By BILL CHAISSON
By Bill Chaisson
As the number of species still singing declines through the rest of the summer, it will be come easier to focus on variations among the individual singers. Some species are quite unvarying in their song. My neighborhood house wren seems to have the same cascading musical trill as the first one I ever heard.
Other species have different songs for different occasions like the quiet “rain song” of the robin, the least cheerful one in its repertoire. Still others seem to have an entire catalog through which they rotate. Margaret Morse Nice found that the average song sparrow had seven to nine different songs.
In wide-ranging species there are often regional variations, which some field guides, like David Sibley’s, are quite good about describing. The warbling vireo is found from the Yukon to Virginia; Sibley says the “song of western averages slightly higher-pitched, choppier, and buzzier, often ending with a descending buzzy note.”
It isn’t just the song that varies. Some birds, like the blue jay and the tufted titmouse, have an incredible variety of calls, some given more often than others. I have lost track of the number of times I have been convinced I was looking for something new and fascinating only to find a tufted titmouse looking down at me, emitting one of the many “simple whistled notes” Sibley doesn’t have room to list.
How do birds learn to make all this sound? Is it “in born” or do they require lessons? The question was put to me by a reader; she was specifically wondering about the brown-headed cowbird. This species is the most common nest parasite in North America; female cowbirds lay one or more eggs in the nest of a warbler or vireo and then go on their merry way. The cowbird young are raised by an entirely different species, so how do they know to make cowbird sounds?
Most male song birds spend months defending a territory with their voices. Many birds will sing hundreds, even thousands of times per day as part of this mission. (Yes, people have counted.) Because cowbirds are nest parasites, they don’t have this mission. But they do have a courtship song, which Roger Tory Peterson describes as a “bubbly and creaking, glug glug glee (last note thin and on a high pitch).” How do cowbirds know how to attract other cowbirds?
My reader was not the first person to think of this question (great minds…). There is an article the addresses the issue at allaboutbirds.org, which allows that the question has not been entirely answered. It seems that, in the case of the cowbird, the young birds must make the association with their own kind before their first winter. One study found that 6-day-old cowbirds could distinguish the call of an adult Molothrus ater from that of other birds. Furthermore, the begging call of the cowbird nestling resembles the “rolling chatter call” of the adults, which sounds oddly like a babbling brook.
A second experiment showed that there is a visual component. Researchers added markings to young cowbirds and found that fledglings were more attracted to birds with the same markings than ordinary cowbirds. The young were actually comparing their own appearance to other birds they saw and gravitating toward birds that looked like them.
A third experiment raised cowbirds among canaries through their first winter. These New World icterids learned to sing like an Old World finch. This suggests that while calls are innate, songs are learned.
It has been known for some time that bird song is learned. The National Geographic’s “Song and Garden Birds of North America” was published in 1964. In a chapter called “Courtship and Nesting Behavior,” Robert McClung, former curator of birds and mammals at the New York Zoological Society (i.e., the Bronx Zoo), described an experiment conducted at the Cornell Laboratory of Ornithology. Bluebirds were raised in isolation; they did not hear the vocalizations of any other birds, including their own species. After six months the captive birds had uttered only call and alarm notes — showing that these are inherited — but no songs. The experimenters first played recordings of several other species for the captive birds and got no reaction.
Then they piped in bluebird songs. “The effect was amazing. The young birds crouched, cocked their heads, listened raptly– then attempted to repeat what they had heard. In five minutes they were singing recognizable bluebird music!” In other words, the potential to sing the correct song is there in the DNA of some birds.
Sometimes not just any member of one’s own species will do. Black-capped chickadees sing nearly the same song from coast to coast, but not on Martha’s Vineyard. In the mid 1990s, Prof. Donald Kroodsma of UMass Amherst did an exhaustive survey of the islands’s chickadee population. Mainland chickadees sing a two-pitch song that goes from higher (hey) to lower (sweetie). At the west end of the Vineyard this is reversed (sweetie-hey) and both parts at the same pitch. Mid island they sing sweetie-sweetie at a higher pitch and sweetie-hey at a lower one. In the east the sweetie-sweetie is low and there is a higher so-sweetie-sweetie. Chappaquiddick is even more varied, with some even singing like mainland birds.
Chickadees don’t migrate and don’t fly across miles of water, so the Vineyard population has been isolated since the end of the Ice Age. After European settlement most of the island forest was cut down. Kroodsma believes the variability was produced during this period of secondary isolation. He also found that captive island birds refuse to learn the “normal” song and will only repeat what they hear from members of their own “tribe.” Human Vineyarders, as you might imagine, are very proud of their eccentric fellow islanders.
Bill Chaisson, who has been a birdwatcher since age 11, is a former editor of the Eagle Times. He now works for the Town of Wilmot and lives in Sutton.
As your daily newspaper, we are committed to providing you with important local news coverage for Sullivan County and the surrounding areas.