The Science of Sustainability

Get Your Binoculars, It's Raptor Viewing Time

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Volunteers from the Golden Gate Raptor Observatory collect data on Hawk Hill in the Marin Headlands. Photo by Jessica Weinberg, courtesy of GGRO.

The raptor migration over the Marin Headlands is one of fall’s best, limited-engagement spectacles.  Every September a highly-trained cadre of volunteers from the Golden Gate Raptor Observatory (GGRO) mounts Hawk Hill with binoculars and spotting scopes to document the passage of raptors as they gather to ride the rising warm air over the headlands before gliding across the mouth of the Bay.  Reluctant to waste energy flying over open water, they “kettle” in flocks of mixed raptors of every kind to rise high in the air.  While they’re rising in lazy circles, the hawk watchers busily identify as many as they can and count individuals.  Some of the daily hawk counts from dawn to dusk (or inundation by thick fog) reach over 700 individuals.  Their work has contributed so much knowledge about the ecology of raptors.  Similar counts take place around the US with famous spots on the East Coast and in Texas.

A Cooper's hawk is captured and banded before being released for future tracking. Photo by Jessica Weinberg, courtesy of GGRO.

GGRO volunteers also capture individual birds to tag or attach radio transmitters to track their migration path.  A broad-winged hawk merited special attention this year. The individual, which the team named named Marathon, is unusual. The species is primarily found across Canada and throughout the eastern US during the breeding season, then most of them travel south to the tropical forests in Central and South America averaging 7,000 miles at 100 miles per day. They’re rarely seen on the West Coast, but regularly show up over Hawk Hill in small numbers during fall migration. You can track Marathon’s southward migration flight on GGRO’s blog. The other long-distance migrants seen in eastern Contra Costa County and the Central Valley are Swainson’s hawks. Their long-distance migration range spans from northern Canada to Argentina, averaging about 14,000 miles accomplished over the course of two months each way in spring and fall.

The next week or two should still be good for raptor viewing at Hawk Hill. Volunteers will be available to help you view and identify hawks overhead (with the exception of Oct. 6th and 7th during Fleet Week when even the volunteers won't brave the crowds!). If you’re interested in year-round raptor viewing and would like to be part of a team, you can also join EBRPD naturalist Mike Moran in eastern Contra Costa County. His fourth Thursday morning “Raptor Baseline” program counts and tracks raptors in this rich habitat area. No previous experience is necessary.

A small "kettle" of raptors rises on thermals near San Francisco. Photo by Jessica Weinberg, courtesy of GGRO

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Sharol Nelson-Embry

About the Author ()

Sharol Nelson-Embry is the Supervising Naturalist at the Crab Cove Visitor Center & Aquarium on San Francisco Bay in Alameda. Crab Cove is part of the East Bay Regional Park District, one of the largest and oldest regional park agencies in the nation. She graduated from Cal Poly, San Luis Obispo with a degree in Natural Resources Management and an epiphany that connecting kids with nature was her destiny. She's been rooted in the Bay Area since 1991 after working at nature centers and outdoor science schools around our fair state. She loves the great variety of habitats stretching from the Bay shoreline to the redwoods, lakes, and hills. Sharol enjoys connecting people to nature with articles in local newspapers and online forums. Read her previous contributions to QUEST, a project dedicated to exploring the Science of Sustainability.
  • Cal Walters

    September & October are great birding times in the Bay Area. You can chase migrants til the cows come home! Great work being done up at GGRO, PRBO and other sites. I took a lunch break yesterday and chased a Northern Parula yesterday – and there were 7 other birders already there.

  • Sue

    Sharol, nice write up ….. great pics …. You perhaps do not know by now that on Saturday, the 29th they banded and outfitted a 2nd Broad-winged for the telemetry team …. tracking is happening right now ….. See you soon Sue T4B

  • Sharol

    Sue, it was a sad ending for the 2nd Broad-winged juvenile (see link to GGRO blog above), but a record-breaking number of Broad-winged Hawks have come through the Bay Area this year: Sept. 27, 295 BWHA, Sept. 29, 133 BWHA, and Sept. 30, 103. It makes me wonder if we'll see similar numbers next year. Are some of the BWHA changing their migration path? Could it be due to the drought in the mid-section of our country? More to come!