Wintering shorebird abundance on Tomales Bay, Marin County, California, USA, 1989-2018

Contains data on abundance of shorebirds on Tomales Bay, Marin County, CA, USA from Nov 1989 through Feb 2019. Data were collected as part of an ongoing, long-term monitoring project. Surveys covered all appropriate shorebird habitat on Tomales Bay, and counted all individual shorebirds in those areas.Contact nils.warnock@egret.org or cgrc@egret.org for additional information.Study area and monitoring Wintering shorebirds were monitored at Tomales Bay, Marin Co., California from Nov 1989 to Feb 2019. Surveys covered all shorebird habitat along Tomales Bay and counts were standardized on tide level and conducted on rising tides between 0.76 and 1.22 m above mean lower low water. Distinct survey sites were established that could be simultaneously surveyed in approximately 90 minutes by teams of 1-3 observers using binoculars and scopes (mean observers per site = 1.6; mean observers/survey = 20.2, range = 10-42 observers/survey). Rarely, count teams had more than one count area; this happened only with smaller, adjacent areas. All shorebirds and raptors seen were counted, and counters attempted to identify all individual birds to species. Observations were occasionally pooled into species groups including the golden plovers (Pacific Golden-Plover Pluvialis fulva and American Golden-Plover P. dominica), dowitchers (Short-billed Dowitcher Limnodromus griseus and Long-billed Dowitcher L. scolopaceous) and yellowlegs (Greater Yellowleg Tringa melanoleuca and Lesser Yellowleg T. flavipes) because of the difficulty in separating these species in the field. Intermittently (e.g. when visibility was poor or distances were far), small shorebirds (Dunlin, Least Sandpiper Calidris minutilla, Sanderling, and Western Sandpiper) were pooled by counters