Black Guillemot Cepphus grylle


Justification of Red List Category
This species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). The population trend is unclear but it is not thought to approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size is very large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.

Population justification
The European population alone was recently estimated at 304,000-742,000 mature individuals (BirdLife International 2015). Europe forms c.50-74% of the global range; thus, a very preliminary estimate of the global population size is 410,000-1,484,000 mature individuals, although further validation of this estimate is needed. The population is therefore roughly placed in the band 400,000-1,499,999 mature individuals.

Trend justification
The overall population trend is unclear. In North America, the population is increasing (based on BBS/CBC data: Butcher and Niven 2007). In Europe, the population is estimated to be decreasing by less than 25% in 32.7 years (three generations) (BirdLife International 2015).

Distribution and population

This species can be found throughout Arctic waters on the northern coasts of Russia, Alaska (U.S.A.), Canada and Norway, in the Atlantic Ocean off Greenland (to Denmark), eastern Canada as far south as the United Kingdom including the North and Baltic Sea (del Hoyo et al. 1996).


Behaviour Black Guillemots are pursuit divers that propel themselves through the water using their wings.
Diet The species is probably primarily a benthic forager, since much of the prey consists of benthic fish and invertebrates, including crustaceans (Bradstreet and Brown 1985, Cairns 1987, BirdLife International 2000). Various studies find sandeels (Ammodytes spp.) and blennies (particularly butterfish Pholis gunnellus) to be the most important prey species of fish, although the relative contributions of each of these to the overall diet differs (Harris and Riddiford 1989, Ewins 1990, BirdLife International 2000). Flatfish and gadoids are also sometimes important (Ewins 1990, Harris and Riddiford 1989). Amongst invertebrates, sea-scorpions are noted as an important prey item (Harris and Riddiford 1989). Adults tend to consume a higher proportion of invertebrates than chicks (Ewins 1990). In general, the importance of invertebrates increases with latitude (presumably reflecting overall availability) in the summer diet of both adults and chicks. The few data on winter food suggest that invertebrates are of greater importance during the winter than during the summer (Ewins 1990).
Breeding site Both early spring and breeding distributions appear to be influenced by the Hell Gate and Cardigan Strait polynya located in western Jones Sound, Canada, between Ellesmere and Devon islands. The evidence presented suggests that annual variation in the distribution of ice edges in Jones Sound may influence the distribution of breeding birds among suitable breeding habitat. The observed distribution of Black Guillemots in March, April, and May is coincident with the location of open water and the associated ice edges. Thereafter, as the ice margin recedes and shoreleads open, the distribution of guillemots tends to reflect the location of breeding colonies (Prach and Smith 1992).
Foraging range Birds feeding in the eastern Canadian Arctic fed principally in waters 10-130 m deep (Cairns 1987). Birds have been caught in nets up to 50 m deep, but have a theoretical maximum dive of 130 m. They have been observed actively feeding in water 35-45 m deep (Uspenski 1956). However, in Kattegatt, Denmark, approximately 80% of all Black Guillemots were recorded in water with depths of 10-30 m (Durinck et al. 1994). Black Guillemots were always recorded less than 5 km from the coast of Caithness, Scotland, during May-July (BirdLife International 2000). At the Bay of Fundy, Canada, almost all birds remained within 300 m of the shore (Ronconi and St. Clair 2002). At Papa Westray, Scotland, the mean foraging distance was 2.4 km away from the colony, and birds were recorded foraging in areas up to 3.9 km away from the colony, but despite this large variation in foraging range, feeding sites were never located further than 1.5 km from the shore (BirdLife International 2000). At Rockabill, Ireland, birds forage within 1 km of the colony or else fly 7 km or more to reach the mainland coast (BirdLife International 2000). In the eastern Canadian Arctic, censuses indicated that most birds were feeding within 13 km of breeding colonies, with a few found as far as 15 km (BirdLife International 2000). Sightings were frequently highest within 5 km of the colony (BirdLife International 2000). Several studies (at the Bay of Fundy, Finland, Denmark and Iceland) found that Black Guillemots foraged between 0.5 and 4 km from nest sites, and occasionally beyond 7 km away (BirdLife International 2000). By contrast, in the NW Territories, Canada, breeding adults rarely foraged close to the colony, and some birds may have been travelling as far as 55 km (BirdLife International 2000). Birds probably capture some prey in the water column, but forage principally on benthic prey (Cairns 1987). In Shetland, birds tend to forage where the sea bed is rocky and vegetated with dense stands of kelp Laminaria spp. (Ewins 1990) which reflects the habitat preferences of their main prey (BirdLife International 2000).


The following information refers to the species's European range only: This species is likely to be susceptible to the impacts of climate change, such as sea temperature rise and shifts in prey distribution and abundance. The species is vulnerable to oil spills and other marine pollutants, including heavy metals, pesticides, PCBs and other crude oil-residues (HELCOM 2013). At the breeding colonies, the species is vulnerable to invasive predators, such as rats Rattus spp. and American Mink Neovison vison (HELCOM 2013). Bycatch in commercial fisheries is thought to have potentially severe impacts on the species in parts of the range (Nettleship et al. 2018), with birds susceptible to capture in gillnets in particular (Fangel et al. 2011, Žydelis et al. 2013), although other fishing equipment may also trap significant numbers. Increasing numbers of offshore wind farms may result in displacement from habitat, and a low risk of collision (Bradbury et al. 2014). The species is hunted for consumption in parts of Scandinavia (Mendel et al. 2008).

Conservation actions

Conservation Actions Underway
The following information refers to the species's European range only: The species is listed within the African Eurasian Waterbird Agreement. There are 91 marine Important Bird Areas which include this species in Europe. Within the EU, the species is listed within 29 Special Protection Areas. It is listed as Near Threatened by the HELCOM Convention.

Conservation Actions Proposed

The following information refers to the species's European range only: Further identify important sites for this species, particularly in offshore regions and designation as marine protected areas. Identify the risks of different activities on seabirds. Continue eradication of invasive predators from breeding colonies. Manage fisheries to ensure long term sustainability of key stocks (e.g. sandeels). Establish observer schemes for bycatch and prepare National/European Community plans of action on seabird bycatch. Develop codes-of-conduct for more organised activities (e.g. tourism). Ensure that appropriate protection (national laws and international agreements) applies to new areas and times in cases of changes in seabird migration routes and times.


Text account compilers
Butchart, S., Ekstrom, J., Fjagesund, T., Ashpole, J, Calvert, R., Hatchett, J., Martin, R.

Recommended citation
BirdLife International (2023) Species factsheet: Cepphus grylle. Downloaded from on 05/06/2023. Recommended citation for factsheets for more than one species: BirdLife International (2023) IUCN Red List for birds. Downloaded from on 05/06/2023.