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Conditioning of Sandhill Cranes During Fall Migration

Methods

We obtained body mass on adult G. c. canadensis (n = 380) and G. c. rowani (n = 556) shot during fall 1965 (Madsen 1967), 1969-72 (Johnson and Stewart 1973), and 1977-87 in central North Dakota. We determined subspecies by comparing measurements of wing chord, tarsus length, and culmen length (post nares and total) with taxonomic criteria presented in Johnson and Stewart (1973). Adults were distinguished from juveniles by the lack of brown feathering on the occiput (Lewis 1979). Most cranes were shot in Burleigh, Kidder, McLean, and Pierce counties, the principal fall staging areas of sandhill cranes in the state (Johnson and Stewart 1972; U.S. Dep. Inter. 1979a, 1980; Melvin and Temple 1983). A few cranes (< 10% ) were from Benson, Bottineau, McHenry, Sheridan, and Stutsman counties, near the periphery of the major stopover sites. Cranes were weighed on a spring scale in the field to the nearest 10 g, and the sex of adults was determined by gonadal examination. The sex of juveniles was not obtained because limited development of reproductive organs prevented accurate determinations.

A separate sample of 20 adult and 14 juvenile G. c. rowani was obtained in Kidder County in 1978 and 1984 to compare body composition from early to late in the fall staging period. Cranes were shot during 2 periods—after arrival (late Aug–mid-Sep), and before departure (mid-Oct). A maximum of 1 adult and 1 juvenile was collected per flock. Specimens were tagged and were weighed wet at the laboratory to the nearest 1 g on a beam balance. Feathers were plucked, gizzard and esophageal contents were removed, sex was determined by gonadal examination, and birds were reweighed to the nearest 1 g. Each bird was double-bagged in plastic and stored frozen until prepared for chemical analysis. Carcass composition of fat, protein, water, and ash was measured with whole carcass homogenate (Horwitz 1975). Fat content was determined by Soxhlet extraction for 6 hours using petroleum ether and with duplicate analyses for each specimen. Protein determination was by the Kjeldahl method. Statistical analyses were made with SAS (SAS Inst., Inc. 1985) procedure GLM.

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