Southern right whales have been well-studied on their winter breeding grounds, especially at Peninsula Valdés, Argentina, and in Australia and South Africa. Researchers have used callosity patterns to identify individuals on these grounds, and have learned much about the southern right whale's behavior, communication, and reproduction. Females produce calves at 3-5 year intervals, usually three years but with a lengthening of the cycle to five years when feeding conditions are poor (Leaper et al. 2006). Calves are born from June to October with a peak in August after a 12-13 month gestation period (Best 1994). Where feeding occurs north of 40°S the diet consists mainly of copepods, south of 50°S mainly euphausiids (krill), and varying proportions of the two food items at intermediate latitudes (Tormosov et al. 1998).