The amplitude of their annual migrations varies from year to year depending on the amount of rainfall, but in a normal year the range is between 200 and 300 km. During the rainy season in May and June, they move northward to about 16°N (200 mm isohyet) to exploit the seasonally abundant forage. In years with abundant rainfall they may roam as far north as 18°N when milk production at this time is at its highest.