they may nest at as high as . Outside the breeding season, snowy owls may occupy nearly any open landscape. Typically wintering sites are rather windswept with meager cover. These open areas can include coastal dunes, other coastal spots, lakeshores, islands, moorlands, steppes, meadows, prairies, other extensive grasslands and rather shrubby areas of the Subarctic. These may be favored due to their vague similarity to the flat openness of the tundra. Manmade open sites are now perhaps even more used than natural ones, often agricultural fields and rangeland, as well as large areas of cleared forests. During irruption years when they are found in the northeastern United States, juveniles frequent developed areas including urban areas and golf courses, as well as the expected grasslands and agricultural areas that older birds primarily use. On the plains of Alberta, observed snowy owls spent 30% of their time in stubble-fields, 30% in summer fallow, 14% in hayfield and the remainder of the time in pasture, natural grasslands and sloughs. The agricultural areas, large untouched by the farmers in winter, may have had more concentrated prey than the others in Alberta. Perhaps the most consistently attractive habitat in North America to wintering snowy owls in modern times may be airports, which not only tend to have the flat, grassy characteristics of their preferred habitats but also by winter host a particular diversity of prey, both pests which rely on humans as well as wildlife attracted to the extensively grassy and marshy strips that dot the large airport vicinities. For example, Logan International Airport in Massachusetts has relatively one of the most reliable annual populations known in the United States in winter. All ages spend a fair amount of their time over water in the Bering Sea, the Atlantic Ocean and even the Great Lakes, mostly on ice floes. These marine and ocean-like freshwater areas were observed to account for 22–31% of habitat used in 34 radio-tagged American snowy owls over two irruptive years, with the tagged owls occurring a mean of from the nearest land (while 35–58% used the expected preferred habitats of grassland, pasture and other agricultural land). Behavior Snowy owls may be active to some extent at both day, from dawn to dusk, and night. Snowy owls have been seen to be active even during the very brief winter daytime in the northern winter. During the Arctic summer, snowy owls may tend