Walking through Sutro Heights Park last Saturday, I was startled by a small blizzard of black feathers as I passed under a pine tree. Looking up, I could see a Red-Tailed Hawk, systematically plucking a Brewer's Blackbird, while other agitated blackbirds continually attacked the hawk by literally diving into it. After a while, the hawk, tired of the attacks, took its prey and flew to another tree.
Sutro Heights Park is one of the reliable nesting sites for these huge birds. A pair (they mate for life) has nested and raised young in the park across from the Cliff House for many years. There's usually one perched at the very top of a Monkey Puzzle Tree, a native raptor in an imported tree. The park is also one of the best places in the City to see the courtship display of these aerial acrobats, as they dive and roll together, even locking their talons in a dive before separating.
While many birds are found only in specialized habitats in San Francisco, raptors (in Latin, raptor means to seize), including hawks and owls, are found throughout the City. I regularly see Red-Tailed Hawks soaring over the Tenderloin as I walk to work. These magnificent hunters, present in every neighborhood in San Francisco, occupy a wide range in North America, from Alaska to Panama.
Red-Tailed Hawks show up in some unusual places. For example, years ago, Hollywood decided that the distinctive cry of the Red-Tailed Hawk sounded much better than the gull-like call of the Bald Eagle. As a result, every time you see a Bald Eagle (or for that matter, any hawk) calling in a movie, what you are actually hearing is a Red-Tailed Hawk.
Red-Tailed Hawks eat mainly rodents, including rats, mice and gophers, as well as a few small birds, such as Blackbirds. They can spot a mouse from a height of 100 feet.
Although Red-Tailed Hawks are one of the largest birds found in North America, with a wing span that can exceed 4 feet, they are amazingly light. The biggest females (females can weigh twice as much as males), rarely weigh more than 3 pounds. There are 14 different sub-species of this distinctive bird, some of which do not have red tails. Juveniles generally do not get their red tails until they are three years old.
And while Red-Tailed Hawks can reach a speed of 120 miles per hour in a dive, they are not the fastest raptor in the sky. That distinction belongs to the Peregrine Falcon, a bird that evolved nesting on cliffs but now also nests on skyscrapers and bridges, including on downtown buildings and the Bay Bridge in San Francisco. It has been clocked at 200 miles per hour in a dive, making it the fastest animal alive today (which probably led to its nickname as "the great white shark of the sky").
The ancient Egyptians who settled along the Nile River five thousand years ago brought with them a falcon god – Heru, inspired by the Peregrine Falcon. They believed that the Peregrine, in flight before sunrise, brought forth the sun each new day.
Forty years ago, the future looked bleak for these magnificent birds. They had almost stopped reproducing as a result of exposure to DDT, a pesticide that thinned their egg shells, killing most of their young. The banning of DDT in the early 1970s saved them from extinction, and their population began to rebound -allowing them to be removed from the Endangered Species list in 1999.
Although Peregrine Falcons can be found all year in San Francisco, they migrate long distances elsewhere, from the tropics to the tundra. Their long migration is reflected in their name – the Latin word peregrinus means "coming from foreign parts."
They eat mainly birds, and feed routinely on rock pigeons, which gives them a steady source of food in San Francisco. In early February, a pair of falcons usually show up at a nest box on the PG & E building in downtown San Francisco to begin courtship, and by the end of February there are often eggs in the nest, with chicks hatching in March. There is now a year round webcam focused on the nest. Peregrine falcons have been found around the building since 1987, and have used the nest box intermittently since 2003.
One of the raptor species that is often confused with the Red-Tailed Hawk is the Red-Shouldered Hawk, a related, but smaller hawk. Found on both the east and west coasts, its main stronghold in the City is in Golden Gate Park. Unlike many other hawks, it usually doesn't migrate and is found year round on much of its territory. This hawk does have red shoulders, but this feature can only be seen on perched birds.
Red-Shouldered Hawks and American Crows are known to collaborate and work together to mob and attack Red-Tailed Hawks and Great Horned Owls, both of which prey on their nests. Often found in deciduous trees, Red-Shouldered Hawks eat small mammals, reptiles and birds.
Hawks and owls can occupy the same ecological niche, with hawks hunting during the day and owls at night. Just as Red-Tailed Hawks and Great Horned Owls often share the same range, Barred Owls are the nocturnal counterpart to Red-Shouldered Hawks. Born with yellow eyes, the eyes change to brown as the bird matures.
Two other species of hawks found in San Francisco are the Cooper's Hawk and the Sharp-Shinned Hawk. They are similar short-winged, long-tailed hawks, built for agility and bursts of speed as they fly through dense cover searching for small birds to eat. They are hard to tell apart, with the Cooper's Hawk being slightly larger (and as in most hawks, the females are bigger than the males).
The Cooper's Hawk, found across North America, was first described by Charles Bonaparte, a French naturalist who was the nephew of Napoleon. It was named after William Cooper, the first European to collect a specimen.
Male Cooper's Hawks build the nests, and provide virtually all the food for both the female and the young for the 90 days it takes before the young fledge. This hawk eats mainly medium-sized birds, such as starlings, mourning doves, robins and rock pigeons. The species is growing in number, having benefited both from the banning of DDT, and the changing habits of humans.
Called Chicken Hawks by farmers, the Cooper's Hawk was hunted extensively in the past for its habit of going after domesticated fowl, resulting in a significant decline in population. Now protected, and with an increasing supply of food (our cities and suburbs have allowed its prey – Robins, Starlings and Rock Pigeons – to flourish), it has rebounded.
Although both Cooper's and Sharp-Shinned Hawks migrate, the Sharp-Shinned Hawk has a much wider range, extending into northern Canada during the breeding season, and as far south as Argentina in South America in the winter. Large numbers can be seen during migration, with the record being 11,000 seen in just one day in October over Cape May, New Jersey.
Their name comes from their very thin, exposed legs. Sharp-Shinned Hawks have an unusual feeding habit for their newly-fledged young. They will pass food to their offspring in mid-air, hovering and kicking the food out just as the youngsters arrive.
All pictures were taken by David Assmann, former Deputy Director of the San Francisco Department of the Environment. Do not reproduce pictures without permission.