SANTA CRUZ — Marine life and seabirds of all kinds, from pelicans and gulls to migrating terns and shearwaters, have gathered off the coast in recent weeks — fluttering, screeching, swirling and diving, feathers flying in a feeding frenzy as each creature fights for its share of the anchovies floating beneath the ocean’s surface.

The spectacle is an anticipated event in summer for those who want to observe and admire the flocking seabirds, such as the long-distance, deep-diving Sooty Shearwaters, that migrate en masse from east to west along the Santa Cruz coast.

“It’s remarkable that we have large numbers of sooty doves in our bay every year,” said Josh Adams, a wildlife biologist at the United States Geological Survey’s Western Ecological Research Center. “Some years it may seem like there are more of them, or they’re here longer, or they disappear sooner, but it’s hard to get a handle on the numbers because they travel in such large flocks.”

Adams noted that tens of thousands of sooty shearwaters can be seen circling and moving off the coast of Santa Cruz. Although the birds are native to New Zealand, they travel to California and Monterey Bay during the summer months to molt and fatten before returning home.

“When they come to this part of the world, their diet is known to change from juvenile rockfish and krill to a diet consisting primarily of anchovies in late summer,” Adams said. “The anchovies are the real fuel at the end of their migration. Their protein needs fluctuate throughout the summer and by the time they get here, they are exhausted from the journey from New Zealand and Chile and need protein to replace their feathers, which are made of protein.”

Anyone on the water in the eye of a seabird storm may notice that sooty divers have great difficulty taking off again after diving to feed on anchovies.

“There are several things at play here,” Adams said. “They eat so much food relative to their body mass that they have to use a lot more force to get out of the water. They’re also in their first molt, so they have less wing area. They’re cool because they’re designed to fly both underwater and long distances over the ocean. The molt affects their ability to get up and fly quickly, especially when they have a belly full of anchovies.”

For years, the actual diving depth and length of time sooty shearwaters can stay underwater were unclear statistics until Scott Shaffer, a professor of ecology and evolution at San Jose State, and other researchers used archival markers to measure the birds’ habits in the 2000s, when Shaffer was a postdoctoral researcher at UC Santa Cruz.

“We knew they could dive to depths of 60 meters because some researchers had used these capillary depth gauges,” said Shaffer. “These only indicate the maximum depth. They do not tell us how long or how often they dived that deep. When we put our time-depth recorders on the animals, we were able to get a lot more information about their diving patterns. Their typical diving depths are somewhere between 9 and 14 meters.”

Shaffer and the researchers used the information they gathered to co-author a paper on the habits of the sooty seabird, which he studied in California and New Zealand. He mentioned that the sooty shearwater’s migratory habits between the Northern and Southern Hemispheres allow it to experience an endless summer.

“It’s pretty extraordinary to watch the migrations of these birds, and the idea that they live in a perpetual summer is really fitting,” Shaffer said. “They can get the best of both worlds by crossing the equator and coming here.”

Shaffer said that before tagging the sooty grebes, it was assumed that they flew in a giant circular pattern because the birds typically appear in California, Alaska and Japan before returning to New Zealand. But researchers found that the pattern they followed was more like a figure eight.

“The prevailing view was that they made this wide berth around the Pacific, but we were able to show that that is not actually the case,” said Shaffer. “The birds usually select an area in the North Pacific and, as far as we know, stay there.”

Anchovies are visible in the vascular system of a pelican’s throat pouch as the bird forages for food near the dock on Thursday. (Shmuel Thaler – Santa Cruz Sentinel)

Shearwaters, gulls and terns populate the shores of Cowell Beach this week. (Shmuel Thaler – Santa Cruz Sentinel)

This week, Monterey Bay near the Santa Cruz Municipal Wharf is experiencing a feeding frenzy of pelicans, shearwaters, gulls and terns. (Shmuel Thaler – Santa Cruz Sentinel)

A family at Main Beach sits in the front row on Thursday and can witness the feeding frenzy. (Shmuel Thaler – Santa Cruz Sentinel)

Paddlers are surrounded by a feeding frenzy of pelicans, shearwaters, gulls and terns near Cowell Beach on Thursday. (Shmuel Thaler – Santa Cruz Sentinel)

A pelican takes off with an anchovy in its beak. (Shmuel Thaler – Santa Cruz Sentinel)

A pelican dives for anchovies near Cowell Beach on Thursday. (Shmuel Thaler – Santa Cruz Sentinel)

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Anchovies are visible in the vascular system of a pelican’s throat pouch as the bird forages for food near the dock on Thursday. (Shmuel Thaler – Santa Cruz Sentinel)

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