The Marbled Murrelet has a very unique habitat compared to other seabird species. This rare seabird nests in large, mossy branches near the tops of coastal old-growth trees, while other seabirds nest on rocky cliffs or islands. The Marbled Murrelet has evolved adaptations that allow it to utilize forests as nest sites. Some key questions about the unique aspects of the Marbled Murrelet’s habitat include:
Where does the Marbled Murrelet nest?
The Marbled Murrelet nests in mature and old-growth forests within about 50 miles of the coast, from Alaska to central California. Nests are typically built on large, mossy branches near the tops of tall trees. The Marbled Murrelet is the only seabird in North America that nests primarily in trees.
The specific tree species used for nesting varies across the Marbled Murrelet’s range:
Region | Primary Nest Tree Species |
---|---|
Alaska | Mountain hemlock, Sitka spruce |
British Columbia | Western hemlock, Sitka spruce, Douglas-fir |
Washington | Douglas-fir, western hemlock |
Oregon | Sitka spruce, Douglas-fir, western hemlock |
California | Coast redwood, Douglas-fir |
The trees used for nesting are typically very large and old, with platforms of moss and debris for the nest. Nest trees are often found inland within 25-50 miles of the coast. The forests provide protection from predators and from harsh weather. The Marbled Murrelet is uniquely adapted to utilize large, mature trees for nesting compared to other seabirds.
Why does the Marbled Murrelet nest in forests?
There are several key reasons why the Marbled Murrelet nests in coastal forests, an unusual habitat for a seabird:
– Predator avoidance – Nesting high up in the canopy helps avoid many ground predators like raccoons, foxes, bears.
– Stable microclimate – The forest canopy provides a relatively stable, cool, and moist microclimate compared to more exposed cliff/island nest sites.
– Abundant moss – Moss in the canopy provides nesting material to build a nest platform concealed from predators.
– Protection from weather – The forest canopy provides shelter from wind, rain, and storms.
– Wide distribution – Suitable nesting habitat is widely distributed in the coastal forests along the Pacific Northwest coast.
The Marbled Murrelet is thought to have evolved these unique nesting adaptations over thousands of years due to heavy predation pressure from mammals in North America. The forest canopy provides the secrecy and protections needed to successfully hatch eggs and raise chicks.
What forest characteristics are preferred for nesting?
The Marbled Murrelet prefers old-growth coastal forests with certain characteristics for nesting:
– Large, mossy tree branches at least 4 inches in diameter, high in the canopy.
– Tall, mature trees >200 years old or >100 feet tall provide access to high nest sites.
– Presence of epiphytes (plants growing on branches) which produce nesting mosses.
– High canopy closure (>60%) provides cover and stable conditions.
– Trees spaced far enough apart for flight access in and out of the stand.
– Low understory vegetation to allow flight under the canopy.
– Proximity to coast (usually < 50 miles inland) for foraging. The old-growth trees along the Pacific Northwest coast are unique globally in their height, longevity, and moss growth. These characteristics perfectly suit the Marbled Murrelet's nesting requirements, which is why they are dependent on these sensitive forest habitats.
How do the nests themselves look?
Marbled Murrelet nests are quite simple, consisting only of a shallow depression in a platform of moss, lichen, needles, small twigs, and debris. Typical features include:
– Built on large mossy platforms or deformities on large branches.
– Shallow bowl shaped depression approximately 2 inches deep and 5 inches wide.
– No substantial nest structure built up.
– No additional lining added to the nest.
– Cryptic; often concealed below live moss or obscured by branches.
– Typically 65-170 feet above ground.
– Difficult for predators to access and spot.
The simple nests are adapted for secrecy high up in the canopy, and rely on the structures naturally present on the mature tree branches. The nests blend into the mosses and lichens in the tree canopy.
When does nesting occur?
Marbled Murrelets nest during the spring and summer months along the Pacific coast. The timing of breeding varies by region:
Location | Breeding Season |
---|---|
Alaska | May – September |
British Columbia | April – August |
Washington | April – September |
Oregon | May – September |
California | March – August |
In all regions, peak egg laying occurs between late May and early July. The timing allows chicks to hatch during peak prey availability in the marine environment during summer. Nests with eggs or chicks are very sensitive to disturbance during these critical breeding months.
How do the nesting habits vary across the range?
While Marbled Murrelets share core nesting behaviors across their range, some habitat factors vary by region:
Location | Key Factors |
---|---|
Alaska | – Nests near glacial fjords with upwelling – Uses lower slopes and valleys – Bears are main predator |
British Columbia | – Nests often far inland on plateau – Higher density of nests – Uses higher slope positions |
Washington | – Intermediate densities of nests – Mid-slope positions used – Raccoons are main predator |
Oregon | – Highly coastal nesting habitat – Ravens become more of a threat – High densities on coast |
California | – Very coastal nesting sites – Ravens are significant predator – Fire shapes habitat |
These regional variations reflect differences in forest structure, predator distributions, fire regimes, and oceanography along the Pacific coast. But across their full range, Marbled Murrelets are united by their uncommon reliance on coastal old-growth forests for nesting.
How do they access nest sites?
Marbled Murrelets have unique flight abilities that allow them to access forest canopy nest sites:
– Powerful wingbeats – Their wings are shaped for speed and diving to capture fish, allowing rapid flight in open areas.
– Slow maneuvering – Their wings enable dexterous flight to maneuver slowly through small forest openings to nest sites.
– Landing ability – They can perch on small branches and land on nests high in the canopy.
– Takeoff – They can take-off vertically from tree branches, important for leaving the forest.
– Cryptic patterns – Their mottled brown plumage helps camouflage them in forests.
– Navigation – Excellent navigational abilities allow them to return to nest sites at dusk after feeding at sea all day.
The combination of speed, maneuverability, camouflage, and navigation gives the Marbled Murrelet specialized access to forest nest sites that most other seabirds lack. Their agility helps compensate for nesting far from the marine environment.
How do chicks fledge from the forest?
Marbled Murrelet chicks face a challenging journey when fledging from their high forest nest sites:
– Branch jumping – Chicks jump and climb through the canopy to lower branches for several days as their wings develop strength.
– Wing fluttering – On lower branches, chicks exercise and build flight muscles by fluttering wings.
– Solo flights – After leaving the branch, fledglings fly alone through the forest to the ocean, a journey of 25-50 miles.
– Extended period – The fledging process takes around 2-3 weeks from hatching to reaching the sea.
– Predation risk – Fledglings are vulnerable to predators as they move lower in trees and on forest floor.
– Disorientation – Chicks may become disoriented navigating the forest and get stranded far from ocean.
The extended fledging period and long journey make this stage perilous for young murrelets. But evolved capabilities help most fledglings successfully reach the marine environment.
How do populations distribute across nesting habitat?
Marbled Murrelet populations are not distributed evenly across their coastal forest nesting habitats. Some key patterns observed include:
– Patchy distribution – Murrelets tend to cluster nesting in patches of higher quality habitat.
– Forest structure – Areas with taller trees, more moss, and higher canopy closure tend to support more nests.
– Interior forest – Highest densities generally found within 24 miles of the coastline.
– Fragmentation – Murrelets avoid nesting near habitat edges and in fragmented forests.
– Disturbance – Human activity, roads, development, and logging reduce nesting density.
– Declines – Population declines are linked with loss of coastal old-growth habitat.
These patterns illustrate the Marbled Murrelet’s dependency on specific old-growth forest stand characteristics. Loss and fragmentation of prime nesting habitat negatively impacts murrelet distribution and abundance. Careful protection of remaining habitat is critical.
How do humans impact murrelet nesting habitat?
A variety of human activities have altered murrelet nesting habitat, leading to population declines:
– Logging of old-growth – Removal of nesting habitat is the primary threat, especially clearcut logging.
– Habitat fragmentation – Forest roads and land development fragment suitable habitat.
– Nest disturbance – Human recreation activities may impact nest success.
– Increasing predators – Human infrastructure can increase predator populations in forests.
– Climate change – Fire, disease, wind, and logging of border trees impact habitat.
– Pollution – Oil spills, marine debris, and pollution impact the nesting parent’s marine prey sources.
– Fishing bycatch – Gillnet and longline fisheries incidentally catch and drown murrelets.
Protecting remaining old-growth forests is crucial for murrelet recovery. Buffer zones around nesting areas, limited road construction, and public education can also help reduce human impacts. Careful monitoring is essential for maintaining sensitive nesting habitats.
Conclusion
The Marbled Murrelet has a one-of-a-kind nesting ecology that sets it apart from all other seabird species. By utilizing tall, coastal old-growth trees draped in moss, the murrelet has evolved a suite of adaptations to take advantage of this unique forest habitat. Key features like cryptic plumage, maneuverable flight, camouflaged nests, and a dispersed but patchy nesting distribution allow Marbled Murrelets to successfully breed far from the marine environments where they feed. However, this uncommon dependency on old-growth forests makes murrelets highly vulnerable to habitat loss from logging, development, and other human activities. Increased protection of remaining coastal old-growth stands will be critical for ensuring the future survival of the fascinating Marbled Murrelet.