MOCKINGBIRD SONG AIMED AT MATES, NOT
RIVALS — An opportunity to monitor closely
the singing behavior of mockingbirds produced
a result that was entirely unexpected
[From Science, 236, pp 1521-22, Je 19 '87]
Mockingbirds can • be
pretty cheeky creatures.
And noisy too. But to
Randall . Breitwisch and
George Whitesides of the
University of Miami,
these two sometimes annoying habits of mockingbirds . presented an
opportunity. During the
spring of 1985 the researchers were able to
monitor closely the birds'
singing behavior right on
the university campus.
And what they found was
a big surprise. "The birds
appeared to spend a great
deal of their time directing their song irito their
territories rather than out of them," says Breitwisch.
"And that is important, because it tells you something about the function of their song."
Bird song traditionally has been interpreted
principally as a territorial warning from one male
to another. "The idea of a 'keep-out signal' is very
popular among biologists," says Breitwisch, "and very
often it must operate that way. But not always." ■
The discovery that male mockingbirds spend a lot
of time singing into their territories rather than
broadcasting out of them from the edges implies
that in this case at least, it is probably not true.
"This was an unexpected finding," acknowledges Gene
Morton of the National Zoological Park in Washington. "The interesting question now is, how common
When Breitwisch, who is now at the University
of Pennsylvania, first observed this pattern he looked
into the literature and was surprised to find that
no one else had even looked at the question of
directionality of singing. Position of the singer
within the territory, yes. But not direction of the
singing. The problem most observers face in trying
to get data on this is simply being able to be close
enough to the birds to make reliable and repeated
obervation of the position of the beak during singing.
The relatively habituated mockingbirds of the University of Miami campus offered that opportunity.
"Finding out how general a phenomenon this is will
therefore be difficult," says Breitwisch.
The northern mockingbird is, of course, famous
for its extensive repertoire and its mimickry [sic],
both of which properties make it more likely that
the function of the song is male-female attraction.
The starting point for the Miami project was simple:
if the function 'of the song were indeed to attract
a mate for the male rather than to ward off rival
males, then a comparison of the singing behavior of
the mated and unmated males should be different
It turns out that, although mated and unmated
males both direct a lot of their song into rather
than out of their territories, unmated males sing
more than mated males. They are also more active,
flying from perch to perch so as to deliver their
song from more different positions. However, mated
males chased intruders from their territory more
often than unmarried males. And, significantly, says
Breitwisch, the males are usually silent when they
are on these chase and expel ■ missions.. "If. the
function of song really were territorial," he says,
"you might expect it to accompany these episodes."
As well as singing more than mated males,
males who are still looking for a female also vary
the direction of their song more. "If song were a
form of male-male communication (that is, a keep-
out signal)," note Breitwisch and Whitesides, "there
would be no reason to expect unmated birds to display a greater variability in the direction of singing
within bouts than mated birds." But if the song
were a broadcast to potential mates in the vicinity,
but who might not be visible to the singing male,
then the bird might be expected to cast its vocal
net as wide as possible. "This is what they appeared
Although unmated males were apparently casting their voices around in an attempt to snare a
mate, sometimes they appeared to focus quite intently in one direction. "This observation suggests
that events on adjacent or nearby territories may
stimulate unmated males to sing in the direction of
those territories," note Breitwisch and Whitesides.
For instance, they might be attempting to exploit
an opportunity to mate with a neighboring female.
That opportunity might be signaled by the singing behavior of the neighboring male, say the two
researchers. "Unmated males could monitor the
nesting stage for neighboring pairs and direct song
at neighboring females at the most opportune time
for luring those females away from their mates,"
suggest Breitwisch and Whitesides.
NEW AUDUBON CALENDARS ARE OUT
The photographers among us as well as those
who just love to look at beautiful nature photographs
will be hard put to choose among the new Audubon
calendars, and will certainly be interested in the
engagement calendar. With every photograph you
are told not only the subject, location and. photographer's name, but also the type of camera, film,
speed and aperture information. There is, of course,
the Wild Bird Calendar in addition to the Nature,
Sea Life and Wild Animal calendars, all published
by MacMillan and available at The Chickadee and