Why do predators specialize on lemmings? Insights from long-term monitoring in the Norwegian low Arctic

Rodent prey sustains a diverse assemblage of arctic predators. While lemmings and voles cooccur in large parts of the Arctic, certain predators appear to specialize on lemmings. We elucidate reasons for predators´ specialization on lemmings based on two decades’ monitoring of small rodents and their avian predators in low-arctic Norway. We focus particularly on the snowy owl (Bubo scandiacus), which currently is believed to be declining across the Arctic, possibly linked to dampened lemming cycles. While five cyclic vole peaks elicited profound numerical responses of breeding rough-legged hawks (Buteo lagopus) and long-tailed jaegers (Stercorarius longicaudus), snowy owls were breeding in the only peak with high abundance of the Norwegian lemming (Lemmus lemmus) in spring. Lemmings strongly dominated the snowy owls’ diets, while rough-legged hawk diets were dominated by voles. We attribute the snowy owls’ specialization on lemmings to our finding that lemmings have higher supranivean activity than voles when the owls arrive in winter and that lemmings are more exposed in barren tundra habitats where breeding owls hunt in summer. We predict that voles will not be able to replace the crucial role of lemmings as prey to snowy owls and other specialized lemming predators in a warming arctic climate.