San Francisco Environment Department

The Wisdom of Owls

On New Year's Eve, the last day of 2010, this Long-Eared Owl was the 300th species of the year for my list of birds seen in the U.S. This strictly nocturnal bird of prey likes to roost in colonies during the non-breeding season, and true to form, was one of a group of 10 owls visible from a trail in Marin County (a group of owls is known as a Parliament of Owls). This owl stands up to 16 inches tall, with a wingspan that can be up to three and a half feet in length.

This owl is named after the long feather tufts on its head, and its diet consists of small mammals and other birds that it catches while flying low over the ground at night. It's capable of catching mice in complete darkness.

Like some other owls, its left ear opening is positioned higher on its head than its right ear opening, allowing it to better locate prey by sound.

All owls have comb-like serrations on their wing feathers and frayed edges on the tips of their tail feathers to break up air flow when they are flying, allowing for almost silent flight. Some owl species have feathers surrounding their legs to muffle sound even more. That's why you can hear the wing beats of most birds when they fly close to you, but not owls – they are extremely quiet.

Owls also have immense eyes that are proportionally much larger than human eyes. Their eyes are as large as ours, even though owls are so much smaller than humans. In fact, their eyes are so large that there is little room in their eye sockets for muscles allowing them to move their eyes – so instead they move their heads and keep their eyes stationary. Owls can turn their heads 270 degrees – a bit of an unnerving experience when you first see it.

Although Long Eared Owls are predators, they are also preyed upon by Great Horned Owls. That's why the location of the Long Eared Owls I saw in Marin is being kept secret – even from other birders. If this parliament of owls is disturbed by too many people looking at them, they may change their roosting site, which could be fatal for these beautiful birds, since they are roosting uncomfortably close to Great Horned Owl hunting areas.

Long Eared Owls are rarely seen in San Francisco – except on the Farallon Islands, which has seen three stray owls since last summer. Otherwise, the last reported sighting in San Francisco was almost two years ago. Great Horned Owls, on the other hand, are spotted regularly in the City.

The Great Horned Owl is one of the most common and widespread owls in North America. It is generally the top avian predator at night, taking the ecological niche that Red Tailed Hawks occupy during the day.

Great Horned Owls are the only animals known to regularly eat skunks, and will also attack and kill other birds of prey, including Osprey nestlings and even adult Peregrine Falcons.

Great Horned Owls are often harassed by flocks of American Crows, who will get together and yell at these owls for hours, recognizing that Great Horned Owls prey on them and their offspring.

Barn Owls (#284 on my 2010 list) are the only other owl species seen regularly in San Francisco, although they are far less numerous than Great Horned Owl. Although there are not many in San Francisco, the Barn Owl is one of the most widely distributed birds in the world, found on every continent except Antarctica. It has 46 races, with the North American form being the largest, weighing more than twice as much as the smallest race from the Galapagos Islands.

Barn owls have voracious appetites and during breeding season a single owl can catch up to 12 mice a night.

The Barn Owl is well documented in early English folklore, which included the belief that feeding a child raw owl eggs would give lifetime protection against drunkenness.

One of my favorite owls is the tiny Burrowing Owl (# 294 on my 2010 list), which is usually seen on mounds in fields or wintering in a rocky area (for two winters I was fortunate enough to observe a Burrowing Owl in the rocky wall just below Louie's Restaurant near the Cliff House in San Francisco).

Burrowing Owls hunt both during the day and at night, making them one of the few owls that can be seen being active during the daylight hours. They usually eat insects and small rodents, but will also consume snakes and lizards. One of their unique abilities is imitating rattlesnakes, which they can do with uncanny skill.

Burrowing Owls are also unique in that they dig burrows (although they can, and often do, use the abandoned burrows of squirrels and prairie dogs). They also line their burrows and decorate the burrow entrances with a variety of materials, including aluminum foil, shredded paper, shells and feathers.

In addition to these items, Burrowing Owls also line their burrows with dried cow and horse manure – to attract dung beetles - a preferred prey species for the owls. This has led to the theory that these owls are actually tool users – using a foreign object to influence their environment.

Using tools would put the owls in the company of a select group of avian innovators. The Green Heron (# 32 on my 2010 list), a wading bird seen at Lake Merced and in Golden Gate Park, also has been known to use tools to fish. It places insects, crusts of bread, earthworms or bits of vegetation on the surface of the water to attract fish within striking distance.

As you can probably tell by now, like many birders, I am also a bit of a lister, which means I keep a list of the birds I see. I keep a list of all the species of birds I've ever seen (now up to 993 species – about 10% of all bird species on the planet). This is my Life List. Listing can be everything from the simple to the extreme (for example- a few years ago, John Luther became the first birder to meet a goal of seeing at least 200 species in each of California's 58 counties - requiring 11,600 sightings all over the state).

There are lots of variations on listing. Trying to see as many species as possible in one year is a common theme. This is called a Big Year, and has been the subject of several books, and soon will be the subject of a movie.

In addition to my Life List, I've also started to track the number of species I've seen in San Francisco (currently at 234 – a little more than half of the 458 species that have been seen in San Francisco), and over the past two years I've also started to track species seen by year.

It's always a thrill to add a new bird species to a list, and a year list reminds me to pay attention to all birds, even if I've seen them before. Without a year list, I wouldn't have been excited to see a Dark-Eyed Junco out my window the morning of New Year's Day - #1 on my 2011 list.

All pictures were taken by David Assmann, Deputy Director of the San Francisco Department of the Environment. Do not reproduce pictures without permission.

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