academy of Natural Sciences; Washington, DC: The American Ornithologists' Union.
U.S. Fish and Wildlife Service. 1991. Mississippi sandhill crane recovery plan. U.S. Fish and Wildlife Service, Atlanta, Georgia. 42 p.
Valentine, J. M. and R. E. Noble. 1970. A colony of sandhill cranes in Mississippi. Journal of Wildlife Management 34:761-768.