The (Bird) Song Does Not Remain the Same
What’s in a song? Quite a lot, according to Professor of Biology Heather Williams ’77 of Williams College in Massachusetts. She’s the lead author of a recent high-profile study on the cultural evolution of bird song, using decades of data collected on Kent Island.
Williams initially visited the Bowdoin Scientific Station in October 1973 on a first-year field trip as part of Professor Chuck Huntington’s ecology class. “I wanted to come back and see it in the ‘high season,’ when tens of thousands of breeding birds were there,” she recalled.
Williams was able to return and spend the summer of 1975 there. “After my first year I worked two jobs over the summer so I would be able to spend all of the following summer on Kent Island. It was one of the foggiest summers on record, and I spent it having as many adventures as is possible on a small island.”
For her project, Williams mapped the movements of the Leach’s storm petrel, recording the locations of all the burrows she found (FYI—petrels nest in the ground!).
“After Bowdoin (and a few more visits to Kent Island in the interim), I began doing research on animal communication, first on fish, and then on bird song. My focus was on the brain mechanisms associated with vocal learning (something very few species do!)” said Williams. As time went on, she became increasingly interested in the quirks of song learning.
“In aviaries, birds don't always make exact copies of their tutor's song; they may rearrange the syllables, make up new ones, or mix and match parts of different adults' songs.”
Even in laboratory-reared birds, Williams noticed that “young males sometimes converged on similar songs, that females could influence what males learn to sing, and that the songs of the community shifted from year to year.”
She then became curious about how bird song patterns evolve in the wild, and a conversation with Bowdoin professor Nat Wheelwright (who was director of the Bowdoin Scientific Station from 1987 to 2003) revealed that the College had recordings of Savannah Sparrows on Kent Island going back to the early 1980s.
Thanks to the work of numerous researchers—including Williams—from colleges and institutions across the US and Canada, the study was able to draw on a truly impressive data set from Kent Island. This includes continuous recordings from 2003, apart from 2020 when the COVID-19 pandemic prevented such activity.
One of the study’s most interesting discoveries, she said, was how some songs changed systematically over the years. “One note sequence was present in nearly all songs in the early 1980s; a new, simpler sequence of notes appeared a bit later; birds in the 1990s often sang both sequences; and by 2012 a newer, simpler sequence had replaced the old version. In a second step of cultural evolution, the birds elaborated that new simpler sequence.”
Rounds of successive changes in the same socially learned behavior, said Williams, are called “cumulative cultural evolution” and it’s ubiquitous among humans but rarely observed in wild animals. From their research—which included playing altered song recordings back to the birds themselves using outdoor speakers—Williams and her team concluded that the newer type of song pattern was more effective in attracting the attention of the female sparrows: “They behaved as if they were curious and interested—standing upright, looking around, hopping toward the speaker.” In other words, it’s not any specific physical or genetic attribute that ensures the reproductive success of the male Savannah Sparrow, but the ever-changing beauty of his song.