484
Guiana dolphin mean group sizes range from 5.3 to 6.5 individuals (Cremer
2000). Group size across the species geographical distribution ranges from two to
29 individuals in most areas (e.g., Edwards and Schnell 2001; Daura-Jorge et al.
2005; Nascimento et al. 2008) (Fig. 17.6).
Mixed-species groups have not been observed. Large groupings of both Guiana
(Cremer 2000) and franciscana dolphins (Cremer and Simões-Lopes 2005) have
been observed interacting with seabirds while hunting in the bay area. Franciscana
dolphins are known to interact with terns (Sterna spp), cormorants (Phalacrocorax
brasilianus), and brown boobies (Sula leucogaster) (Cremer and Simões-Lopes
2005). Guiana dolphins interact with the same species, as well as frigate birds
(Fregata magnifiscens) and gulls (Larus dominicanus) (Cremer et  al. 2004)
(Figs. 17.7 and 17.8).
Fig. 17.6 Guiana dolphin group in Babitonga Bay
Fig. 17.5 Dive behavior of franciscana dolphin in Babitonga Bay. The long rostrum is first projected out of the water, followed quickly by the back
M.J. Cremer et al.