What is a Marbled Murrelet?
The marbled murrelet is a small seabird that lives along the Pacific coast of North America. Here are some key facts about this unusual bird:
Description
The marbled murrelet is a member of the auk family. It gets its name from the marbled brown and black pattern on its feathers. Here are some physical characteristics:
- Size: 8-10 inches long with a 16-18 inch wingspan
- Plumage: Brownish-black and white marbled pattern on its back and wings. White underneath.
- Bill: Short, pointed
- Legs/feet: Webbed feet for swimming. Legs set far back on body for propulsion in water.
The marbled murrelet has a chunky, seabird body shape with pointed wings. It flies rapidly with fast, erratic wingbeats.
Its marbled brown and black feather pattern provides camouflage when sitting on nests on mossy tree branches.
Range and Habitat
The marbled murrelet lives along the North American Pacific coast from Alaska to central California. Its population centers are in Alaska and British Columbia, Canada.
This seabird nests in coastal old-growth forests up to 40 miles inland. It prefers large, mossy trees and platforms of thick branches for nest sites. Outside of breeding season, it lives entirely at sea.
Here is a map of the marbled murrelet’s range along the Pacific coast:
Breeding and Nesting
The marbled murrelet has unusual nesting habits for a seabird. Instead of nesting on cliffs or shores, it flies inland to nest in the branches of large, old coniferous trees.
Nesting facts:
- Nests are simple depressions built on mossy tree branches, 20-120 feet above ground.
- Lays 1 egg per season, rarely 2.
- Both parents incubate egg for about 30 days.
- Young fledge from nest at 4-5 weeks old.
- Parents fly to sea to catch fish to feed nestling.
- Young are very vulnerable to predators when alone at nest.
Marbled murrelets nest high in the trees, but oddly will fly through open spaces. They have even been known to fly through clearcuts and urban areas during breeding season.
Diet
This seabird feeds on small schooling fish and invertebrates like krill, plankton, and shrimp. Its main prey includes:
- Anchovies
- Sardines
- Sand lance
- Herring
- Crab larvae
- Krill
The marbled murrelet dives underwater to depths of 30-98 feet to catch prey. It is a nimble swimmer and flier, well-adapted for catching fast schooling fish.
Threats and Conservation Status
The marbled murrelet is listed as Threatened under the U.S. Endangered Species Act. It faces a number of threats to its survival:
- Habitat loss from logging of coastal old-growth forests
- Increased nest predation from corvids like jays, crows, and ravens
- Disturbance of nest sites and collisions with human structures
- Changes in prey availability due to changing ocean conditions
- Oil spills along coast
Conservation efforts aim to protect remaining old-growth nesting habitat. Artificial nest sites are also established in some areas as an experiment to help breeding.
Marbled Murrelet Natural History
The marbled murrelet has a fascinating natural history and life cycle adapted to its ocean and old-growth forest home. Here are some details about the behavior and biology of this unusual seabird.
Migration
The marbled murrelet undergoes two types of seasonal movements:
- Inland-coastal migration: In the spring, birds move from wintering areas at sea to inland nesting sites. In the fall, the reverse trip occurs back to coastal waters.
- Latitudinal migration: Northern populations in Alaska undergo longer migrations south to avoid winter ice. Birds in Washington, Oregon, and California are more resident year-round.
These migration patterns reflect how the marbled murrelet’s life cycle depends on both old-growth forests and the marine environment.
Breeding Behavior
The marbled murrelet has unique breeding behaviors and adaptations:
- Breeding season is March to September, beginning earlier in southern range.
- Birds nest solitarily. No colonies.
- Same mate may be kept for more than one year.
- Male selects nest site and prepares branch depression prior to egg-laying.
- Nest exchange: Parents take turns incubating egg and catching fish to feed young. These exchanges happen up to 8 times per day.
- Parents call to locate nest site and exchange incubation duties.
- Chick is very precocial – able to walk and swim shortly after hatching.
The need to fly inland and locate nests in dense forests is a very unusual strategy for seabirds. It shows how the marbled murrelet’s life cycle is split between two very different ecosystems.
Feeding Ecology
Marbled murrelets have a varied diet and several adaptations for feeding at sea:
- Dives underwater from air or surface to catch prey.
- Swims underwater using wings for propulsion.
- Uses serrated bill edge like tiny teeth to grab slippery fish.
- Carries prey items singly back to nest in sublingual pouch under tongue.
- Feeds on range of small fish species depending on availability.
- Young chicks fed up to 8 times per day, mainly with fish but some invertebrates.
This seabird relies on schooling fish and inverts that thrive in cold, nutrient-rich waters off the Pacific coast. Changes in ocean conditions can affect the availability of prey.
Marbled Murrelet Forest Habitat
One of the marbled murrelet’s most unusual traits is that it nests inland in coastal old-growth forests. The specific forests used by this seabird are vital to supporting the breeding population.
Forest Types
The marbled murrelet nests in mature and old-growth forests along the Pacific coast. The main forest types used are:
- Coastal redwoods – Northern California and Southern Oregon
- Douglas-fir – Oregon and Washington
- Western hemlock and Sitka spruce – Alaska and British Columbia
These massive, long-lived conifer species offer the large mossy platforms required for nest sites high in the canopy.
Nest Tree Characteristics
Marbled murrelets are very selective in choosing nest trees:
| Feature | Preference |
|---|---|
| Tree height | Over 200 feet tall |
| Trunk diameter | Over 3 feet wide |
| Platform type | Thick, mossy branches or deformities |
| Canopy cover | Over 30-40% closed |
Nest platforms tend to be very high in the tree, providing protection from predators. Easy flight access is important.
Old-Growth Traits
In addition to large trees, marbled murrelet habitat needs certain traits of old-growth forests:
- Multi-layered canopy
- Downed logs and woody debris
- Canopy gaps for flying through
- Open understory with limited ground cover
These structural elements reduce predators, support nest platforms, and allow access for flight and breeding.
Marbled Murrelet Population and Conservation Status
The marbled murrelet has declined over the last century mainly due to loss of old-growth nesting habitat. Current population estimates and conservation status are reviewed here.
Population Size
The total North American population of marbled murrelets is estimated between 192,000 – 205,000 birds. This includes:
- Approximately 102,000 in Alaska
- 32,000 – 54,000 in British Columbia
- 22,000 – 28,000 in Washington, Oregon, and California
These population sizes represent significant declines from historic levels before logging of coastal old-growth forests.
Population Trends
Many marbled murrelet populations continue to decline, especially in the southern parts of the range:
- Decline of 4.4% per year in Washington
- Decline of 3.9% per year in Oregon
- Decline of 7.4% per year in central California
Causes likely include ongoing habitat loss, nest predation, and changing ocean conditions affecting prey.
Federal Protection Status
The marbled murrelet is federally listed as Threatened under the U.S. Endangered Species Act. It was first listed as Threatened in 1992 in Washington, Oregon, and California. This was extended to include Alaska in 1997.
This listing recognizes the threats to the species and implements protections. However, the murrelet population has continued to decline over much of its range. Some conservation groups argue that an Endangered listing is now warranted given ongoing habitat loss.
How to Conserve Marbled Murrelets
Many conservation actions are underway to try to stabilize declining marbled murrelet populations. These include:
Habitat Protection
- Preserve remaining areas of coastal old-growth forest on public and private lands
- Establish buffer zones around nesting habitat to reduce disturbance
- Restrict logging and development near occupied murrelet habitat
Habitat loss is still the primary threat to marbled murrelets. Protecting both existing and potential future nesting habitat is key.
Reduce Nest Predation
- Limit corvid populations in murrelet nesting zones
- Install nest platforms or artificial nests to reduce ground predators
Predation pressure has increased, especially by jays and crows in fragmented forest habitats. Targeted predator control and providing alternative nest sites may help offset this.
Captive Breeding and Translocation
- Use captive breeding and release programs to augment wild populations.
- Translocate chicks from dense nesting sites to areas with small populations.
These techniques are being tried experimentally to boost murrelet populations in some locations. Further research is needed to see if they are effective.
Monitoring and Research
- Continue at-sea and nest monitoring to track population trends.
- Study effects of ocean conditions and prey availability on breeding success.
- Research impacts of human disturbance like boat traffic or noise.
Better information is still needed on factors limiting murrelet populations. Targeted research and monitoring can help identify the most effective conservation actions.
Conclusion
The marbled murrelet is a seabird with a unique life history tied to both coastal old-growth forests and the Pacific Ocean. Loss of nesting habitat threatens this species across its range. Ongoing conservation efforts aim to stabilize declining populations by protecting forests, reducing nest predation, and researching additional threats. With coordinated action, there is hope that the marbled murrelet’s fascinating natural history will continue to be part of the Pacific Northwest’s coastal forests and marine ecosystems.
