50 Years of Counting Birds on Tomales Bay

The double-crested cormorant population has grown on Tomales Bay, especially since the species began nesting on Hog Island in 2001.

© paloma / Photo 5436140 / 11-4-2016 / iNaturalist.org / CC BY

February 2020 - Tomales Bay is globally significant for waterbirds because an estimated 35,000 of them spend their winters here, often migrating from distant destinations in the northern latitudes to do so. Consequently, Tomales Bay was designated a Ramsar Wetland of International Importance in 2002. One of the longest continuous studies of waterbirds on Tomales Bay is the Point Reyes Christmas Bird Count (CBC), which became an annual event starting in 1970. The 50th Point Reyes CBC, sponsored by the Marin Audubon Society and Point Blue Conservation Science, took place on December 14, 2019. Several National Park Service (NPS) staff volunteered at sites throughout Point Reyes National Seashore. On Tomales Bay, volunteers carried out surveys aboard three boats.

Volunteer and NPS alumnus Sarah Allen describes the scene on board one of the boats: “The first bird entered on the data sheet was an adult bald eagle, which got all of us energized for the day. The wind-whipped waves challenged our observations, as we rocked about with binoculars unsteadily pressed to our eyes. But tucked in coves along the west shore, we feasted on an amazing diversity with loons, buffleheads, black brant and an occasional red-necked grebe. The herring were running with the high tide and we skirted an enormous feeding flock of cormorants, gulls, loons, grebes, flanked by a dozen or more harbor seals. Scattered along the shoreline, kingfishers, egrets and herons picked off herring that ventured closer in.”

The good news is that many species’ populations have trended up at Tomales Bay over the past 50 years. The double-crested cormorant population has grown, especially since the species began nesting on Hog Island in 2001. Black brant numbers have risen as they have been benefiting from expanding eelgrass beds. Bufflehead ducks have been on the rise as well, with 13,499 counted during the 2006 Point Reyes CBC, the highest total ever documented by CBC in North America! Other species, though, have decreased dramatically. White-winged scoters, which numbered over 600 in 1989, now number fewer than 50. Audubon Canyon Ranch surveys have corroborated these general trends.

Learn more about the history of the Point Reyes CBC from this account by naturalist David Wimpfheimer, or visit Audubon.org for more CBC information and results.

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