Moss Landing Sooty Shearwater Bird Flock

The birds resting on this water in Monterey Bay are likely sooty shearwaters, and many of them nest on the far side of the planet. When Scott Shaffer and colleagues fitted geolocator tags to birds from New Zealand colonies, the tracks came back as a figure eight looped across the entire Pacific, a round trip averaging 64,037 kilometers with daily transits reaching about 910 kilometers. At the time of publication in 2006 it was the longest animal migration ever recorded with electronic tags. California is one stop on that circuit, and the birds bobbing here may be only weeks out from the Southern Hemisphere.

Gatherings like this one were once far more common. Sooty shearwaters were the most numerous seabird in the California Current, with roughly 5 million estimated off the coast in the late 1970s, and then three independent survey series recorded a decline of about 90 percent between 1987 and 1994, tracking a rise in sea surface temperature. What keeps the story unsettled is that counts at those same New Zealand breeding colonies fell far more gently, around 1 percent a year, so researchers still argue over how much was true population loss and how much was birds shifting to feeding grounds off Japan and Alaska. The IUCN lists the species as Near Threatened, which makes a flock this size worth watching closely.