It is thought that in ideal conditions they can hear up to 1,000 miles (1,600 km) away. This species sexually matures between 6 and 10 years of age. Calves are born weighing 3 tons (2,722 kg) and are 23 to 27 feet (7-8.2 m) long. The calf will nurse for 7-8 months and, during the nursing period, consume 100 gallons (379 liters) of their mother's fat-rich milk every day. When they reach 52 feet (16 m) in length they are weaned. It is most common to see Blue Whales traveling in pairs, although they may also be observed in groups.