Why bird do this?

Woodcocks and a few other species have mastered this bounce-step in order to trick worms and other Arthropoda into thinking rain has come by sending rhythmic vibrations through the soil as they walk. Many bugs surface during heavy rainfall to avoid drowning, hence why the sidewalks are always littered with earthworms during and after a storm.

If you walk with rhythm you will attract the worm.

No fucking way