Both the thick-billed murre (Uria lomvia) and the common murre (Uria aalge) are medium-sized seabirds that belong to the Alcidae family. They have several key differences in terms of their physical characteristics, breeding behaviors, habitat and distribution.
Physical Differences
The most noticeable physical difference between thick-billed murres and common murres is the size and shape of their bills. As their names suggest:
- Thick-billed murres have short, thick, cylindrical bills.
- Common murres have thinner, more pointed bills.
Some key physical differences include:
Characteristic | Thick-billed Murre | Common Murre |
---|---|---|
Bill shape | Short and thick | Longer and more pointed |
Bill color | Gray with yellowish base | Dark gray |
Body size | Larger | Smaller |
Wingspan | 24-28 inches | 22-26 inches |
Weight | 1.6-2.8 lbs | 1.1-1.9 lbs |
As the table shows, thick-billed murres tend to be larger overall than common murres. Their thicker bill also gives them a distinct look.
Breeding Behavior
Thick-billed murres and common murres have some differences when it comes to their breeding ecology and behaviors:
- Nesting habitat – Thick-billed murres nest on rocky cliffs whereas common murres nest on flatter, open ground.
- Egg color – Thick-billed murre eggs are a paler green-blue compared to the darker blue-green of common murre eggs.
- Parental care – Male and female thick-billed murres share incubation duties equally. For common murres, the female does more of the incubation while the male provides most of the food.
The nesting habitat difference is quite pronounced, with thick-billed murres almost always choosing steep, rocky ledges and common murres nesting on flatter, low-lying areas on islands. The egg color and parental care differences are more subtle.
Habitat and Range
Thick-billed murres and common murres have broadly overlapping ranges but some key habitat differences:
- Thick-billed murres are found mainly in colder, higher-latitude Arctic waters including northern Canada, Greenland, Svalbard and the northern Barents Sea.
- Common murres have a more southerly distribution reaching down to New England, British Columbia, Scotland, and the southern Barents Sea.
- Thick-billed murres tend to occupy more coastal habitats while common murres range further offshore into open oceans.
So while both occupy northern regions, thick-billed murres are more of a high Arctic species usually found closer to shore. Common murres range farther south into temperate regions and are more pelagic.
Some key range differences:
Region | Thick-billed Murre | Common Murre |
---|---|---|
Northern Canada | Abundant | Scarce |
Alaska | Coastal only | Coastal and offshore |
New England (USA) | Not found | Present |
Svalbard | Abundant | Uncommon |
Northern Norway | Common | Abundant |
Taxonomy
Though they were previously considered one species, thick-billed murre and common murre are now classified as two distinct species based on differences in:
- Morphology – bill shape, body size, plumage details
- Genetics – DNA and molecular analysis
- Behavior – breeding ecology, vocalizations
- Geographic range
Recent taxonomic classifications place them in:
- Family: Alcidae (the auks)
- Genus: Uria
- Species:
- Uria lomvia – Thick-billed murre
- Uria aalge – Common murre
The two species are believed to have diverged approximately 1.5 million years ago based on genetic studies.
Population and Conservation
Both thick-billed and common murre populations declined in the 20th century due to factors like overhunting, oil spills and introduced predators. Today:
- Global thick-billed murre population: ~7,000,000 breeding pairs
- Global common murre population: ~10,000,000 breeding pairs
Thick-billed murres are still declining in some regions like Newfoundland. However, protections and reduced threats have allowed some recovery from their low points in the 1900s. Both species are considered of Least Concern by the IUCN Red List today.
Ongoing conservation issues include:
- Climate change – habitat loss and food web disruptions
- Oil spills
- Overfishing of prey species like capelin and sandlance
- Disturbance of breeding colonies
Careful monitoring, sustainable fisheries management and reducing anthropogenic threats like oil spills and habitat loss remain conservation priorities for maintaining healthy murre populations.
Conclusion
In summary, the main differences between thick-billed murres and common murres include:
- Thick-billed murres have stockier, shorter bills compared to common murres’ thinner, more pointed bills.
- Thick-billed murres tend to be larger in body size than common murres.
- Thick-billed murres nest on rocky cliffs while common murres nest on open ground.
- Thick-billed murres have a more northern Arctic distribution compared to the more southerly ranging common murre.
- Thick-billed murres occupy cold coastal habitats whereas common murres also range far out to sea.
While closely related, various morphological, behavioral, geographic and genetic differences demonstrate that thick-billed murres and common murres are in fact two distinct species within the Alcidae family. Both face similar conservation threats which warrant continued monitoring and protection of populations.