2nd Owl Symposium Snowy Owl ( Nyctea scandiaca ) Repr oduction in Relation to Lemming Population Cycles on W rangel Island

—Data on Snowy Owl ( Nyctea scandiaca) reproduction on Wrangel Island were collected for six seasons fr om a total of 423 nests. Nest densities ranged fr om 0.15 to 0.40 nests/km 2. Mean clutch size for all 6 years was 6.5 (fr om 5.3 to 8.4) being significantly higher during low lemming season (7.17) (N = 29) than for peak lemming season (6.0, p < 0.001). Clutch size corr elated with weather conditions, females’ age, and lemming numbers. Number of young fledged per nest was the highest during peak lemming numbers. Bigamous units occurr ed only during medium, high, and peak lemming numbers. Nestling mortality was due to lack of food. Snowy Owl (Nyctea scandiaca) biology has been studied in dif ferent parts of its cir cumpolar range, including W rangel Island (Litvin and Baranyuk 1989, Robinson and Becker 1986, Taylor 1974). However, few long-ter m studies on this species have been conducted (Pitelka et al. 1955a,b), and even those did not investigate the whole variety of Snowy Owl population parameters. Watson (1957) suggested that Snowy Owl nest density, clutch size, and reproductive success may dif fer in different areas even under high lemming population numbers. In most of the pr eviously published articles on Snowy Owl biology, the r elationship between the number of nests and clutch size, and lemming numbers is mentioned but without describing the mechanisms of this corr elation (Cramp 1985, Johnsgar d 1988, Krechmar and Dorogoi 1981, Litvin and Baranyuk 1989, Parmelle 1992, Robinson and Becker 1986, Voous 1988). This paper pr esents data on Snowy Owl reproduction on W rangel Island collected fr om a permanent study plot (45 km 2) and on r outes (3,000 km) for six seasons, 1990-1995, during which lemming numbers ranged fr om depression to peak. 1 Research Scientist, Chukotka Division of the Pacific Institute of Geography, Far -East Branch of Russian Academy of Sciences, RF . Objectives of the study wer e: 1. To determine factors r esponsible for the density of Snowy Owl reproductive settlements. 2. To investigate relationships between variations in Snowy Owl clutch size and survival of young, and various envir onmental parameters, including lemming numbers. 3. To estimate the r eproductive contribution of females of different age. 4. To investigate occurr ence of polygyny in Snowy Owls during different phases of population cycle, and r eproductive success in family units of bigamous males.