The Mystery of the Marbled Murrelet

Ground-breaking research is shedding some light on the private life of the Marbled Murrelet--a squat, marbled sized seabird whose nesting habits have remained a mystery to ornithologists until recent years. Since 1998, Environment Canada biologists have successfully radio-tracked this threatened species to its nesting sites, and fledged the first murrelet chick ever hatched in captivity.

Departmental scientists have been studying murrelets since 1990, three years before the first active nest in Canada was found in an old-growth forest on the coast of British Columbia. The discovery was a surprise, since most alcids, like puffins and guillemots, nest on steep cliffs or in crevices or burrows; and 1 000 metres above sea level, high on the mossy side-branch of an ancient cedar, seemed an unlikely place to find a seabird. Although the nest of a Russian murrelet was found in 1961, the first one in North America didn't come to light until 1974. The birds are notoriously hard to spot en route to their nests because most of their trips are made in the dark, and daylight excursions to carry small fish to the nestling are unpredictable and uncommon.

Concerned about declining numbers of this once-common species across its range-limited in North America to the Pacific Coast between California and Alaska, and in Canada to the coastal region of British Columbia-Environment Canada and its partners at Simon Fraser University and the B.C. Ministry of Forests launched a large-scale banding program in 1994. Researchers have captured and banded some 1 500 birds in the Desolation Sound area and other parts of the B.C. coast over the past six years.

Their research showed that murrelets can live 10 years or more and that, despite the direct impacts of oil spills and gill-netting, and displacement from old-growth forests due to logging and from coastal waters due to aquaculture and marinas, they have an annual survival rate of 85 per cent. The fact, however, that juveniles comprise as little as 13 per cent of the total population points to a possible problem with nesting success-a serious concern for a species that lays only one egg a year.

Scientists theorize that the low juvenile recruitment rate may be related to a shortage of suitable nesting habitat brought on by the disappearance of old-growth forests. These have been reduced to roughly half their historical coverage and are shrinking rapidly due to extensive logging. With less prime habitat to choose from, murrelets may be nesting in unsuitable areas, where their eggs are more prone to predation or exposed to the effects of weather.

To determine the precise habitat needs of the species, researchers used the "occupied detection" method of watching and listening for murrelets and assuming that if they were below the forest canopy or circling they had nests nearby. Although these studies showed old-growth forests in valleys as primary nesting habitat, scientists are now realizing that the data may have been skewed by the facts that these areas are more accessible for field work than others, and that many birds use valleys as transportation corridors.

In 1998, biologists found evidence to support this theory after birds fitted with radio transmitters led them to 23 nests-most located on steep slopes in high-altitude forests and most of these completely inaccessible to humans. The same held true last year, when another 46 nests were found in similar circumstances. These discoveries could have a significant impact on habitat conservation efforts, which are currently centred on low-altitude old-growth forests.

Last spring, radio tagging also resulted in two murrelets laying eggs in a research boat while they were being fitted with transmitters. This chance occurrence resulted in one of the eggs being hatched, and the fledged chick released back into the wild. The experience could prove useful if there is ever a need to create a captive population, as no captured murrelet has ever survived in captivity.

This spring, scientists will expand their radio tracking efforts to include Clayoquot Sound. They hope, by identifying and protecting the optimum habitat required by this mysterious bird, to ensure not only its survival, but also the survival of the many other species that rely on these increasingly rare ecosystems.

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