91É«ÇéƬ

Why do wagtails wag their tails? They would be well camouflaged, if it weren’t for their constantly moving tails.

Ìý

Chris Daniel Glan Conwy, Conwy, UK

On a walk the other day, I spent several minutes watching a yellow wagtail darting, its tail bobbing continuously. I wondered about the purpose of this behaviour, then I came home and opened the edition of New Scientist with this very question.

Many bird species move their tails, either bobbing them up and down like the European wagtails or waving them from side to side like the willie wagtail in Australia. Many other birds also exhibit tail-flashing or flicking behaviour.

The wagtail’s eponymous movement is thought to be an evolutionary adaptation to enhance feeding by flushing out hidden insects that it feeds on. has shown that tail-flicking is a positive predictor of foraging performance in a juvenile species of warbler. It may also be used as a sign of submission to other birds of the same species and as a marker of alertness to potential predators to discourage pursuit, in a similar way to the tail-flagging behaviour of deer.

My limited observation of wagtails is that the rhythmic movement is almost continuous, whether or not the bird is feeding, so more than one of these explanations for it may be true. The movement also appears to be involuntary, superimposed on other activities such as walking and preening.

Ìý

Garry Trethewey Cherryville, South Australia

All animals must negotiate a lot of conflicting needs. Being unnoticed is the best way to avoid being eaten. But to be unnoticed also entails not venturing out for food, not seeking or attracting mates and not proclaiming ownership of territory.

Many animals are loud, colourful and display prominently. The risk is offset by the benefits this entails, and their ability to escape danger in other ways.

Ìý

Mike Follows Sutton Coldfield, West Midlands, UK

The most likely explanation is that they wag their tails to give the impression that they are alert, to encourage predators to look elsewhere for an easier meal.

It is unlikely that the wagging is meant to attract a mate, as even juvenile birds do it, which would be a waste of energy. Also, the frequency or amplitude of wagging doesn’t depend on the proximity of potential mates.

There is speculation that the wagging tail flushes out insects, but this seems unlikely as surely other species would also have evolved this trait.

Ìý

To answer this question – or ask a new one – email lastword@newscientist.com.

Questions should be scientific enquiries about everyday phenomena, and both questions and answers should be concise. We reserve the right to edit items for clarity and style. Please include a postal address, daytime telephone number and email address.

91É«ÇéƬ retains total editorial control over the published content and reserves all rights to reuse question and answer material that has been submitted by readers in any medium or in any format.

Terms and conditions apply.