Chapter 15 - Ecological Implications of Habitat Use by Reintroduced and Remnant Whooping Crane Populations

Abstract

Though Whooping Cranes historically nested in ecosystems as varied as taiga, upper tallgrass prairie, and coastal marsh, they also needed specific habitat components located within each of these biomes, such as dense wetland areas or complexes, open topography, water permanence, and hydrological pulsing to maintain wetland productivity. The goal for this chapter is to compare current Whooping Crane habitat use to this historical interpretation and to illustrate the behavioral, demographic, or environmental covariates of habitat use by Whooping Cranes. Together, this analysis can inform predictions related to Whooping Crane recovery and management in today’s changing world. I reviewed studies on home range, natal dispersal distance, and habitat use for four populations of Whooping Cranes (Aransas-Wood Buffalo, AWBP; Eastern Migratory, EMP; Florida Nonmigratory, FNMP; and Louisiana Nonmigratory, LNMP) during summer, winter, and migration. Whooping Cranes used open wetlands dominated by emergent vegetation and open water for foraging and roosting throughout the annual cycle. Amount of wetland use, however, varied among the four populations, primarily in the use of agricultural lands during migration and winter. In summer, territories of Whooping Cranes in the AWBP and EMP averaged 3.68–4.58 km2 while home ranges of nonterritorial cranes were 10–1000 times that size, making habitat availability between the two groups substantially different. Except for the FNMP, average natal dispersal distance was similar between the sexes and was <28 km, making mostly habitats close to natal areas available for territory establishment. Short natal dispersal distances, coupled with broad movements by nonterritorial cranes, suggest a value in exploring alternate habitats as a hedge against dramatic change in habitat quality. Though wing molt was not an annual occurrence, cranes used wetlands 92% of the time while they were flightless. Home range averaged 0.45 + 0.12 km2 (ave. + SE), the smallest home range measured, suggesting that the flightless molt may be the most habitat sensitive period of the annual cycle. In winter cranes in the AWBP used mostly natural salt marshes, both day and night, in a narrow band of the Texas Coast whereas the EMP was distributed from Indiana to Florida and utilized agricultural areas extensively. Cranes in the LNMP used man-made wetlands extensively during summer and winter. The breadth of habitat types used during winter by other populations suggests that the AWBP could utilize alternative habitats if their traditional habitats degrade but this hypothesis requires testing. Strong territorial behavior in winter by the AWBP, though an indication that high quality habitats exist, may reduce the rate at which dispersal outside of the Texas Coast can occur. In fall migration, AWBP cranes staged in Saskatchewan before moving rapidly to winter areas but no staging occurred in spring. In the EMP no staging occurred during either migration. It is possible that, if energetic or nutritional needs are unmet on winter or summer areas, spring and fall staging areas could serve as alternate habitats to provide these needs. Future research should address the role of territoriality in cranes, especially in winter, and the degree to which use of agricultural fields may be beneficial.