Shorebirds and Seabirds

The Great Kelp Grocery Store

Great expanses of sandy beaches punctuate the edge of the continent adjacent to the bull kelp forests of the North Pacific, between rugged rocky outcrops, cliffs, and bluffs. Bull kelp and other kelps wash up onto these beaches creating piles of wrack that perhaps aren’t recognized for the enormous benefits they provide to the entire near-shore ecology. They are known as trophic subsidies to the beach and dunes, a nutritional bridge between the marine world and the world on shore. In their afterlife bull kelp and other kelps form the base of the food chain when washed up on the beach just as they form the base of the food chain when vibrant and alive in the kelp forest below the ocean’s surface. Sand-dwelling invertebrates, such as kelp flies, isopods, beach hoppers, and roly polies consume this organic kelp wrack and, in turn, are the chief target for hungry shorebirds.

Long-term studies have shown a one-to-one relationship between the amount of kelp wrack on the beach and healthy shorebird populations; kelp detritus means invertebrates (tiny) which in turn means healthy birds. How shorebirds find these juicy crustaceans and kelp flies depends on what kind of predator they are. Some, like the snowy plover, are visual predators with big eyes and a high percentage of rods to cones, spotting their insect prey in dim morning or evening light. Others are tactile foragers, think of curlews, sandpipers, and godwits, probing and sensing with their long, sometimes curving, bills.

Seabirds also have an intimate dinner-time relationship with the kelp forest. It is a relationship we know intuitively, as both sea birds and kelp forests are indicators of the health of the marine environment, but the direct connection is hard to quantify. Seabirds depend on the kelp forest as habitat for the small fish they dive for. While kelp forest health is hard to see underwater, seabird nesting colonies are relatively easy to document and it turns out that breeding success of seabirds is a good indicator of general ocean health. If the small fish these seabirds prey on are plentiful in the waters adjacent to the rocks and cliffs where they nest, baby birds fledge, grow to adulthood, migrate by sea, and return to nest, lay eggs, and complete the cycle. But it all depends on the kelp forests’ largesse as fish habitat. Work is happening now to overlay long-term satellite data imaging kelp abundance over time, with the long-term seabird population data sets, to make the kelp-seabird intimacy explicit.

Snowy Plovers, unlike other shorebirds, do not migrate up to the Arctic in spring. They stick around the coastal temperate zone of the Pacific coast, making their home in the upper dunes of sandy beaches from Baja through the great sandy stretches of Oregon. This vulnerable yet resilient powerhouse of a shorebird makes its home in spaces we humans covet, and its biogeography maps directly onto heavily anthropocentric beach zones. They prefer to breed in undisturbed dunes with native diversity of flora and plenty of kelp wrack, not only for food provisions but also for creating the smallest of bulwarks on the sand to lay some eggs. An elegant curve or crook in a piece of bull kelp, with sand blown up against it makes the perfect rampart for the snowy plover’s nest.

The female lays two to six eggs expending enormous energy to lay and brood the eggs. The eggs hatch simultaneously after 26 days in what can seem like barely a divot in the sand. The tiny fuzzball hatchlings are not suckled or fed by the parents at all. They immediately start hunting and eating insects themselves, returning to the father at the nest who takes over brooding the young for about four weeks. And so the snowy plover’s world is intimately tied to the nuances of topography of the upper beach, where the beneficence of the fresh wrack gives way to the structural benefits, as dried bull kelp stipes hide barely discernible nests and plover babies. In the four weeks before hatchlings fledge, they grow from 5 grams to 40 grams, an eightfold increase in biomass, all due to the constant supply of insect protein, the trophic subsidy brought ashore by the bull kelp and other algae from the nutrient dense waters of the Pacific Ocean. Nest predation by ravens and crows, who have adapted so effectively to human environs and become the most successful egg thieves of all, is one of the greatest threats to plover populations.

The Pelagic Cormorant also benefits directly from the bull kelp forest, but as an oceanic, fish-eating bird, the kelp’s benefit to the cormorant is as ecosystem engineer. The bull kelp forest is home to anchovies, herring, and up to thirty different kinds of young and forage fish the cormorants are so good at diving to catch and eat. Despite its name referencing the open ocean, the pelagic cormorant hugs the shores of the North Pacific, rarely flying farther from the coast than the rocky, kelp forest zone. Cormorants are spectacular divers, becoming black torpedoes underwater, and can hold their breath for up to two minutes, preying on fish within the bull kelp forest. They overlap with pigeon guillemots in range and species of prey, but pelagic cormorants eat the larger fish while the guillemots eat the smaller ones. Even the three species of cormorant found along the Pacific Coast—pelagic, Brandts, and double-crested—all have subtle differences in their forage zones so as not to compete with each other. They also nest in different ways. The pelagic cormorants nest on small slivers of shelf on cliff faces facing the ocean, laying eggs and growing young in what seems like impossible circumstances. By late July/early August, each nest might have two or three young cormorants, as big as their parents but identified by their lackluster feathers that are not yet shiny. Their speedy growth, from fuzzy chick to full-sized cormorant in two months—like the nearby gull and common murre young as well—is a testament to the nutrient riches offshore that drive such growth. The subsidies of the bull kelp forest to this seabird lifecycle are tied directly to its status as a habitat-creator for the fish that it depends upon to survive.

Cormorants also use kelp wrack to build their nests along coastal cliffs, using their guano to stick the kelp and seaweed fronds together and in turn glued to the steep rocks, adding stability to the precarious positioning. Cormorants stealing their fresh seaweed collections from each other is not an uncommon sighting. The year-round range of the pelagic cormorant closely mimics the range of bull kelp itself, suggesting a close connection between the kelp forest below the surface and these fantastic fishers who dive into it.

The Marbled Murrelet is the seabird that is, perhaps, the most literal connector between the forests below and the forests above. It is an acrobatic diver, catching sardines, herring, squid, and zooplankton in the bull kelp forests of the North Pacific, but nesting and raising its young in old-growth trees of the adjacent coastal forests. In today’s world, with limited old-growth forests left in the lower 48 states of the US, the marbled murrelet is most commonly found along the foggy coastlines and rocky waters of Alaska and northern British Columbia. Unlike cormorants, it uses its wings underwater, diving quickly to catch small fish relatively close to shore. It is the larger fish however—anchovies and herring—that it brings to nesting young, flying at great speeds, often long distances, to transfer these nutrients from the ocean environment to the forests. It builds nests on the long horizontal branches covered in moss and lichen of old Sitka spruce, Douglas-fir, Alaska yellow cedar, western red cedar, western hemlock, mountain hemlock, and coast redwood, most often choosing the tallest tree in the area. But building is perhaps too suggestive as there is no nest built: a single egg is laid in a depression in the moss on a large branch in the forest canopy, and a single chick is hatched and fledged.

Marbled Murrelets are elusive birds making their connection between ocean and forest even more poetic. Their nesting habits were a mystery for years because their old-growth habitat had been destroyed in most places where people were trying to find them, like the redwood forests of Northern California. Their nests were only discovered by happenstance in 1974. While their nests and young are raised in the forest canopy, the courtship of two murrelets begins at sea in late winter and continues into the spring. It is an ocean affair. Partners swim side by side, point their bills skyward and then dive and surface simultaneously. Pairs chase each other in flight then suddenly continue the pursuit underwater. It is an aquatic love story, the pair monogamous throughout the breeding season.