Alcids are important top predators, consuming substantial amounts of zooplankton and fish in the northern hemisphere. However, studies of their at-sea foraging behaviour are logistically difficult because of their wide foraging range and small body size. We developed a technique to estimate the approximate foraging area for individual birds using water temperature profiles sampled by both diving birds and a research boat. This technique was applied to chick-rearing Rhinoceros Auklets Cerorhinca monocerata breeding on Teuri Island, Hokkaido, which feed primarily on Japanese anchovy Engraulis japonica in the northern coastal Japan Sea. Annual variations of the warm Tsushima Current may influence the distribution of this prey species. Rhinoceros Auklets foraged mainly in waters with 12–15°C sea surface temperatures (SSTs), which formed in waters north of the breeding colony on 17 June 2002 and in waters south of the breeding colony from 30 May to 3 June 2003. Rhinoceros Auklets dove above or around the thermocline in both years. This indicates that foraging locations and dive depths may be influenced by SSTs and the depth of the thermocline, factors that presumably affect the distribution of their prey.