Azores : Toninha mansa - POR : Golfinho comum - ITA : Delfino comune - SPAIN : Delfin commun - GB : Common dolphin - GER : Gewöhnlicher delphin - NEDER : Gewone dolfijn - SWEEDS : Vanlings delfin - NOORS : Delfin - DEENS : Delfin - JAP : Suji Mairuka
The average adult size is 2.2 m, but they can achieve a maximum body length of 2.6 m. Weight normally varies between 75 and 130 kg. At birth, calves already show a small sexual dimorphism with males slightly larger (about 90 cm long) than the females (about 80 cm long). There are 40 to 55 (perhaps as many as 65) small, conical pairs of teeth in each jaw. Gestation lasts for 10 to 11 months. The end of the lactating period occurs at around 1 year of life. The females bear a single calf every first or second year. Their body shape and colouring varies geographically. This species is characterised by a hourglass (shaped black or dark-gray saddle below the dorsal fin), and a tan or yellowish-tan region making up each side of the posterior region of their body. Their lifetimes range between 25 to 30 years. They feed on octopus, squid, and fish (e.g., herrings, sardines, and horse mackerel). The common dolphin emits clicks that range anywhere from 0.2 to 150 kHz and whistles or hisses of 4 to 16 kHz.
The common dolphin was present 35 % of the time during the total number of field trips we made. They are very playful and frequently ride the bow waves generated by our vessels. Because of this friendly behaviour, they are an easy prey for unscrupulous fishermen. We observed them more frequently during the spring, sometimes associated with spotted and striped dolphins. The common dolphin is gregarious and in the Azores it is not uncommon to find herds of 300 to 400 individuals. This species can sometimes be confused with a spotted or a striped dolphin, but its obvious yellowish colouring in the back of its body is a primary clue distinguishing it from the other two species. When feeding, the common dolphin moves with a speed of 4 to 5 knots (the maximum speed it can reach is 30 knots) and emerges to breathe every 20 to 30 seconds. The longest dive we observed was 3.45 minutes, but there are reports of common dolphins submerging as much as 8 minutes. They can dive as deep as 300 m.