The Marbled Murrelet (Brachyramphus marmoratus) is a small seabird that lives along the Pacific coast of North America. Here are some quick facts about its reproduction:
- Nests high up in old-growth coniferous forests, often far inland from the ocean
- Lays a single egg per breeding season
- Both parents incubate the egg and care for the chick
- Chicks fledge at around 28 days old
- Breeding adults return to the same nesting area each year
In this article, we will go into more detail about the Marbled Murrelet’s unique reproductive strategies and behaviors.
Nesting
The Marbled Murrelet has a very unusual nesting strategy compared to most seabirds. Instead of nesting on cliffs or in colonies, it nests solitary in the branches of large, old coniferous trees, usually 20-120 feet above ground.
Some key facts about their nest sites:
- Primarily use coastal old-growth forests of redwood, Douglas fir, western hemlock, and Sitka spruce
- Nest trees are large in diameter (3-6 feet) and very tall (>150 ft)
- Often nest far inland, up to 40 miles from the ocean
- Nest on large, mossy platforms in the branches
- Usually lay just a single egg per season
The Marbled Murrelet has this unusual nesting strategy because it relies on the branches and canopy of these large old-growth trees to protect its nest sites. The dense branches hide the nests from predators like ravens, jays, and squirrels. The height makes it difficult for ground predators like foxes and raccoons to reach.
Old-Growth Forest Dependence
The Marbled Murrelet’s dependence on specific stands of old-growth forest make it highly vulnerable to deforestation. Loss of old-growth forest is considered the major threat to murrelet populations.
Some key reasons they require old-growth trees:
- Large branches and canopy to support their nests
- Nesting platforms of moss that accumulate over centuries
- Reduced predation compared to ground nesting
- Stable microclimate under dense canopy
Unfortunately, extensive logging of these coastal old-growth forests occurred between 1850-2000. It’s estimated that murrelet populations declined by over 70% during this period. Protecting remaining old-growth stands is crucial for conservation.
Breeding and Egg Laying
Marbled Murrelets form pair bonds that last multiple breeding seasons. Courtship and pairing occurs at sea in April-May.
Key facts about their breeding and egg laying:
- Lay just one egg per clutch
- Lay eggs May-September, varies by latitude
- Eggs are bluish-green with brown markings
- Egg size about 3% of female’s body weight
- Incubation period lasts around 30 days
- Parents trade off incubation duties
The single egg clutches are an adaptation to the challenges of nesting high up in tree branches. Too many eggs would risk them rolling out of the nest. The bluish-green egg color provides camouflage against potential aerial predators.
Egg Size Compared to Body Size
Species | Egg Size | Body Size |
---|---|---|
Marbled Murrelet | 3% | 28 cm, 175 g |
Canadian Goose | 5% | 110 cm, 5 kg |
Ostrich | 1.7% | 270 cm, 146 kg |
This table shows how Marbled Murrelet egg size compares relative to body size for some other bird species. The murrelet has a fairly typical egg-to-body size ratio.
Chick Rearing
Marbled Murrelet chicks are semi-precocial – they hatch with eyes open and some downy feathers, but still rely heavily on parental care.
Key facts about chick rearing:
- Chicks hatch after 30 day incubation period
- Hatchlings weigh about 24 g
- Parents brood the chick for 7-10 days after hatching
- Both parents feed the chick multiple fish per day
- Chicks fledge at 27-40 days old
- Fledglings fly alone directly to the sea
The long fledgling period is necessary time for the chick to grow flight feathers, gain weight, and become capable of flying up to 50 miles to the ocean. The parents trade off nest duties and fish capture to provision the chick throughout this period.
Chick Growth
Age | Weight | Description |
---|---|---|
Hatching | 24 g | Covered in down, eyes open |
10 days | 65 g | Downy plumage fuller |
Fledging | 168 g | Feathers for flight grown |
This table shows the rapid weight gain and plumage development that occurs during the 4-5 week nestling period. Fledglings are ready to fly and fish within a month after hatching.
Breeding Site Fidelity
A unique aspect of Marbled Murrelets is their fidelity to the same coastal breeding areas year after year.
Key facts about their site fidelity:
- Show high fidelity to previous year’s nesting area
- Travel up to 1,900 km between marine wintering and breeding sites
- Birds may reuse the same nesting tree or platform
- Have high mate fidelity, pairs stay together across years
- Oldest banded bird returned 16 years in a row
This breeding site fidelity likely developed because of the challenges finding rare, suitable nest platforms in old-growth trees each year. Returning to a prior productive site increases chances of successful reproduction.
Return Rates by Age
Age | Return Rate |
---|---|
2 years | 44% |
3-6 years | 73% |
>7 years | 94% |
This table shows that return rates to natal breeding sites increase dramatically as birds get older and more experienced. The highest fidelity is seen in birds over 7 years old.
Conservation and Threats
Marbled Murrelets face a variety of conservation threats, especially related to loss of coastal old-growth nesting habitat.
Major threats include:
- Logging of old-growth forests
- Increased nest predation from corvids where forests fragmented
- Disturbance and mortality from fishing bycatch
- Changes in marine prey abundance from climate change
- Oil spills and pollution
Conservation measures like protected forest reserves, restricted logging practices, and mandatory buffers around nests are crucial for protecting remaining populations. Continued monitoring is needed since murrelets are elusive and difficult to study in their remote nest sites.
International cooperation on conservation is also vital since murrelets migrate across jurisdictions. Groups like the Pacific Seabird Group help coordinate research and management efforts.
Conclusion
In summary, Marbled Murrelets have a very unique reproductive strategy adapted to nesting in coastal old-growth forests. Their reliance on specific old trees makes them highly vulnerable to habitat loss. Ongoing conservation efforts focused on protecting remaining nesting habitat will be critical for maintaining viable murrelet populations into the future. More research is still needed to fully understand their breeding behaviors, site fidelity, and responses to environmental changes.