Ecological relationships between two sympatric congeneric species, Common Murres and Thick-Billed Murres, Uria aalge and U-lomvia, breeding in the Barents Sea

Concurrent studies of the breeding ecology of Common Murres and Thick-billed Murres, Uria aalge and U. Lomvia, on Hornoya, a colony in northern Norway, showed significant differences between the species in the timing of egg laying but no consistent differences in food choice, feeding frequency and rhythm, dive depth, or chick growth. Both species fed their chicks an capelin, Mallotus villosus, sand lance Ammodytes sp., and herring Clupea harengus. However, on Bear Island in the Barents Sea, the diet differed significantly, with Common Murre chicks being fed nearly exclusively capelin while Thick-billed Murre chicks received capelin, squid Gonarus fabricii, Arctic cod, Boreogadus saida, sculpins (Cottidae), shannies Lumpenus sp., and eelpouts (Zoarcidae). The lack of dietary segregation on Hornoya was in strong contrast with thr results of earlier studies of sympatrically breeding murres and was probaby due to a near superabundance of food around the colony.