Detecting trumpeter swans harvested in tundra swan hunts

Identifying the less numerous trumpeter swans (Cygnus buccinator) harvested in tundra swan (C. columbianus) hunts is a management concern. As trumpete r swan ranges expand, their populations become more sympatric with tundra s wans 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) a nd with measurements reported on postcards (n = 890) returned by hunters wh o harvested swans in Montana. Mean bill measurements for adult and cygnet t rumpeter 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 < 0.00 1) between species and in each age class. Over 99% of trumpeter swan adults and cygnets measured greater than or equal to 62 mm and greater than or eq ual to 61 mm, respectively, whereas 99% of tundra swan adults and cygnets w ere less than or equal to 60 mm and less than or equal to 59 mm, respective ly. Over 96% of adult tundra swans also were identifiable by yellow lore sp ots, 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, a nd plumage color to assess age. Of 890 swans reported, 19 (2.1%) were judge d to be trumpeter swans. The postcard survey identifies species with minima l 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 techn ique is dependent on accurate measurements and a high compliance rate by hu nters.