The marbled murrelet (Brachyramphus marmoratus) is a small seabird found along the Pacific coast of North America. It is a member of the auk family and gets its name from the marbled brown and gray pattern of its plumage. Here is an overview of the marbled murrelet’s key physical features and characteristics:
Size
The marbled murrelet is a relatively small seabird, typically measuring around 9-11 inches (22-28 cm) in length and weighing 4.9-8.5 oz (140-240 g). Its wingspan is around 16-18 inches (40-46 cm).
Some key size measurements include:
Measurement | Range |
---|---|
Length | 9-11 in (22-28 cm) |
Wingspan | 16-18 in (40-46 cm) |
Weight | 4.9-8.5 oz (140-240 g) |
Its small size makes the marbled murrelet well-adapted for diving and swimming underwater as it hunts for fish and invertebrates. However, this small body comes at a cost in flight performance and efficiency.
Shape
The marbled murrelet has a rounded, chunky body shape typical of auks. It has a thick neck, broad shoulders, a pot-bellied profile, and a short, stubby tail. Its wings are relatively short and rounded compared to other seabirds.
Some key aspects of its body shape include:
- Thick neck
- Broad shoulders
- Pot-bellied profile
- Short, stubby tail
- Short, rounded wings
- Compact, chunky overall body
This body shape reflects adaptations for diving and underwater swimming. The short wings provide power to “fly” underwater. The stubby tail and feet set far back act as rudders for steering underwater. Above water, the rounded wings and body lead to slower, less efficient flight.
Plumage
The marbled murrelet has striking and distinctive plumage patterns. Its name comes from the marbled brown and gray patterning on its back and wings. Some key plumage features include:
- Brownish-gray upperparts with mottled “marbled” pattern
- White undertail coverts
- White belly and throat
- Dark cap on head
- Dark “mask” stripe behind eye
- Dark stripe on side of neck
This plumage provides excellent camouflage when the birds are sitting on nests on the mossy branches of coastal conifer trees. The intricately marbled upperparts in particular help the birds blend into the dappled light and shadow patterns of their nest sites.
Bill
The marbled murrelet has a short but powerful bill that is sharply pointed. The bill is black with yellowish or ivory white stripes along the upper and lower mandible edges. Some key bill features include:
- Short but thick and pointed
- Black with pale yellowish or ivory stripes
- Used for catching small fish and invertebrates
- Hooked tip helps grasp slippery prey
The bill is adapted for quick plunge-diving to grab prey underwater. The hooked tip and sharp point help seize and hold slick fish and squirming invertebrates like krill.
Legs and Feet
Like other auks, the marbled murrelet has short legs set far back on its body and webbed feet for propulsion in water. Key leg and foot features include:
- Legs short with feet placed far back on body
- Reddish-pink colored legs
- Webbed feet for swimming
- Feet lack a hind toe
In flight, the legs and feet are tucked behind the body to reduce drag. On land, the rearward legs provide only weak mobility. But underwater, the powerful webbed feet and rearward position provide excellent propulsion for diving and pursuing fish.
Gender Differences
Males and females have similar overall plumage, but some subtle differences exist:
- Males tend to have darker plumage than females
- Females have more white along the sides of the neck
- Females have a dull grayish wash on the chest
However, these differences are only apparent at very close range. From a distance, males and females look nearly identical.
Juvenile Plumage
Juvenile marbled murrelets less than one year old differ in plumage from adults. Juveniles have:
- Paler plumage overall, lacking dark marbled pattern
- More brownish rather than gray upperparts
- Fuzzy rather than smooth feathers
- Dark bill without pale stripes
After the post-juvenile molt at around one year old, they take on adult plumage features.
Geographic Variation
The marbled murrelet exhibits some subtle geographic variations in size and plumage across its range along the Pacific coast. Key differences include:
- Largest in Alaska, smallest in California
- Darker plumage with more contrast in northern populations
- Birds in southern range have more brownish coloration
These follow “Bergmann’s rule” with larger body size in colder, higher-latitude northern areas. The plumage variation provides slightly better camouflage matching local tree bark and lichen patterns.
Molting
Marbled murrelets molt annually after the breeding season to replace all feathers. Key aspects of molting include:
- Complete simultaneous molt once per year in late summer/early fall
- Molting birds cannot fly so remain on the water
- Takes 4-6 weeks to complete molting
- Juveniles have partial pre-breeding molt at one year old
The molt produces new plumage before migrating and wintering in more exposed marine habitats. Molting is energy intensive, so occurs after chicks have fledged when food is still abundant.
Voice
Marbled murrelets have a variety of vocalizations, mainly heard during courtship and the breeding season. Their calls include:
- Loud, barking “kee-arrr” call made by nesting birds
- Soft, moaning “coo-er” call at nest sites
- Rapid chuckling trills during courtship
- Harsh growling sounds when threatened
- Juveniles beg with buzzy “zeep” calls
These vocalizations help murrelets find mates, defend nest sites, and communicate with mates or young. The nesting “kee-arr” call carries well through the forest.
Vision
Marbled murrelets have excellent vision adapted to both marine and forest environments. Key aspects of their vision include:
- Large eyes provide acute vision
- Able to see well underwater
- Sensitive color vision helps find prey and mates
- Excellent depth perception and motion detection
Their eyes are specially adapted to changing from underwater to aerial vision. Excellent vision helps them find camouflaged prey and navigate through dense coastal forest canopies.
Senses
In addition to keen vision, marbled murrelets have other well-developed senses. These include:
- Hearing – excellent hearing adapted to detect prey and find mates in noisy ocean waves
- Smell – good sense of smell that may aid in navigation and finding nest sites
- Touch – Herbst corpuscles in bill tip detect prey vibrations and feel sensations underwater
Their combination of senses allows marbled murrelets to thrive in both open ocean and dense forest environments across their life cycle.
Conclusion
In summary, the marbled murrelet is a uniquely adapted seabird with a distinctive marbled brown and gray plumage pattern. Despite its small size, chunky auk body shape, and short wings, it thrives in both rocky coastal marine areas and densely forested nesting habitat. The murrelet’s compact shape, powerful feet, sharp bill, and excellent vision and underwater senses allow it to successfully exploit two very different ecosystems.