Migration Dynamics of the Whooping Crane

Home Browse Search

the types of stopover habitat used most frequently. These surveys, which employed airplane and ground support teams to track the movements of radio- tagged birds mile for mile along the flyway, provided an opportunity to observe and detail roost sites used at each stopover, including those in remote areas where confirmed sightings would otherwise be unlikely. Unfortunately, however, available information on the results of these surveys is limited to brief narrative reports on the first two tracking efforts (fall 1981 and fall 1982), and fl i ght -track maps in semiannual progress reports prepared by the Service for the remaining seven surveys. Though the narrative reports (FWS 1981b and 1982b) stated that valuable, previously unknown information on the species' migratory habits and habitat characteristics was collected and analyzed, and that detailed technical reports would be forthcoming, no such reports or analyses have been published to date. Considering the important need to base management strategies on the best available data, and the substantial amount of interest, effort, and expense that have been directed towards the recovery of this species, the lack of substantive survey results is regrettable. Nevertheless, available information from the radio-tracking surveys supports Johnson and Temple's (1980) contention that whooping cranes are flexible and opportunistic in their selection of roost sites during migration. Mi grant birds appear to use small natural and artificial wetlands as stopover sites on a much more frequent basis than was previously apparent from the confirmed sightings record. Family groups monitored during the fall migrations in 1981 and 1982 were observed to roost in small boreal lakes, "pothole" ponds, and marshes, as well as flooded grain fields, farm ponds, and stockponds (Table 2 -5) . The statement in the narrative report for the fall 1981 tracking effort (FWS 1981b, p. 10), that "Ci 7n general, very small wetlands were selected as roosting sites ", appl ies equally well to the fall 1982 survey. The common use of small waterbodi es as stopover roost sites, including f arm ponds and flooded fields contai ni ng as little as 1/4 -acre of open water (i. e. , approximately 105 X 105 feet of surface area) , is in striking contrast to recent agency statements (NGPC 1985, p. 19) that whooping cranes "require" 500 to 1,200 feet of open water in riveri ne settings. Rather, these survey observations suggest that migrant whooping cranes will readily roost in wetlands containing only a limited amount of open water if the site is characterized by good horizontal and overhead visibility, and is removed from areas of heavy human disturbance and /or development. Small natural and artificial wetlands located adjacent to agricultural croplands offer potential access to a variety of plant and animal foods, and, at the same time, minimize further energy expenditures associated with moving between roost and feeding sites. In Nebraska, roost sites used by migrant whooping cranes monitored during the fall 1981 and fall 1982 radio-tracking surveys included a wetland area (Al kal i Pond) approximately 7 miles south of Merritt Reservoir near Valentine, a stockpond 28 miles north of the Platte River near Oconto, and a small pond in the Sandhil l s about 15 miles southeast of Ainsworth (Table 2 -5) . Rel ative to the nine radio-tracking surveys conducted from fall 1981 through spring 1984- - which monitored a total of 27 individual birds (including juveniles, subadults, and adults) as they migrated through Nebraska - -8 stopovers were recorded in the 2 -17