From Dumpster to Roost--The Raven's Winter Commute

By day, they shred garbage bags in the back of open pick-up trucks. By night, they gather by the hundreds in black spruce trees, digest the day's bounty and share information on where the best dumpster in town is.

Ravens, famous in mythology and a favorite winter sight of many Alaskans, are most often spotted in winter as they indulge on our discarded, or unguarded, food. But few people see them after the sun sets, and it's not just because they're the color of night.

Along with other birds such as pigeons, ravens seek the shelter and companionship of a communal roost to get them through the long Alaska winter nights.

Rod King, a wildlife biologist with the U.S. Fish and Wildlife Service in Fairbanks, is one of the few people who have seen a raven roost. King recognizes a roost because of the signs ravens leave behind: snow knocked off the branches of black spruce trees and the ground below littered with feces and the eye-catching, colorful garbage ravens couldn't resist in town but later regurgitate after finding it indigestible. King said observers have even found pieces of belched-up colored glass under the roosting trees.

Of the half-dozen or so roosts King and others have studied in the Interior, the numbers of ravens using them vary from a few dozen to over 800. According to Ravens in Winter, a popular book by Bernd Heinrich, the roost with over 800 ravens is one of the largest ever observed. King said ravens may choose roosting branches based on a hierarchy system--less aggressive birds sometimes show up in town with feces on their feathers, unflattering evidence they roosted below more dominant ravens.

Since ravens are a social, gregarious bird, King said they may roost simply because they want to be together at night. Another theory is that the roost is a communications center, where birds exchange information with body language on where the best and easiest food sources await them at daybreak. Although ravens are among the most garrulous of birds (with more than 30 distinct vocalizations), a roost of ravens is conspicuously quiet once all the birds find a branch for the night. King said silence on the roost and the ravens' preference to roost in large numbers could both be mechanisms by which ravens seek a safe night's sleep from predators such as great horned owls.

King pointed out that he never walks into a roosting area at night because disturbing the ravens, particularly during a cold snap, could be fatal for them if they're not able to quickly restore their body temperatures after being roused into flight. He instead tracks the birds visually and with radio transmitters, and he visits roost sites during the day, when ravens are in town perfecting the art of scavenging.

King has noticed that ravens will sometimes alter their roosting habits according to the weather. When the temperature plunged to 50 below for 10 days in 1989, King noticed ravens decided to roost in town rather than make their long commute.

Ravens' daily trek to and from the roost can be quite a haul. King said one well-used roost is at least 40 miles from Fairbanks, requiring an 80-mile round-trip every day.

King wonders why ravens expend so much energy on such a long commute when the roost area seems to be nothing but a black spruce forest with no other attraction such as a hot springs or buildings.

Roosts are typically far away from humans, King said, although he's studied one that was close to a small cattle farm where the ravens would feast on undigested grains in the cows' manure.

Why ravens choose roosts far out in the boonies is a riddle that makes research fun, King said.

"We need to have a few of these mysteries (unsolved) to keep us curious," he said.