Offspring care (zoology)

In the animal kingdom, there are species in which neither parent cares for offspring, species in which one parent cares for offspring, species in which both parents care for offspring, and species in which individuals other than parents help care for offspring. Patterns of caring for offspring relate to several key factors.

Precocial Species Versus Altricial Species

The most important factor determining the number of caretakers, as well as the quality and duration of parental care, is how much care the offspring need. In species that are born well-developed and capable of surviving independently, there is little reason for parents to provide help. Many fish and baby turtles hatch resembling miniature adults fully capable of moving, running, or swimming and feeding themselves. The young of such species are referred to as precocial and often get no parental care, though, in some species, the parents remain nearby to protect their young. The young of most invertebrate species can survive without help, so they are typically left to fend for themselves. All ungulates are precocial species. Some species, like the megapode, are born exceptionally well-developed.

On the other hand, in species where young are born or hatched quite helpless with no chance of surviving on their own, one or both parents are likely to remain nearby and care for them. Young of such species are referred to as altricial. Dogs, cats, kangaroos, owls, and even humans are excellent examples of species with altricial offspring. Generally speaking, mammals are more altricial than most groups of animals, and all mammalian young initially depend upon their mother for food (milk), delivered by means of lactation.

Compared to other animals, birds are relatively altricial—especially raptors (birds of prey) and songbirds. When altricial birds hatch, they are featherless and unable to regulate their own body temperature; one or both parents must regularly warm the hatchlings just as they earlier warmed the eggs. Furthermore, altricial birds hatch with their eyes closed, and they are not strong enough or coordinated enough to leave the nest to feed or to flee from danger. Because baby birds need tremendous amounts of food and there are usually quite a few offspring, in most species of birds, both parents provide care. However, some bird species are precocial, including ostriches, chickens, and geese.

The precocial and altricial behaviors of offspring care have important impacts on development. Research involving over 1,100 species indicated that animals that receive long-term provisioning and parental care have larger brains. Another study investigated the neocortex development patterns—neurogenesis, gliogenesis, and neuron maturation—of the mammalian brain using altricial dwarf rabbits and precocial guinea pigs. The results indicated that early brain development was relatively similar between the species, but the neocortex of the precocial species began neurogenesis later and the process took much longer than in the altricial species.

Prey Species Versus Predatory Species

Although the young of birds and mammals are quite helpless compared to the young of animals in other taxonomic groups, there are variations. As a rule, prey species tend to be more precocial than predatory species and, therefore, require less parental care.

The young of herbivorous (vegetarian) species are in constant danger of being eaten by carnivorous (meat-eating) species, but cannot afford to be completely helpless, even if they depend on their mother for food. Grazing mammals, such as zebra and deer, are vulnerable to lions and wolves, so the young of these species must be able to stand up and run just a few minutes after birth: they are born with open eyes, well-developed muscles, and a full coat of hair. Although mammalian young need to nurse from their mother, they can start grazing fairly quickly, so typically, it is only the mother who provides support, and her care is not exceptionally prolonged.

Among birds, the same pattern is found: herbivorous species, such as ducks and chickens, that are preyed upon by mammalian, avian, or reptilian predators, hatch with open eyes, the ability to walk, run, or swim, and a coat of downy feathers, so that even though they cannot yet fly, they can leave the nest without the need of further incubation. Offspring of these species can usually eat on their own almost immediately after hatching and, therefore, can often get by with only one parent to show them what to eat and to protect them until they can fly.

Compared to the young of prey species, the young of predatory species tend to be born in a much more altricial state and, therefore, need more parenting. Lion cubs and wolf pups do not have open eyes or the strength and coordination to leave their nest, den, or lair until a few weeks after birth. Even after they can move about and are weaned from their mother’s milk, they are still too uncoordinated to hunt successfully and must be fed by one or both parents. In fact, species such as lions and wolves, which not only have altricial young but frequently have large litters, often recruit other adults to help raise their offspring. Amongst African (but not American) lions, related females form groups called prides that hunt together and help care for one another’s offspring. Wolves form hunting packs, and all members (both male and female) help to feed the young. This behavior is called aunting when it is done by a female relative, or more generally, alloparenting. Alloparenting is also seen among some rodents and primate species.

As with mammals, carnivorous and insectivorous birds come into the world in a more altricial state than their vegetarian brethren and, therefore, need more care. In most bird species, both parents cooperate to raise young and, as with some of the most altricial mammalian species, if there is a large brood, parents of some species recruit helpers. In birds, helpers are usually the parents’ offspring from a previous brood or season and are thus siblings or half-siblings of the young they are helping to raise. Species that use this extended family system are referred to as cooperative breeders—although some are less cooperative than others.

Quantity Versus Quality Parenting

A third factor relevant to parenting is the number of offspring, either sequentially or in litters that an individual produces. All individuals have a limited life span and a limited amount of energy, and during that life span, they can allocate that energy either to producing a large number of offspring or to providing intensive care for a smaller number of offspring. Thus, while animals with altricial young that require intensive care do not have an option of producing huge numbers of offspring, species with precocial young do.

Most invertebrates and many vertebrates (other than birds and mammals) take the “quantity” strategy: they produce large numbers of offspring and provide no parental care. Many offspring of these species die before reaching adulthood, but a small percentage survive and reproduce. An extreme example of taking a “quantity” strategy is semelparous species, which can only reproduce once in their lifetime. Salmon are well-known for this form of reproduction. Many spiders and insects die before their only batch of young hatch.

At the other extreme is the strategy of having a small number of well-cared-for offspring, each with a high probability of survival. All altricial species are constrained to the “quality” strategy, but some precocial species opt for “quality” as well. Alligators and crocodiles are excellent mothers, protecting their eggs before they hatch, then transporting and protecting the young afterward. Some species of amphibians, fish, and even insects are devoted parents.

Maternal Care Versus Paternal Care

In mammals, if only one parent is necessary, it is always the mother who is committed to caretaking because she must provide the offspring with food through nursing. No other animals, however, nurse their young, so in other species, if only one parent is necessary, it does not have to be the mother who becomes the caretaker.

In single-parent species, whether it is the mother or father who becomes the caretaking parent depends, to a great extent, on parental certainty. In viviparous species (species that give birth to live young rather than lay eggs), the parent that gives birth is, for certain, one of the two genetic parents and is, therefore, the parent most likely to care for the young if they need it. With rare exceptions, that means that mothers become the caretaking parent in viviparous species. In egg-laying (oviparous) species, parental certainty depends on whether fertilization is internal (birds and many invertebrates) or external (most fishes and amphibians). If fertilization is internal, only the mother is certain to be a genetic parent of the eggs she lays and is, therefore, most likely to take on the caretaker role when only a single caretaker is needed. If fertilization is external, both parents are equally likely to be the genetic parent of any young that later hatch from eggs at the breeding site, and if parenting is needed, males and females are equally likely to become caretakers. The result is that while most species that have external fertilization do not remain with their eggs or provide any parental care, in those that do, factors other than parental certainty determine which sex becomes the guardian.

In species with internal fertilization, the probability that a particular male is the father (or one of the fathers) of a particular set of offspring depends on how many males the female mated with and when. In well-studied species, if a mother needs help to raise her offspring, males expend effort in proportion to the probability that they are the genetic father. This is because males that are parenting or otherwise providing resources for offspring that are not genetically their own are wasting their effort in terms of evolutionary value. A male animal caring for another male’s offspring is called a cuckoldry. Scientists have documented this behavior in vultures, gibbons, chimpanzees, and bonobos.

The Spectrum of Parental Behavior

Most parents are good to most of their offspring most of the time. Parents provide food and sometimes shelter; they protect their offspring from danger and chase away predators; they may place their offspring in safe refuges; they may even teach their offspring necessary information or skills such as how to hunt, the location of productive feeding sites, or traditional migration routes.

At some point, however, there may be conflict between parents and offspring; conflict is especially common over how much care the parents provide versus how independent the offspring have become. Avian parents, for example, may displace their offspring from the nest to make way for a new brood; mammalian mothers may resort to force to wean their maturing offspring so they can nurse a new infant or litter. Alternatively, offspring may be sexually mature and ready to leave but remain in the family to act as helpers.

The most extreme forms of parental manipulation involve neglect and what is called tolerated siblicide. In particularly bad times when resources are scarce, parents may provide care for only one or a few offspring, allowing the others to die. Even in good times, parents with very large broods or litters may neglect the smallest and weakest young. Parents of some species allow older siblings to kill and sometimes eat their younger siblings; in fact, this behavior is the norm in some species.

Humans tend to equate parenting with moral goodness; among other animals, it equates simply to survival and reproduction. Different species provide parental care—or not—as it is needed to maximize the probability that at least a few offspring will survive to maturity. In some vertebrate species, parenting may be associated with intense emotions and bonding, as it is in humans, but across the animal kingdom, there is no one right way to parent; what works is what works.

Principal Terms

Alloparenting: performance of parenting duties by an individual, not the parent of the offspring (though usually a relative)

Altricial: the condition of being weak and relatively undeveloped at birth (or hatching) and thus dependent upon parental care for a prolonged period

Cuckold: a partnered male who is helping his mate to raise offspring which are not genetically his own

Nest-Parasite: also called brood-parasite; an individual (or species) that lays its eggs in the nest of another individual (or species) and does no parenting at all

Precocial: the condition of being strong and relatively well developed at birth (or hatching) and thus not particularly dependent upon parental care

Sex-Role Reversal: generally used to refer to species in which the male does most of the parenting

Viviparous: characterized by live birth (as opposed to egg-laying)

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