as permafrost thaws (temp. increases), wetlands expand, attract more migratory birds. influxes of spring migrants from S occur earlier, longer breeding season. meanwhile, southern fringes of tundra will lose open aspect as tree line advances N, habitat changes. predators like snowy owls, which rely on lemming pop. will be forced northwards. migration patterns of animals e.g. caribou (type of reindeer), which spend summer on tundra, will be disrupted.