letter from the field
C'est Moi. Soy Yo. It's Me!
A light broke in upon my brain
–Lord Byron, "The Prisoner of Chillon"
On March 25, 1961, I arrived in San Francisco from my native Hong Kong to be reunited with my brother, Antonio. He had immigrated to Mozambique twelve years earlier and then relocated to San Francisco on the eve of the revolutionary wars in Portugal's African provinces. Studying animals had been our passion since childhood, and Antonio was anxious to share his latest acquired natural history lore.
He told me of a strange bird that visited the garden at his home near the western edge of the city. He described the bird as plain brown, like a Eurasian sparrow, (the bird most familiar to us as boys), but with a canary-like song and a striking white streak on the top of its head. Not until 1964 when Robert T. Orr, the Curator of the California Academy of Sciences' Ornithology and Mammalogy Department, introduced me to Roger Tory Peterson's Field Guide to Western Birds did I identify the bird as the white-crowned sparrow. Little did I know then that this common but charming bird would become the center of my research for almost three decades.
In the fall of 1967, my graduate advisor at Berkeley, Ned K. Johnson, introduced me to the work of Academy Fellow Peter Marler, who had discovered that white-crowned sparrows from different parts of Berkeley sang different, region-specific songs that he called dialects. With his student, Miwako Tamura, Marler showed that young birds learned these dialects from adults, and that birds raised in soundproof boxes and isolated from adults sang much simpler songs, the analog of baby-talk in children.
White-crowned sparrows are found throughout the United States in winter, but are year-round residents in only a few parts of coastal California. From September through April, sparrows from Washington, Oregon, British Columbia, and Alaska come to California to enjoy the relatively mild winter, while one subspecies of white-crowns, Zonotrichia leucophrys nuttalli, is found along the California coast and throughout the San Francisco Bay Area all year long. Alaskan birds are recognized as Zonotrichia leucophrys gambelii, and the migratory race from the other coastal states as Z. l. pugetensis. These feathered tourists sing songs distinctly different from those of our local resident white-crowns.
In 1970, I took a camping trip up the coast of Oregon, Washington, and British Columbia, recording white-crown songs along the way. A few years later, my friend Barbara DeWolfe, a professor at University of California at Santa Barbara, catalogued the dialects of Alaskan white-crowns. Combining our research, we were able to determine where winter visitors to California came from. For example, resident white-crowned sparrows in Berkeley, Fort Baker (in Marin County), San Francisco, and the islands in the San Francisco Bay sing dialects with long canary-like trills. Alaskan birds sing dialects of a song that begins with a whistle, is followed by a warbled note, and ends with three buzzes (vibrati), in descending pitch. The trained ear can easily distinguish the song of the Alaskan white-crown from the basic local song of nuttalli and from pugetensis, which is similar to nuttalli but has an extra buzz.
One morning in May 1993, while driving past St. Ignatius School in the Sunset District of San Francisco, I was surprised to hear the distinct song of an Alaskan white-crowned sparrow. DeWolfe's extensive work with this subspecies had revealed that Alaskan white-crowns arrive in San Francisco between mid-September to late October and return north in mid- to late April. Was this a winter visitant who had stayed behind? Was it a local bird that had learned a foreign dialect? Or was this bird perhaps the product of a liaison between a local nuttalli and an Alaskan gambelii that had not returned north prior to the mating season? Though they winter throughout the state, Alaskan migrants are uncommon in the San Francisco Bay Area: years of intense banding by DeWolfe had revealed that only about one percent of wintering migrant flocks in the Bay Area consisted of gambelii; the rest were mostly pugetensis. Unable to stop and investigate at that moment, I would have to return later to seek out this sparrow and attempt to solve the mystery.
Two weeks later, I was waiting quietly in the school garden. After only about ten minutes I was rewarded with a whispered Alaskan song-I had found the bird! I recorded the whispers and the long series of loud Alaskan songs that followed. Then, to my surprise, I heard him interject a familiar trilled San Francisco dialect. I eventually recorded 27 renditions of his Alaskan song and eight of his San Francisco song. I determined to capture this feathered chorister and examine it in hand to ascertain whether it was a gambelii, nuttalli, or hybrid.
With the help of my student Andrea Jesse, I set out to catch the mystery bird. White-crowned sparrows are highly territorial. They will respond to a recorded tape of a white-crown's song by approaching the tape recorder, displaying aggressive behavior, then singing as if a real bird were encroaching on their territory. To begin, we placed a miniature tape recorder next to a small trap in the middle of the bird's territory. We scattered millet seed at the trap entrance and piled more seed deep inside the trap, and I pressed the play button. Each previously recorded white-crown song was separated by a silent interval of about twelve seconds, approximating the natural rhythm of a white-crown singing bout. Within seconds, the territorial white-crown flew to the trap entrance. It sang at the tape recorder, quivering its wings and periodically eating a seed. Such eating activity of an agitated bird, occurring between bouts of song and aggressive trilling and wing-quivering, is an example of "displacement behavior," in which animals under stress will engage in activities that have no observable relevance to the situation. Eventually our bird ate its way into the trap, stepping on the treadle that released the trap's door.
Our captive was a male bird with very dark plumage like that of local white-crowns and not the light color of the Alaskan birds. His bill was yellow, typical of nuttalli, and not the pink typical of gambelii or an intermediate hue, which would indicate a hybrid. There was a distinct yellow patch on the bend of each wing, a feature characteristic of nuttalli and absent in gambelii and hybrids. Finally, he had short wings typical of the non-migratory local birds rather than the long wings of the migratory gambelii. This bird, which we christened "G1," was indeed a local bird that had learned both a local and an alien gambelii dialect. We banded G1 with a numbered identification tag, and fitted him with two yellow plastic bands, which would enable us to distinguish him at a distance from other banded white-crowns. Then we let him go.
Could G1 have learned songs from over-wintering gambelii? In the winter of 1994, we heard an Alaskan song coming from the shores of Fern Lake in San Francisco's Golden Gate Park. This individual was territorial, responded to playback of both nuttalli and gambelii songs, and, when captured, was identified as a visiting gambelii. He was banded and released and, astonishingly, returned the following year to winter in the same location. Then, in June 1996, we recorded a second territorial individual singing a song typical of gambelii. This individual, whom we called G2, was captured and identified as another local nuttalli that had learned a gambelii song. How could G1 and G2 have acquired the foreign song?
If local birds learn songs from migrant visitors, why are there so few locals singing alien songs, and why have the local songs persisted over several decades? The answer, it seems, lies in a phenomenon known as match-countersinging, or "naming." Quite often, at a boundary between two different dialect populations, one may find "bilingual" individualsÑbirds that sing dialects from each side of the boundary. One can easily demonstrate that these birds distinguish dialects, for if one plays a recording of dialect A, the bird will respond with its renditions of dialect A. Conversely, if we play dialect B, the bird will sing its versions of dialect B. This means that during bouts of countersinging, one bird will try to match the song used by the other bird, as a way of angrily "pointing its finger" at the intruder, and proclaiming its presence and territory.
Though the territorial wintering gambelii we heard in the park in 1994 never sang the local dialect, it responded to recorded nuttalli song, which was likely stored in its memory. A local nuttalli approaching the gambelii's wintering territorial boundary would invite reproach, threats, and singing. Although I have never witnessed a nuttalli singing back to a wintering gambelii, I have observed a nuttalli and a wintering pugetensis fighting; between fights, each combatant sang the song of its own subspecies. Very likely, as youngsters, G1 and G2 had interacted aggressively with territorial wintering gambelii. During these social interactions, they acquired songs from the winter visitors.
A year after we first captured G1, I again sought him out near St. Ignatius School and easily identified him by his yellow bands. He soon produced a long bout of nuttalli themes, but no gambelii songs. Had this bird retained the gambelii song in memory, and could it be evoked experimentally? I played G1 78 repetitions of the gambelii song he had sung the previous year. He responded by countersinging four renditions of the gambelii song: "It ceased and then it came again...."
This experiment supported my thesis that during bouts of countersinging with neighbors, the local song is evoked by the vocal majority while rare "foreign" tunes soon fall into disuse, but are stored in memory for future encounters with visiting birds. In this manner, local dialects may be preserved for many years. Incredibly, when I compared descriptions Barbara DeWolfe had made in the 1930s of the songs of Berkeley and Carmel white-crowns with recordings I made in 1970 in those same areas, I could tell that the syntactical arrangements of syllables had persisted for some 40 years!
Luis E. Baptista is the chairman and curator of the Academy's Department of Ornithology and Mammalogy. He is an authority on regional dialects in a number of avian species.