BIOLOGICAL DATA AND HABITAT REQUIREMENTS
WILDLIFE SPECIES: Brachyramphus marmoratus | Marbled Murrelet 



TIMING OF MAJOR LIFE HISTORY EVENTS : 
Age at sexual maturity - Marbled murrelets do not breed until they are
at least 2 years old [16].

Nesting and brooding - Marbled murrelets nest from mid-April to late
September [16].  Peak activity occurs from mid-June to late July in
California, and the second week of July to mid-August in Oregon [17].
Marbled murrelet are semicolonial in nesting habits.  Two nests found in
Washington were located only 150 feet (46 m) apart.  Not all mature
adults nest every year [4].  Marbled murrelets lay only one egg.  The
egg is incubated by both parents for about 30 days.  Adults fly from
ocean feeding areas to inland nest sites, mostly at dusk and dawn.  They
feed nestlings at least once and sometimes twice per day or night.
Usually only one fish is carried to the young [4,16].

Fledging - Nestlings fledge in 28 days.  Young marbled murrelets remain
in the nest longer than other alcids and molt into their juvenile
plumage before leaving the nest [16].  Fledglings fly directly from the
nest to the ocean [4].

Migration - Some marbled murrelet populations probably migrate south in
fall and north in spring.  However, these migration patterns are not
well understood [7].


PREFERRED HABITAT : 
Marbled murrelets are coastal birds that occur mainly near saltwater
within 1.2 miles (2 km) of shore [16].  However, marbled murrelets have
been found up to 59 miles (80 km) inland in Washington, 35 miles (56 km)
inland in Oregon, 22 miles (37 km) inland in northern California, and 11
miles (18 km) inland in central California.  Over 90 percent of all
marbled murrelet observations in the northern Washington Cascades were
within 37 miles (60 km) of the coast.  In Oregon, marbled murrelets are
observed most often within 12 miles (20 km) of the ocean [4].  Many
marbled murrelets regularly visit coastal lakes.  Most lakes used by
marbled murrelets are within 12 miles (20 km) of the ocean, but a few
birds have been found at lakes as far inland as 47 miles (75 km).  All
lakes used by marbled murrelets occur within potential nesting habitat
[8].

Nesting habitat - From southeast Alaska southward, marbled murrelets use
mature or old-growth forest stands near the coastline for nesting
[4,7,16,27].  These forests are generally characterized by large trees
(>32 inches [80 cm] d.b.h.), a multistoried canopy, moderate to high
canopy closure or an open crown canopy [17,26], large snags, and
numerous downed snags in all stages of decay [4].  Marbled murrelets
tend to nest in the oldest trees in the stand [4].  In Oregon, forests
begin to exhibit old-growth characteristics at about 175 to 250 years of
age [17].  Moss, on which marbled murrelets nest, forms on the limbs of
Douglas-fir that are more than 150 years old [16,17].

The only four marbled murrelet tree nests found before 1990 shared the
following characteristics:  (1) located in a large tree (>47 inches [120
cm] d.b.h.) with an open crown structure, (2) on a moss-covered limb
that is camouflaged, partially shaded, and approximately horizontal with
a diameter (including associated moss) of at least 14 inches (36 cm),
and (3) located within the middle or lower part of a live crown [26].
However, Marshall [29] stated that because of their low aerial bouyancy
marbled murrelets often nest high in the treetops or on steep slopes.
Habitat must be sufficiently open to allow for easy flight [17].  All
marbled murrelet nests found in Washington, Oregon, and California were
located in old-growth trees that ranged from 38 inches (88 cm) d.b.h. to
210 inches (533 cm) d.b.h. with a mean of 80 inches (203 cm) d.b.h.
Nests were located high above the ground and had good overhead
protection but allowed easy access to the exterior forest [4].  Marbled
murrelets may use the same nest in successive years [17,29].

Stand size is also important in nest sites.  Marbled murrelets more
commonly occupy stands greater than 500 acres (202 ha) than stands less
than 100 acres (40 ha).  However, marbled murrelets may nest in remnant
old-growth trees or groves that are surrounded by younger trees [17].
In California, marbled murrelets are usually absent from stands less
than 60 acres (24 ha) in size.  In Washington, marbled murrelets are
found more often when old-growth and mature forests make up over 30
percent of the landscape.  Fewer marbled murrelets are found when
clearcut and meadow areas make up more than 25 percent of the landscape.
Concentrations of marbled murrelets offshore are almost always adjacent
to old-growth or mature forests onshore [4,16], although marbled
murrelets may not use the interior of dense stands [29].
  
Where large trees are absent in the northern parts of marbled murrelet
range, marbled murrelets nest in depressions on the ground, in rock
cavities on the ground, or on rock outcrops [9,13,25,26].  Marbled
murrelets are both ground nesters and tree nesters where forests and
treeless areas meet [16].

Foraging habitat - Marbled murrelets forage in the ocean near shore and
in inland saltwater areas such as bays, sounds, and saltwater
passageways.  Some also forage on inland freshwater lakes [17].  Flocks
of 50 or more birds have been observed near freshwater lakes [8].
Subadults occur at sea throughout the summer.  Sealy [30] determined
that marbled murrelets feed within 1,640 feet (500 m) of shore.

Winter habitat - Marbled murrelet winter habitat is the same as the
nesting and foraging habitat.  During the winter marbled murrelets use
inland old-growth or mature sites for roosting, courtship, and
investigating nest sites [17,18]. The use of inland lakes during the
nonbreeding season occurs in conjunction with visits to nesting areas
[8].


COVER REQUIREMENTS : 
NO-ENTRY


FOOD HABITS : 
Marbled murrelets feed below the water surface on small fish and
invertebrates [16,17].  Some principal foods include sand lance
(Ammodytes hexapterus), Pacific herring (Clupea haringus), capelin
(Mallotus villosus), and the invertebrates Euphausia pacifica and
Thysanoessa spinifera [16,17,23].

Marbled murrelets do not feed in large flocks as do other alcids,
although loose aggregations occur in winter.  While feeding during the
breeding season marbled murrelets occur in pairs or as single
individuals.  Subadults feed singly; but in early July, when pairs of
adults are still feeding young, mixed flocks begin to form [16].
Marbled murrelets feed during the day and at night [17].


PREDATORS : 
Steller's jays (Cyanocitta stelleri) and common ravens (Corvus corax)
prey on marbled murrelet eggs and nestlings [26].


MANAGEMENT CONSIDERATIONS : 
The principal factor threatening the persistence of marbled murrelet
over the southern portions of its range is harvesting of old-growth and
mature forests [17].  Old growth harvesting has been heavier in coastal
forests than further inland; and short rotation ages (currently < 80
years) do not allow conifers to develop the large diameter flat limbs
with thick moss layers used for nesting.  Old-growth and mature forests
within the range of marbled murrelets are essential to marbled murrelet
perpetuation [16,29].

Mortality from gill-net fisheries - Marbled murrelets are the alcid most
frequently killed by gill-nets.  In Barkley Sound off Vancouver Island,
British Columbia, an estimated 380 marbled murrelets were killed by
gill-nets in 1980.  This accounted for 7.8 percent of the potential fall
population in the area [29].  Sealy and Carter [24] reported that 600 to
800 or more marbled murrelets are killed (almost exclusively at night)
annually in Prince William Sound, Alaska, due to gill-nets.  Recommended
conservation measures include changes in areas where the gill-net
fishery takes place and prohibition of night fishing.  Gill-net fishing
does not occur off the Oregon coast, but is widespread in Puget Sound
[16].

Mortality from oil pollution - Marbled murrelets have been rated as
having the highest oil vulnerability index of any seabird in southeast
Alaska.  This is based in part on their feeding in loose aggregations
close to shore.  Development in the petroleum industry along the Pacific
coast will increase the threat of oil pollution [24].


REFERENCES : 
NO-ENTRY

Related categories for Wildlife Species: Brachyramphus marmoratus | Marbled Murrelet