38 Scientific American, May 2022
Birdsong, which has intrigued scientists since Aristotle’s time,
is traditionally defined as the long, often complex learned vocal-
izations birds produce to attract mates and defend their territo-
ries. Modern researchers categorize it in contrast to bird calls,
which are usually shorter, simpler, innately known and used for
a more diverse set of functions, such as signaling about preda-
tors and food. These definitions are by no means clear-cut. For
instance, some species have songs that are simpler than their
calls. But when I refer to birdsong, I mean those longer, more com-
plicated sounds as opposed to the short cheeps and peeps.
The very terminology researchers and laypeople alike use to
talk about birdsong reflects the musical and languagelike way it
strikes our ears. Getting deeper into the lingo for a moment,
when researchers analyze birdsong, we usually break it down
into smaller units, termed notes or syllables. We then group the
syllables into sequences called phrases or motifs that have char-
acteristic rhythms and tempos. In this way, we can measure
potentially important aspects of song, such as the number of syl-
lable types in a bird’s repertoire or the patterns in which phrases
are arranged. These descriptions also parallel the ways we mark
the relations among words in human syntax or among notes in
musical compositions.
But what do the birds think about all these features? How does
birdsong sound to them? Recent research that my colleagues and
I have conducted, along with work from a growing number of
other scientists around the world, has revealed that birdsong
sequences do not sound to birds like they do to us. Moreover,
birds appear to listen most closely not to the melodies that catch
our ears but rather to fine acoustic details in the chips and twangs
of their songs that lie beyond the range of human perception.
BEYOND MELODY
Birdsong researchers have known since at least the 1960s that
birds hear song differently than we might expect. One of the clas-
sic ways to test perception in birds in the wild is through so-called
playback experiments, in which investigators play songs to birds
and measure their behavioral response. Many birds respond to
playback of a typical song of their species as if a territorial intru-
sion were occurring—they approach the speaker from which the
song is playing, fly around the sound’s source to look for the
intruder, and emit their own threatening calls or songs. By com-
paring responses to natural and manipulated songs, researchers
can learn which features are important in perception. In the pre-
digital age, they would capture song on tape recorders and liter-
ally splice together the magnetic tape to create manipulated songs
with, for example, rearranged syllables or shorter silent intervals
between notes. Today digital recording equipment and sound-
editing software make such manipulations much easier to create.
In one classic playback study in the 1970s, Stephen T. Emlen of
Cornell University studied song perception in the Indigo Bunting.
The vibrantly blue males of this species deliver songs consisting
of syllables that they almost always utter two at a time. Ornitho-
logical field guides often call attention to this pattern of paired syl-
lables when describing the song, and it is easily seen in a spectro-
gram, a visual depiction of song that shows the frequency and
amplitude of its signal over time. (The perceptual equivalent of
frequency is pitch, and that of amplitude is loudness.) Despite the
prominence of the paired pattern to human ears and eyes, when
Emlen played a modified song with unpaired syllables to the birds,
they reacted with the same intensity of territorial response they
exhibited when they heard the natural paired song. This re sultW
hen we humans hear Birdsong, which many have appreciated
more than ever during the pandemic, we can’t help but think
about parallels to human music and language. We discern dis-
tinct melodies linking the clanks and buzzes of Song Sparrow
songs, sentencelike structure in the Red-winged Blackbird’s pro-
nouncement of conk-la-ree! and a cheery whistle in the wide-
open-beaked songs of the White-throated Sparrow.Adam Fishbein is a postdoctoral researcher at the University
of California, San Diego. He studies the cognitive and neural
bases of animal social interactions.