Tail Waggers

I found these curious looking birds in the canal by the dam, they were running around the semi-dry canal looking for food and ever so often they would wag their tails. They were also extremely hard to approach and they moved around too much.
These small graceful yellow and green birds are yellow wagtails. According to what I could find, they spend much time walking or running on the ground. As its name implies, it wags its tail from time to time.