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How male birds affect female fertility

Felix Kaestle / AP

A blue tit is reflected in a wing mirror of a car that is covered with raindrops in Friedrichshafen, southern Germany in this file photo. Female blue tits who mate with experienced males have slower ticking biological clocks, a new study says.

Biological clocks tick more slowly for female blue tit birds that consistently choose mates whose first reproductive success came in their first year, according to a new study.

The finding suggests that males, who help build the nest and feed mom and her chicks, create an environment that influences how the female interacts with the world.

"The thought was that males didn't matter," Josh Auld, a study co-author at the National Evolutionary Synthesis Center in Durham, North Carolina, said in a news release.

It turns out that they do.

Auld and his fellow researcher, Anne Charmantier of the French National Center for Scientific Research, don't know exactly why certain male blue tits fail to reproduce in their first year, nor do they know what cues a female uses to pick different males. But the birds mate once a year, often with a different partner, and the females with mates that started reproducing early have slower-ticking biological clocks.


The age of the male in a given mating year doesn't matter; the key factor is his history. Males with early experiences are somehow superior.

"These males that are able to reproduce early may in some way ameliorate the decline and fitness of the females," Auld told me today.

French data
To determine the male factor in female fertility, the researchers took advantage of a long-term data set from the yellow and blue forest birds on the French island of Corsica. The birds were outfitted with identification tags on their ankles, allowing researchers to track who mated with whom, how many eggs they laid, and when and how the fledging birds fared over time.

Auld and Charmantier analyzed data collected between 1979 and 2007 for nearly 600 female and 600 male birds. They found that the positive effect of experienced males is greatest a bit later in the birds' 6-year or so lifespan, Auld noted.

"Going through parenting once means the second round might go a little bit better … so when that 4- or 5-year-old female chooses even a 4-year-old male, and he started reproducing when he was 1, that's when we see that decline was lower," he said.

Broader effect?
Whether this positive effect of male experience on female fertility is broader than just the world of blue tit birds is, for now, unknown. Auld and Charmantier are currently studying swans, and they're not getting exactly the same result.

"But they are very different," Auld said of the swans. "They are long-lived. So it is a little early to say. Certainly we would like to know that, but I really don't know for sure how general these effects are," he said.

The study was funded by the National Science Foundation, and the findings were published online last week in the journal Oikos.

More stories on bird mating:


John Roach is a contributing writer for msnbc.com. Connect with the Cosmic Log community by hitting the "like" button on the Cosmic Log Facebook page or following msnbc.com's science editor, Alan Boyle, on Twitter (@b0yle).