Following a large kill of Black Guillemots in the Esso Bernicia oil spill in Shetland, this study was initiated to determine the population size and distribution of the species at different times of year and to investigate its ecology. The results will enable oil spill contingency plans to be made for this species and provide a base-line against which future work can be compared. This is the first major study of Black Guillemots in the UK. There were large diurnal and seasonal fluctuations in colony attendance patterns which were investigated in relation to various factors. Reliable census techniques were devised and suitable stretches of coastline were established as monitoring units. Black Guillemots rarely foraged in water more than 40-50 m deep, and seldom moved more than 3 km from the nest during the breeding season. The proximity of suitable breeding sites to shallow water feeding grounds accounted for the fairly regular breeding dispersion. On islands with mammalian predators only nest sites in inaccessible cliffs were used. In many areas breeding numbers were limited by nest site availability. The distribution at other times of year was more irregular. After breeding adults congregated in traditional moulting areas where they became flightless for 4-5 weeks. These flocks of up to c.600 adults constitute vulnerable "hot spots" at which the effect of oil pollution would be most severe. In winter there was some movement away from exposed coasts, resulting in concentrations in more sheltered, inshore waters. A wide range of fish and invertebrates were eaten by adults, largely reflecting the diversity of inshore benthic communities. There appears to be a greater dependence on invertebrates during the winter months, when fish are scarcer. Chicks were fed almost exclusively on fish: their diet composition was determined primarily by local availability, although some adults specialised on particular species. When large gadoid fish became available in late summer adults were able to provide more energy per feed and consequently chicks were heavier at fledging. Breeding parameters were quantified and analysed in relation to various factors. Breeding success and chick growth compared very favourably with results of studies elsewhere, indicating that conditions for breeding were good for Black Guillemots in Shetland. In a year of more favourable environmental conditions a greater proportion of inexperienced birds were able to reach the condition threshold for breeding. These birds tended to lay single-egg clutches, in sub-optimal sites at which egg predation was heavy and breeding success low. Some pairs of Arctic Skuas benefit ed considerably from kleptoparasitism of chick feeds at larger colonies, but Black Guillemot breeding success was not affected and chick growth was only depressed at high rates of piracy. Overall, conditions in Shetland are favourable throughout the year for this seabird, whose ecology is moulded to the exploitation of an inshore feeding niche.

Since 1974 a population study of Black Guillemots has been conducted on Flatey Island, NW Iceland. The main aspects are summarized below. Population numbers and distribution. The population has been censused several years, also those of 20 islets near Flatey. Information was collected on past status. Great changes have occurred since turn of the century. Last major change began in 1967; the population started increasing of such a scale that it can only have resulted from massive immigration. These changes are thought to be due to rats and Mink. Attendance and population structure. Data was gathered on timing of spring return to nesting areas, status of attending birds, sex ratio, area and nest-site fidelity, pair-bond maintenance, and post-breeding departure. Special attention has been given to the problem of censusing birds attending nesting areas. Breeding biology. Breeding biology variables were quantified and studied on a seasonal basisj;timing of laying, clutch size, interval between eggs, egg size, reproductive output, lengths of incubation and nestling periods. Supernormal clutch and brood experiments were conducted. I looked at length of replacement time of lost clutches, factors influencing timing of laying, its effect and that of clutch and egg size on breeding performance. Egg and chick losses were analyzed. Many interesting population phenomena seem to have been associated with the unusually rapid population increase. Feeding ecology. Analyses were made of prey taken, feeding rhythm and areas, and factors influencing feeding rate and prey selection. Some information was collected on share of the sexes in feeding chicks, and kleptoparasitism. Study was made of chick growth, fledging condition and postfledging survival. Population dynamics. About 3300 birds were ringed, providing basis for determining age at maturity, adult survival, and mortality. Pre-breeding survival was calculated using data from ringing schemes. A population model was constructed for the population, showing magnitude of immigration. Ringing provided data on dispersal.

This study attempted to explain an apparent inverse relationship between pack ice proximity and breeding success of Black Guillemots (Cepphus grylle) on Cooper Island, a barrier island in the western Beaufort Sea near Barrow, AK. I elucidated the first linear relationship between energy density and body size for the elusive Arctic Cod (Boreogadus saida). I discovered and ground-truthed the existence of previously unknown guillemot foraging habitat on small 50 m2 ice floes distant from the pack ice. I developed new daily metrics for quantifying the provisioning to linear (8 d – 18 d) and Post-Linear (19 d – fledge) chicks. I found daily consensus between Linear and Post-Linear chicks about the level of provisioning at the colony. Finally, I explained those daily changes with significant correlations with wind speed and direction. / October 2007

This study attempted to explain an apparent inverse relationship between pack ice proximity and breeding success of Black Guillemots (Cepphus grylle) on Cooper Island, a barrier island in the western Beaufort Sea near Barrow, AK. I elucidated the first linear relationship between energy density and body size for the elusive Arctic Cod (Boreogadus saida). I discovered and ground-truthed the existence of previously unknown guillemot foraging habitat on small 50 m2 ice floes distant from the pack ice. I developed new daily metrics for quantifying the provisioning to linear (8 d – 18 d) and Post-Linear (19 d – fledge) chicks. I found daily consensus between Linear and Post-Linear chicks about the level of provisioning at the colony. Finally, I explained those daily changes with significant correlations with wind speed and direction.

This study attempted to explain an apparent inverse relationship between pack ice proximity and breeding success of Black Guillemots (Cepphus grylle) on Cooper Island, a barrier island in the western Beaufort Sea near Barrow, AK. I elucidated the first linear relationship between energy density and body size for the elusive Arctic Cod (Boreogadus saida). I discovered and ground-truthed the existence of previously unknown guillemot foraging habitat on small 50 m2 ice floes distant from the pack ice. I developed new daily metrics for quantifying the provisioning to linear (8 d – 18 d) and Post-Linear (19 d – fledge) chicks. I found daily consensus between Linear and Post-Linear chicks about the level of provisioning at the colony. Finally, I explained those daily changes with significant correlations with wind speed and direction.