A new study has revealed that birds called blue tits use "aromatherapy" to disinfect their nests.
These birds have been found to line their nests with aromatic plants like mint or lavender, which kill bacteria.
The study suggests that doing so helps the birds create more sterile environment for chicks, which, in turn, grow faster and have a better chance of survival.
However, individual blue tits are quite picky about which plants they use, and the study has yet not explained how they pass their knowledge on to other birds.
On Corsica, according to a report describing the study, blue tits also incorporate fresh fragments of aromatic plants, including lavender, mint and curry plants, into their nests.
"We hypothesised that aromatic plants used by blue tits had some anti-parasite properties, because most of these plants, or close species of the same genus, are traditional Mediterranean plants with well-known medicinal properties," the BBC quoted Adele Mennerat, a biologist now at the University of Bergen in Norway, as saying.
Working with collaborators from France's National Centre of Scientific Research and the University of Toulouse, Mennerat initially tested whether these plants deterred blow fly larvae that commonly live in tit nests and feed on chicks' blood, significantly damaging their health.
"Despite repeated attempts we could never find any effect of these plants on blow fly infestation. So we tested the effects of these plants on the bacteria living on birds," Mennerat says.
Writing about their findings in the journal Oecologia, the researchers said that aromatic plants, including lavender (Lavandula stoechas), apple mint (Mentha suaveolens), the curry plant (Helichrysum itlaicum) and Achillea ligustica, significantly changed the composition of bacterial communities living on blue tit nestlings.
"They reduce the number of different bacterial species, and the total number of bacteria, especially on chicks that are most vulnerable because they are both highly infested by blow fly larvae and carry great amounts of bacteria on their skin," says Mennarat.
The researcher admitted that it was yet to be found out as to how volatile compounds produced by the aromatic plants kill the bacteria.
However, Mennerat said, blue tit chicks living in nests adorned with aromatic plants were found to grow faster and had a higher proportion of red blood cells, a strong indicator of a chick's future chances of survival after fledging.
Mennerat suspects that living in a disinfected nest enables the chicks to allocate less energy to their immune systems and more to growing physically.
"One of the most unexpected findings we got was that female blue tits display individual preferences in their use of aromatic plant species," she says.
"For example, in a territory with big bushes of lavender, for some reason blue tits at this site still collect mint that can only be found far away from their nests. We still don't know why and how blue tits have such individual preferences," she adds.
The researchers are also keen to discover how these personal aromatic preferences are passed on between birds.