Cowbirds are any of a number of small American blackbirds (especially 'Molothrus
ater') often seen near cattle. Cowbirds lay eggs in other birds' nests.
David White
At Canada's McMaster University, David White (above) studied the social
factors that affect mate choices of Japanese quail (Cotumix japonica) and
was drawn to post-doctoral work at IU because of the international
reputation of animal researchers at the school. And, he said, there are
few laboratories in the world with "football-field sized aviaries at
their disposal."
|
Whom, you might ask, will love a big old cowbird?
Cowbirds are, after all, "brood parasites" not exactly a
parenting skill rife with admiration. But there you have it. And for the
sake of this story, try not to anthropomorphize the ethics of abandonment.
Cowbirds hatch in the nests of more than 200 different species or
subspecies of birds genetically not their own. The cowbird parents deposit
their eggs in the nests of others, and the nestholders raise the baby
cowbirds as if they were their very own. Which could raise a host of
interesting questions related to Nature vs.
Nurture if you believe in that
sort of dichotomy.
Since animal behaviorists have found compelling evidence that each
songbird's signature‹its songs‹is the product of guided learning, what
happens to a young male cowbird and his ability to court? Will his genetic
programming‹his "genetic safety net" ‹be sufficient to
ensure that he develops a song and uses it to attract a mate? Those are questions IUB animal behaviorists Andrew King and Meredith West
have addressed with colleagues as part of on-going research at their
93-acre field station north of Bloomington.
One scientist working along with King and West is IUB Department of
Psychology's David White, a Canadian post-doctoral affiliate of IU's
Center for the Integrative Study of Animal Behavior. He will have none of
that Nature vs. Nurture talk.
"Behavior and physiology are composed of intricate weavings of genes
developing in an environment: it makes no sense to me to try to pull the
two factors apart," explained White. "It would be like me asking
you to look at your hand and to tell me how many of your fingers are due
to genetics and how many are due to the environment. There are no fingers
without genetics. There are no fingers without environment."
King, West and White are currently at work on a project investigating how
different social environments impact the development of cowbirds'
communication and courtship abilities.
"We created different social environments with a very simple, natural
manipulation: we put cowbirds of different age classes together,"
White said.
Four distinct "cowbird cultures" at the field station differ in
the age classes of the males present. Each aviary has adult and juvenile
females. In addition, one has adult and juvenile males; one has only adult
males and no juveniles; one has juvenile males and no adults; and one has
only females, no males.What White has noted thus far:
- Juvenile male cowbirds housed without adults sing more than any of the
other birds. Their songs are well developed, but they don't know
"what to do with them," said White. "They never sing
directed songs to females‹a must for courtship success‹and they rarely
sing directed songs to males." Instead, they sing soliloquies all day
long and act "spaced out."
- Adult males housed with juvenile males stopped singing early in the
fall. White thinks the adult males don't want the juveniles to steal their
best "grown-up" cowbird songs.
- Female behavior differs across cowbird cultures. Females housed with
just juvenile males stay to themselves, never interacting with males.
Females housed with just adult males sit very near males, approach them
and allow male serenades with relish.
The breeding season is coming up, and White will be documenting the mating
behavior to see what differences there will be in the males' reproductive
success across groups.
"At which point," said White, "we want to make a conclusion
that the social environment had the effect of launching these groups of
birds down very different developmental trajectories that can lead to very
substantial differences in reproductive success and, thus, be of
evolutionary importance."
Interacting in a social setting is hard, because conditions are always
changing, White said, and the cowbirds have to learn to deal with these
changes and change with them‹hard-wired programs of behavior just don't
work well, and the animals have to learn and adapt quickly.
"But even though some aspects may change daily, the social
environment is, at the same time, stable and dependable across
generations," White explained. "This stability allows the new
generation to inherit the secrets of social success-‹good genes, a good
environment and good information."
|
