San Francisco Environment Department

The Next Generation - Birds Raising Their Young in the City

Birding at this time of year shows the remarkable adaptability of birds as they find places to raise the next generation – often in the most unlikely of places. This past weekend I spent an hour in the Succulent Garden in the San Francisco Botanical Garden in Golden Gate Park, watching three different species at nest holes just feet from each other. All three had discovered that dead flower stalks of Agave Americana provided an ideal environment for raising their young. This enormous cactus, commonly known as the century plant (under the mistaken assumption that it needed to be 100 years old before it could flower), shoots up a flower stalk that can be up to 25 feet tall.

The first species I spotted at a nest hole in the century plant was a Pygmy Nuthatch, a small western songbird that lives primarily on insects and seeds. Some species of nuthatches wedge nuts into a woody crevice and hammer it open with their beak (hence the name Nuthatch – the Pygmy Nuthatch is the smallest of the Nuthatches). This gray, brown and white bird nests in cavities, is extremely social (you almost never see one by itself), and nesting parents often have helpers. Offspring from previous years (usually males) will help their parents raise young by bringing food to the nest. Pygmy Nuthatches don’t migrate – they live year round as far north as British Columbia and as far south as central Mexico. They normally raise their young in cavities in pine trees, but here they were in the dead stalk of a cactus (I’ve also seen them nest in cavities in palm trees in San Francisco).

About three feet above the nuthatch nest, but facing a different direction, a Tree Swallow watched me from the edge of its cavity nest. Seemingly unperturbed by my presence (I always take care to use binoculars and maintain a healthy distance so as not to disturb nesting birds), this shiny blue-green and white bird doesn’t excavate its own nest, but relies on using the abandoned nests of other birds. It is the hardiest of the swallows, and while the vast majority migrate south in the fall and congregate in flocks that can number in the hundreds of thousands, a small number stick around all year in California.

Just about six feet away from the Pygmy Nuthatch and the Tree Swallow, a pair of Downy Woodpeckers were feeding young in the next century plant. These checkered black and white woodpeckers (the male has a red patch on the top of its head) don’t sing songs, but use drumming on pieces of wood or metal as a substitute. So when, you hear a Downy drumming, it is actually communicating. When they feed on insects, they actually make very little sound.

While many birds nest in trees and plants, some actually nest on the ground. A couple of days before watching the birds in Golden Gate Park, I spent a morning on Alcatraz, observing nesting seabirds, many of them with nests on the ground. Thirty years ago, there were virtually no nesting seabirds on the island (the “ Bird Man of Alcatraz” actually saw all his birds while incarcerated in Kansas), but when the island became a national park, the seabirds multiplied and the number of nesting seabirds can now reach 3,000 in a good year.

Typically the most common nesting seabird on the island is the Brandt’s Cormorant (a black bird with a brilliant blue throat during breeding season), and in 2007, there were almost 2,000 nesting Brandt’s Cormorant on Alcatraz. Then El Nino hit, dramatically decreasing available food, and there were no nesting cormorants on the island last year. This year the birds have returned, but in much smaller numbers, and the few hundred that are there have chosen nesting sites that are not visible to visitors.

However, nesting Western Gulls are everywhere, including hundreds nesting on a big concrete pad on the southern side of the island. Whatever you think of gulls, there are few birds as cute as a baby Western Gull. While their nests on the ground may seem extremely vulnerable, the gulls defend them vigorously, particularly against repeat approaches (which is how researchers discovered that these gulls can recognize individual humans by face, even if they wear disguises). One reason Western Gulls and other ground nesting seabirds nest on Alcatraz is that there is no fresh water on the island, which makes the island inhospitable to rats, which otherwise would be a major predator.

Other nesting marine birds on the island include Pigeon Guillemots, California Gulls, Pelagic Cormorants and Black Oystercatchers. Black Oystercatchers, a large black shorebird with a bright red bill, also nests around the Cliff House. This western bird eats mainly mussels and limpets, which accounts for its name. Pelagic Cormorants are the smallest of the three Cormorants found in the Bay Area, and are the only cormorant species that is truly a seabird.

Other birds that nest on Alcatraz include the Snowy Egret, with its exotic breeding plumage, and the Black Crowned Night Heron, which has two white plumes extending from the back of its blue neck. This showy bird is actually the most common heron in the world, and can be found on five continents. Every year Canada Geese also try to nest on the island, but lose most of their young to Ravens and Gulls. Only one gosling was left to the pair of Canada Geese I saw on Alcatraz last week (they typically lay eight eggs!).

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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