California Gulls are the most common gull species in the South San Francisco Bay, especially during the breeding season. Since 1980, San Francisco Bay Bird Observatory biologists have monitored California Gull populations in the South Bay, and documented a dramatic increase from less than 50 breeding birds in 1980 to over 45,000 breeding gulls in 2010. California Gulls may have negative effects on other ground-nesting birds and have been found to be significant predators on American Avocet, Black-necked Stilt and Western Snowy Plover eggs and chicks.
Recently, gull numbers have been decreasing in the Bay.
The former South San Francisco Bay salt pond where 23,000 California Gulls nested until 2010 (pond A6) was restored to tidal action in December 2010. Many of the gulls presumably displaced by the restoration moved to new nesting colonies in Alviso. This breeding season, Bird Observatory biologists and the Don Edwards San Francisco Bay National Wildlife Refuge will determine if and where displaced California Gulls establish new colonies. We have banded over 1000 California Gulls at A6 in order to track their movements and need your help finding new colonies and banded gulls!
Report California Gull Nesting Colonies and Banded Gulls
We need your help locating new gull colonies. Gulls often nest on islands, piers and levees. Breeding colony activity includes carrying nesting material or delivering food to mates or young. If you think you've found a new colony, please record the following: Location seen, date seen, and approximate number of gulls.
Banded Gulls: The San Francisco Bay Bird Observatory has banded over 10,400 California Gulls since 1983. California Gulls are banded with one of three possible combinations: 1) a silver USGS band on one leg and a and color-band on the other, 2) a single silver USGS band, or 3) silver USGS band and a field-readable band that is black with three large white numbers. The field-readable bands can be read from a distance.
If you see a banded California Gull, please record the band colors and numbers (if you can read them) and the location of the gulls.
Please send all reports and any additional information to Max Tarjan, Waterbird Program Director at firstname.lastname@example.org.