Monitoring Western Snowy Plover Nests with Remote Surveillance Systems in San Francisco Bay, California

Abstract

Abstract The western snowy plover Charadrius nivosus nivosus is listed as threatened under the U.S. Endangered Species Act of 1973 due to long-term population declines related, in part, to nest predation and human disturbance. In San Francisco Bay, California, numbers of predators of western snowy plovers and the potential for recreation-based human disturbances have increased during the past few decades and will likely increase for the foreseeable future. In an attempt to increase the reproductive success of western snowy plovers, managers have dedicated considerable resources to management practices including predator removal and habitat enhancement projects in San Francisco Bay. The unequivocal identification of western snowy plover nest predators and information regarding the behavioral responses of nesting plovers to human disturbance would inform management practices for this species. Therefore, we examined the efficacy of using a digital video surveillance system to identify nest predators of western snowy plovers in former salt evaporation ponds in San Francisco Bay and to assess its potential for use in behavioral studies. This system was designed to minimize disturbance to nesting plovers and limit predator bias at breeding sites that had little or no cover to camouflage or protect the equipment. The system included a small camera with infrared lights placed approximately 20 m from nests and a continuously operating recording unit and power supply that was positioned up to 300 m from nests. The system could be deployed within 20 min, run continuously for up to 5 d, and data could be retrieved without disturbing nesting birds. During a 2-y study period, we recorded six species depredating plover eggs and chicks: red-tailed hawk Buteo jamaicensis, common raven Corvus corax, California gull Larus californicus, northern harrier Circus cyaneus, ruddy turnstone Arenaria interpres, and gray fox Urocyon cinereoargenteus. Our results suggest that this surveillance system was effective for identifying western snowy plover nest predators, and the presence of the camera did not influence nesting success of monitored nests. This system could be integrated into conservation programs intended to improve reproductive success of this species and could be useful for conducting behavioral studies of western snowy plovers and other species.