THE ANIMAL FILES

White wagtail

Motacilla alba

A wagging tail is obvious; its purpose is less settled.

White wagtails search for small invertebrates while frequently wagging their tails. Their black, white and grey patterns vary with geography and season. Several functions have been proposed for tail wagging, but no single explanation is settled.[1]

Follow the evidence ↓
White wagtail
Image: Jac. Janssen from BAARLO LB, NL · Commons · CC BY 2.0
The moving tail
Tail wagging is frequent.[1]
Insects across habitats
Terrestrial and aquatic insects supply prey.[1]
Patterns change
Back and throat colours can change with moult.[1]

The moving tail

Tail wagging has been proposed to flush prey, signal submissiveness to other wagtails, or show vigilance to predators. These are alternative explanations; the function is not fully understood.[1]

Insects across habitats

Beetles, flies and other invertebrates form the main food, with exact composition varying by location. In resident populations in parts of the range, insect feeding can continue through winter rather than requiring a complete switch to seeds.[1]

Patterns change

Subspecies differ in head, back and wing patterns, and seasonal moult changes some dark-backed or dark-throated forms. Wintering areas can contain several forms together. An identification based on one colour patch needs to account for the bird's season and geographical context.[1]

A COMMON MIX-UP

Is prey flushing the proven reason for every tail wag?

No. That is one proposed explanation among several.[1]

TRY A LITTLE REASONING

Why could winter throat colour mislead someone using a breeding illustration?

Reveal the explanation

Seasonal moult changes some head and throat patterns, so the same form can look different across the year.[1]

Sources & editorial notes

Adapted and translated from the cited Wikipedia revisions, with source-linked reasoning. Image credit and licence are listed separately above.

Adapted and translated from Wikipedia contributors; exact revisions are linked below. CC BY-SA 4.0

  1. Wikipedia contributors — White wagtail (cited revision)
  2. NCBI Taxonomy — Motacilla alba

Last fact check:

One discovery leads to another

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