Lots of leg bands. From the SBD Facebook page: "The birds get a set of color bands and a metal USFWS band as chicks, and then if they return and nest they are recaptured and given a new set of color bands, the metal band stays the same. Each breeding adult has a unique color combination on their legs that help plover monitors identify each bird in the field with the use of optics. A banded adult keeps its bands for life."