page_title: Baleen whale
section_title: Reproduction and development
hierarchical_section_title: Baleen whale / Behavior / Reproduction and development
caption_attribution_description: A right whale cow and calf
context_page_description: Baleen whales, also known as whalebone whales, form a parvorder of the infraorder Cetacea. They are a widely distributed and diverse parvorder of carnivorous marine mammals. Mysticeti comprise the families Balaenidae, Balaenopteridae, Cetotheriidae, and Eschrichtiidae. There are currently 15 species of baleen whales. While cetaceans were historically thought to have descended from mesonychids, molecular evidence supports them as a clade of even-toed ungulates. Baleen whales split from toothed whales around 34 million years ago.
  Baleen whales range in size from the 6 m and 3,000 kg pygmy right whale to the 31 m and 190 t blue whale, the largest known animal to have ever existed. They are sexually dimorphic. Baleen whales can have streamlined or large bodies, depending on the feeding behavior, and two limbs that are modified into flippers. The fin whale is the fastest baleen whale, recorded swimming at 10 m/s. Baleen whales use their baleen plates to filter out food from the water by either lunge-feeding or skim-feeding. Baleen whales have fused neck vertebrae, and are unable to turn their head at all. Baleen whales have two blowholes.
context_section_description: Before reaching adulthood, baleen whales grow at an extraordinary rate. In the blue whale, the largest species, the fetus grows by some 100 kg (220 lb) per day just before delivery, and by 80 kg (180 lb) per day during suckling. Before weaning, the calf increases its body weight by 17 t (17 long tons; 19 short tons) and grows from 7 to 8 m (23 to 26 ft) at birth to 13 to 16 m (43 to 52 ft) long. When it reaches sexual maturity after 5–10 years, it will be 20 to 24 m (66 to 79 ft) long and possibly live as long as 80–90 years. Calves are born precocial, needing to be able to swim to the surface at the moment of their birth.
  Most rorquals mate in warm waters in winter to give birth almost a year later. A 7-to-11 month lactation period is normally followed by a year of rest before mating starts again. Adults normally start reproducing when 5–10 years old and reach their full length after 20–30 years. In the smallest rorqual, the minke whale, 3 m (10 ft) calves are born after a 10-month pregnancy and weaning lasts until it has reached about 5 to 5.5 m (16 to 18 ft) after 6–7 months. Unusual for a baleen whale, female minkes (and humpbacks) can become pregnant immediately after giving birth; in most species, there is a two-to-three-year calving period. In right whales, the calving interval is usually three years. They grow very rapidly during their first year, after which they hardly increase in size for several years.  They reach sexual maturity when 13 to 14 m (43 to 46 ft) long. Baleen whales are K-strategists, meaning they raise one calf at a time, have a long life-expectancy, and a low infant mortality rate. Some 19th century harpoons found in harvested bowheads indicate this species can live more than 100 years. Baleen whales are promiscuous, with none showing pair bonds. They are polygynous, in that a male may mate with more than one female. The scars on male whales suggest they fight for the right to mate with females during breeding season, somewhat similar to lek mating.
  Baleen whales have fibroelastic (connective tissue) penises, similar to those of artiodactyls. The tip of the penis, which tapers toward the end, is called the pars intrapraeputialis or terminal cone. The blue whale has the largest penis of any organism on the planet, typically measuring 2.4–3.0 metres (8–10 ft). Accurate measurements of the blue whale are difficult to take because the whale's erect length can only be observed during mating. The penis on a right whale can be up to 2.7 m (8.9 ft) – the testes, at up to 2 m (6.6 ft) in length, 78 cm (2.56 ft) in diameter, and weighing up to 238 kg (525 lb), are also the largest of any animal on Earth.
caption: Female right whale with calf
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