Science
Daily ? An Australian bird has been found to produce smaller, less
nourishing eggs when it breeds in the presence of other 'helper' birds that
provide child-care assistance. This unique adaptation enables the birds to live
longer and breed more often than females without helpers. The research, led by a
University of Cambridge academic, was published in Science.
In many animal species, parents
caring for their offspring are assisted by so-called 'helpers', adults that
forego reproduction to help others raise young. Although parents decrease the
amount of food they provide to offspring when helpers are present, the
additional supply provided by the helpers more than compensates for this
reduction. As a result, chicks fed by parents and helpers tend to receive more
than those raised without helpers.
However, research has shown that these offspring
who receive additional food do not appear to gain any advantage as a result.
This has raised the question of who really gains from helping behaviour -- a
question that has baffled scientists until now. The research on a common
Australian bird species has provided a novel answer.
Researchers have discovered that in the 'superb
fairy-wren'*, mothers benefit more from helping behaviour than their offspring.
As helpers provide chicks with a significant amount of additional food, mothers
can afford to skimp on nourishing their eggs. Females that are assisted by
helpers were found to lay smaller eggs with disproportionately smaller yolks,
thereby saving energy during egg laying. As a result, they live longer and breed
more often than females with no helpers.
The scientists predict that this phenomenon occurs
in other cooperative breeding bird species.
"Helper birds offer mothers a form of child-care",
says Dr Rebecca Kilner from the University of Cambridge's Department of Zoology,
one of the leaders of the research team that made this discovery. "In this
species, mothers effectively steal the child-care from their current brood and
spend this energy on producing more young in the future."
Superb fairy-wrens sometimes breed as pairs, and
sometimes as pairs assisted by between one and four helpers. Helpers are always
male and often sons from previous breeding. Females are drab brown in colour,
but males moult into a striking blue plumage to breed, hence the species'
superlative name.
The article 'Reduced Egg Investment Can Conceal
Helper Effects in Cooperatively Breeding Birds' is scheduled for publication in
the 17 August edition of Science.
The research was carried out by a team from the
Universities of Cambridge and Sheffield in the UK and the Australian National
University, and Macquarie and Wollongong Universities in Australia. It was
funded by The Leverhulme Trust, The Royal Society and The Australian Research
Council.
* Superb fairy-wrens Malurus cyaneus are small (10
g) garden birds, common to south-eastern Australia.
Note: This story has been adapted from a news
release issued by University of Cambridge.
Source: http://www.sciencedaily.com/releases/2007/08/070816143814.htm
