ASSIMILATION EFFICIENCY OF ADULT KITTIWAKES AND BRUNNICH GUILLEMOTS FED CAPELIN AND ARCTIC COD

The mean assimilation efficiencies of 10 adult Kittiwakes (Rissa trida ctyla) and 10 Brunnich's Guillemots (Uria lomvia) fed on Capelin (Mall otus villosus) were 77.5% and 74.4%, respectively. When fed on Arctic Cod (Boreogadus saida) they were 83.1% and 78.2%, respectively. After correction for nitrogen retention, the assimilation efficiencies decre ased to 72.2%, 70.6%, 81.2% and 74.7%, respectively. Kittiwakes and Br unnich's Guillemots seem to have the same ability to utilize the energ y of the different food items. The differences in assimilation efficie ncies when fed two fish species was mainly related to the fat content of the fish.