A Summary of Trumpeter Swan Production at Malheur National Wildlife Refuge, Oregon

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Prior to 1939, only 2 records of Trumpeter Swans (Cygnus buccinator) had been reported from Malheur National Wildlife Refuge (NWR) and no records of breeding swans were known. Attempts to establish a breeding population at Malheur NWR with transplants from Red Rock Lakes NWR, Montana, began in 1939. Several transplants were made before the first broods of swans were produced in 1958. From 1958 through 1984, 288 cygnets fledged at Malheur NWR. Most Trumpeters nested in the Blitzen Valley, but some nested on Malheur Lake, in the Double-O area, and on the Island Ranch north of the refuge. The population now appears to be stable, but the limiting factors are largely unknown. Circumstantial evidence suggests that some young swans are leaving the area prior to sexual maturity. There were no records of Trumpeter Swans (Cygnus buccinator) nesting in Oregon prior to the establishment of a population at Malheur National Wildlife Refuge (NWR). Although the species was not described until 1832 (Swainson and Richardson 1832), accounts by Lewis and Clark indicated that they observed both Trumpeter and Tundra (Cygnus columbianus) Swans near the mouth of the Columbia River in 1806 (Banko 1960, Burroughs 1961). Other early migration records included those of Townsend (1829), Newberry (1857), Bendire (1877), Mearns (1879), Johnson (1880), Anthony (1886), Wood- cock (1902) and Prill (1922). Bendire (1877) collected a Trumpeter Swan at Malheur Lake on 24 March 1877. Johnson (1880) reported Trumpeter Swans to be common migrants in the Willamette Valley. Prill (1922) observed a pair of Trumpeters on the Blitzen River The information in this report is derived from letters, memos, reports and unpub- lished data in the biological files at Malheur National Wildlife Refuge. Each of us was involved at one time or another in acquisition and summarization of Trumpeter breed- ing data at the Refuge. Waterfowl census techniques and coverage have changed occa- sionally since active refuge management began in the mid-1930's. From 1935 to 1955 waterfowl were censused predominantly along ground routes at irregular intervals. Since 1955 Trumpeter Swan production has been determined by using aerial surveys. These flights were conducted in August in fixed-wing aircraft. All aquatic habitat was surveyed and an attempt was made to count all cygnets. Beginning in the late 1970's three aerial counts were made annually. A late May flight was used for counting breed- ing pairs, an early July flight was used to locate active nests, and in August cygnets were counted. Flights were made in Cessna 182 or 185 aircraft at 30 to 60 m above the ground at about 150 kph. Information from these flights was supplemented by obser- vations made during other field activities throughout the year.