Seasons in the Sea - A month-by-month guide to Central California sea life

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Cormorants: Image credit-Mary Hollinger - NOAA


in April

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Migratory birds congregate on the Central Coast, then leave

April is perhaps the busiest month on the Central Coast for birds, as most are in the process of migrating from winter feeding areas to summer nesting areas or are already setting up nests locally.

  • Many nearshore birds, including surf scoters, grebes, loons, and some gulls spend their winters on the Central Coast travel north and east to nest in the northern Great Plains or the cold, barren lands near the Arctic Circle.
  • Other seabirds, such as cormorants and murres nest locally on offshore islands such as the Farallones, as well as on rock pinnacles, sea cliffs, and man-made coastal structures such as old piers.
  • Beach and shore birds, including surfbirds, turnstones, sanderlings, willets, and godwits, also head north at this time of year.

See the accompanying table for a summary of where these various sea and shore birds are heading during their spring migrations. The shorebirds and wetland birds will be discussed in greater detail below, as well as under rocky intertidal, sandy beach, and estuary sections of this month.

It amazes me that so many coastal birds have found it evolutionarily beneficial to migrate thousands of miles so they can nest in the far reaches of the Alaska or the Canadian Arctic. Why these birds should travel so far to nest is still somewhat of a mystery, but it may have to do with the scarcity of predators or the abundance of food in Arctic regions. Certainly there is no shortage of insects in the Arctic during summer; such insects provide essential food for many small birds that nest in the Arctic.

April is a great time for bird watching on the Central Coast because so many migrating birds stop here to rest and eat for a few days during their northward migration. As winter-residents get ready to leave the Central Coast, they are joined by others of their species that have spent the winter farther south, and have already begun their northward migration along the coast.

Note: The second best time of year for bird watching is fall, when many birds wing their way south after mating and nesting. However, compared with fall, the spring migration seems more intense and of shorter duration. Perhaps this reflects the birds' need to migrate, court, build nests, lay eggs, and fledge their young before the end of summer (which may be only a month or two long in sub-arctic regions).

During April, you may see flocks of migrant seabirds floating just off the coast, their numbers gradually increasing as the month progresses. Then suddenly, perhaps following a change in the weather, the flocks will simply disappear, heading onward, northward.

When the migrating flocks leave, most local birds will go with them, adding to their numbers. Thus, the flocks of migrating birds grow in size as they move northward, like an avalanche picking up snow as it speeds down a mountainside.

Each year, some birds that might normally migrate north decide to spend the summer on the central coast, much to the confusion of dedicated bird watchers. These stay-at-home birds are often young or immature, but they also include adult birds taking a break from the effort of migrating and nesting.

Note"Seabirds and shore birds are not the only birds migrating northward along the Central Coast during April. All kinds of land birds use this region as a stopover point on the Pacific Flyway. This aerial express route up the West Coast of North America that has been used by migrating birds for thousands of years.

Nearshore birds (scoters, loons, and grebes) leave the area

Surf scoters congregate and leave

Male surf scoter (Source: Steve Lonhart / SIMoN NOAA)
As early as March, you can sometimes see flocks of several dozen surf scoters (Melanitta perspicillata) floating just outside the breaker zone (this is a large gathering in comparison with the groups of five or ten scoters that you see diving or swimming together during the winter months). By April, flocks of 100 migrating scoters may gather in favored staging areas. By the end of April, however, virtually all of these scoters will have disappeared.

After leaving Monterey Bay, the scoters fly offshore and northward toward Puget Sound, British Columbia, and Southeast Alaska. Despite their squat, duck-like bodies and stubby wings, individual scoters can make the long journey from the Central Coast to Southeast Alaska in about a week.

Some scoters stop on the Pacific Northwest coast and spend their entire summer feeding there. Others keep moving, heading inland and farther north. When they reach the forests and Arctic tundra of Alaska and northern Canada, they stop and built nests.

Surf scoter nests are little more than small depressions in the ground, tucked away underneath small bushes and marsh vegetation. When all is ready, the female scoters lay clutches of 5 to 8 eggs. [Add details of raising young?]

Surf scoters often flock and migrate long distances along with their close relatives, white-winged scoters (Melanitta fusca) and black scoters ((Melanitta nigra). White-winged scoters nest around wetlands and lakes in Central Alaska and Western Canada. Black scoters make an equally long journey to breed in forests and coastal plains of western Alaska, along the shores of the Bering Sea.

Grebes congregate and leave

Grebes also gather in large numbers to feed in Monterey Bay during April and May, just before heading north to breed. During some years, thousands of these black birds, with their graceful, white-striped necks, can be seen floating just outside the surf zone, particularly in sheltered parts of the coast such as the inner part of Monterey Bay. These migrating flocks typically consist of a large number of Western grebes (Aechmorphorus occidentalis), as well as a few Clark's grebes (Aechmorphorus clarkii).

From December to April, pairs and flocks of grebes are common along the sandy beaches of Monterey Bay (between Capitola and Monterey). However, grebes usually stay just far enough offshore that they are hard to see from shore. From a distance, it's easy to mistake a flock of grebes for a flock of seagulls or cormorants. but with a decent pair of binoculars, you can often make out the grebes' graceful necks, relatively small heads, and sharp, pointed bills.

Western grebes eat small fish such as anchovies and young rockfish, both of which are abundant in spring. With their narrow bills, grebes cannot swallow many fish whole, as cormorants do, but must chop the fish up with quick jabs of their bills before consuming the pieces.

Western grebe in mixed plumage. (Source: Steve Lonhart / SIMoN NOAA)
In April, you may see Western grebes with a variety of color patterns, as their dapper black and white winter plumage gives away to lighter breeding plumage. You may also see them practicing courting behavior [add brief description].

In late April or May the Western grebes in Monterey Bay congregate at the north end of the bay, then leave the Central Coast, flying inland at night to their breeding areas in the sagebrush-covered hills of the Great Basin, from Nevada to south-central Canada. There they will court, breed, and raise their young in floating nests on freshwater lakes and mashes.

Horned grebes (Podiceps auritas) also leave the Central Coast in April, flying off to nest around lakes and marshes in southern Alaska and Western Canada. Mated pairs and small flocks of these birds feed in the ocean during the winter months, but head to fresh water to breed. Another small grebe, the eared grebe (Podiceps nigricollis), winters on the Central Coast, but leaves in to breed in marshy areas across the Western United States and southern Canada.

Loons congregate and leave

Though less numerous than grebes, loons also gather in the nearshore waters during April. Pacific loons (Gavia pacifia), common loons (Gavia immer), red-throated loons (Gavia stellata), and Arctic loons (latin name) all pass through the Central Coast on their way to breeding grounds in the Arctic and SubArctic regions. During this time, the males begin to develop their beautiful breeding plumage--midnight black wings overlaid with an intricate pattern of white specks.

===== Photo of common loon in spring plumage ======

Winter gulls leave as summer gulls arrive

You can find gulls along the Central California coast at any time of year. Several of the species look similar, especially the juvenile birds. Unless you look closely, you might not notice that different gull species are present at different times of year. Some spend summers here. Others feed locally in winter, but leave in spring to breed.

April is a busy time for the migrating gulls, just as it is for other seabirds. At least seven different species of gulls migrate through the Central Coast each spring. Most of them are heading north to nesting areas in Canada and Alaska.

California gulls (Larus californicus), and Bonaparte’s gulls (Larus Philadelphia) both spend their winters in Monterey Bay, but typically leave in April. Like Western grebes, most California gulls nest by inland lakes across the Pacific Slope, from Nevada to South Dakota, and north to the Canadian prairie (a few stick around to breed in San Francisco Bay.

Other gull-relatives that spend the winter on the Central Coast, then leave in March or April, include Thayer’s gulls (Larus thalyerii), Glaucous-winged gulls (Larus glaucescens), and Black-legged kittiwakes (Rissa tridactyla).

Open-ocean birds (murres, auklets, storm petrels) nest on rocky islands

Several open-ocean seabirds spend their winters feeding in the relatively protected waters of Monterey Bay and the Gulf of the Farallones. In April, these birds congregate to nest on offshore islands and exposed headlands. In such isolated areas, their birds' eggs and young are less likely to be eaten by rats, raccoons, and other terrestrial predators.

In April you can see these birds, including murres, auklets, and storm petrels, gathered at breeding colonies along the Big Sur Coast, on Ano Nuevo island, near Devil's Slide in San Mateo, and along the Marin Headlands. By far the largest colonies, however, are located on the Farallon Islands, off San Francisco.

Murres build nests

By far the most abundant of these island-nesting birds are the murres. As their name implies, flocks of common murres (Uria aalge) are a frequent sight in Central Coast waters. In fact, they are the most abundant seabird that nests along the Central Coast. However, because murres fish over the continental shelf, they are not as easy to see from shore as other seabirds.

Note: With their dark wings and white bellies, common murres look similar to Western grebes from a distance. However, murres have stockier bodies and shorter, stouter necks and bills. Also, murres have black necks, without the western grebe's distinctive white stripe.

===== Photo of common murre in breeding plumage =====

Large flocks of murres typically spend winter and early spring in Monterey Bay and in the Gulf of the Farallones, chasing schools of anchovies. In April, most of these murres gather at breeding colonies on the Farallon Islands, where hundreds of thousands of murres congregate during productive years. Huge flocks of murres also migrate northward from Southern California to the Farallones during March and April.

Note: During years when upwelling is weak and schooling fish are scarce in the offshore waters during spring, many murres die of starvation and wash up on Central Coast beaches. Common murres may also be caught in drift nets when they chase schools fish in offshore waters.

In addition to the main nesting area at the Farallones, smaller groups of murres nest on small islands at the most exposed rocky headlands on the mainland, such as Hurricane Point in Big Sur and Devil's Slide in San Mateo County. Since the Farallon Islands are not accessible to the public, these mainland nesting areas are good places to watch the murres courting and nesting (you will need binoculars to see them well).

If you visit a murre nesting colony in March or April you may see male and female birds standing on the rocks, bobbing and weaving, or swimming together in the water. [Add more details of murre courtship ritual?] These courtship rituals help the pair bond in preparation for the arduous nesting process.

Auklets build nests

Like common murres, auklets leave Monterey Bay in April to begin building nests at the Farallones and at Ano Nuevo Island. About 40,000 Cassin's Auklets (Ptychoramphus aleuticus) and 1,000 Rhinoceros auklets (Cerorhinca monocerata) nest on the Farallon Islands during a typical summer.

Auklets nest in burrows and crevices, which they must maintain all year long, because competition for space on the islands is so intense. Cassin's auklets are nocturnal, and only leave their burrows at night to forage over offshore waters for krill. [what about Rhinoceros auklets? add one sentence to describe spring plumage of each]

===== Photo of rhinoceros auklet in spring plumage ====

Ashy storm petrels build nests

Yet another open-ocean bird that migrates to the Farallones to nest in April is the Ashy Storm Petrel (Oceanodroma homochroa). Like Cassin's auklets, ashy storm petrels nest in deep burrows. However, as if trading shifts with the auklets, storm petrels feed during they daytime.

Ashy storm petrels are truly birds of the open ocean. In fact, the only time they come ashore is at night during nesting season. Ashy storm petrels fish even farther from shore than do auklets and murres, in the waters over the outer continental slope, 30 to 100 miles from shore [check this]. There they hunt krill and fish larvae. They also use their keen sense of smell to find schools of small fish such as anchovies, which they can smell from miles away.

==== Photo of ashy storm petrel in spring plumage ====

Nearshore seabirds (cormorants, western gulls, guillemots) nest on coastal bluffs

While many seabirds leave the coast in April, a few species stick around to build nests on rocky sea cliffs, offshore islands, and man-made structures. These local nesting birds include Brandt's cormorants, pelagic cormorants, and western gulls, and pigeon guillemots.

These birds typically feed close to shore, in or just beyond the kelp beds. For food, they rely heavily on anchovies and juvenile rockfish, which come close to shore during the spring and summer months.

Some of these birds are easy to observe, since they build their nests in exposed locations, often just out of reach of the breaking waves. They also nest on navigation markers, abandoned piers, and even derelict buildings such as the old canneries in Monterey.

Brandt's cormorants build nests

Source web page:
Close-up view of an adult Brandt's cormorant during breeding season, showing blue throat patch. (Source: Chad King/SIMON)
Some Brandt's cormorants (Phalacrocorax penicillatus) begin building nests as early as March. These early birds take the most favored nesting spots at the seaward edges of islands or rock ledges. However, these nests are very susceptible to wave damage during late winter storms.

Brandt's cormorants are the most common of the three different species of cormorants that live and breed along the Central Coast (the other two are pelagic cormorants and double-crested cormorants). All have glossy, jet-black bodies, long thin necks, and long, rapier-sharp bills. During their nesting season, you can tell Brand's cormorants by their bright, iridescent blue throat patches.

===== Photo of Brandt's cormorants in breeding plumage ====

"Flying" through the water like feathered torpedoes, cormorants feed on juvenile rockfish and schools of anchovies, market squid, and midshipman.

Note: Brandt’s cormorants, murres, and other birds that rely on fish from coastal waters alternate between successful and unsuccessful nesting years, depending on how much food is available. For example, a single pair of cormorants may raise 4-5 chicks in a good year, but during a bad year, only one or no chicks at all may survive.

Brandt's cormorants must be persistent and adaptable in their nest building because their nesting sites are continually being destroyed by coastal retreat and the collapse of derelict human structures. For several years, I watched as a group of up to two dozen cormorants built nests on a narrow sea stack near Lighthouse Park State Beach in Santa Cruz. Then, during a severe winter storm, the sea stack collapsed. The following spring, the cormorants found a new nesting spot--a narrow ledge about a mile away, near Natural Bridges State Park.

During March and April you can see large flocks of Brandt's cormorants fishing or flying low over the sheltered waters of Monterey Bay or the inner Gulf of the Farallones. By May, however, cormorants will be scarce along much of the coast, because the birds have congregated at a few nesting colonies.

The world's largest colony of Brandt's cormorants is located on the Farallon Islands. On these barren, sea-whipped islands, an average of 12,000 cormorants nest each year. They must share this protected nesting space with literally hundreds of thousands of murres and other seabirds.

On the mainland, one of the largest cormorant nesting colonies is at Point Lobos, where several thousand Brandt's cormorants gather during years when food is abundant. Dozens of Brandt's cormorants also nest on decrepit piers in Moss Landing Harbor and near the town of Davenport. Others nest along West Cliff Drive in Santa Cruz and near Seal Rock near the Cliff House in San Francisco.

If you visit one of these cormorant nesting areas in March and early April, you will probably see male birds flying low over the water, carrying bits of nesting material (usually surf grass, eel grass, or filamentous algae) that they have dredged up from the sea floor.

In Moss Landing harbor, I watched a male cormorant surface with a mat of eelgrass that was so heavy he could hardly carry it. After a labored take off and flight back to the nesting colony, he paraded through the crowd of birds and dropped his slimy bundle at the feet of a female who was already sitting on the beginnings of a nest.

After presenting the seaweed, the male repeatedly bobbed his head and arched his back. He then tilted his head forward and bent his long neck back so it looked almost in a figure eight. In response, the female craned her neck in a similar pattern. The male cormorant then mounted the female while she sat on the nest and they mated for a minute or two, followed by more neck craning by the male. Then off he went for more nesting material.

By late April, most cormorants have finished building their nests. These sturdy structures form volcano-shaped mounds about eight inches high and 15 inches across. In the middle of the mound is a depression that fits perfectly around the lower half of the female's body. The nests must be very sturdy to survive the constant spring winds and spray from rogue waves.

While the female cormorants sit in their custom-fitted thrones, the males stand nearby, guarding the nests from marauding gulls. But even the male birds keep a wary distance from the nesting females, who will lunge and peck at any bird that comes too close.

Pelagic cormorants build nests

April also sees the nesting of pelagic cormorants (Phalacrocorax pelagicus), with the largest colony (up to 800 birds) at the Farallones, and smaller breeding colonies at Pt Reyes, on either side of the Golden Gate, at Ano Nuevo, a few places in Monterey Bay, Point Lobos, and along the Big Sur coast.

Like the Brant's cormorants, the nesting success of pelagic cormorants varies greatly from year to year. Even at the Farallones rookery, in one out of three years, no eggs are hatched at all.

==== Photo of pelagic cormorant in breeding plumage ====

Unlike the gregarious Brandt’s cormorants, pelagic cormorants seldom gather in large flocks. On the mainland, you may find a few pairs nesting on isolated cliff faces, coastal structures, or even in coastal trees.

One April afternoon, while walking along the wind-swept bluffs northwest of Santa Cruz, I discovered two pairs of pelagic cormorants nesting on two tiny rock ledges above a little wave-carved inlet. The ledges were so narrow that the females had to sit facing the sea cliff to keep from falling out of their nests. Their mates were forced to perch on other narrow ledges 20 to 30 feet away.

During nesting season, adult pelagic cormorants have distinctive white patches on either side of their tails as well as a small dark red patch on their throats. Pelagic cormorants are a little smaller than Brandt's cormorants. Despite their common name, pelagic cormorants feed mostly near shore, diving to the rocky seafloor to hunt small fish such as blennies and sculpins or small crabs and shrimp.

Pelagic cormorants also nest in tall trees next to coastal wetlands. For example, you can see their nests in eucalyptus trees near Schwann Lake and the mouth of the San Lorenzo River, in the Santa Cruz area.

Western gulls build nests

Aside from cormorants, western gulls (Larus occidentalis) are the only seabirds that live on the Central Coast mainland all year long and do not migrate elsewhere to feed or breed. They are also the most common type of gull on the Central Coast.

Western Gulls are relatively large compared to other gulls, with a wingspan of up to 54 inches across. Their heads and bodies are white, their backs are dark gray, and their legs pink. However, western gulls often mate gulls of other species, and the resulting offspring may have characteristics of both parents.

Given that the different species of gulls can’t tell each other apart, it’s not surprising that humans sometimes have a hard time with this too. However, if you see a gull nesting on the Central Coast, the chances are good that it's a Western Gull.

===== Photo of Western gull in breeding plumage =====

Western gulls are opportunists, both in their feeding baits and their nesting behavior. Western gulls typically build their nests on the same sea cliffs and man-made structures as do Brandt's and pelagic cormorants. However, western gulls are not exactly what you'd call good neighbors. In fact, the adult gulls keep a sharp eye on the nests of their neighbors, and will rapidly descend to eat cormorant eggs or chicks if the parents relax their guard for even a few seconds.

The nests of Western gulls are typically just loose bundles of sticks or other vegetation. One researcher found gull nests in Elkhorn Slough to be made of pelican feathers, pickleweed stems, dried grasses, dried fish, and other remains of prey. On coastal cliffs, gulls will sometimes just dig a small pit in the dirt and use that as a nest.

Not surprisingly, the largest nesting colony of Western Gulls is located on the Farallon Islands. In addition to eating eggs and chicks of many nesting birds (including those of their own kind), western gulls on the Farallones will attack small adult seabirds such as Cassin’s auklets and storm petrels. This extra protein helps the gulls and their young survive the rigors of the nesting season.

Pigeon guillemots build nests

If you walk along West Cliff Drive in Santa Cruz during April, at some point you are likely hear high-pitched whistling cries, as small birds with stubby winds fly out across the nearshore waters. These are pigeon guillemots (Cepphus columba). If you scan the kelp beds, you may be lucky enough to see pairs of guillemots courting.

Pigeon guillemots are small birds, all black except for a small white patch on each wing. They have thin, dark bills but red legs and feet, which often dangle beneath the birds like as they.

When swimming, pigeon guillemots float low in the water and look somewhat surf scoters. However scoters are stockier and have thicker bills. Over the course of the years, the two birds take turns occupying the nearshore waters--guillemots typically arrive in spring just as surf scoters leave the area.

Pigeon guillemots live dual lives. From March through September, they are homebodies, living in cozy little burrows and fishing in kelp beds from southern California to Southern Oregon. Then, come late fall, they fly far out to sea and spend the stormy winter months feeding on small fish in the open North Pacific and the Gulf of Alaska.

Guillemots first begin arriving on the Central Coast in March. At this time of year, you might see a pair or a loose group of three to five birds floating within a few hundred yards of shore. At the Farallon Islands, guillemots may form large rafts, with dozens of birds. In either case, the birds soon begin to stake out nesting sites in shallow rock crevices or loose material in the upper parts of sea cliffs.

Up to 2,000 guillemots nest at the Farallones each year. On the mainland, scattered pairs of pigeon guillemots nest on exposed sea cliffs near Point Reyes and the Marin Headlands, near San Francisco's Cliff House, along West Cliff Drive in Santa Cruz, at the old canneries in Monterey, at Point Lobos, and along the Big Sur coast, as well as other spots.

Along West Cliff Drive, between the Santa Cruz Wharf and Natural Bridges State Beach, guillemots typically nest in burrows dug into the soft, sandy "terrace deposits," about 2/3 the way up the cliff face. The entrances to these burrows are usually obscured by overhanging vegetation, making them very difficult to see.

After emerging from its burrow, a guillemot will leap off the cliff face and fly in a long, swooping arc over the water, emitting a series of rapid, high-pitched squeaks.

Pigeon guillemots seem to spend hours just floating around the kelp beds, perhaps keeping an eye on their nests from the relative safety of the water. When hunting for food, they leap from their nests, fly fast and low over the water, and then land just beyond the kelp beds. Having reached their foraging grounds, they dive down to the seafloor by flapping their wings and kicking their feet.

Pigeon guillemots dive as much as 50 feet below the ocean surface to hunt small sea-floor animals such as juvenile rockfish, young octopus, blennies, sculpins, and grass shrimp. Soon after guillemots arrive on the Central Coast, the first young rockfishes and octopus give up their drifting larval stages and settle down to the seafloor around the kelp beds. [Are blennies and sculpins also more abundant during upwelling season or perhaps later in summer?]

One April afternoon, I watched a pair of pigeon guillemots courting in the kelp beds off Lighthouse Point. First the male and female birds swam slowly around each other, but kept their distance, like wrestlers circling before a match. Then, as if on cue, both birds turned abruptly and faced each other, about six feet apart. Like tango dancers, the two birds swam slowly toward each other, then passed side by side, their wings barely touching.

They repeated this pax de deux several times. Each time they swam past each other, the male and female birds turned their heads to nuzzle one another. Several times, at this point in the dance, the male swam around behind the female and tried to mount her. But most of the time, after approaching one another, the male and female guillemots just continued to swim straight ahead until they were about six feet apart once again. Then they turned, face one another, and began the dance anew.

Marbled murrelets nest in old-growth trees

While some local seabirds find safe nesting places on offshore islands or remote wilderness areas (many of which are threatened by oil and gas development). Marbled murrelets (Brachyramphus marmoratus) have come up with yet another strategy for protecting their young (which also puts them at risk from human resource extraction). Beginning in March or April, they nest in the upper branches of old-growth Douglas fir and redwood trees.

Note: Not all marbled murrelets nest locally. Some spend winters on the Central Coast, but migrate to nest above tree line in the mountains of Alaska and Canada.

During the fall and winter, you can occasionally see these small seabirds foraging nearshore or offshore waters. Diving as far as 100 feet below the surface, they hunt small fish, shrimp, and amphipods. Slow and inconspicuous at the sea surface, murrelets are fast and agile underwater, and will chase and capture schooling fish such as anchovies.

In spring however, marbled murrelets become much less common, though pairs are occasionally seen in local waters. Until the 1970s, no one knew exactly where these birds went during summer. In 1974, however, a tree trimmer discovered a nesting pair of marbled murrelets 140 feet up in the branches of a Douglas fir within Big Basin State Park, high in the Santa Cruz Mountains.

At dawn these little birds fly twenty miles or more from their nests in coastal mountains to hunt for food along the coast. At dusk they fly back to their tiny nests of mosses and lichens. In late May or June, each pair of birds lays a single egg, covered with a mottled pattern of light-green and yellow that blends in perfectly with their nest and with the surrounding foliage.

The adult murrelets are also colored so that they are nearly invisible in their nests. During winter, their bodies are gray above and light underneath--typical colors for open-ocean seabirds. In spring, however, their plumage changes to a mottled brown color that blends perfectly with the tree limbs where they nest.

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