All three of Britain’s breeding wagtails – the pied, grey and yellow – are characterised by their wagging tails, which are frequently ‘pumped’ up and down.
A number of theories have been put forward to explain this behaviour, including the suggestions that tail-wagging helps a bird to capture its insect prey by flushing it out; that it is used to signal social status; and that it indicates an individual’s state of alertness to potential predators nearby.
However, because tail-wagging is also associated with activities such as preening, it is unlikely to be simply a means of flushing prey from cover.
Similarly, since the behaviour is seen in all age and sex classes, it probably doesn’t have a distinctly social function, particularly given that the frequency of wagging does not seem to increase when individuals interact with one another.
Evidence does, however, support the notion that tail-wagging is used to portray a wagtail’s level of vigilance.
Tail-flicking and tail-pumping are also known from a number of other bird species (including the moorhen),
with some studies revealing that the frequency of tail movement increases in the presence of predators, thereby demonstrating the role it plays in communicating the bird’s awareness.
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