Attributes / relations provided by
♦ ¹del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona.
♦ ²Offshore diet of grey seals Halichoerus grypus near Sable Island, Canada, W. D. Bowen, G . D. Harrison, Mar. Ecol. Prog. Ser. 112: 1-11, 1994