Here’s a story that should gladden the hearts of all packrats and stringsavers. Sometimes there are good reasons not to throw stuff out.
In the early 1960s, a graduate student from Macao named Luis Baptista heard his first white-crowned sparrow on the UC Berkeley campus. That common songbird became the focus of his research on how birds acquire their songs, and the subject of 60 or so of his 120 scientific papers.
Baptista, who became curator of birds at the California Academy of Sciences, field-recorded white-crowned sparrow vocalizations from California to British Columbia in 1970. He loaded an old Mercedes with acoustic gear and drove up and down the West Coast, screeching to a halt whenever he heard an unfamiliar song. In the process, he documented and mapped local dialects. At Point Reyes, for example, Baptista found distinct song patterns for Drake’s Bay, Limantour Estero, and Palomarin.
This was at a time when bird song was thought to be a stereotyped, hardwired phenomenon. Baptista was one of the first to show that young male songbirds acquired their vocal repertoire from their fathers and neighbors, and that females preferred singers with the “correct” dialect as mates.
A colleague once wrote that Baptista could hear a sparrow song in the middle of Golden Gate Park and declare that the bird had “half an Alberta accent and half a Monterey accent,” and that its parents had probably met at Tioga Pass in Yosemite.
Baptista moved on to study chaffinches, doves, hummingbirds, and other species. At his untimely death in 2000, his white-crowned sparrow tapes were stashed away somewhere in the academy’s labyrinthine files.
Enter, a few years later, Elizabeth Derryberry, a Duke University graduate student and researcher at the Lousiana State University Museum of Natural Science in Baton Rouge. She was trying to determine how the songs of birds varied over time, and how those changes might reflect altered environments. Derryberry really wanted to hear Baptista’s tapes, but no one at the academy could lay hands on them. She was persistent, though, and the tapes were eventually unearthed in Baptista’s old office in 2003.
So Derryberry embarked on her own road trip in 2005, revisiting 15 of Baptista’s field locations and recording a new generation of white-crowned sparrows. It’s not clear from what I’ve read where all the sites still had resident sparrows, but she seems to have found enough for a detailed comparison with the tapes from the 1970s.
What she found was that the trill with which the sparrows ended their songs had become lower in pitch and slower, with a rate of 10.3 trills per second instead of the historical 11.8. That was enough of a change to make a difference in the response of both males and females to the historic tapes. Males behaved more aggressively when contemporary songs were played to them, and females got more excited.
The change in the song ending seemed to correlate with changes in the singers’ habitats, as shown in archival aerial photographs. In the ’70s, the white-crowns’ territories were predominantly grassland, with only 11 percent coastal scrub cover. Thirty-five years later, coastal scrub made up 26 percent of the territories. The lands were no longer being grazed, and the shrubs that the cattle had kept in check were taking over. In the one site where the scrub component had not increased, the sparrows still sang the old way.
It seems to be a matter of acoustics. The lower, slower songs reverberate less in dense foliage and are more likely to be copied accurately by young birds who are learning the local song variant.
“This is the first time that anyone has shown that bird songs can shift with rapid changes in habitat,” Derryberry said in a Duke press release. “Given how much the world’s habitats are changing, this is sort of an unexpected but useful factor to monitor.” She’s now studying how deforestation and other ecological changes are influencing song evolution in South America.
Her timing with the sparrow research could not have been better. I shudder to think what might have happened to the Baptista tapes in the move to the academy’s new quarters.