Antagonism in nature: Intraspecific fights

This text examines intraspecific antagonism in wild animals. For other forms of antagonism in nature see Interspecies conflict and Sexual conflict. This part deals with other forms of conflict among animals of the same species. For information about other ways in which animals in the wild suffer see the main page on the situation of animals in the wild.

Antagonistic relationships are found not only between animals of different species, but within species too. Intraspecific conflict occurs when the interests of individual animals within a given species conflict. This happens when there is a limited supply of a valuable resource. For example, some areas are better than others for finding food, shelter from the elements, places to hide from predatory animals, or opportunities for attracting a mate. Conflicts occur frequently because animals of the same species have very similar requirements for their wellbeing, survival and reproduction, yet their demand for those resources exceed what is available.¹ Animals also compete with each other for access to mates, social status, food, and parental care. The conflict may be direct, with animals fighting each other (called “interference”) or indirect, with animals competing without fighting each other directly (called “exploitation”).² Both forms of competition can be harmful. Fighting can result in injury or death. Even if animals aren’t directly harmed by others, they can be harmed by deprivation.

Fighting over territory

Territoriality is a widespread cause of intraspecific conflict. It occurs when an individual animal defends a particular area (the territory) against intrusion by other animals, and thereby maintains exclusive access to the resources within that territory.³ Those resources may include food or nesting sites. The territory might give them more access to mates. Animals use a variety of methods to demarcate and defend their territories. These methods include scent marking, where the animal marks her territory with strong smelling substances;⁴ visual marking, for example by clawing at trees, or rubbing against them to leave fur deposits;⁵ and vocalizations such as birdcalls or wolf howls.⁶ Sometimes, however, animals use force to defend their territories, and this means risking injury or even death for the defender or the intruder.

Birds

Many species of birds are territorial, at least during the breeding season, and some will fight to defend their territory.⁷ These fights can be brutal, leaving one or both parties with painful injuries. Blackbirds are extremely territorial, with both males and females fighting to protect their territory. In the video below, we see two mature males fighting over territory. The bird who loses the fight is pinned to the ground and pecked viciously by the other bird. After the fight, the loser is badly injured, seemingly dazed and unable to fly.

Bluebirds fight to defend their nesting sites from other bluebirds as well as birds of other species such as sparrows and wrens. The video below shows two males fighting. According to the photographer, the fight lasted for forty-five minutes.

Mammals

Intergroup violence is common among chimps. These conflicts have been compared to human wars, due to their duration and high levels of planning and coordination. Such conflicts usually center around control of territory or the kidnapping of fertile females. Jane Goodall was the first scientist to witness war among chimpanzees. Here she recounts her experience of the “Gombe Chimpanzee War”:

For several years I struggled to come to terms with this new knowledge. Often when I woke in the night, horrific pictures sprang unbidden to my mind—Satan [one of the apes], cupping his hand below Sniff’s chin to drink the blood that welled from a great wound on his face; old Rodolf, usually so benign, standing upright to hurl a four-pound rock at Godi’s prostrate body; Jomeo tearing a strip of skin from Dé’s thigh; Figan, charging and hitting, again and again, the stricken, quivering body of Goliath, one of his childhood heroes.⁸

Big cats are frequently territorial. Tigers are generally solitary, maintaining individual territories. The size of these territories depends on many factors such as the type of habitat, the density of animals to hunt, and the size, sex and age of the tiger.⁹ Tigers will fight to maintain their territories against intruders. Generally these fights result in the weaker individual submitting, though sometimes injury or death can result. The video below shows a young female tiger hunting in the territory of a mature male. He attacks her, and though she quickly submits, she is left with a gash on her paw.

Insects

Many species of ant are highly territorial. Honey ants are found in arid environments in North America, Australia, and Africa. They are known for their specialized workers called repletes. The repletes are fed by the other workers and are used as living larders, storing honey for the winter. Territorial conflicts with other colonies are often resolved by ritualized display fights. When one colony is significantly stronger than the other, however, it will raid the weaker colony, killing or driving away the queen, enslaving the workers and capturing the honey-rich repletes to feed their own colony.¹⁰ The video below shows one colony raiding another. Having overcome the opposition, they drag the repletes back to their nest. In order to access the honey, the workers chew through the abdomen of the replete.

Fighting over mates

Polygyny is a mating system in which a single male lives and mates exclusively with multiple females. This system has been observed in elephant seals, gorillas, pheasants, and baboons. Since the numbers of males and females in most species are approximately equal, polygynous mating systems lead to competition between males for access to females. Elephant seal males fight to control a beach and thereby to have exclusive mating rights over the females in that territory. A successful male can have a harem of up to 100 females, while most males will not have a chance to mate at all. The fights between males can be brutal, especially when the males are evenly matched. The video below shows two mature elephant seals fighting for control of a beach.

Male zebras control harems of females and will fight other males who attempt to mate with them. These fights can be violent, with the males biting each other in the neck and head. The video below shows two stallions fighting for control of a harem. Notice how they attempt to bite the vital tendons on each other’s hind legs.

Stallions expand their harems by abducting mares from their birth harem once they have reached sexual maturity, or by “stealing” them from other males. If the captured female is already pregnant, the male will forcibly copulate with her until the fetus is either reabsorbed or miscarried. Studies of captive zebras show that abortion rates are three times higher when a new male is introduced to a herd containing pregnant females.¹¹ The video below shows a male zebra attempting to drown a foal fathered by a rival.

Male kangaroos fight for privileged access to females. These fights can be brutal, though serious injury is rare. Dominant males rarely maintain their status for longer than a year, and due to constant fighting, energy expenditure, and reduced feeding time, their physical condition worsens significantly, even to the point of death.¹² The video below shows two mature males fighting for access to a female in estrus.

Social status

In social animals, social status is important because a higher rank may mean better access to mates and resources like food and territory. Chimpanzees have been witnessed killing members of their own groups over social status, mating rights, or in apparent political power struggles. In other case, Foudouku, a previous leader of his group before losing his closest ally and being driven out, attempts to rejoin his old group in order to find a mate. While some of the older chimps accepted Foudouku back into the group, some of the younger males, perhaps displeased about having more competition for mates, didn’t accept him, and chased him away several times. Eventually this sub group attacked Foudouku and killed him. His body was found with a multitude of serious injuries including a severe bite wound in his foot, a large gash in his back, a ripped anus and cracked ribs. After his death, the group continued to attack Foudouku’s body with rocks and sticks, and even ate part of his flesh. The video below shows a similar intragroup killing:

Cannibalism and infanticide

Cannibalism is common in nature. It has been observed in around 1,300 species,¹³ in a wide variety of social and ecological contexts.¹⁴ The cannibal benefits both from the extra nutrition and by eliminating a competitor.¹⁵ The victim, of course, loses his life. Cannibalism may also be a factor in intraspecific disease transmission, at least in species that practice group cannibalism.¹⁶ Some species have evolved morphologically distinct specialist cannibals. This is called cannibalistic polyphenism, and it means that the cannibals within a population are phenotypically distinct from the non-cannibals. This has been observed in the larval forms of the tiger salamander and several species of toads.¹⁷ In many cases, cannibalism is practiced on infants. In some cases, this allows the cannibal both to gain valuable nutrition and to eliminate the progeny of a rival. In other cases, it is the parent who kills, and sometimes consumes, their own children.

Cannibalism has been observed in wild octopuses. The cannibal is generally around 4 to 5 times larger than the animal who is consumed. Octopuses engage in cannibalism even when other animals they usually prey upon, such as mussels, are available. This may be because octopus flesh has a higher protein content per gram than mussel flesh, or because of the difficulty and energy expenditure involved in opening mussels’ shells.¹⁸ The video below shows one octopus cannibalizing another in the wild.

Many species of insect practice cannibalism. The common wasp turns to cannibalism of larvae when the colony starts to break down, usually after the death of the queen.¹⁹ The video below shows a colony of killer hornets attacking another colony. They use their mandibles to decapitate their enemies. Once they have defeated the defenders, they enter their nest and eat the larvae within.

Sexual cannibalism is common in insects and spiders. The below video shows a female praying mantis devouring a male while he continues to mate with her.

Infanticide followed by cannibalism has been observed several times among chimps. Males have been witnessed killing and eating infants both within their own group²⁰ and those captured from rival groups.²¹ The video below shows a raid by one group of chimps into the territory of a rival group. They capture and kill a young chimp then they share the carcass among them.

When parents kill their own offspring this is called filial infanticide. When they then eat their offspring, this is filial cannibalism. These behaviors have been observed in fishes,²² birds,²³ rats,²⁴ sloths,²⁵ and beetles.²⁶ It isn’t always clear what causes parents to kill their own children. In some cases, it may be to cut their losses or recoup the energy expended in a “bad investment,” for example if the infants are developing too slowly, are sick, or there isn’t enough food for them all. The parent might be starving or stressed, due to difficult environmental conditions. In some cases, parents kill their offspring in order to make themselves available for mating so that they can “try again” for a better brood.²⁷

The video below shows a dickcissel female throwing one of her chicks out of the nest.

The video below shows a female sparrow-lark partially cannibalizing one of her chicks. It isn’t clear from the video whether she killed the chick herself.

Sibling rivalry

Whenever an animal has multiple offspring at once, there is the potential for sibling rivalry. Food and parental attention are limited. In situations where the resources available aren’t sufficient, either because of poor environmental conditions or the large size of the brood, siblings have to compete with each other for the resources they require. Sometimes this conflict is non-aggressive. For example, American robin chicks compete with each other for food by engaging in begging behavior, and the chicks who display the most intense begging behavior receive more food from their parents. It has been shown that this is not merely meant to communicate hunger; rather it is an attempt by the chick to receive more resources at the cost of leaving fewer resources for their current nest-mates (intra-brood competition) or at the expense of reducing the parents’ future reproductive potential (inter-brood competition).²⁸ Though not directly aggressive, such manipulative behavior has negative consequences for those nest-mates who receive less food than they require, and for the parents, who may be driven to over exertion and increased exposure to predation in order to provide food to their begging chicks. The video below explains some of the methods baby birds use to manipulate their parents into giving them a greater share of the food. This includes loud chirping, coloration of the mouth, and positioning within the nest.

Sibling rivalry can also be aggressive, and can result in siblicide. Siblicide may be obligate or facultative. Obligate siblicide means that the larger sibling will kill the smaller one, regardless of the level of resources available. Facultative siblicide, on the other hand, is conditional – it occurs only when resource availability drops below a certain level.²⁹ Siblicide is most frequently observed in birds. Nazca Boobies are large seabirds and the chicks engage in obligate siblicide. The mother lays one or two eggs in each clutch. The first chick is usually born around five days before the second, and almost invariably kills the younger sibling by dragging him from the nest.³⁰ Blue-footed boobies are facultatively siblicidal, with the older chick killing the younger only in times of food shortage.³¹ The video below shows a Nazca booby chick removing his younger sibling from the nest, where he will die. The mother doesn’t intervene.

Spotted hyenas also engage in facultative siblicide. Hyena cubs are born with their eyes open and with developed teeth, and begin fighting each other shortly after birth.³² These fights function to establish rank, but in times of intense food competition they can result in death. One long term study of wild hyenas in Serengeti National Park found 37 siblicides out of 384 litters.³³ The video below shows new-born hyena cubs attacking each other only moments after birth. The two strongest cubs then join forces against the weakest, attacking her before she has even fully emerged from her amniotic sac. They don’t kill her directly, but limit her access to her mother’s milk, eventually starving her to death.

Intraspecific conflict arises whenever there is a conflict of interests among members of the same species. Individuals’ interests conflict over territory, food, access to mates, social status, and the allocation of parental care. Whether these conflicts are openly aggressive or simply involve non-violent competition over limited resources, the result is the same: individual animals suffer from violence or deprivation. Those who are unable to secure a territory might not be killed directly by other members of their species, but without territory they will struggle to find enough food. Those who lose out in competitions for mates may not be killed by stronger males, but they will be unable to breed, and they will suffer from sexual frustration. Nonhuman animals find themselves struggling to survive from the very moment they are born. Among the grave dangers they face are those that come from animals of their own species. For some species, even their parents and siblings can pose a threat.

For other information about intraspecific antagonistic relations see Sexual conflict.

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Notes