Image: Fairy-wren
A male "helper" superb fairy-wren perches on a branch.
updated 8/16/2007 2:57:48 PM ET 2007-08-16T18:57:48

Whose offspring do better, families in privileged circumstances or those struggling to keep food in the kids’ mouths?

For a type of Australian bird called the superb fairy-wren, it turns out it doesn’t make any difference.

Researchers found that wren moms with little help lay larger eggs, getting their chicks started off on the right foot. But mother wrens who have a lot of helpers around don’t have to bother; they produce smaller eggs, knowing there will be plenty of birds bringing home food for the little ones.

Researchers, led by Andrew F. Russell of the University of Sheffield in England, studied these birds because they knew that some of the parents raise chicks on their own while others live in cooperative groups with lots of helpers.

They wanted to see how the two groups of chicks compared, and their results are reported in Friday’s edition of the journal Science.

It turned out that both groups of chicks did equally well, even though those that lived in cooperative situations got 19 percent more food than those fed only by their parents.

They needed it.

Those chicks were hatched from eggs that were 5.3 percent smaller than those of parents without help, and their eggs contained 12 percent less fat and 13 percent less protein, “suggesting that mothers invest less energy in their eggs when breeding in the presence of helpers,” the scientists reported.

The probable reason, they suggested, was that the females breeding in groups were “reducing their own investment in reproduction to save resources for future breeding attempts.”

The research was funded by the Royal Society, Australian Research Council and The Leverhulme Trust.

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