Observing yellowlegs through the years, I have noted that they become very territorial in protecting their feeding area. Yellowlegs have put up an aggressive stance against another yellowlegs that is in their location. As the yellowlegs advances toward the second bird, many times the second bird just takes off. Other times there will be a battle. Therefore, if you see a pier of yellowlegs near each other keep observing and you may be able to get interesting images. I obtained my pictures on the mud flats at Bombay Hook National Wildlife Refuge.