ScienceDaily, May 4, 2012
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| A male-directed display by male cowbirds tends to be more intense than female-directed displays. (Credit: Sonia Fernandez/UCSB Public Affairs) |
More modest male
displays attract the females when it comes to brown-headed cowbirds, contrary
to sexual selection theory, according to UC Santa Barbara researchers Adrian
O'Loghlen and Stephen Rothstein.
Their findings are
published May 2 in the open access journal PLoS ONE.
While sexual selection
theory predicts that females should find more flamboyant displays the most
sexually attractive, the opposite holds true for brown-headed cowbirds, a small
songbird common in North America. Using audiovisual recordings of displaying
males shown to captive females, the scientists found that the less intense the
wing spreading, feather puffing, and bowing were during a display, the more
sexually interested the female would be.
"Although
cowbirds have been studied for years, it hadn't really been noticed that
displays directed at females were different in intensity than those directed at
other males," said O'Loghlen, a research scientist in the Department of
Ecology, Evolution and Marine Biology. However, technical advances in the area
of audiovisual recordings made it possible for the researchers to investigate
the brown-headed cowbirds's display behaviors in greater depth. O'Loghlen and
Rothstein, a professor of Zoology, are the first to use AV technology to study
the sexual responses of female songbirds to male displays.
Several things
factor into cowbird displays, said O'Loghlen. For one thing, displays are
typically targeted directly toward another cowbird. The display is a
coordinated song and dance, with the bird singing as it puffs its feathers,
spreads its wings, and bows. While earlier experiments had shown that female
cowbirds are sexually responsive to some male songs and not to others (for
example, they prefer local over foreign song types), this study shows that they
also respond to the visual display that usually accompanies cowbird song.
"With these
new audiovisual techniques we have developed, we can basically ask a female,
'Which type of displays does she find more sexy?'" said O'Loghlen.
A previous study
had shown that the most intense wing-spread displays are directed at other
males and are used to signal strength and establish position in the birds's
social hierarchy. Female cowbirds may not like intense displays because they
are generally used by males as aggressive signals.
"She may be
frightened; she may be threatened by these more intense displays,"
O'Loghlen said.
This audiovisual
research is still at an early stage and there are many questions yet to be
answered about these displays.
"For example,
why do males bother to display at all when they sing to females?" asked
O'Loghlen.
A possible answer
may be the presence of light-colored feathers under the wings of younger male
cowbirds. Older males are preferable as mates to female cowbirds, possibly
because they are likely to have better quality genes, having survived longer.
Females may require males to display to them so that they can tell if a
"suitor" is a young or older male. When a male suitor displays, he
spreads his wings, showing the age-revealing color of his under wing feathers.
Brown-headed
cowbirds are among the most-studied species of songbird. They are brood
parasites, laying their eggs in other birds's nests, and leaving their young to
be raised by their foster parent "hosts." In some cases, this can
have drastic consequences for the host parents, as their own young may die when
the cowbird chick outcompetes its adopted siblings for food.
The
next steps for the researchers include looking for reasons why females respond
to these male displays, and how males develop their display skills.
Story Source:
The above story is reprinted from materials provided by University of California - Santa Barbara.Note: Materials may be edited for content and length. For further information, please contact the source cited above.
Journal Reference:
- Adrian L. O'Loghlen, Stephen I. Rothstein. When Less Is Best: Female Brown-Headed Cowbirds Prefer Less Intense Male Displays. PLoS ONE, 2012; 7 (5): e36130 DOI: 10.1371/journal.pone.0036130
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