Since the early 1990s, a colony of Caspian terns - the world's largest terns - has bred on an island in the Reserve's restored South Marsh area. The colony has suffered various disasters over the years, from pesticide contamination during the 1995 floods to raccoon predation in 2000, but recently has had excellent reproductive success. We monitor the number of breeding pairs and track fledging success. In addition, we patrol the area to try to discourage predators from attacking the colony.