Love is in the Air

Presidio of San Francisco (February 18, 2009) — Birds do it. Bees do it. Even great horned owls do it. Volunteer birdwatchers at the Presidio have been hearing the telltale mating call of the park’s resident owls, signaling the start of the owl’s mating season.

“The mating call is much more distinctive than the ‘hoo, hoo’ most people think of as the traditional owl call. And the female’s is even more distinctive. It’s a much faster and higher pitched call than the male’s,” says Peter Ehrlich, the Presidio Trust’s forester.

According to Ehrlich, there are at least four great horned owl nests scattered throughout the Presidio. Getting an exact count however can be tricky, since the owls have no trademark nests of their own. They often just take over the nests of other birds like ravens or crows.

“Just looking at a nest, you’d never know it was an owl’s nest,” says Ehrlich. “You have to actually see the bird in it.”

Great horned owls, which grow to about two feet tall with a wingspan up to five feet, are among the earliest nesters both in the Presidio and among birds in general. The males and females actually begin their courtship in late fall and can often be heard calling to each other in a kind of duet, the calls sometimes overlapping or “stepping on” each other. By the middle of February, the eggs, one or two per nest, have been laid. They’ll hatch about a month later, in the middle of March. The young owls will remain in the nest for a couple of weeks, but by the end of April, they will begin to venture out onto nearby branches and about a week later they’ll start to fly down to the ground.

Great horned owls are extremely protective of their young, so people are advised to avoid any young owls walking along the ground they might come across.

During this time, the Presidio goes to great lengths to protect and avoid disturbing the owls.

“We’ll do some hazard removal, that type of thing,” says Ehrlich. “But we won’t do any major trimming or cutting projects. We don’t want to be working anywhere near an owl nest.”

Year-round, the owls are quite at home at the Presidio. “They’re very cosmopolitan. Very urban. People don’t seem to bother them,” says Ehrlich, who calls the great horned owl his favorite bird. “They’re just a big, powerful bird. Very respect worthy. I also love their piercing yellow eyes. They are mesmerizing.”

Prolific hunters — they’re sometimes referred to as the “Tiger of the Night” — the owls perform a measure of rodent control at the Presidio. In fact, they’re the only animal to make skunks a regular part of their diet (like all birds, says Ehrlich, the owl has a very poor sense of smell). Still, young owls have been known to hang around begging for food as much as six months after leaving the nest, until they’re finally forced out by their parents at the start of the next reproductive cycle.

Once they find a mate, the owls become permanent residents of their territory. Until then, however, the young and “single” owls are like “vagrants,” moving around in search of a mate and territory of their own.

The Presidio Trust was established by the United States Congress in 1996 to oversee the Presidio of San Francisco, an urban national park located at the base of the Golden Gate Bridge. The 1,500-acre site contains expansive open space and spectacular views, a 300-acre historic forest, and rare and endangered plants and wildlife. It also comprises nearly 6 million square feet of buildings, including 469 historic structures that contribute to its status as a National Historic Landmark District.