Snowy owls only appear when lemming numbers have fallen because lemmings make a vital part of their diet.
It should be noted that lemmings make up the main part of the diet of the snowy owls. Lemmings also play an important role in influencing the breeding distribution and the nesting success of snowy owls.
Therefore, snowy owls only appear when lemming numbers have fallen. This is because it plays an important role in their population.
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