Geographical variation
The last taxonomic delineation of the jaguar subspecies was performed by Pocock in 1939. Based on geographic origins and skull morphology, he recognized eight subspecies. However, he did not have access to sufficient specimens to critically evaluate all subspecies, and he expressed doubt about the status of several. Later consideration of his work suggested only three subspecies should be recognized.
Recent studies have also failed to find evidence for well defined subspecies, and are no longer recognized. Larson (1997) studied the morphological variation in the jaguar and showed that there is clinal north–south variation, but also that the differentiation within the supposed subspecies is larger than that between them and thus does not warrant subspecies subdivision. A genetic study by Eizirik and coworkers in 2001 confirmed the absence of a clear geographical subspecies structure, although they found that major geographical barriers such as the Amazon River limited the exchange of genes between the different populations. A subsequent, more detailed, study confirmed the predicted population structure within the Colombian jaguars.
Pocock's subspecies divisions are still regularly listed in general descriptions of the cat. Seymore grouped these in three subspecies.
(1)Panthera onca onca: Venezuela through the Amazon, including
.....P. onca peruviana (Peruvian Jaguar): Coastal Peru
(2)P. onca hernandesii (Mexican Jaguar): Western Mexico – including
.....P. onca centralis (Central American Jaguar): El Salvador to Colombia
.....P. onca arizonensis (Arizonan Jaguar): Southern Arizona to Sonora, Mexico
.....P. onca veraecrucis: Central Texas to Southeastern Mexico
.....P. onca goldmani (Goldman's Jaguar): Yucatan Peninsula to Belize and Guatemala
(3)P. onca palustris (the largest subspecies, weighing more than 135 kg or 300 lb): The Pantanal regions of Mato Grosso & Mato Grosso do Sul, Brazil, along the Paraguay River into Paraguay and possibly northeastern Argentina.
The Mammal Species of the World continues to recognize nine subspecies, the eight subspecies above and additionally P. o. paraguensis.

Biology and behavior

Physical characteristics
The jaguar is a compact and well-muscled animal. There are significant variations in size: weights are normally in the range of 56–96 kilograms (124–211 lb). Larger males have been recorded at 159 kilograms (350 lb) (roughly matching a tigress or lioness), and smaller ones have extremely low weights of 36 kilograms (80 lb). Females are typically 10–20% smaller than males. The length of the cat varies from 1.62–1.83 meters (5.3–6 ft), and its tail may add a further 75 centimeters (30 in). It stands about 67–76 centimeters (27–30 in) tall at the shoulders.
Further variations in size have been observed across regions and habitats, with size tending to increase from the north to south. A study of the jaguar in the Chamela-Cuixmala Biosphere Reserve on the Mexican Pacific coast, showed ranges of just 30–50 kilograms (66–110 lb), about the size of the cougar. By contrast, a study of the Jaguar in the Brazilian Pantanal region found average weights of 100 kilograms (220 lb) and weights of 300 lb or more are not uncommon in old males. Forest jaguars are frequently darker and considerably smaller than those found in open areas (the Pantanal is an open wetland basin), possibly due to the smaller numbers of large herbivorous prey in forest areas.
A short and stocky limb structure makes the jaguar adept at climbing, crawling and swimming. The head is robust and the jaw extremely powerful. It has been suggested that the jaguar has the strongest bite of all felids, and the second strongest of all mammals; this strength is an adaptation that allows the jaguar to pierce turtle shells. A comparative study of bite force adjusted for body size ranked it as the top felid, alongside the clouded leopard and ahead of the lion and tiger. It has been reported that "an individual jaguar can drag a 360 kg (800 lb) bull 8 m (25 ft) in its jaws and pulverize the heaviest bones".The jaguar hunts wild animals weighing up to 300 kilograms (660 lb) in dense jungle, and its short and sturdy physique is thus an adaptation to its prey and environment.
The base coat of the jaguar is generally a tawny yellow, but can range to reddish-brown and black. The cat is covered in rosettes for camouflage in its jungle habitat. The spots vary over individual coats and between individual Jaguars: rosettes may include one or several dots, and the shape of the dots varies. The spots on the head and neck are generally solid, as are those on the tail, where they may merge to form a band. The underbelly, throat and outer surface of the legs and lower flanks are white.
A condition known as melanism occurs in the species. The melanistic form is less common than the spotted form (it occurs at about six percent of the population) of jaguars in their South American range have been reported to possess it—and is the result of a dominant allele. Jaguars with melanism appear entirely black, although their spots are still visible on close examination. Melanistic Jaguars are informally known as black panthers, but do not form a separate species. Rare albino individuals, sometimes called white panthers, occur among jaguars, as with the other big cats.
While the jaguar closely resembles the leopard, it is sturdier and heavier, and the two animals can be distinguished by their rosettes: the rosettes on a jaguar's coat are larger, fewer in number, usually darker, and have thicker lines and small spots in the middle that the leopard lacks. Jaguars also have rounder heads and shorter, stockier limbs compared to leopards.

Reproduction and life cycle
Jaguar females reach sexual maturity at about two years of age, and males at three or four. The cat is believed to mate throughout the year in the wild, although births may increase when prey is plentiful. Research on captive male jaguars supports the year-round mating hypothesis, with no seasonal variation in semen traits and ejaculatory quality; low reproductive success has also been observed in captivity. Female estrous is 6–17 days out of a full 37-day cycle, and females will advertise fertility with urinary scent marks and increased vocalization. Both sexes will range more widely than usual during courtship.
Mating pairs separate after the act, and females provide all parenting. The gestation period lasts 93–105 days; females give birth to up to four cubs, and most commonly to two. The mother will not tolerate the presence of males after the birth of cubs, given a risk of infant cannibalism; this behaviour is also found in the tiger.
The young are born blind, gaining sight after two weeks. Cubs are weaned at three months but remain in the birth den for six months before leaving to accompany their mother on hunts. They will continue in their mother's company for one to two years before leaving to establish a territory for themselves. Young males are at first nomadic, jostling with their older counterparts until they succeed in claiming a territory. Typical lifespan in the wild is estimated at around 12–15 years; in captivity, the jaguar lives up to 23 years, placing it among the longest-lived cats.

Social activity
Like most cats, the jaguar is solitary outside mother-cub groups. Adults generally meet only to court and mate (though limited non-courting socialization has been observed anecdotally) and carve out large territories for themselves. Female territories, from 25 to 40 square kilometers in size, may overlap, but the animals generally avoid one another. Male ranges cover roughly twice as much area, varying in size with the availability of game and space, and do not overlap. Scrape marks, urine, and feces are used to mark territory.
Like the other big cats, the jaguar is capable of roaring (the male more powerfully) and does so to warn territorial and mating competitors away; intensive bouts of counter-calling between individuals have been observed in the wild. Their roar often resembles a repetitive cough, and they may also vocalize mews and grunts. Mating fights between males occur, but are rare, and aggression avoidance behaviour has been observed in the wild. When it occurs, conflict is typically over territory: a male's range may encompass that of two or three females, and he will not tolerate intrusions by other adult males.
The jaguar is often described as nocturnal, but is more specifically crepuscular (peak activity around dawn and dusk). Both sexes hunt, but males travel farther each day than females, befitting their larger territories. The jaguar may hunt during the day if game is available and is a relatively energetic feline, spending as much as 50–60% of its time active. The jaguar's elusive nature and the inaccessibility of much of its preferred habitat make it a difficult animal to sight, let alone study.

Hunting and diet
Like all cats, the jaguar is an obligate carnivore, feeding only on meat. It is an opportunistic hunter and its diet encompasses 87 species. The jaguar prefers large prey and will take deer, capybara, tapirs, peccaries, dogs, foxes, and sometimes even anacondas and caiman. However, the cat will eat any small species that can be caught, including frogs, mice, birds, fish, sloths, monkeys, and turtles; a study conducted in Cockscomb Basin Wildlife Sanctuary in Belize, for example, revealed that jaguars there had a diet that consisted primarily of armadillos and pacas. Some jaguars will also take domestic livestock, including adult cattle and horses.
While the jaguar employs the deep-throat bite-and-suffocation technique typical among Panthera, it prefers a killing method unique amongst cats: it pierces directly through the temporal bones of the skull between the ears of prey with its canine teeth, piercing the brain. This may be an adaptation to "cracking open" turtle shells; following the late Pleistocene extinctions, armoured reptiles such as turtles would have formed an abundant prey base for the jaguar. The skull bite is employed with mammals in particular; with reptiles such as caiman, the jaguar may leap on to the back of the prey and sever the cervical vertebrae, immobilizing the target. While capable of cracking turtle shells, the jaguar may simply reach into the shell and scoop out the flesh. With prey such as dogs, a paw swipe to crush the skull may be sufficient.
The jaguar is a stalk-and-ambush rather than a chase predator. The cat will walk slowly down forest paths, listening for and stalking prey before rushing or ambushing. The jaguar attacks from cover and usually from a target's blind spot with a quick pounce; the species' ambushing abilities are considered nearly peerless in the animal kingdom by both indigenous people and field researchers, and are probably a product of its role as an apex predator in several different environments. The ambush may include leaping into water after prey, as a jaguar is quite capable of carrying a large kill while swimming; its strength is such that carcasses as large as a heifer can be hauled up a tree to avoid flood levels.
On killing prey, the jaguar will drag the carcass to a thicket or other secluded spot. It begins eating at the neck and chest, rather than the midsection. The heart and lungs are consumed, followed by the shoulders. The daily food requirement of a 34 kilogram animal, at the extreme low end of the species' weight range, has been estimated at 1.4 kilograms. For captive animals in the 50–60 kilogram range, more than 2 kilograms of meat daily is recommended. In the wild, consumption is naturally more erratic; wild cats expend considerable energy in the capture and kill of prey, and may consume up to 25 kilograms of meat at one feeding, followed by periods of famine. Unlike all other species in the Panthera genus, jaguars very rarely attack humans. Most of the scant cases where jaguars turn to taking a human show that the animal is either old with damaged teeth or is wounded. Sometimes, if scared, jaguars in captivity may lash out at zookeepers.