As summer fades into a beautiful but brief golden autumn in Jackson Hole, we welcome shorter days and snow much sooner than the rest of the country. The seasons change beckons in change for raptor species of this ecosystem as well, with many of our common raptor species beginning their fall migration. 26 species of North American raptors are partial migrants, with their breeding territory located in the Greater Yellowstone ecosystem, species like the Swainson’s Hawk and American Kestrel will fly south for the long winter. These Northern breeders will migrate thousands of miles to their wintering grounds. Raptor migration is a favorite time of year for ornithologists and casual birders alike, this is because raptor species such as the Golden Eagle, take advantage of warm air fronts during the daytime to fly and rest at night so we are able to easily observe these historic migrations. The best way to spot raptors during fall migration is to study their tail feather and wing shape, then compare silhouettes in the sky to identify which birds of prey may be passing over your home.
Other species are well adapted morphologically and behaviorally to the winter climate of the Tetons, these species would be classified as year-round residents to the Tetons. There are many species of owls in Jackson Hole and surrounding areas that tend to hang around the same general area throughout spring, summer, fall, and winter. The Great Gray Owl is one example of a bird adapted to overwinter in the Tetons, to catch their prey they often need to break through hefty layers of snow. These owls have wonderful hearing because of slightly asymmetrical ear openings paired with a disc-shaped face, this allows them to pinpoint even the subtlest of movements of prey under thick layers of snow. This type of hunting behavior is known as the “snow-plunge” requiring the bird to burst through a snow pack that is deeper than their own body size. Owls also stay warm thanks to their feathered tarsus, which importantly insulate their feet in comparison to southern owl species such as the aptly named Cuban Bare-legged Owl. Raptor and bird species also take on a more full winter plumage to help them brave the harsh winter months.
Some raptor species are so well adapted to the cold that they actually head south to Jackson Hole for the winter months. The Rough-legged Hawk, or buzzard, is one of our winter migrants to this region, arriving from the Arctic tundra and far north Canadian taiga in October or November. In March they will return to open habitat in the circumpolar region of Canada to breed. Rough-legged hawks also have feathered legs as an adaptation to their cold home range, which makes them perfectly adapted to Jackson Hole winters. Rough legged hawks are thought to feed mostly on rabbits and small mammals during the winter months and will also compete with species like Raven and Red-tailed Hawk for prey and carrion during this time when prey availability may be lower.
Great Gray Owl photo by Irene Greenberg