Biology Reference
In-Depth Information
low males to communicate their intentions before deciding whether to fight. Depending
on how they sing, they can direct threats to specific neighbors or back down from a chal-
lenge.
In addition to vocal sparring, birds may use their repertoires to impress potential
mates. Male Song Sparrows with larger repertoires have a longer lifespan than do males
with fewer songs. This is probably because males that are better nourished and defend
better territories are able to learn more songs.
YoungmaleBewick'sWrensthathatchearlyinaseasonhavemoretimetolearnsongs
before winter than later-hatching males do; those with more songs in their repertoire can
successfully defend the best territories. In these species, females prefer to mate with the
males with the most song types, an easy way of discerning which males are robust and
experienced, and thus, most likely to help her successfully raise healthy young.
Q My son says he's been tired lately because the birds wake him up at dawn. Is it
my imagination, or do the birds sing especially loudly at first light?
A
It's true: more birds sing at dawn than later in the day, and they sing with more energy
and variety. This “dawn chorus” actually starts an hour or so before dawn in spring and
early summer. The chorus often begins with American Robins singing a much more rap-
id,excitedversionoftheirdaytimesong.ChippingSparrowssingtheirsongsatafrenetic
pace, and many other birds sing with exceptional energy as well. As more birds join in,
the chorus crescendos. At its peak, the dawn chorus can be so richly complex that it can
be tricky for human ears to pick out many of the individual voices.
Ornithologists are still debating why birds sing so vigorously during the dawn chorus.
Do birds simply have a lot of pent-up energy after a good night's sleep? Is dawn the best
time to sing because in the dim light, territorial competitors and prospective mates don't
have much else to do other than listen? Is morning the best time to make a statement to
competitors and potential mates that may have landed in the morning after a night of mi-
