A humpback whale can easily be identified by its stocky body with an obvious hump and black dorsal coloring. The head and lower jaw are covered with knobs called tubercles, which are actually hair follicles, and are characteristic of the species. The fluked tail, which it lifts above the surface in some dive sequences, has wavy trailing edges.[8] The four global populations, all under study, are: North Pacific, Atlantic, and Southern Ocean humpbacks, which have distinct populations which complete a migratory round-trip each year and the Indian Ocean population, which does not migrate, prevented by that ocean's northern coastline.
The long black and white tail fin, which can be up to a third of body length, and the pectoral fins have unique patterns, which make individual whales identifiable.[9][10] Several hypotheses attempt to explain the humpback's pectoral fins, which are proportionally the longest fins of any cetacean. The two most enduring mention the higher maneuverability afforded by long fins, and the usefulness of the increased surface area for temperature control when migrating between warm and cold climates. Humpbacks also have 'rete mirabile', a heat exchanging system, which works similarly in humpbacks, sharks and other fish.[
Humpbacks have 270 to 400 darkly coloured baleen plates on each side of the mouth. The plates measure from a mere 18 inches (46 cm) in the front to approximately 3 feet (0.91 m) long in the back, behind the hinge. Ventral grooves run from the lower jaw to the umbilicus about halfway along the underside of the whale. These grooves are less numerous (usually 16–20) and consequently more prominent than in other rorquals
The stubby dorsal fin is visible soon after the blow when the whale surfaces, but disappears by the time the flukes emerge. Humpbacks have a 3 metres (9.8 ft) heart-shaped to bushy blow, or exhalation of water through the blowholes. Because Humpback Whales breathe voluntarily, it is possible that the whales shut off only half of the brain when sleeping.[11] Early whalers also noted blows from humpback adults to be 10–20 feet (3.0–6.1 m) high.
Newborn calves are roughly the length of their mother's head. At birth, calves measure 20 feet (6.1 m) at 2 short tons (1.8 t) The mother, by comparison, is about 50 feet (15 m). They nurse for approximately six months, then mix nursing and independent feeding for possibly six months more. Humpback milk is 50% fat and pink in color. Some calves have been observed alone after arrival in Alaskan waters.[
Females reach sexual maturity at the age of five, achieving full adult size a little later. Males reach sexual maturity at approximately 7 years of age. The humpback whale lifespan ranges from 45–100 years
Fully grown, the males average 15–16 metres (49–52 ft). Females are slightly larger at 16–17 metres (52–56 ft), and 40,000 kilograms (44 short tons); the largest recorded specimen was 19 metres (62 ft) long and had pectoral fins measuring 6 metres (20 ft) each.
Females have a hemispherical lobe about 15 centimetres (5.9 in) in diameter in their genital region. This visually distinguishes males and females. The male's penis usually remains hidden in the genital slit. Male whales have distinctive scars on heads and bodies, some resulting from battles over females.[
Identifying individuals
The varying patterns on the tail flukes are sufficient to identify individuals. Unique visual identification is not currently possible in most cetacean species (other exceptions include orcas and right whales), making the humpback a popular study species.[ A study using data from 1973 to 1998 on whales in the North Atlantic gave researchers detailed information on gestation times, growth rates, and calving periods, as well as allowing more accurate population predictions by simulating the mark-release-recapture technique (Katona and Beard 1982). A photographic catalogue of all known North Atlantic whales was developed over this period and is currently maintained by College of the Atlantic Similar photographic identification projects have begun in the North Pacific by SPLASH (Structure of Populations, Levels of Abundance and Status of Humpbacks), and around the world.
Life history
Reproduction
Females typically breed every two or three years. The gestation period is 11.5 months, yet some individuals have been known to breed in two consecutive years. The peak months for birth are January, February, July, and August. There is usually a 1-2 year period between humpback births. Humpback whales can live up to 48 years.
Recent research on humpback mitochondrial DNA reveals that groups that live in proximity to each other may represent distinct breeding pools
Social structure
Humpbacks frequently breach, throwing two thirds or more of their bodies out of the water and splashing down on their backs.
The humpback social structure is loose-knit. Typically, individuals live alone or in small, transient groups that disband after a few hours. These whales are not excessively social in most cases. Groups may stay together a little longer in summer to forage and feed cooperatively. Longer-term relationships between pairs or small groups, lasting months or even years, have rarely been observed. It is possible that some females retain bonds created via cooperative feeding for a lifetime. The humpback's range overlaps considerably with other whale and dolphin species — for instance, the minke whale. However, humpbacks rarely interact socially with them, though humpback calves in Hawaiian waters sometimes play with bottlenose dolphin calves.[
Courtship
Courtship rituals take place during the winter months, following migration toward the equator from summer feeding grounds closer to the poles. Competition is usually fierce, and unrelated males dubbed escorts by researcher Louis Herman frequently trail females as well as mother-calf dyads. Groups of two to twenty males gather around a single female and exhibit a variety of behaviors over several hours to establish dominance of what is known as a competitive group. Group size ebbs and flows as unsuccessful males retreat and others arrive to try their luck.
Behaviors include breaching, spyhopping, lob-tailing, tail-slapping, fin-slapping, peduncle throws, charging and parrying. Less common "super pods" may number more than 40 males, all vying for the same female.
Whale song is assumed to have an important role in mate selection; however, scientists remain unsure whether song is used between males to establish identity and dominance, between a male and a female as a mating call, or both.[
Both male and female humpback whales vocalize, however only males produce the long, loud, complex "songs" for which the species is famous. Each song consists of several sounds in a low register that vary in amplitude and frequency, and typically lasts from 10 to 20 minutes.[16] Humpbacks may sing continuously for more than 24 hours. Cetaceans have no vocal cords, so whales generate their song by forcing air through their massive nasal cavities.
Whales within a large area sing the same song. All North Atlantic humpbacks sing the same song, and those of the North Pacific sing a different song. Each population's song changes slowly over a period of years without repeating.[
Scientists are unsure of the purpose of whale song. Only males sing, suggesting that one purpose is to attract females. However, many of the whales observed to approach a singer are other males, and results in conflict. Singing may therefore be a challenge to other males.[ Some scientists have hypothesized that the song may serve an echolocative function During the feeding season, humpbacks make altogether different vocalizations for herding fish into their bubble nets
All these behaviors also occur absent potential mates. This indicates that they are probably a more general communication tool. Scientists hypothesize that singing may keep migrating populations connected. Some observers report that singing begins when competition for a female ends.[
Humpback whales have also been found to make a range of other social sounds to communicate such as "grunts", "groans", "thwops", "snorts" and "barks".[
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