The Snowy Owl ( Bubo scandiacus ), a majestic bird of the Arctic, is a fascinating subject when it comes to its dietary habits. As the largest owl in North America by body mass, this species has a diet as unique and adaptable as its environment. These owls are not always snowy white - they range from all white to black and white, with a pattern of dark, prominent bars - except on the face, which is always white.
Habitat and Distribution
During the breeding season, which begins in May, Snowy Owls are found on the open tundra all around the Arctic Circle. Some owls remain on the breeding grounds throughout the year, enduring temperatures as low as -80°F. Others migrate south, reaching the northern half of the lower 48 states, and during irruptions, even Bermuda, Cuba, and Hawaii. Snowy Owls regularly visit New England from November through April, seeking habitats that mimic the Arctic tundra, such as salt marshes, agricultural fields, and airports.
Physical Characteristics and Hunting Behavior
Snowy Owls range in length from 20 to 28 inches, with a wingspan of 54 to 66 inches, and weigh between 3.25 and 6.5 pounds. Females are typically larger than males and have more dark markings. Their eyes, like those of all owls, are enormous relative to their heads. Because owls cannot move their eyes, they swivel their heads a full 270° with the help of 14 neck vertebrae. Snowy owls have deep yellow eyes, with a protruding upper eyelid acting as a shade from sunlight. Fine, fur-like feathers cover their face, beak, legs, and feet, providing warmth.
Snowy Owls are both specialized and generalist hunters. On their summer breeding grounds, where daylight lasts 24 hours, they hunt in the light. In winter, they prefer to hunt under the cover of darkness. They use a variety of hunting techniques, including hovering in the air and watching from a perch. They have excellent eyesight and hearing.
Primary Food Sources
In the Arctic, Snowy Owls primarily eat lemmings. When they are in winter in the US they eat rodents, rabbits, other small mammals, many bird species, especially waterfowl including geese, Great Blue Herons, gulls, and even other raptors including American Kestrels, Northern Harriers, and Short-eared Owls. Lemmings make up the main part of the snowy owls' diet, and lemming population numbers rise and fall naturally. Sometimes, if there is not enough prey around to feed baby owls, the adult pair won't lay any eggs at all until the supply of food improves.
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Adaptability in Diet
Snowy Owls are opportunistic hunters, meaning they will prey on almost anything they can catch. They have been known to hunt other mammals, such as squirrels and hares, and birds, including ptarmigan and seabirds. When available, they will even take fish, amphibians, crustaceans, and insects. This adaptability allows them to survive in various environments and during times when their primary food source is scarce.
Hunting Techniques and Strategies
Snowy Owls employ several effective hunting strategies. They often perch on posts, rocks, or the ground, silently watching for their next meal. They can spend a good part of their day sitting and waiting. Alternatively, they may fly low over the ground in search of prey. Once they spot something moving along the ground, they swoop down and snatch their prey. When hunting birds, they take their quarry directly in the air, and when hunting fish, they snatch them from the water's surface. They have even been known to snatch prey while walking on the ground.
Digestion and Pellets
Snowy Owls swallow their food whole or in large chunks. The indigestible parts, such as fur, feathers, and bones, are compressed into a fur ball called a pellet, which they regurgitate daily. These pellets can be dissected to determine what the owls have been eating. However, field observations are also necessary because when they capture large prey, such as a duck, they will pluck off the feathers and eat the breast, which may not show up in a pellet.
Threats to Snowy Owls
The breeding population of Snowy Owls is declining, and research is ongoing to understand why. Young, inexperienced owls face many challenges, including mastering hunting skills, evading predators, avoiding vehicles and electrocution, fending off disease and rodenticide poisoning, and dealing with disturbance from people while roosting and hunting.
Conservation Efforts
Mass Audubon is working to protect Snowy Owls. Norman Smith, former director of Mass Audubon's Blue Hills Trailside Museum, has been studying them since 1981. He attaches bands and transmitters to Snowy Owls at Boston Logan International Airport to track their travels.
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How to Help Snowy Owls
To help these spectacular raptors, it is important to give them plenty of space. When observing an owl, stay at least 50 yards (150 feet) away. Protecting birds means giving them the space they need while roosting and hunting so they can hopefully make it back to the Arctic to breed.
Snowy Owl Vocalizations
Snowy owls are known to be largely vocal only during their breeding season, yet some vocalizations have been recorded during the winter in the northern United States. The sounds they make include a raspier bark, sometimes called a "watchman's rattle" call, that may be transcribed as rick, rick, rick, ha, how, quack, quock or kre, kre, kre, kre, kre. When females attack to protect their nest, they let out a crowed ca-ca-oh call. Other owls attacking to protect the nest do a loud version of the typical call while circling before dropping down. They may also clap their beak in response to threats or annoyances, though it is believed this sound may actually be a clicking of the tongue, not the beak. Initially, the young of the snowy owl have a high pitched and soft begging call which develops into a strong, wheezy scream at around 2 weeks.
Snowy Owl Appearance and Plumage
The snowy owl is mostly white. Females are almost invariably more duskily patterned than like-age males. In mature males, the upper parts are plain white with usually a few dark spots on the miniature ear-tufts, about the head and the tips of some primaries and secondaries whilst the underside is often pure white. Despite their reputation for being purely white, only 3 out of 129 Russian museum specimens of adult males showed an almost complete absence of darker spots. The adult female is usually considerably more spotted and often slightly barred with dark brown on the crown and the underparts. On rare occasions, a female can appear almost pure white, as has been recorded in both the field and in captivity. There is some evidence that some of the species grow paler with age after maturity. One study's conclusions were that males were usually but not always lighter and that correctly aging is extremely difficult, sometimes individuals either get lighter, darker or do not change their appearance with age. On the other hand, with close study, it is possible to visually identify even individual snowy owls using the pattern of markings on the wing, which can be somewhat unique in each individual. After a fresh moult, some adult females that previously appeared relatively pale newly evidenced dark, heavy markings. The chicks are initially grayish white but quickly transition to dark gray-brown in the mesoptile plumage. This type of plumage camouflages effectively against the variously colored lichens that dot the tundra ground. This is gradually replaced by plumage showing dark barring on white. At the point of fledging, the plumage often becomes irregularly mottled or blotched with dark and is mostly solidly dark gray-brown above with white eyebrows and other areas of the face white. Recently fledged young can already be sexed to a semi-reliable degree by the dark marking patterns about their wings. The juvenile plumage resembles that of adult females but averages slightly darker on average. By their second moult fewer or more broken bars are usually evidenced on the wing.
Snowy Owl Adaptations
The snowy owl does have some of the noise-canceling serrations and comb-like wing feathers that render the flight of most owls functionally silent, but they have fewer than most related Bubo owls. Therefore, in combination with its less soft feathers, the flight of a snowy owl can be somewhat audible at close range. The flight of snowy owls tends to be steady and direct and is reminiscent to some of the flight of a large, slow-flying falcon. Though capable of occasional gliding flight, there is no evidence that snowy owls will soar.
Snowy Owls and Irruptions
The number of Snowies that appear each season varies from year to year. They are considered an irruptive species-one that responds to changes in the conditions of its home territory by moving elsewhere in search of food. Some of the factors that may trigger these irruptions include variations in food supply in the Arctic, severe snow and ice cover in their usual wintering areas, or a superabundance of owls resulting from an exceptional nesting season prior to a southward irruption.
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