Furthermore, when a new male lion takes over the pride, subadult lions, both male and female, may be evicted. Life is harsh for a female nomad. Nomadic lionesses rarely manage to raise their cubs to maturity, without the protection of other pride members.
One scientific study reports that both males and females may interact homosexually. Male lions pair-bond for a number of days and initiate homosexual activity with affectionate nuzzling and caressing, leading to mounting and thrusting. A study found that about 8 percent of mountings have been observed to occur with other males. Female pairings are held to be fairly common in captivity, but have not been observed in the wild.
Health
Though adult lions have no natural predators, evidence suggests that the majority die violently from humans or other lions. This is particularly true of male lions, who, as the main defenders of the pride, are more likely to come into aggressive contact with rival males. In fact, even though a male lion may reach an age of 15 or 16 years if he manages to avoid being ousted by other males, the majority of adult males do not live to be more than 10 years old. This is why the average lifespan of a male lion tends to be significantly less than that of a lioness in the wild. However, members of both sexes can be injured or even killed by other lions when two prides with overlapping territories come into conflict.
Various species of tick commonly infest the ears, neck and groin regions of most lions. Adult forms of several species of the tapeworm genus Taenia have been isolated from intestines, the lions having ingested larval forms from antelope meat. Lions in the Ngorongoro Crater were afflicted by an outbreak of stable fly (Stomoxys calcitrans) in 1962; this resulted in lions becoming covered in bloody bare patches and emaciated. Lions sought unsuccessfully to evade the biting flies by climbing trees or crawling into hyena burrows; many perished or emigrated as the population dropped from 70 to 15 individuals. A more recent outbreak in 2001 killed six lions.[98] Lions, especially in captivity, are vulnerable to the Canine distemper virus (CDV), feline immunodeficiency virus (FIV), and feline infectious peritonitis (FIP). CDV is spread through domestic dogs and other carnivores; a 1994 outbreak in Serengeti National Park resulted in many lions developing neurological symptoms such as seizures. During the outbreak, several lions died from pneumonia and encephalitis. FIV, which is similar to HIV while not known to adversely affect lions, is worrisome enough in its effect in domestic cats that the Species Survival Plan recommends systematic testing in captive lions. It occurs with high to endemic frequency in several wild lion populations, but is mostly absent from Asiatic and Namibian lions.
Communication
When resting, lion socialization occurs through a number of behaviors, and the animal's expressive movements are highly developed. The most common peaceful tactile gestures are head rubbing and social licking, which have been compared with grooming in primates. Head rubbing—nuzzling one's forehead, face and neck against another lion—appears to be a form of greeting, as it is seen often after an animal has been apart from others, or after a fight or confrontation. Males tend to rub other males, while cubs and females rub females. Social licking often occurs in tandem with head
rubbing; it is generally mutual and the recipient appears to express pleasure. The head and neck are the most common parts of the body licked, which may have arisen out of utility, as a lion cannot lick these areas individually.
Lions have an array of facial expressions and body postures that serve as visual gestures. Their repertoire of vocalizations is also large; variations in intensity and pitch, rather than discrete signals, appear central to communication. Lion sounds include snarling, purring, hissing, coughing, miaowing, woofing and roaring. Lions tend to roar in a very characteristic manner, starting with a few deep, long roars that trail off into a series of shorter ones. They most often roar at night; the sound, which can be heard from a distance of 8 kilometres (5.0 mi), is used to advertise the animal's presence. Lions have the loudest roar of any big cat.
Interspecific predatory relationships
In areas where lions and spotted hyenas are sympatric, the two species occupy the same ecological niche, and are thus in direct competition with one another. In some cases, the extent of dietary overlap can be as high as 68.8%. Lions typically ignore spotted hyenas, unless they are on a kill or are being harassed by them. Spotted hyenas themselves tend to visibly react to the presence of lions, whether there is food or not. Lions will readily appropriate the kills of spotted hyenas: in the Ngorongoro crater, it is common for lions to subsist largely on kills stolen from hyenas, causing the hyenas to increase their kill rate. Lions are quick to follow the calls of hyenas feeding, a fact which was proven by Dr. Hans Kruuk, who found that lions repeatedly approached him whenever he played the tape-recorded calls of hyenas feeding. When confronted on a kill by lions, spotted hyenas will either leave or wait patiently at a distance of 30-100 metres until the lions have finished. In some cases, spotted hyenas are bold enough to feed alongside lions, and may occasionally force the lions off a kill. The two species may act aggressively toward one another even when there is no food involved. Lions may charge at hyenas and maul them for no apparent reason: one male lion was filmed killing two matriarch hyenas on separate occasions without eating them, and lion predation can account for up to 71% of hyena deaths in Etosha. Spotted hyenas have adapted to this pressure by frequently mobbing lions which enter their territories. Experiments on captive spotted hyenas revealed that specimens with no prior experience with lions act indifferently to the sight of them, but will react fearfully to the scent.
Lions tend to dominate smaller felines such as cheetahs and leopards in areas where they are sympatric. They will steal their kills and will kill their cubs and even adults when given the chance. The cheetah has a 50 percent chance of losing its kill to lions or other predators. Lions are major killers of cheetah cubs, up to 90 percent of which are lost in their first weeks of life due to attacks by other predators. Cheetahs avoid competition by hunting at different times of the day and hide their cubs in thick brush. Leopards also use such tactics, but have the advantage of being able to subsist much better on small prey than either lions or cheetahs. Also, unlike cheetahs, leopards can climb trees and use them to keep their cubs and kills away from lions. However, lionesses will occasionally be successful in climbing to retrieve leopard kills. Similarly, lions dominate African wild dogs, not only taking their kills but also preying on both young and adult dogs (although the latter are rarely caught).
The Nile crocodile is the only sympatric predator (besides humans) that can singly threaten the lion. Depending on the size of the crocodile and the lion, either can lose kills or carrion to the other. Lions have been known to kill crocodiles venturing onto land, while the reverse is true for lions entering waterways containing crocodiles, as evidenced by the fact that lion claws have on occasion been found in crocodile stomachs.