The common murre (Uria aalge) is a medium-sized seabird that belongs to the auk family. It is also known as the common guillemot. Murres are highly adapted for life in the cold waters of the North Pacific and North Atlantic Oceans. They have several distinctive characteristics related to their marine lifestyle. In this article, we will explore the common murre’s anatomy, breeding biology, habitat, diet, and conservation status. Understanding the murre’s adaptations and environment provides insights into the lives of seabirds.
Common Murre Characteristics
Appearance and Anatomy
The common murre is a stocky, short-necked seabird that measures around 16-20 inches in length and weighs 1-2 pounds. Its wingspan is around 2 feet. It has a rounded head and thin, pointed bill. Murres come in two color phases:
- Dark phase: Head, neck, back, wings are blackish-brown. Throat and sides of neck are white.
- Light phase: Head, neck and upperparts are dark brown. Throat and sides of neck are white.
In all plumages, the belly and underwings are white. Murres have webbed feet with sharp claws that provide traction on rocky cliff surfaces. Their short wings, dense plumage, and torpedo-shaped bodies make them excellent divers and swimmers. Other adaptations include:
- Salt glands – To remove excess salt from the body after drinking seawater
- Nostril covers – Valves that close over the nostrils to prevent water entry when diving
- Transparent third eyelid – Protects the eye underwater
- Dense feathers – Provide insulation in cold water
- Compressed plumage – Reduces drag while swimming
Overall, the murre’s anatomy reflects its life as a pursuit-diving seabird that catches fish underwater.
Breeding Biology
Murres are colonial breeders that nest in large groups along rocky cliffsides. They form monogamous pair bonds that may persist for multiple breeding seasons. Breeding takes place from May to August depending on latitude. Nests consist of bare rock with no nesting material.
Female murres lay a single pear-shaped egg directly onto the bare rock ledge. Parents take turns incubating the egg by resting it on their feet and pressing it against their lower belly. Incubation lasts around 5 weeks. The egg has speckles and streaks that camouflage it against the rocky background.
Once hatched, the chick is brooded for a few days before leaving the nest. At around 3 weeks, the chick will jump off the cliff and plunge into the sea. This is known as the “fledging” period. The parents continue to care for the flightless chick at sea for several weeks as it learns to find food and avoid predators. Murres reach sexual maturity at 2-6 years old.
Vocalizations
Common murres are quite vocal birds, using calls to communicate with their mate or colony. Some common vocalizations include:
- Moan – Low, moaning contact call at nest
- Raarr – Loud, raucous call in flight
- Ur-ur-urrr – Throaty threat call on cliffside perches
Chicks give loud, snapping begging calls when parents arrive with food. At the breeding colonies, the din of murre calls is deafening! Murres may also clap their bills during displays.
Common Murre Habitat and Environment
Breeding Habitat
During the breeding season, murres nest at coastal cliff colonies ranging from a few dozen to over a million breeding pairs. Major nesting sites include:
- Northern Atlantic Ocean – Newfoundland Grand Banks, Labrador, Greenland, Iceland, Norway, Ireland, Scotland, Faroe Islands
- Northern Pacific Ocean – Alaska, Russia, Japan, California
Nesting habitat consists of rocky islands and coastal cliffs made of granite, basalt, or limestone. Murres choose steep cliff faces with narrow ledges for nesting. Cliff heights can range from just a few feet above the water to over 1,300 feet tall.
Ideal nest sites provide quick access to productive feeding areas. They also have takeoff points for flight and offer protection from terrestrial predators. Murres nest in extremely dense groups, with neighbors just inches apart.
Non-Breeding Habitat
After breeding, murres undergo a simultaneous, rapid molt of their flight feathers. This renders them flightless for several weeks. During this time, they occupy sheltered bays and inlets near their colonies.
The rest of the year is spent dispersed widely over continental shelf waters and offshore banks. Murres winter as far south as northern California and the Carolina coasts. They avoid areas with extensive sea ice cover in winter.
Oceanic Habitat
Common murres are pursuit divers that catch small fish and invertebrates. They forage in shallow, productive waters over continental shelves, seamounts, and ocean banks. Access to upwellings with abundant prey is key.
Murres may dive to depths over 200 feet, though most dives are much shallower. Their average diving depth is around 60-100 feet. Dives last 30-75 seconds, followed by a surface pause. Murres capture prey items one at a time, swallowing them whole underwater.
Common Murre Diet and Feeding
Common murres are generalist predators that eat a wide variety of small fish, crustaceans, and invertebrates. Prey availability varies by location and season. Their diet may include:
- Sand lance
- Capelin
- Herring
- Lanternfish
- Cod
- Rockfish
- Squid
- Euphausiids (krill)
- Amphipods
Fish make up over 75% of food intake by biomass. Sand lance are a vitally important prey species across much of the murre’s range. Parents capture up to 10-15 fish per hour to provision chicks.
Murres locate prey using excellent underwater vision and by dipping their heads underwater to spot fish silhouettes from above. They swallow small fish whole underwater. Larger prey are surfaced and then manipulated and swallowed head first.
Murres exhibit a fascinating at-sea feeding method called “rafting.” Birds that locate large prey fish will land next to conspecifics and transfer the prey to their neighbors via billing. A fish may get passed over a kilometer between multiple birds in this fashion. This allows the original captor to dive again more quickly to maximize calorie intake.
Conservation Status
Overall, common murre populations are abundant and the species is classified as Least Concern by the IUCN Red List. However, some localized populations have experienced concerning declines, especially in the North Atlantic. Threats include:
- Oil spills – Murres are vulnerable to spills near breeding colonies
- Overfishing – Reduces food availability
- Predation – By foxes, gulls, eagles near breeding sites
- Disturbance – From low-flying aircraft, boats, researchers
- Climate change – May affect prey abundance and distribution
Establishing protected breeding reserves and monitoring colonies are key conservation priorities. Spill mitigation and sustainable fisheries practices also help protect murres.
Conclusion
In summary, the common murre is a highly adapted seabird that flourishes in northern marine environments. Key characteristics include its dense plumage, excellent diving ability, cliffside nesting habits, and flexible diet. Murres rely on productive waters over continental shelves and banks to sustain their energetic lifestyle. They face threats from oil spills, overfishing, predation, and climate change disruption in some areas. Overall, the common murre remains a widespread and resilient seabird of the northern oceans.