Shorebird monitoring plays a crucial role in guiding conservation priorities. Dedicated monitoring efforts can identify critical habitat areas and provide the evidence to justify their protection. But the need for these monitoring efforts doesn’t end when a site receives recognition as a key site for shorebirds. Shorebird numbers can change over time, as can our knowledge and understanding of how shorebirds are using a site.
When the Humboldt Bay Complex on the coast of northern California joined WHSRN in 1998, it was designated as a Site of International Importance based on surveys from the early 1990s that documented more than 100,000 shorebirds using Humboldt Bay. In spring 2018, a bay-wide survey revealed that more than 500,000 shorebirds used Humboldt Bay during spring migration alone – a number five times greater than was previously estimated almost a quarter century ago.
Large flocks of shorebirds on Humboldt Bay during the spring 2018 surveys. Photos: Kellie Brown/Humboldt State University.
This coordinated survey effort was led by Humboldt State University shorebird ecologist Dr. Mark Colwell and California Audubon, with the support of the local Redwood Region Audubon Society. The team of biologists, students, and local birders conducted four surveys, 14 days apart, over 46 days. Their findings were published in the August 2018 issue of Wader Study, documenting that Humboldt Bay surpasses the 500,000 bird threshold and therefore qualifies as a WHSRN Site of Hemispheric Importance.
Humboldt Bay is the second largest estuary in California, providing a vast intertidal zone for foraging shorebirds. One of the primary reasons the Bay attracts so many shorebirds is its diverse array of habitats, from the invertebrate-rich mudflats to salt marsh, rocky intertidal, and seasonally flooded agricultural fields, which together provide reliable food resources for non-breeding shorebirds year-round.
What does it look like to see thousands and thousands of shorebirds in flight? Audubon California’s Khara Strum captured this video of large flocks of migratory shorebirds during the spring 2018 surveys at Humboldt Bay. Video: Khara Strum.
The 2018 surveys documented 26 shorebird species using the Bay and surrounding habitats. This included local breeders (such as Black Oystercatcher Haematopus bachmani and Snowy Plover Charadrius nivosus), as well as medium-distance migrants departing to interior breeding grounds on the Great Basin and prairies (such as Long-billed Curlew Numenius americanus and Willet Tringa semipalmata). The most abundant species, however, were long-distance migrants using Humboldt Bay as an essential stopover near the end of their journey from South America to breeding grounds in the Arctic. Western Sandpiper (Calidris mauri) was most numerous, followed by Dunlin (Calidris alpina). Colwell and his team used multiple, coordinated surveys to estimate that 313,750 – 536,750 Western Sandpipers were present at Humboldt Bay during a two-week period. Combined with maximum counts of other species, Humboldt Bay now has the monitoring data to show it hosts half a million shorebirds during spring migration alone.
Dr. Mark Colwell and his students from Humboldt State University counting shorebirds during the surveys. Photos: Kellie Brown/Humboldt State University.
The WHSRN Executive Office is pleased to announce that the Humboldt Bay Complex has been officially upgraded to a Site of Hemispheric Importance, thanks to this comprehensive survey effort and the collaboration of federal, state, local, tribal, and private partners to conserve this site. Please join us in congratulating Humboldt Bay on this achievement!
Cover Photo: Mixed flock of shorebirds at Humboldt Bay. Photo: Kellie Brown/Humboldt State University.
