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A Comprehensive Review of Observational and Site Evaluation Data of Migrant Whooping Cranes in the United States, 1943-99

Introduction


Palustrine and riverine habitats in the central Great Plains provide roosting and foraging habitat to whooping cranes (Grus americana) during spring and fall migration. Characteristics of roost habitat have been examined in detail for the Platte River in Nebraska (Johnson 1982, Lingle et al. 1984, Faanes 1992, Faanes and Bowman 1992, Faanes et al. 1992), an area long recognized as a critical habitat for whooping cranes during migration. Although the Platte River is the best known spring stopover area for migrating whooping cranes, whooping cranes also use many other areas during spring and fall migration. Whooping cranes have been observed on various roosting and feeding areas throughout the migration path, which extends through North and South Dakota, Nebraska, Kansas, Oklahoma, and Texas. Because these areas play a key role in crane migration, the recovery plan for the whooping crane identified the collection of data on the use of these habitats as an important task in the conservation of the species (U.S. Fish and Wildlife Service 1994).

The Whooping Crane Recovery Team compiled a list of documented whooping crane observations for the period 1943-79. Collection of information on whooping crane use of roost and feeding areas began in 1975. Observations were categorized as confirmed (verified by state or federal biologist or other known, qualified observer), probable (no verification, yet details seem to identify the birds as whooping cranes, based on factors such as location within normal migration corridor and on appropriate site, accurate physical description provided, number of birds is reasonable, and behavior does not eliminate whooping cranes), and unconfirmed (details of sightings met some but not all of the factors listed for a probable sighting). Basic data collected for these records included number of birds, sex, age class, location, and number of days observed. Beginning in 1978, site evaluations were initiated for collection of more extensive information on roost and feeding sites. This greatly expanded the scope and detail of data collected to include wetland type and size, water quality, substrate, water depth at specific roost or feeding sites and at intervals along a transect, visibility, vegetation, land cover, etc. More than 25 parameters were recorded for each site that was evaluated (U.S. Fish and Wildlife Service 1980). The Nebraska Field Office of the United States Fish and Wildlife Service (USFWS) has maintained these data in 2 databases: 1 for observational sightings (containing 1352 confirmed sightings, 1943-99) and 1 for site evaluation data (1060 sightings, 1977-99).

Data from the confirmed sightings and site evaluation databases have been used by a number of researchers for various projects. Johnson (1982) used observational data to investigate the use and significance of habitat in the Platte River valley for whooping cranes. Lingle et al. (1984) used observational and site evaluation data to characterize whooping crane use in the Platte River valley. Carlson et al. (1990) and Ziewietz (1992) used roost and feeding site data to develop a habitat suitability model for the Platte River. Roost site data were used by Stahlecker (1997) to correlate stopover habitat availability with wetlands identified on National Wetland Inventory (NWI) maps. However, there has been no comprehensive summarization of the USFWS databases to characterize roosting and feeding site use throughout the flyway, to explore temporal or spatial patterns, or to examine differences among social groups (families, singles, or groups). Nor has there been a comprehensive review of the data sets to detect and correct errors.

At the 1998 meeting of the Whooping Crane Recovery Team in Calgary, Alberta, team members recommended that, although observational data should continue to be collected, no additional site evaluations should be done until the existing data were analyzed. The analysis of habitat use for the Platte River was identified as a high priority in 2000 by the Technical Committee of the Cooperative Agreement among Colorado, Nebraska, and Wyoming. In a January 1999 letter to Mr. Wallace Jobman, USFWS Nebraska Field Office, Whooping Crane Coordinator Thomas Stehn (USFWS, Region 2) reiterated the need to analyze existing data as expressed by the Recovery Team. As a result, a group of state and federal biologists and other interested parties met to discuss objectives for a better understanding of the USFWS database. The following 12 priority objectives for data analyses were identified: 1) Characterize habitat for palustrine and riverine roost and feeding sites. 2) Determine behavior and use patterns for roost and feeding sites using individually-marked cranes. 3) Determine migration patterns of individually-marked birds. 4) Determine use patterns of family units versus individual and non-family groups. 5) Determine use patterns for fall versus spring. 6) Determine use patterns for palustrine versus riverine habitat throughout the flyway. 7) Determine climatic influence on palustrine versus riverine use. 8) Determine use patterns by state and region throughout the flyway. 9) Determine temporal changes in use patterns B year to year and over time. 10) Determine influence of other species, i.e., sandhill cranes (Grus canadensis), waterfowl, and shorebirds, on use patterns. 11) Assess site evaluation data against NWI classification. 12) Assess length of stay regionally for fall versus spring migration.

The goal of this project is to conduct a comprehensive summary of existing observational and site evaluation data for habitat use by whooping cranes through the migration flyway from Texas to North Dakota. This report provides a summary of the sighting locations for 1943-99 and habitat description information for 1977-99. We provide recommendations on data needs, limitations, and survey methods for future monitoring of whooping cranes during migration.


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