After vegetation recovered in some empty lands in California, Oregon and Washington, during the last three decades, a scientist noticed a lowered pitch in male white-crowned sparrows. She also discovered that the birds slowed down their singing. The biologist Elizabeth Derryberry considers that in such a way the love songs of this species of sparrows are carried better through a more abundant landscape.
“This is the first time that anyone has shown that bird songs can shift with rapid changes in habitat,” says Derryberry. Her findings were included in a dissertation research that she presented at Duke University.
Derryberry performed a comparative analysis of recordings of individual birds, which were made in 15 different regions, and some old recordings that were made in the same places back in the 1970s by a scientist from the California Academy of Sciences. She discovered that both the musical pitch and the warble of the sparrows’ short songs significantly lowered. “I was really surprised to find that songs had changed in a similar way in so many different populations,” she said.
After analyzing the recordings, Derryberry observed archival aerial photography in order to see how the landscape changed from 1970s to present day in the regions were the recordings were made. She found that in the areas where the foliage did not change, the songs of white-crowned sparrows hadn’t slowed down.
There is less echo in a slowed song when sang in an abundant foliage, which is why it will be heard more accurately. Thus it is possible that young males pick the song they will learn according to the surroundings. This means that with the alterations in the foliage songs will become slower and have a drop in pitch. The results of this research add more evidence to the belief that animals change their acoustic and visual communication depending on the habitat.
Currently Derryberry is carrying out her studies at Louisiana State University. Her latest discoveries will be published in the July edition of American Naturalist.