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Wild Animals/Animals that kill their young

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Question
I am doing a report on abortion and I was wondering if you could give me a few examples of animals that kill their young?  Animals that are most commonly known would be very helpful.  Thanks!
Andrea


Answer
Dear Andrea

Thanks for your question. I have looked up several websites and various books. I have taken a general view of adult animals killing young of their own species, rather than be specific in the case of a mother or father killing her/his own young, although there are cases of this. I have not gone into details about humans. This area is controversial and there have been several cases where a mother has been accused of killing her child, but has been later found ‘not guilty', due to the difficulty of proving that a person is responsible for ‘cot deaths'. How much a parent under stress is responsible for the death of a child is debatable and is, as far as I can gather, outside the remit of your question.

One of the main reasons for adults killing young is due to males taking over leadership of a group. If they wait for young animals to become independent of their mothers, the males may not sire offspring before new males take over the group. Alternatively, if they kill the young, the females often become fertile soon afterwards, so the males are more likely to become fathers. Some dominant animals may eat young animals in order to enforce their dominance over submissive group members. Other animals may eat young in order to satisfy hunger pains or due to psychological stress, due to overcrowded conditions. If there are too many animals in a limited area, the whole group may die out, due to too little food being available. If many of the animals die, the food supply goes further and the survivors can produce young when conditions are ideal. All of these mechanisms may seem cruel, but many of the strategies have a logical basis, as they are geared towards survival of animal groups, rather than the survival of each individual.  

Infanticide has been found in many species, including humans and other primates, cats, dogs, whales, rodents, insects and fish. http://www.ratbehavior.org/infanticide.htm gives the following reasons for infanticide: to gain food; to gain increased access to physical resources like food, nesting sites or space; to avoid caring for unrelated offspring; to bias the sex ratio of the litter. Adult males may kill a female's young to increase his chances of mating. Infanticide may also be due to aggression or to disturbances in the physical or social environment. For example when female voles, mink and other mammals are in a state of psychological stress, they may eat their young.

1.   Many rodents show infanticide, including rats, ground squirrels, lemmings, hamsters, mice, voles, muskrats, gerbils, prairie dogs and marmots.
2.   Rats and mice: When populations of mice and rats rise rapidly, the hungry and stressed survivors may kill and eat young.  http://www.ratbehavior.org/infanticide.htm goes into detail about infanticide in Norway rats. This is usually directed towards newborn rats. A mother pet rat may eat her own offspring. Mothers tend to kill deformed or wounded infants, which may allow her to allocate resources to the healthy pups, which are more likely to survive. Mothers may also kill litters when they are stressed, perhaps because she perceives the environment as too hostile for pup survival, or if she cannot to rear the litter successfully. She recuperates some her energetic investment by consuming the young. Malnourished mothers, and mothers who have an abnormal birth experience, may also become infanticidal. An unrelated adult male rat may kill young to bring the mother back into oestrus sooner, so he can sire a litter of his own. Maternal aggression after the birth of a litter may reduce infanticide. Unrelated females may kill young rats to gain food and take over the nest.
3.   Eastern grey squirrels: http://www.blackmouthcur.com/Gray%20Squirrels.htm  states that some males kill the young so that the females re-enter oestrus. http://fwie.fw.vt.edu/TN/TN10056h.htm states that captive, stressed females may kill their young.
4.   Belding's ground squirrels: When Belding's ground squirrels fail to attend their territories, unrelated females or one-year-old males may arrive and kill pups. Yearling males usually eat the carcasses, so their infanticide may be motivated by hunger. When a predators kill a female's young, the female often emigrates to a new, safer site and kills the young there before she can settle. By removing juvenile females who may remain in the preferred area, infanticidal females educe further competition for a nest site. Mothers with close relatives as neighbours lose fewer young to infanticides than females without neighbouring kin. This is because groups of females detect marauders more quickly and expel them more rapidly than individuals acting alone, and because a female's relatives defend her young when she is away from home.
5.   African hunting dogs: I remember a documentary about hunting dogs, where a dominant female tried to kill all the pups of another female. The documentary crew retrieved the last pup and named it Solo. Eventually Solo was reintroduced to the pack.
6.   Lions: http://animaldiversity.ummz.umich.edu/site/accounts/information/Panthera_leo.htm... and other websites state that when new adult lions take over a pride, they often kill the young and thus eliminate the chance of any rivalry against offspring he later fathers. This often causes the females to enter oestrus after 2-3 weeks, much more quickly than if a female came into oestrus after her cubs have become independent. The males mate with the female and help protect the females and their offspring, rather than protecting the young sired by the previous males. Lions may occasionally eat the cubs. Successful males that takeover a pride have about 2 years before another younger, stronger coalition will replace them. This is the same time a male would have to wait before nursing females entered oestrus after their cubs became independent – by this time, a new male would probably take off the pride and the ‘patient' males would not longer be able to mate. Killing the cubs means that the males have a cahnce of leaving offspring, although females vigorously defend their cubs during a takeover.
7.   Butterflies: The caterpillars of Monarch and Queen butterflies often eat the eggs of the species.
8.   http://www.polperro.com.au/s15.html states that adult bottle-nosed dolphins kill the young of their own species. This may because competing adult males may be killing the offspring of their rivals so that the dead dolphin's mother will be receptive to mating. Researchers believe that females remain sexually inactive for years when raising their young, but become active again soon after their loss. This murderous behaviour is not an uncommon feature within the animal kingdom. Large terrestrial carnivores, such as bears and lions, have been known to perform similar acts of infanticide to help start up their own dynasties to compete with their rivals.
9.   Baboons: http://www.rci.rutgers.edu/~palombit/ studies male infanticide in chacma baboons, where a social relationship between males and lactating females leads to a decrease in infanticide. Similar relationships occur in olive baboons, where male infanticide is much less common.
10.   Langurs and other primates: The males of several primate species, including the common langur, practice infanticide. Bands of male langurs will attack a mixed troop, driving off the males and killing the offspring before mating with the females. Baboons also kill their young and occasionally even eat them. Dominant male gorillas and chimpanzees may kill the young of their species, but infanticide does not seem to occur in bonobos.
11.   Gulls and other birds: http://ladywildlife.com/animal/cannibalisminanimals.html states that many species of gull that nest in large colonies eat eggs and young. This may be a response to crowding, but male gulls, which lack young of their own, are more likely to eat the eggs and young of their own species. Some parent birds may eat the young when populations become dense, or food scarce. Crows may eat eggs and chicks of rivals to improve their own chance of successful breeding.
12.   Kangaroos: Kangaroos can have three young at different stages of development. One inside the body, one in the pouch and one that lives outside the pouch for much of the time, but still suckles from the mother. In severe conditions, the mother may not have enough energy to feed the older young, so this is left to its own devices. If conditions deteriorate, the mother will remove the pouch young. This means that the embryo in the body develops and soon occupies the vacant pouch. Whether this course of action counts as infanticide is debatable, but if the mother died, so would the young.   

I hope that this gives you enough examples for your report. If you require any additional information, please contact me.

All the best

Jonathan  

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Jonathan Wright

Expertise

I can answer questions about wild mammals and other animals, as well as extinct animals and zoos. I am not an expert about every animal species. I can look up information from books and the internet, but can't verify if all the information is true. Please don't ask questions about: 1. Pets. I am not a vet. Please contact a vet if your pet is ill. You may need to spend some money if you want your pet to live. Don't get a pet if you don't know how to look after it and if you can't provide it with the space, food and possible companions that will help it live a healthy life. Don't take animals from the wild, unless they are ill and/or injured and you can protect them until a wildlife charity can help. It is cruel to take animals from their parents, especially if the parents will look for the babies, while putting their other babies at risk. You may be breaking the law by keeping wild animals or you may need a licence to look after some species. Please check with a local wildlife group. 2. Eggs: Please don't remove eggs from nests. The mother birds provide the right temperature for the eggs and won't sit on them if the temperature is warm enough for them to develop naturally. It is illegal to remove eggs of some species and, unless you have an incubator or a broody hen, the egg may not develop. If you are allowed to touch the eggs, you can candle them to see if they are fertile. If theys aren't fertile, they won't hatch. 3. Fights: Please don't ask about fights between different animals. These questions assume that individuals of two species fight each time they meet and that one species will always be victorious over another. This is untrue. There are cases where a live mouse has been fed to a venomous snake, bitten the snake leading to the snake's demise. 4: Diseases: Please ask doctors or other medical experts about diseases that you may catch from animals. I can't advise on how to deal with viruses, bacteria etc.

Experience

I have a zoology degree and have been interested in animals since I was two. I am a zoo volunteer at London Zoo. I have appeared on a BBC Radio Quiz, 'Wildbrain'.

Organizations
WWF. ZSL. Natural History Museum. RSPB. London Bat Group.

Publications
Newsletters of London Zoo volunteers and the London Bat Group

Education/Credentials
BSC degree in Zoology. 'A' level in Zoology. 'O' Level in Biology.

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