The current health condition of male birds may have a direct impact on its song performance. With bird songs often used in resource gathering or mating, a negative impact on its song performance may lead to disadvantages in competing with other birds.

The research done by Dr. Jenny York and her colleagues focused on investigating how the song production of male birds is affected by their immune response. In doing this, they exposed 12 dominant male white-browed sparrow weavers with a substance that will trigger their immune response. They were then compared with another 12 dominant male white-browed sparrow weavers as the control group.

These white-browed sparrow weavers have been identified as highly cooperative breeding birds that hold year-round territories. Previous studies also suggest that the health of male birds may have an effect in mate selection or competition among species.

The results of the study revealed that sparrow weavers with triggered immune responses produced a shorter dawn song as compared to the control group. The effect occurred even if there were no significant effect on the birds’ body mass has been observed. The research proved that the activation of the birds’ immune response may have a negative effect on the song performance of dominant males.

'Our findings provide the first experimental evidence that the song performance of dominants in a cooperatively breeding society is impacted by their current state, and therefore highlights the potential for within- and extra-group same-sex competitors to monitor local dominants acoustically with a view to challenging weakened individuals,' the researchers wrote in their study published in the journal Ecology and Evolution. 'Future studies might now profitably investigate the extent to which subordinates in social species do indeed utilize the song performance of dominants when making adaptive decisions about whether and when to challenge for the dominant position,' they added.

The research was done by Dr. York and Andrew Radford from the University of Bristol, Ton Groothuis from the University of Groningnen and Andrew Young from the College of Life and Environmental Sciences in Cornwall. You may access the full research of Dr. York colleagues here: http://dx.doi.org/10.1002/ece3.1938.