Wagtail
/ˈwæɡteɪl/
Definition 1 of 2
Pro Tip 1/3Bird Behavior
The wagtail gets its name because it wags its tail; a behavior often observed by birdwatchers. 
The wagtail is named aptly, as it kept wagging its tail while searching for insects.
Pro Tip 2/3Birdwatching Term
Bird enthusiasts use 'wagtail' to identify the bird species; it's a handy term for birdwatching activities. 
At the birdwatching event, we learned to recognize a wagtail by its distinctive tail movement.
Pro Tip 3/3Native Habitats
Wagtails are often found near water, so the term may evoke imagery of rivers, lakes, or wetlands. 
Walking along the stream, I saw a wagtail fluttering around the reeds.