Washington: In birds like in humans, female fertility declines with age. Some female birds can slow their declining fertility by choosing the right mates.
Female birds become progressively less fertile as age takes its toll, said co-author Josh Auld of the National Evolutionary Synthesis Centre in Durham, North Carolina.
Older females lay fewer eggs and they lay them later in the season -- at a time when less food is available for their chicks, he explained, the journal Oikos reports.
But despite abundant evidence of fading fertility in females, scientists know little about the role played by their mates.
"The thought was that males didn`t matter," Auld said, according to a National Evolutionary Synthesis Centre statement.
The authors took advantage of a long-term data set of birds known as blue tits. Since the late 1970s, scientists have studied thousands of these blue and yellow forest birds on the French island of Corsica.
When the authors analyzed lifetime data for nearly 600 females and 600 males from 1979 to 2007, they found a surprise: how fast a female`s fertility fades with age depends partly on her partners.
The important thing for females is not the age or identity of her mates, they discovered, but her partners` paternal past.
"The `history` of the male matters," said co-author Anne Charmantier of France`s National Centre for Scientific Research, also known by its French initials CNRS.
Fertility declined less quickly for females whose mates became first-time fathers young. "Females that repeatedly pair with early-reproducing males are better off. They don`t age as fast," Auld said.
Males who got a head start on fatherhood -- within their first year of life -- may be healthier or more experienced mates than dads that delayed.