This species is very similar to the much more abundant and widespread Common Murre, but is fortunately not likely to be confused with any other alcid in B.C. The Thick-billed Murre is a bulkier, thicker-necked, and chunkier species than Common Murre in all plumages, with a somewhat thicker and heavier bill that has a more strongly decurved culmen, but these structural characteristics are difficult to apply without experience with the species. At a distance, one of the most prominent distinguishing characteristics of Thick-billed Murre is its blacker head and upperparts that contrast much more cleanly and sharply with the entirely gleaming white underparts. Common Murre, in comparison, has somewhat duller blackish-brown on the head and upperparts (brownest on the head) that is not as sharply demarcated from the white underparts due to the presence of blackish-brown streaks on the sides and flanks (these are lacking in Thick-billed Murre). The overall difference is that the Thick-billed Murre appears as a more cleanly black-and-white species, and this applies to all plumages (including newly fledged juveniles). At very close range, Thick-billed Murre can be seen to have a thin white line above the cutting edge at the base of the bill (most prominent in breeding plumage) which is not present in any plumage of Common Murre.
Non-breeding and immature Thick-billed Murre can be distinguished from similarly-plumaged Common Murre by its largely black head and neck, with white restricted to the chin and throat. Common Murre, in contrast, has an extensively white head, with black restricted to the forehead, crown, nape, and sides of the neck. Most importantly, Common Murre shows a narrow black line extending back from the eye into the white area of the face; this feature is not usually shown by Thick-billed Murre, although some individuals in their first summer (e.g., ~1 year old) can show some white behind the eye and can approximate this pattern. Additional caution should also be applied when assessing face pattern, as molting and fledgling Common Murres can show a face pattern that is intermediate between breeding and non-breeding plumage and can approach the typical appearance of Thick-billed Murre. In such instances, attention should be paid to other field marks mentioned previously.
Source: Sibley (2000)
| Juveniles regularly vocalize at sea, producing a loud whistling call, but adults rarely vocalize away from the nesting site. The most commonly heard call is a loud, groaning, crowing aarr-rr-rr or aooorrr; this is the only call that is occasionally given at sea by non-breeding adults. Other calls (all given at the breeding site) include a faint urr, a loud, emphatic aargh, a descending, laughing RAH-rah-rah-rah-rah, a rapid, two-syllable adow, and a short, abrupt yuk. Source: Gaston and Hipfner (2000); Sibley (2000) |
Courtship
The mechanism of pair formation in this species is not known, and birds usually appear at breeding colonies already in pairs. The Thick-billed Murre is a monogamous breeder, with pairs often persisting for many years.
Nest
The egg is usually aid on a bare, rocky ledge on a steep cliff, although some eggs are laid on bare soil near the top a seaside cliff. There is no nest construction in this species, although it often gathers pebbles and other debris from the vicinity of the egg and cements them into place to prevent the egg from rolling off the ledge. The height of the nests above the surface of the ocean in B.C. ranges from 76-91 m.
Eggs
A single egg is laid in mid-summer (July) and is incubated by both sexes for 28-37 days before hatching. Egg-laying in B.C. appears to occur about a month later than in arctic areas of the north Pacific, despite the more southerly latitude. The texture of the egg is somewhat rough and chalky. Its shape is distinctly pyriform (‘pear-shaped’) with one end narrower and more pointed than the other; this egg shape prevents the egg from rolling off the cliff ledge because it will invariably roll in a circle. The colour of the egg is extremely variable. The ground colour ranges from chalky-white or turquoise-blue to buffy, greenish, or even reddish-brown, and there are variable blackish, dark brown, or purplish scrawls, splotches, spots, lines, and streaks. These markings are often denser towards the larger end, sometimes forming a ‘wreath’. The egg is often densely coated in feces, sometimes to the point of completely obscuring the colouration. During incubation, the egg is commonly placed on top of the webbed feet and covered by the belly feathers. Eggs are apparently present in B.C. between mid-July and late August, although there is little data on active nests in the province.
Young
The young are altricial and completely downy at hatching. The colouration of the down is variable and ranges from silvery-grey to brown or blackish, usually paler on the head (caused by fairly extensive pale shaft streaks on the feathers of the head and neck), with a much paler and mottled belly; some chicks have pale flecking or mottling over much of the body. The young remain in the nest for 15-33 days before fledging, with the timing of fledging more closely related to the mass of the chick (usually 200-250 g at fledging) than to the age of the chick; slower-growing chicks tend to depart the nest later than fast-growing individuals. While in the nest, the young are brooded continuously by both parents for the first ~12 days, after which time brooding becomes intermittent or ceases. Upon fledging, the young leap from the nest and glide or flutter to the water below, closely attended by one or both adults during the descent. Most chicks in B.C. fledge in late August or early September. The fledgling then remains with the male parent, who provides it with food, for an additional 4-8 weeks before becoming totally independent.
Source: Campbell et al. (1990b); Baicich and Harrison (1997); Fraser et al. (1999); Gaston and Hipfner (2000)
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This species feeds primarily on midwater schooling fish such as herring, cod, smelt, and sandlance, as well as on squid and pelagic crustaceans (shrimp, amphipods, krill, etc.), but will also capture benthic fish such as sculpins when foraging in shallower waters. It captures all prey by diving, often to great depths (maximum recorded dive depths 210 m, although most dives go no deeper than 50 m). Foraging areas are often located away from breeding sites, and some birds (often in flocks) may travel as far as 170 km each way to gather food during nesting and chick-rearing. Most foraging is done alone or in small, loose groups, although larger aggregations may occur in areas of high prey abundance. In British Columbia, it sometimes occurs with flocks of Common Murres when foraging or while travelling to and from feeding areas; however, Thick-billed Murre tends to prefer colder offshore waters for foraging than Common Murre.
Source: Fraser et al. (1999); Gaston and Hipfner (2000)
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