California Gulls at Dungeness Spit - Photo: Bob Boekelheide
Wish they all could be California Gulls
by Bob Boekelheide
September 2021
In place of the former Bird Sightings column, Bob is exploring data from OPAS Community-Science Projects. If you are interested in local bird sightings, check out eBird at https://ebird.org/explore, then under "Explore Regions" enter Clallam or Jefferson County. Please join eBird and add your own sightings, as well.
One of the most overlooked bird migrations in the Pacific Northwest is happening right now, right on our doorstep. Hundreds of thousands of birds participate in this migration, but most people don't even notice. The birds aren't songbirds that migrate surreptitiously under the cover of darkness. The birds aren't shorebirds that hide out on beaches and mudflats, only visible with expensive optics. No, these birds are easy to see, bold and boisterous, flying right in front of our noses during broad daylight.
I'm talking, of course, about California Gulls (CAGU). The incredible post-breeding migration of CAGUs is one of the most unappreciated bird movements in the Pacific NW, perhaps because they are just "seagulls." This time of year CAGUs line coastal river mouths, spits, mudflats, beaches, log yards, breakwaters, and parking lots. They are scrappy little beggars that look askance at your lunch one moment, then become the main component of pelagic feeding flocks at the continental shelfbreak the next.
Adult California Gull in late August - Photo: Bob Boekelheide
Two OPAS community-science projects show the timing of CAGU migration very well. First, from 2014 to 2018, OPAS cooperated with North Olympic Salmon Coalition to count birds as part of the Three Crabs Restoration Project. Remember the old Three Crabs restaurant? Our goal was to see if the project caused any changes to bird populations using habitats near the mouth of Meadowbrook Creek, including birds on the mudflats visible from Three Crabs Beach. OPAS volunteers counted birds three times each month within 10-day periods, adjusting our counts for time of day, tides, and weather.
Figure 1 shows the monthly high counts of CAGUs roosting and feeding at Three Crabs during the four years from 2015 to 2018. Every year looks remarkably similar. CAGU numbers in Dungeness Bay start picking up in June and July, peak at several thousand in August and September, then quickly decline through October. By the time we hold our Sequim-Dungeness Christmas Bird Count in mid-December, they are long gone. For the entire 45-year history of the SDCBC, our record count for the whole Sequim-Dungeness area is only 22 CAGUs.
Another OPAS community-science project that clearly shows the post-breeding migration of CAGUs is our offshore surveys of birds within the Protection Island Aquatic Reserve (PIAR). The PIAR is an area of biological importance established by WDNR in the waters around Protection Island, from the mouths of Discovery and Sequim Bays to about 5 miles north of Protection Island. Since 2016, OPAS volunteers have cooperated with Port Townsend Marine Science Center and WDNR to do monthly boat surveys in the PIAR, covering a 25-mile route each time. We count birds within a 200-m wide transect, which we then use to calculate densities of birds within the Aquatic Reserve.
Just like at Three Crabs, the PIAR data (Figure 2) show that migrant CAGUs start arriving in June, peak in late summer, then quickly disappear through October and November. By multiplying the highest densities of CAGUs observed on our surveys (up to 80 CAGUs/sq km) by the total area of the PIAR (96.23 sq km), we can estimate that about 8000 CAGUs may occur on one day within the PIAR during peak passage in late summer.
It's curious that the peak densities in the PIAR show on the graph during August, whereas the peak numbers on the surveys at Three Crabs occur in September. I suspect this might be an artifact of our sampling, because we counted total numbers every 10 days at Three Crabs, but we only surveyed once per month at PIAR, usually near the middle of the month. This shows the danger of lumping data into human time periods we call "months," which does not apply to birds that live day to day.
Suffice it to say, the passage of CAGUs is miraculous. From June through October, the gulls move constantly through our area. We don't know how long individual birds stay in specific areas, but the movements of gulls at Three Crabs and Dungeness Spit suggest that they keep moving from east to west. The age composition of flocks changes as well during their migration. In early July, the CAGUs here are heavily weighted towards immature pre-breeders, mostly subadult birds that probably don't return all the way to nesting colonies. Adult birds predominate during peak passage in August and September, probably fresh from nesting. The very first fledglings from the nesting season appear in late July, then hatching-year birds steadily pick up during fall, sometimes outnumbering adults in September.
California Gulls at Dungeness Spit. The adult in the middle shows its brighter yellow bill with red and black feeding spots. The darker speckly birds, two to the right of the adult and one in front of the adult, are second-cycle immatures. The two on the left of the adult with gray wings and backs, along with dark tips to their bills, are third-cycle immatures. Photo: Bob Boekelheide
Where do the CAGUs come from and where are they going? CAGUs nest in the interior of western North American, nearly all on islands in big lakes. According to Birds of the World, six of the nine largest nesting colonies in the world are found at lakes in Alberta, to the east of the Canadian Rockies. Their nesting range extends from the Northwest Territories of Canada through Alberta, Manitoba, Montana, and the Dakotas, down to Great Salt Lake in Utah and Mono Lake in eastern California. The largest U.S. colony is typically at Great Salt Lake. Low water levels due to drought may seriously threaten CAGUs if their nesting islands stop being islands, making them accessible to terrestrial predators such as coyotes.
After nesting, CAGUs from inland colonies fly over the Rocky Mountains, then down the Columbia and Fraser Rivers to saltwater. Birds nesting at Mono Lake fly over the Sierra Nevada. California Gulls are renowned for their high-altitude flights, soaring over the high peaks with no problems. I remember sitting on mountaintops in Yosemite National Park and being amazed at flocks of CAGUs circling around in the sky at 13,000 ft, heading west after nesting at Mono Lake. The northern populations, including many from the big colonies in Alberta, apparently fly over the Rockies then down the Fraser River valley to the Salish Sea, heading straight towards the Strait of Juan de Fuca and our front door in Clallam County.
In late summer many years ago, I tried to do a California Gull/Clallam County Big Day, counting all the CAGUs I could find on only one day roosting at river mouths, harbors, and other sites in coastal Clallam County. Starting at Dungeness Bay and ending at Hobuck Beach, my one-day count was over 35,000 CAGU. I likely missed more than I saw, because I couldn't get to many roost sites and I didn't even make it to La Push. Regardless, the number of CAGUs passing Clallam County each summer certainly numbers in the hundreds of thousands. This is a significant portion of the world population, which Birds of the World estimates to be between 500,000 and one million.
Other places where you can see big numbers of CAGUs in western WA is at offshore feeding flocks, both in the Salish Sea and off the west coast of WA. In fact, CAGUs are often the most numerous components of these giant feeding flocks this time of year, not only in the eastern Strait of Juan de Fuca, but even at places like at the continental shelfbreak miles off the coastline. On one of our September pelagic boat trips to Swiftsure Bank, 15 mi west of Cape Flattery, we estimated a whopping 20,000 CAGU feeding and loafing in one area around the southern edges of the bank. There were probably many more. What are they eating in the feeding flocks? Small fish is the likely answer, possibly sandlance and herring.
California Gulls at Swiftsure Bank, 15 mi WNW of Cape Flattery. Nearly all the gulls in the photo are CAGUs, but not all. Can you identify the other gull species? Photo: Bob Boekelheide
What else do the CAGUs do while they're here? Other than eating all they can, one very important job in summer and fall is molting feathers. The juveniles don’t need to molt, because they already have brand new feathers. But all the other age classes go through heavy molt this time of year, replacing all their feathers all over their bodies. Piles of dropped gull feathers stack up on beaches and spits, providing a big hit of carbon and nitrogen into local biogeochemical cycles.
By November each year, the big numbers of CAGUs are gone. They mostly spend the winter in California, where they become one of the most abundant gull species throughout the state. From the Bay Area to the Central Valley to the Salton Sea, CAGUs line the fields, lawns, and beaches. On most Sequim-Dungeness Christmas Bird Counts we're lucky to tally even ten.
Curiously, there is no equivalent spring migration of CAGUs past Dungeness. It appears CAGUs mostly fly straight inland from California to their nesting areas in the interior of North America, without passing through the Strait of Juan de Fuca. The one exception is CAGUs can be found in good numbers at herring spawns in the Salish Sea in February and March, along with other gull species. Unfortunately, with the decline of herring in Dungeness and Sequim Bays, they don't stop here much anymore.
As all birders know, gull plumages can be confusing, so how do you know you're looking at a CAGU? First, focus on adults. During nesting, CAGU are fairly unique because the "feeding spot" near the tip of their bill is both black and red. They are medium sized - clearly smaller and with a thinner bill compared with our local-nesting Glaucous-winged Gulls, but larger and larger-billed than either Ring-billed or Mew (aka Short-billed) Gulls. A flashy CAGU breeding adult has medium-gray back and wings, yellow legs, and dark eyes.
This is the time -- go enjoy the wonder of the California Gull migration right now in Dungeness Bay.