Shearwaters Make a Great Showing on Outer Cape

Aug 23, 2017

Shoreline swarms of seabirds known as shearwaters have long-time Cape birders searching their vocabularies for superlatives in recent weeks. If you’ve been on a whale watch recently, especially out of Provincetown, you may also have noticed the impressive shearwater flocks blanketing the in-shore waters along both Long Point and Race Point.

Many thousands of these normally open-ocean seabirds have been hugging certain beaches, causing some seasoned but normally understated local birders to utter words like “unprecedented.”

 

 


If you went on a whale watch that didn’t get close to the Provincetown shoreline, you may not have seen any shearwaters, and the blame lies with the whales, or maybe with the fish the whales are feeding on. Humpback Whales are those charismatic, flipper flapping drivers of the local whale watching economy, and when they feed at the surface it creates a bonanza for seabirds who are able to literally snatch fish out of the gulping mouths of the whales. But when the bait fish, mainly sand lances, are sticking to the bottom, the whales feed on the bottom, and there are no leftover fish available for the birds at the surface.

Luckily for the birds, huge schools of another bait fish, known locally as peanut bunker, have been concentrating along the beaches of Provincetown. Peanut bunker are just the juvenile form of a herring relative known as menhaden, and are eaten by everything from stripers to mackerel to birds. As a result of this baitfish bonanza, tens of thousands of shearwaters were drawn in to ankle-deep water at Race Point. In most parts of the world, shearwaters are denizens of deep offshore waters, visible only from boats. So the opportunity to literally wade among them was a memorable one for a few lucky birders.

Great Shearwaters
Credit Mark Faherty

We have four species of shearwater in Massachusetts, and they come from several far-flung corners of the globe to be here. Great and Sooty Shearwaters who nest on islands off the southern end of South America are feeding side by side with Cory’s Shearwaters from the Mediterranean and Manx Shearwaters from the North Atlantic. Great Shearwaters have been the overwhelmingly most common of the four species, with estimates of over 18,000 one day at Race Point.

Shearwaters have always amazed me for their ability to navigate enormous areas of featureless ocean to find food and nesting areas. In the Pacific, Sooty Shearwaters migrate over 40,000 miles a year between breeding islands in New Zealand and their wintering areas off California, Alaska, and Japan. And Great Shearwaters span the entire Atlantic from north to south each year.

So how do these birds find their way around millions of square miles of trackless ocean? The answer lies in having a nose for plankton and in their ability to cheat the wind. All shearwaters are in a group of seabirds known as tubenoses, named for the specialized nostril tubes that help them smell their way around the ocean. While most birds can’t smell much of anything, shearwaters can at great distances detect a chemical given off by plankton, giving them a scent map of productive and unproductive areas of the ocean. Where there is plankton, there are likely to be fish and squid, their main foods.

Cory's Shearwater
Credit Mark Faherty

To get them over the huge distances necessary to find this food, these birds have mastered the dynamic ocean surface winds, using them to move nearly without effort over many miles. As the wind reflects upward off of waves, shearwaters catch it with their long, narrow wings, allowing them cruise without flapping. They bounce from updraft to updraft with a characteristic arcing, swerving flight that easily distinguishes them from other seabirds at a distance.

If you want to see these amazing ocean wanderers for yourself, you can usually seem them from shore along the outer beaches of the Cape between Chatham and Provincetown, and a whale watch always offers a chance at seeing at least a few, if not thousands. You might also see some other late summer whale watch specialty birds, like the ocean going sandpipers known as phalaropes or a beautiful and rare arctic gull called Sabine’s Gull. Oh, and I guess there are also whales, too, if you are so inclined…