biology – Bean Thinking

blue tits, mint water, mint infusion, mint leaves in water — Mint in a glass of water. Do other species appreciate a mint aroma too?

Very often, in a café, there will be a jug of mint infused water sitting in a corner, offered as a complimentary accompaniment to the coffee. A fragrant way of ‘refreshing our palate’. Mint is one of many aromatic plants that we use to scent our rooms or freshen our breath. But are we the only species that uses mint and similar aromatics such as lavender in this way? Do other animals appreciate the aroma that a freshly plucked mint leaf can provide?

A few weeks ago (in mid-spring in the northern hemisphere), I noticed some odd bird behaviour going on just outside the window. A blue tit (Cyanistes caeruleus) had landed on the edge of a pot of mint and was busy tearing leaves off the plant that was growing just outside. We watched as the bird hopped around to the other side of the pot, tearing off the younger, fresher leaves. What on earth was it up to?

the blue tits didn't get this one — A sprig of mint growing in a pot.

A quick use of duckduckgo (or google if you’d prefer), revealed a surprising answer (or at least further questions) to this odd behaviour. It would appear that blue tits have been observed to pick mint, lavender and curry plant leaves and use them to line their nest. Moreover, individual blue tits have a preference for different plants. Some females (it appears to be the female that collects the leaves) prefer mint, some lavender, and presumably some prefer curry. There is even a video from “Springwatch” that filmed this behaviour in a blue tit nest a few years ago (link is here). Similar behaviour has been observed in some other bird species such as the Starling (Sturnus vulgaris) but not in other, related bird species such as coal tits or great tits. So what could be driving this behaviour, is it, as the BBC said in its headline “aromatherapy”?

This image is copyrighted gardensafari.net — Does this blue tit prefer mint or lavender?
Image used with permission and © Gardensafari.net (thanks)

According to research, in fragranced nests, the number of bacteria/pathogens on the chicks was significantly reduced compared with non-scented nests. The chicks also seemed healthier, not only did they have a higher red blood cell count, they grew faster. What remains unclear is the reason that this should be so. Is it that the mint is anti-bacterial? Or is it, as suggested in the programme Springwatch, that the smell can perhaps relax the immune system of the birds allowing them to “put more effort into their growth”. Moreover, how did the birds first know how to pick these plants? How did this behaviour spread?

There is always a risk that we anthropomorphise other animals and consider that they appreciate aromatherapy when they are not doing so. There is however an alternative risk that we reduce animals almost to biological automata that manifest different behaviours purely for the biological advantage it gives them (as if they know that in advance). These questions are too far outside my ‘specialist’ area, for me to attempt to consider on Bean Thinking. However, as an ‘interested observer’ I can still appreciate and wonder at the interesting sights that five minutes spent observing our surroundings can provide. I will also enjoy the feeling it brings to know that we are sharing the mint on the window sill with the blue tits and their chicks.

Have you ever observed similar behaviour by birds in your neighbourhood? What birds around the world share our preference for mint? Comments are always welcome either here or on Facebook or Twitter.