London, Oct 25 : Scientists at the Riken Brain Science Institute, in Wako, Japan, have found that birds that come from the earlier eggs in a brood are more likely to be better singers.

Most male birds use songs to show their fitness to potential mates, and previous studies have demonstrated that the healthiest males tend to sing the longest, loudest and most complex songs.

Masayo Soma and her colleagues from the Riken Brain Science Institute wanted to find out if the order in which birds hatch affects their song.

"I expected to detect age hierarchy in song, because older siblings are stressed less and obtain more resources growing up," Nature quoted Soma, as saying.

In order to test the idea, the researchers cross-fostered Bengalese finches (Lonchura striata domestica) so that the age hierarchies formed in fostered broods were independent of the order in which the eggs were laid.

Nine pairs of finches raised a total of 16 clutches of four chicks. Nine more adult males were also introduced to breeding cages at time of fledging so the young heard more than one bird''s song. When the fostered finches had matured, the researchers recorded their songs.

The researchers found that their initial hypothesis was wrong - hatching order and nest hierarchy had no noticeable impact on the songs.

In fact, the order in which eggs were laid was important in determining how complex a particular hatchling''s song would be when it matured.

The researchers found that finches hatching from earlier eggs in a brood consistently sang songs that were more complex than those of siblings coming from eggs laid later.

Roxana Torres, a biologist at the National Autonomous University of Mexico, in Mexico City, said: "Evolutionary ecologists are increasingly realizing that females of some species can differentially allocate key resources in their eggs."

However, scientists are still not sure about what these resources are.

"Androgens are involved in the mechanisms of sexual development, and androgen concentrations in egg yolk are likely to be influenced by egg order," Soma said.

Soma said that whatever the chemical cause, it is unusual for altricial birds, -- such as these finches - to give their first offspring additional advantages over their siblings.

She now hopes to conduct experiments that add androgens and other compounds into the eggs of finches to see what effects it might have on song quality.

The study is published in Behavioural Ecology and Sociobiology. (ANI)