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Crepuscular, a classification of animals that are active primarily during twilight, making them similar to nocturnal animals. Diurnality, plant or animal behavior characterized by activity during the day and sleeping at night. Cathemeral, a classification of organisms with sporadic and random intervals of activity during the day or night.
Arctic tundra is the northernmost (and coldest) of European habitats, in extreme northern Scandinavia, Svalbard archipelago, northernmost part of Russia. Some typical animals include reindeer, Arctic fox, brown bear, ermine, lemmings, partridges, snowy owl and many insects. Most tundra animals undergo hibernation during the colder season.
The biodiversity of tundra is low: 1,700 species of vascular plants and only 48 species of land mammals can be found, although millions of birds migrate there each year for the marshes. [9] There are also a few fish species. There are few species with large populations.
Nocturnal species take advantage of the night time to prey on species that are used to avoiding diurnal predators. Some nocturnal fish species will use the moonlight to prey on zooplankton species that come to the surface at night. [8] Some species have developed unique adaptations that allow them to hunt in the dark.
Gymnotus species are nocturnal and mainly feed on aquatic insects, crustaceans, small fish and other small animals, [9] but may also take plant material. [8] Being electric fish, they generate weak electric fields used for navigation, finding prey and communicating with other individuals of their species.
Both plant species and animal species have become endangered. The Aleutian shield fern is a plant species that have been endangered due to caribou tramping and grazing, slumping from growing substrate, and human foot traffic. [9] Animal species that are endangered in the tundra include the Arctic fox, caribou, and polar bears.
Some species that always live in shoals or that swim continuously (because of a need for ram ventilation of the gills, for example) are suspected never to sleep. [4] There is also doubt about certain blind species that live in caves. [5] However, other fish do seem to sleep, especially when purely behavioral criteria are used to define sleep.
The snowy owl (Bubo scandiacus), [4] also known as the polar owl, the white owl and the Arctic owl, [5] is a large, white owl of the true owl family. [6] Snowy owls are native to the Arctic regions of both North America and the Palearctic, breeding mostly on the tundra. [2]