Beach nesting waterbirds are among the most vulnerable groups of birds that are threatened by climate change, habitat loss, predation, and human disturbance. To improve conservation management strategies, causes of nest failure for ground-nesting waterbirds and effectiveness of mammalian predator control were investigated. Changes in breeding population size and hatching success of Royal (Thalasseus maximus) and Sandwich (T. sandvicensis) terns were evaluated based on pre-mammalian removal (2012-2014) vs. post-mammalian removal (2015-2016) breeding data. Video systems were used at colonies in 2015 and 2016 to determine causes of nest failure. No differences in breeding parameters were found between removal periods, however video data confirmed nest predation as the primary cause of nest failure. Laughing Gull (Leucophaeus atricilla) was the top predator and accounted for 63% of all detected predation events. In 2015, video monitoring identified a novel predator, exotic and invasive nutria (Myocastor coypus), that were responsible for 43% of predation events. In 2016, following a 280% increase in nutria removal from 2015, no nutria predation was recorded.