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Arctic ground squirrels (Urocitellus parryii) have virtually disappeared from the boreal forests of southwestern Yukon,Canada since 2000.From 1973 to 2000 they were the second most abundant vertebrate in this forest community.We ask two questions: why have they disappeared? Will they come back? There are three major habitats in the Yukon – low elevation white spruce boreal forest,low elevation meadows,and high elevation alpine tundra.Ground squirrels are abundant in alpine tundra but they have not re-colonized low elevation habitats.Two competing hypotheses are that they are in a predator pit from which they cannot escape because they are alternative prey for snowshoe hare predators.Alternatively,climate change has increased icing of hibernation sites so overwinter survival is very low.Arctic ground squirrel populations from the 1970s to 2000 rose and fell with the 9-10 year hare cycle.They disappeared in 2000 in both the boreal forest and in low elevation meadows where they were very common.No obvious diseases have ever been noted.Both habitats have increased plant production probably due to climatic warming.Increased vegetation density removes the advantages ground squirrels have of avoiding predation by issuing alarm calls.If this idea is correct,they could be in a permanent predator pit in the lowland habitats.In spite of high densities of ground squirrels in the alpine tundra,there is no evidence of colonization back into the forest.We are now investigating whether ground squirrels have also disappeared from specific alpine sites in recent years.