The Thick-billed Murre breeds chiefly in immense colonies in the eastern Arctic, where more than 95% of the Canadian population breeds at only 11 sites. There is one small colony in Mackenzie, N.W.T. (Cape Parry), and a few small colonies are scattered through Newfoundland and Labrador and the Gulf of St. Lawrence (Gaston and Hipfner 2000). In the Atlantic, the Thick-billed Murre winters mainly off Newfoundland and Labrador and in smaller numbers south to Massachusetts; Cape Parry breeders presumably winter in the Pacific (Brown 1985).
Most banding was carried out at a few eastern colonies, in Hudson Strait and Lancaster Sound in the 1950s, in the Lancaster Sound/Jones Sound region from 1975 to 1993, and in Hudson Strait from 1980 to 1995. An analysis of encounters to 1978 was given by Gaston (1980). A recent summary of encounters in Newfoundland and Labrador was made by Donaldson et al. (1997).
Long-distance encounters are the rule; 87% of encounters were 1000 km or more from the banding site. Moreover, straight-line encounter distances are misleading for this species, which rarely flies over land. Birds from Coats Island encountered off Newfoundland (great-circle distance approximately 2300 km) had probably travelled more than 2700 km.
The pattern of encounters probably reflects hunter distribution and the long-standing traditions of seabird hunting on Newfoundland. Encounters are concentrated during the hunting season (November–March), and there are few summer encounters, because at that time most birds are within the breeding range, which has a very low density of human population. Over 90% of birds encountered ere shot by “turr” hunters off Newfoundland and Labrador (records 1–4); the heavy losses inflicted by salmon fishing nets off West Greenland colonies (Tull et al. 1972) occurred during a period when little banding was being carried out in Canada (Gaston 1980). First-winter birds tend to arrive off Newfoundland earlier than adults and make up the bulk of hunter-killed birds up to December, with older birds predominating later in the winter. Very few encounters come from south of Newfoundland (<1%), but two birds from each of Digges and Coburg islands were encountered in Nova Scotia (records 5 and 6): one of these holds the record for rate of movement, covering a sea distance of about 3700 km in 99 days, averaging >35 km/day (record 6). One bird banded at Cape Wolstenholme, Quebec (record 7), and one from Coats Island, Northwest Territories (record 8), were encountered in Massachusetts. Only one encounter came from the Gulf of St. Lawrence.
Many encounters of birds from the Lancaster Sound/Jones Sound colonies occurred off Greenland in September–November, with smaller numbers throughout the winter (record 9). All six encounters of birds banded at Prince Leopold Island were from Greenland, and a proportion of the Canadian High Arctic population may overwinter there, at least in some years, as well as a few birds from Hudson Strait (e.g. record 10, from Coats Island) (Tuck 1961; Kampp 1991). Over 150 birds banded in West Greenland (mainly as chicks) have been encountered in eastern Canada (records 11 and 12) (Salomonsen 1947–1979; Tuck 1971), suggesting that much of the West Greenland population also winters in Canadian waters, at least in their first year (Donaldson et al. 1997). Small numbers of encounters of birds banded at the Norwegian Barents Sea colonies (Spitsbergen, Bear Island) and Iceland have also occurred on Newfoundland (V. Bakken, pers. commun.).
Although there are few summer encounters, Thick-billed Murres are known to return to the same colony each year to breed (Gaston et al. 1994). Eighteen encounters from Ivujivik, northern Ungava, in summer were all of birds banded at the nearby Digges Sound colonies. At Coats Island, Northwest Territories, up to 60% of birds banded as chicks were sighted at the colony as adults, suggesting strong philopatry. By 1992, more than 15000 chicks had been banded at Coats Island, but observations of thousands of adult breeders and non-breeders at the nearest other colony (Digges Island) in the summers of 1992–1994 failed to reveal any birds banded at Coats Island (A.J. Gaston and G. Donaldson, unpubl. data). However, a single bird banded as a chick at Coats Island in 1989 was found breeding in Thule District of northwestern Greenland in 1997 (Kampp and Falk 1998), demonstrating that some long-distance dispersal does occur. A bird banded at Digges Island in 1994 was seen at Coats Island in 1997 (G. Donaldson, pers. commun.). Young birds do not visit their breeding colony in their first summer, but two encounters near Cape Dorset, Nunavut, of birds banded as chicks at Cape Wolstenholme and Digges Island, about 200 km away (record 13), show that some birds are not far rom their natal colony during their first summer.
The longevity record for this species is held by a bird encountered in 1978, 23 years after banding (record 4) (Clapp et al. 1982). A bird recaptured at Digges Island in 1980 almost certainly had been banded at the same site in 1955, but the number was illegible.