December Nature Notes

By December, the bird migrations associated with approaching winter have typically ended. Shorebirds fly through the state as early as July, and waterfowl and sandhill cranes are most numerous in migration during October and November. Yet, some years when conditions are right, South Dakota can be visited by a spectacular bird from the north in December and throughout the winter.

Snowy owls are birds from the very far north—they nest in Alaska, arctic Canada and Greenland (as well as northern Eurasia) above 60 degrees North Latitude on the treeless tundra. Their plumage reflects their northern home: the birds are white as snow, although females and young birds are barred with black. Their face is always bright white and highlights their brilliant yellow eyes. The owls hunt the Arctic’s abundant lemmings and occasionally take ducks, ptarmigans and other birds. Dense and heavy feathers keep snowy owls warm and extend even onto their toes (bare on most birds) ending only at their talons.

When winter comes to the Arctic, many snowy owls move south and their travels can take them to South Dakota. Some years bring more owls than others, and typically every four to five years those numbers can be notably higher, reflecting what is called an owl “invasion” or irruption. The winter of 2011-12 was such a year: snowy owls were reported from at least 26 counties across South Dakota. One hot spot was Lake Andes National Wildlife Refuge and the owls there attracted birders from as far away as England. An excellent summary of owl numbers and distribution (with detailed maps showing sighting locations) is available from the online resource eBird. Although snowy owls were seen across the northern United States, their numbers were unusually high in the Great Plains, making the 2011-12 irruption exceptional.

Why snowy owls are irruptive some winters and not others is unclear. It used to be thought that owls move south in greater numbers when lemmings are scarce, forcing hungry birds to travel farther to find food. Dead owls examined during an irruption winter often are emaciated. But it may be instead that too many lemmings are responsible—when the hunting is good during the summer, nesting owls produce more chicks resulting in a larger population that must compete for prey. 

Many of the snowy owls banded at Boston’s Logan Airport (a location that attracts more overwintering owls than any other in North America) are birds hatched that year. Ongoing telemetry research of these owls is revealing fascinating details of their natural history.

No one knows when snowy owls will next visit South Dakota in large numbers. They are impressive birds and worth looking for every winter. Surprisingly, a big white owl with a five-foot wingspan can be hard to spot. The owls are active during the day and favor open areas resembling their tundra home. They blend in with their surroundings when sitting calmly on the ground, or atop a fence post drifted with snow. Find an owl by patiently scrutinizing with your binoculars any unusual white shape to see if it swivels its head to stare back at you with large yellow eyes.