|
Deepseawaters
Home Deep
Sea BirdsMarbled
Murrelet
Marbled Murrelet
Common Name: Marbled Murrelet
Scientific Name: Brachyramphus marmoratus
Description
Marbled
Murrelets are small seabirds. They are members of the same
family as auks, puffins and murres. In winter, they have black
and white plumage and conspicuous white wing patches. During
the breeding season, they have mottled-brown plumage. Chicks
have yellow or greyish yellow down, with dark spotted upperparts.
Murrelets fly very quickly with rapidly beating, pointed wings.
Distribution and Population
Marbled
Murrelets occur along 4 000 kilometers of coastline extending
from California to Alaska. Within this range, they can be
found up to 75 km inland. The geographic centre of the species’
range is in southeast Alaska, and Alaska and Canada are home
to the largest numbers of birds. Populations in California,
Oregon and Washington are fragmented. The winter range of
the species is not well known, but in the southern parts of
the range some birds may remain at breeding sites throughout
the year. In Canada, Marbled Murrelets are found only in British
Columbia. Here they occur in coastal areas in both summer
and winter.
The
Marbled Murrelet is very difficult to survey. The total population
size is unknown, but it is estimated to be between 263 000
and 841 000 individuals, at least 50 000 of which occur in
Canada. The status of the species in various areas is not
well documented, but a preliminary estimate at one site indicates
a 4% decline.
Habitat
Marbled
Murrelets forage in the inshore marine environment, primarily
in protected waters where both sand lance and surf smelt occur.
They travel long distances between at-sea locations and nest
sites. They require old-growth forest for their nests, which
they place high in the trees. They need tree cover above the
nest, but small gaps in the canopy for accessing the nest.
The birds do not build nests, but use a large limb covered
with deep moss that serves as a platform in which they make
a depression for their single egg. In addition, in Alaska
a very small percentage of birds nests on the ground. It is
estimated that a large percentage of old-growth forests within
this species’ range has been removed over the last 150
years.
Biology
Marbled
Murrelets nest singly or in loose associations in inland areas.
Their nests are very difficult to find and access, and the
species is sensitive to disturbance. These factors make them
very difficult to study. Their lifespan remains unknown, but
the oldest Marbled Murrelet that has ever been found was more
than 10 years old. Marbled Murrelet movements are not well
understood either, but the birds carry out partial migrations
outside the breeding season. The age at which they begin breeding
is unknown but it is assumed to be about two years. Marbled
Murrelets have a protracted breeding period, with the individuals
of a population not all breeding at the same time. Both females
and males share in incubating the eggs and caring for the
young. Each pair has only one egg per season and incubation
lasts about 28 days. Nesting success is low, mainly because
of predation from other birds.
Threats
The
greatest threat to Marbled Murrelets is thought to be loss
of their nesting habitat. They have specific nesting needs
in old-growth forests, which are the focus of much commercial
activity. There are also substantial threats from oil contamination,
and entanglement in gill-nets when the birds forage at sea.
The species has a very low reproductive rate. Conservation
is dependent on the species being long-lived and each pair
producing many young over its lifetime. Human-induced factors
threaten the survival of the adults, thereby putting the population
at substantial risk.
|
