| Habitat and Ecology: |
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 crustaceans1,4,8. Various studies find sandeels (Ammodytes spp.)5,9 and blennies (particularly butterfish Pholis gunnellus)1,5,9 to be the most important prey species of fish, although the relative contributions of each of these to the overall diet differs. Flatfish9 and gadoids5 are also sometimes important. Amongst invertebrates, sea-scorpions are noted as an important prey item9. Adults tend to consume a higher proportion of invertebrates than chicks5. The general trend is for increasing importance of invertebrates 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 summer5. 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 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 colonies3. Foraging range Birds feeding in the eastern Canadian Arctic fed principally in waters 10-130 m deep4. 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 deep6. However, in Kattegatt, Denmark, approximately 80% of all Black Guillemots were recorded in water with depths of 10-30 m7. Black Guillemots were always recorded less than 5 km from the coast of Caithness, Scotland during May-July1. At the Bay of Fundy, Canada, almost all birds remained within 300 m of the shore2. 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 shore1. At Rockabill, Ireland, birds forage within 1 km of the colony or else fly 7km or more to reach the mainland coast1. 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 km1. Sightings were frequently highest within 5 km of the colony1. 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 away1. 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 km1. Birds probably capture some prey in the water column, but forage principally on benthic prey4. In Shetland, birds tend to forage where the sea bed is rocky and vegetated with dense stands of kelp (Laminaria spp.)5 which reflects the habitat preferences of their main prey1.
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