William A. Watkins, William E. Schevill; Aerial Observation of Feeding Behavior in Four Baleen Whales: Eubalaena glacialis, Balaenoptera borealis, Megaptera novaeangliae, and Balaenoptera physalus. J Mammal 1979; 60 (1): 155-163. doi: 10.2307/1379766
Distinct behavioral differences were noted from aerial observations of four species of baleen whales (Eubalaena glacialis, right whale; Balaenoptera borealis, sei whale; Megaptera novaeangliae, humpback whale; Balaenoptera physalus, finback whale) feeding together on 30 April and 1 May 1975. The right and sei whales fed together on patches of plankton. Right whales fed steadily with mouths open in the densest areas, while the sei whale followed a faster but more erratic path through the patches, alternately opening and slowly closing its mouth with slight throat distension at each closing. Humpback and finback whales fed together on dense schools of fish associated with the patches of plankton. The humpback fed by rushing, generally from below the schools of fish, while finback feeding was by more horizontal passes sometimes characterized by sharp turns and rolls within the fish schools and often with enormous throat distension.