Scientific name:Cepphus grylle
Danish: Tejst
English: Tystie
French: Le Petit Guillemot Noir
Greenland: Serfaq
Old English: Greenland Dove; Turtle

The Tystie, as the Black Guillemot is sometimes called in England, is primarily an Atlantic and Arctic Basin species ranging from the New England states northward throughout the Canadian Archipelago and sparsely to the northern Alaskan coast. Eastward it inhabits the southern coasts of Greenland, Iceland, the British Isles, Norway, Sweden, Spitsbergen, and most of the islands north of the Soviet Union: it has been observed as far north as 89° latitude. ³³⁹

The total population of Black Guillemots probably does not exceed 700,000 birds. On Prince Leopold Island of the Canadian Archipelago, a colony of at least 4,000 nest among the talus and rock crevices of the cliffs.^{45, 435, 440} Some arctic areas such as Iceland, have up to 100,000 birds. Estimates for Norwegian coast equal more than 44,000 individuals.⁴³⁹ The total for major colonies of the Canadian Archipelago is more than 80,000, forming the center of distribution for the North American coast.¹⁰⁷ These figures are not precise because estimates are difficult and the records incomplete and sometimes misleading.

In behavior and appearance the Black Guillemot is similar to the Pigeon Guillemot of the eastern Pacific. The former is blacker however, and the underwing coverts are much whiter than in the Pacific species, although in the more northern part of its range the Pigeon Guillemot varies in this respect. The outer white wing epaulettes are solid in the Tystie and divided in the Pigeon.

The Black Guillemot in its mottled white-and-gray plumage remains throughout the winter in the vicinity of its breeding grounds, although it ranges into deeper water. In the Bay of Fundy area, the first birds appear in their nuptial plumage by early March, and usually by the end of the first week in April all birds are in breeding plumage. At this time large numbers gather offshore during high tide but they do not make landings ashore until the beginning of May. ⁶⁶³ Where tidal rise and fall is moderate two to three meters littoral feeding habits are not greatly affected by tide levels. However, at Kent Island in the Bay of Fundy where the tidal rhythms are as much as 30 meters: at low tide the fishing areas may be several kilometers away.⁴⁹⁷

All pairs in a breeding area make their first spring landing within a few minutes of one another. However, they remain for only about an hour. This phenomenon has been seen among Black Guillemots breeding along the Murman Coasts of Siberia and on Kent Island in the Bay of Fundy early in May.^{322, 497} Black Guillemots are cavity and crevice nesters. They prefer a cavity with a natural base of small pebbles but they also nest in sandy cliffs where they enlarge swallow burrows, and in shelters provided by driftwood.^{13, 185}

In the Bay of Fundy area mature birds apparently remain paired throughout the year but they first come ashore for copulatory activity on the second or third day of May and visit their nests for the first time a few days later. They then continue to visit the nest on a daily basis until the eggs are laid in late June or early July.¹⁶³ Variation in the onset of breeding occurs from one locality to another.¹²⁰

Guillemots have a strong nest site bond. Birds that have bred before tend to use the same cavity year after year and this enhances breeding success by permitting experienced birds to use a known nest site as early as possible in the season.¹³ A few late layers may not deposit eggs until the end of June. These late nests are often not as successful as the early ones because young gulls seek shelter in the nesting cavities. The presence of crows may also influence nesting success of late nesters in Shetland.¹⁸⁵ In the absence of intruding species and in areas where food is in constant supply, late nesting may have little disadvantage.

If two eggs are laid they are produced three days apart, incubation beginning after the laying of the second egg, although incubation may be delayed until the fourth or fifth day even when a single egg is laid. Twenty-three percent of all nests have one egg, and the incubation period averages 28 days.^{120, 497, 663} In nests with two eggs, hatching occurs in the same twenty-four hour period and eggs which fail to hatch are usually discarded from the nest. William Preston saw an adult Black Guillemot emerge from a nest carrying an unhatched egg in its bill. The bird flew with it and dropped it into the sea on its way to the feeding area.⁴⁹⁷ Such occurrence must be very rare, since the 40 to 50 gram weight of an egg is a considerable load for a guillemot to carry in its bill. It is more usual to roll an unhatched egg out of the cavity or merely push it aside.

In a Gulf of St. Lawrence colony two-egg nests were more successful than single-egg clutches. In the study of 212 nests, two-egg nests had a 58 percent hatching success and a 39 percent fledgling rate, while nests with one egg yielded only 32 percent hatching and 12 percent fledgling success.¹²⁰ Figures from Denmark showed similar rates although, in Iceland, overall breeding success was 68 to 76 percent.¹³

The first chicks appear late in June or early July at lower latitudes and a month later at more northern breeding sites. They are brooded for three to four days until able to maintain body temperature. For the next thirty-four to forty-one days the chicks are fed regularly between sunrise and sunset with feeding peaks midmorning and midafternoon. Food items, mainly fish, brought to the young increase in size as the chicks grow and early in the day chicks are fed almost twice each hour.^{289, 290} On the average each chick receives about twelve fish per day although in the latter stages of growth each may receive up to fifteen fish. Generally the Black Guillemot takes any slender fish or invertebrate inhabiting the bottom of the littoral zone, particularly in rocky areas, but there are individual preferences for food even within a mated pair-- one bird frequently will bring in only one type of fish.^{18, 120} In Alaskan waters, sculpins and arctic cod are the chief prey,¹⁶³ while in the high Canadian arctic Black Guillemots rely heavily on amphipods.⁹³ Further south they bring to their chicks a high percentage of bottom dwelling blennies.¹²¹

A chick may choke on oversized food. George Divoky and others noted the death of a 35-day-old juvenile with a 15 centimeter, four-horned sculpin lodged in its throat.¹⁶³ On the average, each chick consumes 2400 grams of fish during the nestling period to provide growth from 40 to 350 grams in body weight.¹²⁰ (See Figure 8 in the Appendices for seasonal variations of adult body weight).

A chick which hatches early in the season tends to stay longer in its nest than one which hatches later. For example, chicks on Seven Islands, Siberia, which hatched between 8 and 10 July fledged at thirty-nine to forty-one days of age, while those that hatched between 21 and 23 July fledged in only thirty-four days.⁶¹

Fledglings begin leaving their nesting cavities after sunset on their own initiative about the middle of August. Rarely, as has been seen in the Pigeon Guillemot, one may be enticed from its nest by its parents.^604,663 They are not strong fliers at fledging, having a wing length of 82 percent of the adult wing length, but they gain wing strength by underwater pursuit of prey before making their first sustained flights about two weeks after entering the water.¹³ By this time, however, they have dispersed considerable distances from the nesting island. They are good divers, remaining underwater for up to sixty seconds. Adult birds often continue to frequent their nests for several days after their chicks have left.⁶⁶³

By observing marked populations over a four-year period, William Preston concluded that only a small number of birds reared on Kent Island return there to breed and that considerable dispersal takes place in the two or three years before young birds begin to breed.⁴⁹⁷ It is possible that most guillemots, though capable of breeding at two years of age, may not breed until they are at least four or five years of age. If this is true, then additional observation on marked populations may show that most young reared at a particular location, do eventually return there to breed.

On Kent Island, 88 percent of the prefledging deaths occurred during the egg stage. The remaining 12 percent of the deaths mostly occurred during the first week after hatching. Little is known about survival after fledging, although on Kent Island Preston noted an annual death rate of 19.6 percent among the adult birds.⁴⁹⁷ He also suggests that the Black Guillemot survives best when the breeding density is not high. On the contrary, David Cairns studying two separate breeding locations in the St. Lawrence River estuary, found no evidence for any link between breeding density and success.¹²⁰ Also, the high concentrations in Iceland, Norway, and the northern Canadian islands,are apparently very successful breeders at least when all environmental factors are favorable.

At Point Barrow, Alaska, the Black Guillemot is apparently increasing in numbers due to man-made debris which provides nesting places for it. Hatching success in this region has been 52 to 67 percent, a higher rate than on Kent Island.¹⁶³ That the birds soon find and occupy cavities created by ornithologists reinforces the theory that guillemot numbers are limited by available nesting sites. This has been demonstrated for Black Guillemots on Kent Island and for Pigeon Guillemots in the San Juan Islands area of Washington.

The total nesting time in Alaska is about sixty-eight days if the water remains ice-free. On Prince Leopold Island of the Canadian Archipelago, Black Guillemots are known to be present on the cliffs by mid-May and possibly sooner and they are seen there at least until the end of August.^{435, 440} Winter open water areas, called polynyas, which are comparatively ice free, and the fact that abundant suitable nest sites are available, probably account for the large numbers present there.¹⁰⁶

Adult Black Guillemots molt twice each year. After breeding they begin molting the covert feathers. Wing and tail feathers follow in sequence. During the winter the plumage is a mottled black and white dorsally, with white under parts. The partial spring prenuptial molt involves only the body coverts which return to the charcoal-black color of the summer plumage. In the young, wing and tail feathers are not affected by the full postjuvenile molt.³³⁹ (Timing of molts in the Black Guillemot is illustrated in the Appendices Figure 17).