Biology Reference
In-Depth Information
But females of many tropical species sing, and also females of several northern spe-
cies, including Northern Cardinals, Black-headed Grosbeaks, Rose-breasted Grosbeaks,
and White-throated Sparrows. Scientists are still teasing out the reasons why some fe-
males sing while others don't — this is yet another area where the more we learn, the
more questions we come up with.
Female White-throated Sparrows have a very interesting and unusual singing pattern.
The species has two color forms — one has white stripes on the head and the other has
tan stripes. This is a genetic difference like that underlying human eye color. Birds of
either sex can have head stripes of either color.
Both male and female sparrows with white head stripes are more aggressive than tan-
striped birds. Female white-striped birds sing, but tan-striped females do not. In laborat-
ory tests where birds were separated by a glass partition but could see those of the op-
posite sex through the glass, females of both color forms preferred tan-striped males, but
the more aggressive white-striped females outcompete the tan-striped females for tan-
striped mates. Those same laboratory tests indicate that males prefer the appearance of
white-striped females, but that when white-striped females start to sing, the aggressive
white-striped males attack them. So virtually all pairs of White-throated Sparrows have
a male and female of opposite color forms.
What Do Birds Sing About, Anyway?
Q The cardinal outside my window has been singing all morning. Why does he spend
so much time singing?
A
Hesingstoattract amate andtoannounce hispresence toother males sothey will stay
off his territory. Some birds sing tens of thousands of songs each day. Defending a territ-
ory requires constant vigilance!
If you listen carefully, you may hear
countersinging
, when neighboring birds sing in
response to each other. When Marsh Wrens countersing, they may match each other by
singing the same song type as a neighbor. Or they may sing an entirely different song
type, or anticipate the song the other will sing next and sing it first. All these choices al-
