We are lucky in Santa Cruz to be visited annually by sooty shearwaters (Puffinus griseus) as they make their spectacular circum-global migration of 40,000 miles: the longest recorded migration of any bird. Each year, they spend about 5 months breeding and rearing their young and the rest of the year they are migrating!

All sooty shearwaters breed on small islands in the south Pacific and south Atlantic oceans, beginning in October. Their population is estimated at well over 20 million. They incubate their young for 2 months, and raise their chicks for 3 months. They then fly north up the western side of the Pacific and Atlantic oceans in March–May. They reach sub-Arctic waters in June–July where they cross from west to east and return south down the eastern side of the Pacific or Atlantic ocean in September–October. All to arrive back at their breeding colonies and start the process over again.

Amazingly, they do not migrate as a flock, but rather as single individuals. They associate in groups only as the opportunity arises. When they are here you can see them stream by in what seems like an endless chain.

Research Brings Understanding

It was once thought that the migration was a fairly neat figure eight, with each bird covering the entire Pacific Basin from the Alaska area to the Antarctic. Now, thanks to electronic tagging research done in the mid-2000s, we know this is not true. Instead, individual birds go to either, Japan, Alaska or California and stay there until it is time to return south to breed.

This work also shows that the birds that travel to different regions do not represent distinct shearwater populations; two birds from the same nest can end up going to opposite sides of the Pacific, and birds from different breeding colonies can end up in the same place.

The Name Fits

The “sooty” part of the name is appropriate as the entire bird is a dusty, dark ash-gray color. They have long narrow wings with a silver sheen on the under-wing. The bill is also dark and has what looks like two short pieces of soda straw attached to the top near the head. These “straws” are highly sensitive to the smell of fish, squid, and krill: their main food. The “shearwater” part of the name comes from their flying style: a few fast flaps followed by a stiff glide just inches above the water.

Feeding Frenzy

If you are lucky, you might see them encounter a school of fish. It is quite a sight to see hundreds, perhaps thousands, of shearwaters crash-diving into the water. They may be joined by pelicans, cormorants, terns, gulls, and even sea lions. The water looks as though it’s boiling from the activity that goes on until the food is decimated.

If food isn’t near the surface, electronic tags on shearwaters have shown that they often dive up to 50 feet, while they are capable of diving to well over 200 feet.

Conservation

In spite of the shearwater population being over 20 million, there is concern because the numbers are declining. During the last 20 years the number of sooty shearwaters on the California coast has declined 90%. Reasons for this are many. A nesting pair hatches only a single chick per year, and the birds do not breed until about 8 years of age, which is unusually old for birds.

Their long migration pattern makes them susceptible to predation and bad weather anywhere along the migration route. They are often killed by modern fishing practices because they dive for freshly baited longline hooks and get caught in trawl nets. More research on their physiology, mating, and migration is essential to ensure their long-term survival.

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This piece is part of the Marine Life Guide. Download the free app with many tours of the Santa Cruz area and beyond.