Excirolana isopods carry eggs

Beach wrack and molted mole-crab carapaces-perfect food for Excirolana isopods (note carapace of the spiny mole crab at middle-top). (Source: Kim Fulton-Bennett)

Nestled within the grains of sand on the rebuilding beaches are 1/4-inch-long, multi-legged Excirolana isopods. Like their Like their tide-pool-dwelling relatives, these beach isopods typically carry eggs in brood pouches from April through June. The female isopods release their young at the highest spring tides. Carried on the tide, the young swim out into the surf zone (Estelle 1991).

After mole crabs, Excirolana isopods are probably the most common and ecologically important animals living in the "swash zones" of sandy beaches. Marine biologists have counted more than 800 of these tiny isopods in a single square meter of sand. They are especially important as food for surf perch and small, scurrying beach birds such as sanderlings (MBNMS 2019).

Excirolana isopods eat mostly dead mole crabs and mole-crab eggs, so you can usually find them in the same areas as mole crabs. At low tide, you may find the isopods burrowed about 1/4 inch below the surface of the wet sand (you will need a good hand lens to see them because they are so tiny). At high tides the isopods swim around in the waves looking for cast off mole crab skeletons and other debris (MBNMS 2019).

Note: These isopods have such a strong internal biological clock that their daily activities follow the cycle of the tides even when they are placed in aquaria on land (MBNMS 2019).

Many beach and shorebirds leave the area to nest

Walking along Central Coast beaches in April, you may either see large flocks of shore birds, or none at all. The majority of Central Coast shorebirds leave this area some time between March and May to nest far to the north, far inland, or both.

Note: A few shorebirds of many species, especially juveniles, stay on the Central Coast all year instead of leaving to nest and breed.

During early April, you may be lucky enough to see large flocks of shorebirds flying rapidly and purposefully along the coast or refueling (feeding) along the water's edge. These large flocks form as migrating birds from the south pass through the area and are joined by birds that have wintered locally.

Although they often spend high tide resting in coastal wetlands, at low tide these shorebirds congregate on Central Coast beaches. They feed by poking their beaks into the wet sand, searching for mole crabs, beach hoppers, Cirolana isopods, and other prey.

Large flocks of migrating shore birds reach Central Coast beaches just in time to feast on the year's first generation of mole crabs. As described in March, these young mole crabs began settling onto Central Coast beaches in February or March. By April they are just the right size for the larger shorebirds to feast upon (Morris et al 1980).

Even the casual observer will notice that Central Coast shorebirds come in two distinct sizes. Some are relatively large, with bodies the size of pigeons (but much longer beaks and legs). These larger birds include willets, godwits, and whimbrels. Birds in the second group are much smaller, but more numerous. These sparrow-sized birds include sanderlings, sandpipers, dunlins, and snowy plovers.

Except for the snowy plovers, all of these birds, both large and small, leave the Central Coast in spring. These migrating birds will spend their summers in nesting areas thousands of miles away.

Marbled godwits congregate and migrate

Marbled godwits feeding at the edge of the wet sand.
(Source: Kim Fulton-Bennett)

Marbled godwits (Limosa fedoa) are one of my favorite beach birds because of their beautiful plumage. The wings of the adult birds are covered with intricate patterns of mottled brown, black, and white feathers. These complex patterns contrast with the simple, rapier-like appearance of the godwit's beak. Godwits can be easily identified by their amazingly long, thin, straight beaks, which are pinkish red in color with black tips.

Most adult godwits leave the Central Coast in March or April (MBNMS 2006). These birds will migrate north and east, heading toward the northern Great Plains, from Montana east to Alberta. By late April or early May, they will be settling into grassy nesting sites near marshes or streams (O'Brien et al 2006).

Marbled godwits will begin building nests in May and lay eggs in June. Their eggs will hatch in early July after about 24 days of incubation. By the end of the July, the young godwits will be fledged and able to fly. The godwits will return to the Central Coast in August and September (O'Brien et al 2006).

Western willets congregate and migrate

Western willets (Caoptrophorus inornatus) are about the same size a marbled godwits, but have shorter bills and gray and white bodies. Like the marbled godwits, flocks of willets gather along Central Coast beaches in April before heading north and east. Willets nest on prairies and high plains over a broad area from northern California through Colorado and up to southern Alberta and Manitoba (O'Brien et al 2006).

Flying mostly at night, the willets will arrive in their nesting areas by early May. By early June, they will have built nests on the ground, in thinly vegetated prairie-grass or wetland areas. For protection from the prairie wind, godwits often nest in the lee of a piece of wood, a rock, or even a dried cow pie (O'Brien et al 2006).

The willets will lay their eggs in late May or June and incubate them for about a month, with both parents sharing nesting duties. However, about two weeks after the young hatch, female willets often abandon the young to the care of the male, and may nest a second time before returning to the Central Coast in fall (O'Brien et al 2006).

Whimbrels congregate and migrate

Whimbrels (Numenius phaeopus) are similar in size to godwits and willets, but have distinctly downcurved bills. They can often be seen foraging for crabs, worms, and small clams along wetland areas, beaches and tide pools. You are most likely to see whimbrels on Central Coast beaches during April, when large flocks gather for their northern migration (CDFG 2019).

Whimbrels are long distance migrators. Some whimbrels spend their winters on the coast of South America. These birds fly north in spring and are joined by others that wintered in Southern California. Like willets, the whimbrels typically migrate at night, flying rapidly just off along the coast (O'Brien et al 2006). If you walk along the coast on a spring evening, you may be able to hear the whimbrels' high, repetitive cries (peepeepeepee!), even if you can't see the birds themselves.

These flocks of whimbrels will reach the Pacific Northwest around the end of April. From there, they will head out across the Gulf of Alaska and arrive in their Alaskan nesting areas in mid May. A few birds continue even farther north and east toward the Canadian Arctic, where they will begin nesting in late May (O'Brien et al 2006).

Like many birds that nest in the Arctic, the whimbrels are on a tight schedule. Their eggs, laid in early June among the low shrubs of the Arctic tundra, hatch in late June or early July. After five or six weeks of constant feeding by their parents, the young chicks are fledged and ready to fly. Like the other shore birds, the whimbrels will return to the Central Coast beginning in August (O'Brien et al 2006).

Sanderlings congregate and migrate

Sanderlings (Calidris alba) are the most common species of small scurrying birds you are likely to see on Central Coast beaches. During spring, sanderlings generally have white bodies with pale gray-brown backs and dark shoulders. They look very similar to Western sandpipers, but are slightly browner in color. Sanderlings are also likely to be found on sandy beaches, while sandpipers are more common around coastal wetlands.

Flocks of sanderlings begin to migrate northward up the California coast in February. As described in March, they arrive on Central coast Beaches just in time to feed on mole-crab larvae that are settling out of the plankton at this time of year.

These flocks of sanderlings leave the Central Coast in April, joining others of their species that are flying up from the south to nest in the Canadian Arctic. By late July or August, some of these birds will already be back on the Central Coast, having completed the process of migration, mating, and parenting in just three months (MBNMS 2006).

By late May or early June, most of these sanderlings will have arrived at their nesting areas along the rocky, barren Arctic coast of northern Canada or along alluvial plains within about 200 feet of sea level. They will build nests in the coastal tundra, feed on seasonally abundant insects in this area, and raise their young, all in about two months. Sanderling nests are usually solitary, shallow scrapes in ground, sometimes lined with dry leaves. The young leave the nest within hours of hatching, and can fly when they are only about 17 days old (CDFG 2019).

Note: In an amazing display of nesting efficiency, female sanderlings will sometimes lay several sets of (3-4) eggs (one right after the other), with the male incubating the first clutch, the female incubating the second, and another male incubating the third (CDFG 2019).

By early August, the adult sanderlings and most of their young will have left the nesting grounds. Most of these birds will head south for their feeding areas along the West Coast. However, a few will take "the long way home," by making a clockwise circumnavigation of both North and South America (O'Brien et al 2006).

Instead of heading back south after nesting, these birds will fly east across the Canadian Arctic, reaching the Atlantic seaboard around October. At that point, they will turn right and head south, flying down the east coast of North America, across the Caribbean Sea, and then along the east coast of South America as well (O'Brien et al 2006).

These sanderlings then spend the southern summer (November and December) feeding along the coasts of Peru and Chile. By January or February, they are off again, heading north toward the California coast to complete the cycle (O'Brien et al 2006). Like some surfers, these tiny birds have evolved a lifestyle that involves traveling around the world, following the "Endless Summer."

Western sandpipers congregate and migrate

The second most common species of small shore birds on Central Coast beaches are the Western sandpipers (Calidris mauri). These birds occasionally feed on beaches at low tide, but spend most of their time around mudflats and coastal wetlands (they are by far the most abundant wading bird in Elkhorn Slough). They look very much like sanderlings, but move with a slightly slower, more hesitant gait.

At high tide, Western sandpipers can be seen resting or hunting insect in marshy areas at the edges of coastal wetlands. As the tide recedes, they follow the water's edge, snapping up amphipods, worms, and small clams that have been exposed by the receding tide. After peak low tide (when element of surprise is lost) the sanderlings fan out across the mud flats to look for leftovers.

You can see Western sandpipers on the Central Coast at any time of year except from May though July, when they head up to the Arctic to nest during the brief Arctic summer (CDFG 2019). The largest flocks appear during March or April, when almost all of the western Sandpipers in the world migrate north along the Pacific Coast (O'Brien et al 2006).

Like many other shorebirds, sandpipers do most of their migrating at night. By May the migrating sandpipers will have reached western Alaska, gathering by the millions at the Copper River Delta (O'Brien et al 2006). From there many will head farther north` to nesting areas on the remote western and northern coasts of Alaska (O'Brien et al 2006).

By the end of May, most sandpipers will have already built their nests in dry patches of heath, often near water or wetlands (CDFG 2019). Summer comes so late to far reaches of the Arctic that sometimes the sandpapers must wait for the snow to melt before they can build their nests.

Once their nests are built, the sandpipers make short work of the nesting process. By early June they will have laid a small clutch of eggs, which hatch in just three weeks. Although both parents share incubation duties, the females will leave shortly after the young hatch in late June (O'Brien et al 2006).

The male sandpipers will hang around for another three weeks to feed their chicks a high protein diet of predigested insect larvae, worms, and crustaceans. After only 17 or 18 days, the newly hatched chicks will have learned to fly (CDFG 2019). By late July to mid August, the adult sandpipers will have returned to the Central Coast. Their offspring will follow a few weeks later.

Snowy plovers nest locally

Snowy plovers (Charadrius alexandrinus nivous) are the only species of shore bird that commonly nests on Central Coast beaches. Unfortunately, these tiny birds must share their nesting areas with large numbers of clueless humans and their canine and equine companions.

At first glance, snowy plovers look somewhat like sanderlings and sandpipers, but at six inches from beak to tail tip, they are even smaller than these other beach birds. Snowy plovers' most distinguishing marks are a black line through each eye and a black patch on each shoulder. The black shoulder patch always reminds me of an old-fashioned, starched bow-tie that has come undone.

You are most likely to see snowy plovers feeding along the dry upper portions of remote Central Coast beaches that are backed by sand dunes. Unlike sandpipers, snowy plovers don't run continuously back and forth with the waves, but make short dashes across the sand, then freeze. If frightened, they often run up the beach instead of down toward the water, like sanderlings (Personal observation).

When running, snowy plovers look very much like pieces of kelp or other beach debris blowing in the afternoon sea breeze. When resting or nesting, snowy plovers blend in so well with their surroundings that they become practically invisible. The little birds often crouch in small depressions in the sand for protection from April's howling sea breezes. Even tire tracks or human footprints are deep enough to provide a modicum of shelter for these tiny birds.

In March or April, snowy plovers return to the Central Coast from their winter feeding grounds in the Great Plains and other inland areas. Groups of plovers often nest along the same stretch of beach each year (Roberson and Tenny 1993). From March through September, they build nests in the most exposed locations imaginable, laying eggs in shallow depressions in the sand, amidst the kelp wrack and driftwood, and just above the high tide line.

Female snowy plovers lay one to three eggs in a clutch. Exposed to the howling northwest winds, these eggs would only survive for an hour or two without a parent bird sitting on them to keep them warm. During the daytime, female plovers incubate the eggs while the males forage for food. At night they trade places (CSP-2002).

Unfortunately, many of the beaches where snowy plovers nest are also very popular with humans during the summer months. Because snowy plover eggs and nests are so tiny and well camouflaged, it is very easy for humans to walk past nests or even step on them without even noticing.

Even seemingly innocuous human activities, such as sunbathing, camping, picnicking, playing catch, or flying kites can frighten snowy plovers from their nests. At first the nesting plover may try to chase or lure the human intruder away from its nest. If this doesn't work, the bird will leave its nest and will not return the intruder is at least 300 feet away. This leaves the plover's eggs exposed to the cold wind, as well as to predators such as dogs, gulls, crows, ravens, skunks, and foxes (CSP-2002).

If a snowy plover's eggs are not stepped on, abandoned, or eaten, the young will hatch in about 27 days. Within a few hours of hatching, the young downy chicks will be dashing across the sand on spindly little legs, hunting for insects and beach hoppers. In another month, the young plovers will be on their own, and the female plover may try to nest again. In August or September, most plovers will leave the Central Coast and fly back to their winter feeding areas (CSP-2002).