The Night Shift

Adult Great Horned Owl with a rabbit for a midnight snack (click to enlarge)

I read somewhere that owls are 80% feathers and 100% attitude. I think that's still an underestimate of the attitude displayed by Great Horned Owls (Bubo virginianus).

As of midnight we now have one less rabbit in the yard, compliments of a hungry Great Horned Owl. One evening several summers back, our company here at the end of the road watched a Great Horned Owl pluck a sleeping duck off a floating log at dusk. American Coots and striped skunks are both favored dinner fare for these, our largest owls, who will take on most anything their size and smaller.

Many years ago, we hiked in to find out why a Bald Eagle nest near Waterton Lake, on the Glacier Park side, had failed after the lone chick was almost one month old. We found the young but large eagle carcass on the ground below its nest, decapitated, apparently by a Great Horned Owl. They've been known to take other large raptors as well, like Osprey, Peregrine Falcons, and even other owls.

(On a side note, we used a cheap, white Styrofoam cooler to smuggle the Bald Eagle carcass across the border into Canada, and then from Canada back into the U.S., without any of the necessary permits. If any one of the Border Patrol agents had bothered to look in the cooler, I would have had another interesting story to reminisce about.)

Folded primary feathers showing leading
edge (left) and trailing edge adaptations

Another long-ago spring and summer, I conducted owl surveys one night each week along the Camas Road on the west side of Glacier Park. The protocol at the time was to play a cassette tape of recorded owl calls, one species at a time, and record the locations of any owl responses. But you had to start with the smallest owl species and finish with the largest, otherwise all of the other owls would turn silent after hearing a Great Horned call.

Most birds make a fair amount of noise in flight, including day-hunting owls. But nocturnal owls like the Great Horned have several feather adaptations to soften and disperse the noisy turbulence that occurs during flight.

If you look closely at the folded flight feathers on this owl's wings (left), you'll notice two adaptations. First, the leading edge has a row stiff hairs sticking up that look like a short comb. These mostly help with stability, but they also offer some sound dampening effect. Second, the trailing edges of these feathers are flexible and tattered, and this is the area most responsible for the owl's noise reduction.

The third adaptation is mostly noticeable if you get the chance to stand up close, like at a rehab center. The small, body and leg feathers are mostly velvety-soft down and contour feathers. This fuzziness further reduces the amount of noise created when air passes over the owl in flight.

Great Horned Owls also have a talon adaptation for feeding that I once felt on the feet of a deceased owl. The inner side of the middle talon has a sharp, knife-like edge. Holding its prey with one foot, the owl uses its hooked, upped mandible to pull the prey against this sharp edge, helping it tear the meal into bite-sized chunks.

No doubt last night's rabbit snack was eaten this way. And soon, somewhere in the nearby woods, coughed-up pellets of rabbit fur will fall around the base of another tree. The pellets might eventually add to the duff layer under the tree, and help grow a little bit of pine grass to be nibbled on by a hidden rabbit.

Bunny Behaviors

Mountain cottontail, ears down, ears up, sideways to the threat

Take heart, fellow pacifists, for the bunnies of the world are succeeding quite well, thank you. All it requires is commitment to a set of passive behaviors to avoid the aggressive animals who'd like to have them over for lunch.

Keeping your cool goes a long ways towards survival for our local rabbits and hares. Here in western Montana, we have lots of laid back mountain cottontails (Sylvilagus nuttallii) and chilling snowshoe hares (Lepus americanus). The cottontails are easy to identify by their small size, relatively short and rounded ears, and a distinctive brown nape on the back of the head. Some biologist types also call them Nuttall's cottontail, while most of us just call them cute bunnies.

Cottontails rely on a caravan of cryptic behaviors to keep out of sight. First, they are crepuscular. This means they restrict most of their activity to dawn and dusk. Their brown fur helps them blend in with the grasses they eat in the wooded and brushy habitats where they live. Snowshoe hares go a step further by moulting to a white fur during winter. (This moult, however, is driven by day length and not temperature, so climate change might eventually leave hares out of sync with their background color.)

When a bunny catches the sight or sound of a potential threat, they turn perpendicular to it and freeze. Their vision does not overlap between their eyes, so turning sideways faces one eye square on. It also turns a radar-like ear towards the threat, but the ears are lowered at first. The ears only come up after the bunny realizes it's been spotted.

Once spotted, the bunny runs a few meters and freezes again, this time with the ears up. If shelter is available, it will hide in brushy thickets or rock crevices. If none are nearby, the speedy bunny will run in a semicircular path to get away from its pursuer.

Of course, not all bunnies avoid their aggressors or we would soon be overrun with them. That's because bunnies also employ certain reproductive behaviors as part of their successful strategy.

Solitary cottontails are actively on the move all year, except when the female is nesting. The adults do not form pair bonds and only become social during courtship and mating, which only occurs under the cover of darkness. A female can bear 4-5 litters each year, averaging 5 young per litter. The youngsters are born blind and naked, and are weened at 28 days. Young males and females both can become sexually mature as early as 90 days old, but often older.

So basically bunnies succeed by laying low, reproducing at a young age, and reproducing often. It's sort of like a furry version of America's 1960's all over again. Be cool, dude, and love some bunny tonight.