This might be a strong reasons why those birdcall sound are important.
They actually help to excite those female birds to produce better eggs and quality chicks?
ScienceDaily —
In a new study published in the latest issue of Ethology researchers show that female songbirds can alter the size of eggs and possibly the sex of their chicks according to how they perceive their mate's quality.
The researchers played back attractive ("sexy") songs and less attractive control songs of male canaries to female domesticated canaries. When the females started egg-laying they varied the size of their eggs in the nest according to the attractiveness of the male's song. That is, the more attractive the song, the larger the eggs.
However it is remarkable that while larger eggs were more likely to contain male offspring in natural environments, in the experiment there was no difference in brood sex ratio between the different songs played to the females, which suggests different levels of female control. Male birdsong has long been known to attract females and influence mate choice decisions and even induce an alteration in the offspring's sex ratio.
This study by Leitner et al. now shows experimentally that hearing attractive song also has a selective impact on female physiology.
45 female domesticated canaries participated in this study that was a collaboration of Royal Holloway, University of London and the Max Planck Institute for Ornithology in Seewiesen and Radolfzell in Germany. The birds were kept in large aviaries where their daily behaviour was monitored in a colony before they were tested in the song experiments. The females showed a remarkable consistency in their behavioural and reproductive performance and the song stimuli alone were sufficient to elicit a profound physiological change.
This study further highlights the importance of behavioural stimuli for reproductive physiology. Bathroom Pavarottis beware.
Article copied from: http://www.sciencedaily.com/releases/2006/06/060607171611.htm
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