http://www.nature.com/news/2005/050214/full/050214-8.html
16 February 2005; | doi:10.1038/news050214-8
Social sounds boost bird breeding
Emma Marris
Zebra finches base their mating decisions on group consensus.
Birds that live in bunches work each other up into a reproductive
frenzy with their songs, according to research that confirms an old
hypothesis.
As far back as the 1930s, ornithologists proposed that large, sociable
colonies of birds would tend to have earlier, bigger and more closely
synchronized clutches of eggs.
Known as the Darling hypothesis, after F. Fraser Darling who first
suggested the idea, it has finally been supported by experiments in the
laboratory, and the research appears online in the Proceedings of the
Royal Society1.
Postitive feedback
To test Darling's hypothesis, the researchers set up two indoor
colonies of the zebra finch (Taeniopygia guttata), a smart little
Australian bird often seen in pet shops.
The first group of birds was played recorded sounds of its own colony,
but the second group heard a playback that blended its own colony
sounds with noises from extra finches.
Females in the second group had more eggs, laying them earlier and more
synchronously than controls, confirming the theory.
Peter Boag, a biologist at Queen's University in Ontario, Canada, who
worked on the study, explains the advantages of this mating pattern. It
is probably beneficial for a bird to have its chicks at the same time
as the couple on the next nest, he says. With more chicks around, the
risk to each individual chick from predators is reduced.
It is also advantageous for a female to start laying early in the
season, because this gives her more time to invest in her brood and
makes it likely that she will fledge more chicks successfully.
However, laying too early will isolate chicks and put them at risk, so
how do females decide when to lay?
Safety in numbers
Finches are known to use environmental cues like rainfall and length of
the days, but the experiment by Boag and his colleagues shows that they
also respond to bird calls associated with reproduction. After all, if
everyone else sounds as if they are laying, it's probably safe to lay
your eggs too.
"A single bird on its own might be right or might be not right," says
Boag, "but if you have fifty birds reacting to those cues, and if the
majority decides it's time to breed and they get excited, then they
sing a lot."
He suggests that the volume of social sounds acts as a kind of
information feedback loop. "It leads almost to a crescendo and feeds
upon itself and suddenly, boom: everybody mates," he says.
The exact mechanism for the effect is still being worked out, says
Boag, but other studies have shown that hearing social sounds can cause
changes in hormone levels in birds.
--------------------------------------------
Birding-Aus is now on the Web at
www.birding-aus.org
--------------------------------------------
To unsubscribe from this mailing list, send the message 'unsubscribe
birding-aus' (no quotes, no Subject line)
to
|
