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Detecting Trumpeter Swans Harvested in Tundra Swan Hunts

Roderick C. Drewien, Jeffrey T. Herbert, Thomas W. Aldrich and Stephen H. Bouffard
Wildlife Society Bulletin (1973-2006)
Vol. 27, No. 1 (Spring, 1999), pp. 95-102
Published by: Wiley on behalf of the Wildlife Society
Stable URL: http://www.jstor.org/stable/3783945
Page Count: 8
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Detecting Trumpeter Swans Harvested in Tundra Swan Hunts
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Abstract

Identifying the less numerous trumpeter swans (Cygnus buccinator) harvested in tundra swan (C. columbianus) hunts is a management concern. As trumpeter swan ranges expand, their populations become more sympatric with tundra swans during fall and winter, but the 2 species are difficult to separate in the field. Eight states currently allow limited permit hunting for tundra swans. The hunting of trumpeter swans is currently limited by experimental quota to 3 states in the Pacific Flyway. We compared bill measurements (tip to posterior edge of nares opening) for trumpeter swans captured in Idaho (n=672) with measurements of tundra swans harvested in Utah (n=1,414) and with measurements reported on postcards (n=890) returned by hunters who harvested swans in Montana. Mean bill measurements for adult and cygnet trumpeter swans were 68.8 mm and 67.6 mm, respectively, and for tundra swans, 54.0 mm and 52.4 mm, respectively; differences were significant (P<0.001) between species and in each age class. Over 99% of trumpeter swan adults and cygnets measured ≥62 mm and ≥61 mm, respectively, whereas 99% of tundra swan adults and cygnets were ≤60 mm and ≤59 mm, respectively. Over 96% of adult tundra swans also were identifiable by yellow lore spots, which were rare (0.3%) in adult trumpeter swans. Utah data showed that 10 (0.7%) of 1,424 swans checked during the 1994-96 seasons were trumpeter swans. A Montana postcard survey was mailed to swan hunters during 1992-96 requesting bill measurements, presence or absence of a yellow lore spot, and plumage color to assess age. Of 890 swans reported, 19 (2.1%) were judged to be trumpeter swans. The postcard survey identifies species with minimal error, is a useful and inexpensive technique to monitor minimum trumpeter swan harvest in tundra swan hunts, provides age composition of the harvest, and could be used in tundra swan hunting states. The utility of the technique is dependent on accurate measurements and a high compliance rate by hunters.

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