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2.2 MIGRATION CH RON OL OG Y <br />The spring migration from wintering grounds at Aransas NWR to breeding grou <br />at Wood Buffalo Nati onal Park proceeds rapidly. Johnson and Temple (1980, pp. <br />21 -26) reported that whooping crane departures from Aransas NWR start as early <br />as late March and continue until late April or early May; the majority of <br />departures take place from March 28 to April 16, with median departure dates <br />occurring around April 6 -7. Birds begin arriving at Wood Buffalo National Park <br />by approximately April 20 and may continue to arrive through the middle of May. <br />In the fall, initial departures from Wood Buffalo National Park occur around <br />September 12 and by September 26 all birds have usually left. Whoopi ng cranes <br />typically arrive at Aransas NWR from early October through mid - November, with <br />the majority of arrivals occurring between October 20 and November 14. <br />Analysis of the temporal occurrence of whooping cranes in Nebraska, based on <br />confirmed sightings from 1940 -1984 (FWS 1985)., indicates that most spring <br />migrants have been observed in the state from April 7 through April 20 with the <br />peak number of birds occurring on April 17 (Figure 2 -2). However, individual <br />birds have been sighted as early as March 29 and as late as May 9. Most fall <br />migrants have been sighted in the state from October 17 through November 10 <br />with peak occurrence on October 29; extreme sighting dates are October 3 and <br />November 21. <br />The si gh ti ngs of single birds shown in Figure 2 -2 from May 20 -June 18 (3 0 <br />days) , and July 16 -23 (8 days) , are clearly anomalous. Because both sightings <br />occurred during the same year (1950) they may refect the errant wanderings of <br />the same bird. Allen (1952, pp. 48-50) reported other observations of "summer <br />wanderers" and commented that "since the summer distribution of these <br />individuals is abnormal, then the birds themselves must be abnormal as well ". <br />He suggested that the explanation was physiological, perhaps resulting from an <br />injury of some kind, or from the ingestion of 1 ea d pellets known to retard <br />gonadal development and affect failure to migrate in waterfowl. Johnson and <br />Temple (1980, pp. 23 -24) also cited records of whooping cranes (predominantly <br />single birds) apparently summering in areas other than Wood Buffalo National <br />Park, and the Service (FWS 1982a, p. 2) noted that one bird remained at Aransas <br />NWR during the summer of 1981. <br />2.3 FL OCK S IZ E <br />In contrast to sandhill cranes (Gros Lanadensis) which <br />large flocks, whooping cranes migrate as individuals, typically al ly migrate i n <br />small flocks, sometimes in the company of sandhill cranes. Based longaoreviewd <br />of 351 conf i nmed whooping crane sightings, the Service (FWS 1982a, p. 1) <br />reported that the number of birds per sighting ranged form 1 to 22 and averaged <br />3.2; birds migrating individually, in pairs, or in threesomes were sighted most <br />frequently throughout the flyway. Moreover, the Service noted that 70 percent <br />Of all confirmed sightings from 1975 through spring 1982 were reported in the <br />fall. The disparity between the number of spring and fall sightings was <br />greatest in the Canadian portion of the flyway where 78 percent of the <br />conf i rmed si ghti ngs were made duri ng f al l migrati ons. It was speculated that <br />the greater number of fall sightings may be caused by slower migration during <br />2 -3 <br />