The Morro Bay Winter Loon Study Common loon species account
There are five species of loons in North America (genus, Gavia); common loon, red-throated loon, Pacific loon, Arctic loon, and yellow-billed loon. Arctic loon and yellow billed loon sightings are very rare in Morro Bay. These birds breed, migrate and winter north of the Canadian border and into the Arctic
The red-throated and Arctic loon are a more pelagic species. While these two species can be seen in our area there are usually found offshore. Oftentimes they will seek to shelter of our estuary during very strong storms or when ill or weak.
Migrations of hundreds of Pacific loons per hour can be seen in April (the first two weeks) along our coast. Observation posts near the Piedras Blancas lighthouse are the best viewing points. Red throated migration can be seen albeit in smaller numbers during the same time. Both of these birds employ a lower, slower flight strategy, seldom higher than 30 feet above the water.
The predominant species on our Bay is the common loon. While all loons have similar adaptations, this paper will focus on the common loon, gavia immer.
The common loon’s range is the widest of all five species. The common loon breeds on inland lakes from southern New York State through the lower Great Lakes / St. Lawrence seaway along the Canadian-American border to the West Coast. Their migration patterns have been speculated but field biologists are presently confirming these routes (first generation, subcutaneous radio and satellite transmitters yielded poor results but new technology has greatly improved and good results are now being gathered). Last spring, we tracked for the first time on the West Coast, the departure of a common loon from it’s wintering grounds (Morro Bay, California) to its breeding territory (Lower Stillwater Lake, Montana). This particular bird was banded in Montana in 1997 and we speculate she has spent each winter here since then. We observed her almost daily during the 2004 2005 winter season. We don't know if she flew up the coast and turned east at the Columbia River or moved directly inland from Morro Bay, over the Sierra. Common loons stop each evening and rest and feed before continuing their migration, so their routes must follow inland water courses. As is true for many species, spring migration is much quicker. This particular bird took five days to cover almost 1000 miles. Common loons can fly at 60 miles an hour or faster, and have been recorded in flight at 8000 feet. Our surveys show from 30 to 50 use our Bay during the winter season (late October through April). The population trails off after April to as low as one or two birds in late summer, early fall. Early in the week of October 17 there were three loons in our Bay, a week later there were 12.
The loon is most closely related to alcids, Penguins and albatross. Loons are densely feathered and spend all of their time in the water, save nest building, copulation and incubating duties. Adult common loons range from 2100 g to 6000 g., can have a wing span of up to 46 inches and measure almost 3 feet from tip of bill to tail. Loons are visual predators, have excellent eyesight and a nictitating membrane to protect their eyes during dives is deep as 200 feet and up to 15 minutes long. They employ their sharp bill and strong neck as a final thrust after pursuing prey. They do not use their wings underwater (for propulsion) as cormorants or murrelets. They have a unique adaptation that allows a greater range of motion and more power to their legs. Their fibula extends beyond their femur in what is called on cnemial process. This projection allows for attachments of muscles past the point of the fulcrum, giving their leg greater leverage, strength and flexibility. This gives them the advantage in chasing and (very successfully) catching piscine prey. Loons lack many of the hollow bones of other birds to help facilitate their diving and foraging. They possess very large, strong webbed feet, another adaptation making them excellent swimmers. This ability comes at a cost, loons are unable to walk upright and must push themselves along the ground on their chests.
Certainly the image of the common loon foremost in everyone’s mind is that of the breeding adult with the striking, checkered black-and-white feathers on the back and distinct white necklace on the iridescent black neck and head, red eyes and snow white breast. But loons do not exhibit this type of plumage until they reach four years and only during the breeding season (April through August). The winter plumage of the adult loon is much more subdued. The checkered pattern on the back is less distinct, the black head becomes grayish-brown, the throat and breast assume an egg white hue. The eyes of adults are always red (an indicator of adulthood in many species) and the adult bill remains dark gray/black all year. First-year, second-year, and third-year birds are similar to winter-plumage adults, but have rusty, brown eyes and show much more (light) gray in the bill, these non adults also show more scalloping on their backs, the white trailing edge of the feather. Both adults and juveniles go through a cataclysmic molt in February and March, losing all of their heavily worn flight feathers. During this time they are flightless, in fact any loss of feathers can affect loons. Their wing loading is such that they are just on the verge of not being unable to fly, like their relative the Penguin.
Loon behavior differs markedly from summer to winter. A breeding adult is extremely territorial, especially the males. They have been known to attack and kill intruders on their breeding lake. On the wintering ground however, we have found a communal behavior, much less aggressive. Adults are perhaps most aggressive when their precocial chicks are a few weeks old. Their aggressive behavior diminishes as the chicks reached two to four weeks old and are able to dive on their own and have become more adept swimmers. The soft gray, down feathers of the chick makes it difficult for them to dive for any duration. In general, eggs are laid in May or June, and chicks hatch in June or July and are able to fly by August or September. By the end of September loons start leaving the breeding grounds. Whether the chicks follow the adults to the wintering grounds, whether they share the same wintering grounds, whether they are members of the same raft, we have not determined yet. But it is sure that the chick makes this journey the first year and not again for another three years. The return trip to the wintering grounds is much less hurried than the migration north and may take a month or more. While wintering birds vocalize amongst themselves (clucks and hoots), the long tremolos and wails of the breeding grounds diminish soon after their arrival on the wintering territory.
We see and hear what appears to be a different bird on Morro Bay during the winter than in Minnesota, Washington State, Montana or Wisconsin in the summer. But deep down this is the same bird answering the same rhythms of migration, molt, choosing a mate, rearing young, hunting, avoiding predators and carrying the same genes of a species that is over 9 million years old.
