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By Robyn Smith, GGRO Intern
For many visitors to the Marin Headlands, the main draw to Rodeo Lagoon may be a willow-lined walk to the beach, a picnic by the historic buildings of Fort Cronkhite, or a chance to watch some interesting wildlife.
In August, the east end of Rodeo Lagoon provides a more critical resource for a slender, migratory shorebird called the Red-necked Phalarope. An 8-inch, white-bellied bird with a gray back, phalaropes would easily blend into the whitecaps of the waves if not for its striking black cap and facial mask.
The Red-necked Phalaropes use the lagoon as a feeding station, gobbling up tiny crustaceans and insects as fast as they can. They feed by swimming in tight circles and dabbling at the water’s surface with their slender, long bills.
Although Red-necked Phalaropes appear delicate, they undertake one of the longest North American migrations of any bird, breeding in the high Arctic tundra and wintering off the coast of western South America. Since they must cover such a long distance, they do not stay in stopover sites like Rodeo Lagoon for very long.
Thus, the window of opportunity to see a Red-necked Phalarope up close and personal is pretty limited. The birds usually show up during the last week in July and stay halfway into August. For many Bay Area birders, this short window may be the best opportunity to see this species.
Particularly interesting to ecologists is the fact that Phalaropes are one of the only bird species of which females are bigger and more brightly colored than males. The females compete with each other to impress the males, and often mate with more than one. This type of mating system, known as polyandry, is extremely rare in birds. All three species of phalarope practice polyandry.
Ornithologists believe that since their migration is so long and arduous, the female phalaropes cannot afford to invest more than a minimal amount in the reproductive cycle. And because egg-laying is such a physical stress on the female’s body, the brunt of the egg- and chick-care falls to the males. The female can then freely seek other mates and spend time feeding and preparing for her long journey.
So the next time you visit the Marin Headlands in August, make sure to check out the east end of the lagoon—you don’t want to miss an opportunity to see these fascinating phalaropes in action!