Nature Watch: Life on the Rocks

About the author: Steve Ellis is a naturalist and Land Trust member who enjoys sharing his love of the natural world. His blog series, “Nature Watch,” will appear each month in “Habitchat,” chronicling native plants and wildlife you can expect to see during that particular time of year. We thank Steve for sharing his passion, illustrating the importance of island conservation.

Overview

Of all our islands’ beach types, rocky beaches attract some of the most unusual shorebird species.

Rocky beaches can be classified by the size of the rocks: large rocks that are greater than 10 inches in diameter, cobble consisting of rocks with average diameters of 3 to 10 inches, and gravel with stones smaller than cobble.

Large rocks are the home of mussels and barnacles permanently attached to the hard surfaces. Limpets move about on the rock faces but have a home etched into the surface. Each of these creatures has armor to protect against wave action and predators.

Cobbles support small barnacles and snails. Mobile animals such as crabs may be found between the rocks.

Gravel beaches usually have a mix of sand with the small stones. Animals here tend to be highly mobile and include marine worms, crabs and clams that can burrow into the substrate.

Shorebirds from the 18-inch Black Oystercatcher to the 7-inch Sanderling have adapted to life on the rocks. Most species are migrants from Alaska and Canada, with only the Oystercatcher being a full-time resident.

The most numerous “rock piper” is the aptly-named Black Turnstone. Flocks of these birds begin arriving as early as late August, but the numbers don’t peak until November. A little smaller than American Robins, these unusual birds use their tapered bill to flip over rocks and unattached marine algae such as rockweed and kelp in their search for prey. They also have the ability to peck into or dislodge barnacles and small mussels. Another tactic they deploy is to “snowplow” through layers of algae while looking for food.

Surfbirds often accompany turnstone flocks and feed in the same manner. In addition to barnacles and other animals, they also include some algae in their diets. Surf may account for their name in fall and winter, but the breeding season finds them on the flanks of Alaskan mountains, far from the nearest coast.

Watching these and other birds of rocky shores is always interesting. Sanderlings, a light-colored shorebird species, may mix in with turnstones. Unable to peck into a barnacle themselves, they rush in to grab leftovers exposed by the turnstones. A Sanderling may defend the area around an individual turnstone from other Sanderlings.

Crows pirate food from Black Turnstones, and these small birds are hunted by falcons. We once watched a falcon arrow down towards a flock of turnstones feeding on the rocks at Oak Harbor’s Windjammer Park. An alarm call was given and all the flock members scrunched down, looking like so many dark-colored rocks. Taking flight would have meant certain death for a turnstone. Confused by the apparent disappearance of its potential prey, the falcon circled once over the beach and departed.

Penn Cove attracts many turnstones. It has the requisite rocky beaches and offers protection from the worst storms that batter Whidbey’s west side. Look for Black Turnstone flocks along Madrona Way, the beach at Captain Coupe Park, and Fort Ebey State Park. At high tide they can sometimes be found on the log boom at the Oak Harbor Marina boat launch. I know of no public beaches on Camano Island that regularly attract rock pipers.

Occasionally other species may join the Black Turnstone and Surfbird flocks, including Rock Sandpipers, Killdeer and Ruddy Turnstones. Whimbrels, those large shorebirds with downcurved beaks, stop to use this habitat in spring and fall.

The fact that so many birds can thrive here through fall and winter is a testament to the abundance of life on the rocks.

Black oystercatcher by Cara Hefflinger.

Fauna: Black Oystercatcher (Haematopus bachmani)

A “wheep-wheep-wheep” is heard as a flock of plump dark birds wheel out of the air to land on a rocky beach. The restless oystercatcher flock immediately takes to the air again to circle over the water and lands on the rocks to preen and feed.

The clownish-looking Black Oystercatchers are unmistakable if the long, straight red bill is seen. These birds measure 16 to 18 inches in length and have a wingspan of 32 inches. The back and wings are brownish-black, while the head, neck and breast are basic black. Reddish eye rings round out the field marks.

Present year round, Black Oystercatchers do most of their foraging in the intertidal zone where they prey on invertebrates. Most of their diet consists of mussels and limpets that are pried off rocks. Many individuals are left-or right-billed when it comes to separating prey from the rocky substrate. There is evidence that young birds imitate their parents’ preference and learn to peck only from either the left or right side.

Despite their name, oystercatchers rarely eat oysters, but they do include marine worms and barnacles in their diets. The latter are hammered open with their bill.

Black Oystercatchers form long-term pair bonds and may reuse the same nest for several years. Nests are bowls hollowed in the gravel and sand above the high tide line but not in thick vegetation. At times the nests can be flooded by large waves. Eggs remain viable and may be incubated where they’ve landed or will be returned to the nest by a parent bird.

Peregrine Falcons are about the only documented predator of adult oystercatchers. Eggs and young chicks are vulnerable to gulls, crows and raccoons. Some oystercatchers live up to 16 years.

Look for oystercatchers on the rocks at Fort Ebey State Park, Libbey Beach at the end of Libbey Road, or the Keystone ferry jetty. A good spot at high tide is the large rocks just offshore from the main parking lot on the Whidbey Island side of Deception Pass State Park.

The sight of a Black Oystercatcher flock on a blustery November day is an ample reward for venturing forth into the fall weather.

Rockweed by Martha Ellis.

Flora: Rockweed (Fucus species)

Rockweed is the most abundant seaweed in the Salish Sea. There are two species whose differences are minor, so they’ll be treated as one in this article.

The holdfast (rootlike structure) of rockweed anchors it to rocks in the mid to high intertidal zone. It grows best on gentle slopes rather than sheer vertical rock faces.

Above the holdfast is a stemlike stipe that supports many branches, each ending in 2-pronged bulbous tips. The entire structure can reach 16 inches in length. The branches are olive-green to brown in color.

Rockweed tips contain air for buoyancy and also hold the means of reproduction. The shortened daylight of October and November prompts the release of eggs and sperm that eventually form new plants. After reproduction is complete, the rockweed dies and becomes dislodged by winter’s waves.

The reproduction and growth of rockweed can cover rocks with layers of branches. Small fish such as gunnels shelter in this habitat, as do crustaceans and gastropods. The branches are also used by Pacific herring as places to attach their eggs during the spawning season.

The luxurious growth of rockweed that occurs in spring and summer is protected by phenols, chemicals indigestible by most herbivores. A few species of limpets and periwinkles are capable of grazing on rockweed. The latter are tiny snails whose small size prevents them from consuming large portions of the plants. Periwinkles are in turn eaten by turnstones and surfbirds.

This important seaweed can be found at low tide at several locations on Camano and Whidbey Islands. Try Camano Island State Park, Keystone Spit and Fort Ebey State Park.

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