For a week in early November, local birders flocked to Fort Mason to catch a glimpse of a bird rarely seen in San Francisco – a Black-Throated Blue Warbler. This pretty, diminutive warbler spends its summers in the northeastern states of the U.S. or the southeastern provinces of Canada, and its winters in the Caribbean. It is rarely found west of the Mississippi, which is why its presence on the West Coast excited birders.
Birds that show up way outside their normal territory are called vagrants, and San Francisco sees a number of these lost birds every fall and winter. It's not known why the internal compass of vagrant birds fails them, and why they end up thousands of miles off course.
Some of the vagrants stay all winter, and migrate back north in the spring, presumably to their normal summer homes. Some return for a few years; most show up once and are never seen again. Unfortunately many of them stay only a few days, then continue migrating in the wrong direction and end up dying, exhausted, in the Pacific Ocean. Biologists on the Farallon Islands have seen an astonishing array of eastern vagrants.
Last month, three species of tanager were spotted at the San Francisco Zoo – not only the expected Western Tanager, but also Summer and Scarlet Tanagers (not as specimens in the zoo's cages, but in the wild – they were hanging out near the warthog). Local birders were lined up at the entrance gate at opening time to see these rarities for the City. Scarlet Tanagers spend their summers in the eastern U.S., whereas Summer Tanagers are found both in the East and in the South. The males of both Tanagers have brilliant red plumage in the summer (the Summer Tanager is our only all red bird), but by early fall the Scarlet Tanager sports yellowish green plumage.
Scarlet Tanagers are voracious insect eaters, and have been observed eating more than 2,000 gypsy moth caterpillars in one hour. Summer Tanagers like to catch bees in flight, and then kill them by beating them against a branch. Before eating the bee, the tanagers remove the stinger by rubbing it against a branch.
The Summer Tanager at the zoo wasn't quite as lost as the Scarlet Tanager, since its wintering grounds are in Mexico. The Scarlet Tanager was on its way to either Panama or northern South America.
Not only is the Scarlet Tanager a beautiful bird, but it has an engaging song as well. In 1893 classical composer Antonin Dvorak took his family on vacation to Spillville, Iowa. Every morning at five am, the Bohemian composer walked in the woods along a stream listening to American birds, and he was so enthralled with the Scarlet Tanager's song that he incorporated it into his American Quartet in F.
Some species of eastern vagrants show up virtually every winter. There's usually at least one Rose Breasted Grosbeak sighting every fall and winter in Golden Gate Park. The summer range of this member of the cardinal family overlaps with our western Black Headed Grosbeak in the central part of the country, where the two species have been known to hybridize.
In addition to vagrants, we have a large number of species that spend their winters here. One of the sure signs of fall for me in San Francisco is the loud call of the Northern Flicker, an attractive large woodpecker that spends much of its time on the ground eating ants. In the summer you rarely see any Northern Flickers and by October they seem to be everywhere – in mid-October I could hear six different Flickers from one spot behind the Museum of the Legion of Honor in the Presidio.
The Northern Flicker has more than 100 common names – many of them attempts at imitating their distinctive call, including Harry-wicket, Heigh-ho, Wick-up, and Yarrup. Flickers come in two sub-species – the eastern Yellow Shafted Flicker, and the western Red Shafted Flicker – named after the different colors of their feathers under their tail and wings. Flickers like to attract mates by drumming on metal objects – one Flicker drumming on an abandoned tractor in Wyoming could be heard a half mile away.
Flickers climb trees and excavate nesting holes like other woodpeckers, but they get much of their food from the ground. Their tongue is coated with sticky saliva, and any insect they touch is instantly adhered to it.
Then there are birds that appear to be here all year, but still migrate. For example, you can almost always find American Robins in San Francisco, but the robins you see in the summer are often not the same robins that are here in the winter. Observant birders noticed that robins are seen singly or in small groups during the summer in San Francisco, and in large groups in the fall, with a short period in-between when it was hard to find any robins. As it turns out, our summer robins migrate south, and those large flocks of robins showing up in the fall were migrants from further north. In the spring, our winter robins head north, and our summer robins come back from wintering grounds south of the Bay Area. Interesting Robin fact: a group of robins are collectively known as a "worm of robins".
In the same family as the American Robin, Varied Thrushes are uncommon in San Francisco. A few winter in the City, and the Christmas Bird Count (the annual bird census organized by the Audubon Society) usually finds about a dozen of these bright orange and blue gray songbirds. However, about once a decade, a lot more show up in the middle of winter. The last time this happened was in 2006, when instead of finding a dozen, the Christmas Bird Count found 150 in San Francisco. This is known as an irruption, and occurs when food is scarce in Canada and the northern half of the U.S. Looking for food, birds come further south.
Storms can also bring in unexpected birds. The Red Phalarope is normally never seen on the Christmas bird count – in fact it has only been recorded on two counts in the past decade. However, in 2005, observers found 537 Red Phalaropes, blown in by intense December storms. In 2006, a single Red Phalarope was spotted, and since then, none have been seen on Christmas Bird Counts in San Francisco.
All pictures were taken by David Assmann, Deputy Director of the San Francisco Department of the Environment. Do not reproduce pictures without permission.