. The Canadian field-naturalist. 280 The Canadian Field-Naturalist Vol. 98 60 000 50 000 40 000 30 000 20 000- 10 000 Fall Migration. Figure I. Daily counts of Sandhill Cranes during fall migration, upper Tanana River Valley, Alaska. Dots (• ) indicate partial counts made outside of the main count periods. eral automobiles to make daily searches for migrating cranes, primarily from Tetlin Junction to Mt. Fair- play and from Tanacross to Northway. When flocks of cranes were found, counts were made to ascertain the relative intensity of use of different routes. In addition, this crew used small
. The Canadian field-naturalist. 280 The Canadian Field-Naturalist Vol. 98 60 000 50 000 40 000 30 000 20 000- 10 000 Fall Migration. Figure I. Daily counts of Sandhill Cranes during fall migration, upper Tanana River Valley, Alaska. Dots (• ) indicate partial counts made outside of the main count periods. eral automobiles to make daily searches for migrating cranes, primarily from Tetlin Junction to Mt. Fair- play and from Tanacross to Northway. When flocks of cranes were found, counts were made to ascertain the relative intensity of use of different routes. In addition, this crew used small fixed-winged aircraft on occasion to search for and follow migrating flocks and to search for roosting sites. Aircraft proved particularly useful for delineating migratory routes when observers could get airborne during heavy flights. Likewise, information on roost- ing sites was most effectively obtained from early morning flights following a heavy passage late on the preceding day. Unless we knew that a major passage was underway, hunting for migratory flocks by air- craft was ineffective. Field observations were conducted throughout the main fall and spring migration periods, and observers attempted to remain at observation posts and in the field throughout the daily period of crane activity. Thus, on some days observations began prior to 0400 Alaska Standard Time (AST) or ended after 1900, or even 2100 AST. Data recorded for each crane observation were date, locality, number of birds, time of day, flight height and direction, wind direction and velocity, height and percent of cloud cover, and descriptions of any ground utilization or reaction to disturbance. Hourly weather reports for Delta Junction and Northway were obtained from the National Weather Service. These reports included height and characteristics of lowest clouds, height of cloud ceil- ing, total opaque sky cover, horizontal visibility, type of obstruction to visibility (fog, snow, rain), wind speed and
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