Maternal behavior in vertebrates

A baby kangaroo, known as a joey, inside their mother's pouch.

Altricial young are born deaf, blind, almost completely hairless and have very limited motor functioning.[1] The maternal behavior in these species is primarily focussed on providing warmth for the young since they are unable to thermoregulate.[4] This is achieved through the utilization of pouches in marsupial species, such as kangaroos, and the construction of nests in rodents and other altricial species.[4] Because the young are not capable of locomotion, many other maternal behaviors take place at the nest as well, including feeding, nursing and grooming (licking). Members of this species are unable to recognize their own young and therefore will care for all the young in the nest equally, regardless of whether or not it is their own offspring.[4] Once the young reach a point in their sensory, and motor development and no longer require the nutrients from their mothers milk, they will leave the nest and the mother will discontinue her maternal care behaviors.

A baby reindeer (Rangifer tarandus). This species is precocial and young are able to get up and move around on their own within hours of being born.[6]

Precocial young are born with a highly developed sensory and motor system.[1] At birth they are able to see, hear, and most can walk or will learn to walk within the first few days after birth.[4] The females in these species have adapted to be able to recognize their own young, which allows them to be selective about who they choose to care for.[4] They will reject other young who try to nurse from them. The primary focus of these species is to develop an exclusive relationship with their young which allows for the resources and energy expenditure of the mother to be optimized by the offspring and not wasted on other young.[4] This is essential for their success and fitness.

A baby monkey clinging to their mother.

Primates are born with intermediate maturation of altricial and precocial species. Newborns have limited motor functioning, but have highly developed sensory systems and the ability to thermoregulate. A unique characteristic in the maternal behavior in primates is that the mothers carry their young until their locomotive abilities develop.[4] The mother will either carry the young in their arms, or the young will attach itself to the mother and cling to her. This is known as matricolia.[4]

Colosthethus panamansis carrying her tadpoles on her back.

Frogs have developed many different maternal behaviors across varying species. The most common maternal behavior among frogs is egg attendance, wherein the mother will remain near her eggs as they develop to protect them from predators.[9] A mother may also stay with her clutch in order to prevent desiccation, as she can rehydrate them by positioning themselves above the eggs, a behavior known as ventral brooding.[10] Some species have also been observed oxygenating their eggs by moving them around occasionally.[10] Frogs of the genus Hemiphractus carry their eggs around on their back until they hatch.[7] Some species of this genus develop a dorsal pouch to carry their young inside while other leave them exposed.[7] Some frogs, such as poison dart frogs, will lay unfertilized eggs for her clutch to eat.[11]

Herpele squalostoma feeding her young via maternal dermatophagy.

Caecilians can reproduce either by oviparity or viviparity, with some young having an aquatic larval stage while some develop to live on land immediately.[8] Oviparous females build nests on land and keep their clutch there until they hatch, regardless of if they have an aquatic stage or not.[8] Once young with an aquatic stage hatch they are able to survive on their own in the water without any more maternal care, however other young are altricial when they hatch, and rely on their mother to look after them until they develop enough to live fully on land.[8] The mother feeds these altricial young by a process known as maternal dermatophagy, in which she will feed pieces of her skin to her young.[12] Viviparous caecilians also give birth to altricial young.[8] These young may be fed by maternal dermatophagy in the same way that oviparous species are fed, or they may be fed by a more specialized version in which the young eat their mother's hypertrophied oviduct or drink from her cloacal opening.[12]

A female red jewel cichlid (Hemichromis bimaculatus) fanning and protecting her eggs.

Many oviparous fish display no maternal behaviors aside from laying the eggs, but some mothers will stay with their clutch to defend the eggs and fry from predators, a behavior very common among cichlids.[1][15] Many cichlid species, such as Cichla ocellaris, will also remove underdeveloped eggs from the clutch, a behavior performed by both parents.[15] Many female cichlids also fan their eggs with their fins, especially in slower moving water, in order to increase oxygenation and get rid of build up of undesired materials around the eggs.[15]

A Zebra mbuna (Maylandia zebra), a mouthbrooding cichlid, carrying her young in her mouth.

A lot of cichlid species, commonly known as mouthbrooders, carry their eggs and young in their mouth for an extended period of time while they hatch and grow.[15] This behavior is most often displayed by the mother, though there are some species where both parents or just the father mouthbrood.[15] In maternal mouthbrooders, after the eggs are laid the mother scoops them into her mouth and keeps them there, sometimes for multiple weeks. During the brooding period she will not eat and will put all her energy into caring for her young.[16]

In both ovoviviparous and viviparous fish the female incubates her young inside her body before giving birth to live young, the major difference is where the young get their nutrition during incubation.[17] Ovoviviparous fish embryos mostly get their nutrients from the yolk of their eggs while viviparous fish embryos mostly get their nutrients directly from their mother.[17] The gestation period is usually the only maternal care provided in these fish as they are developed when they are born.[17]

The nest of an Eastern Phoebe (Sayornis phoebe) containing its own eggs, along with one egg of a Brown-headed Cowbird (Molothrus ater), a well-known obligate brood parasite.[19]

The parasitic birds have evolved ways to ensure the success of their offspring by having it be raised by a host, allowing them to no longer have to invest energy into maternal care themselves. As a result, their offspring receive maternal care from a host bird, which can cause their natural maternal behaviors to be affected. This results in them often neglecting to care for their own offspring.[20] Although this behavior can be performed occasionally by many different birds, only about 1% of all bird species worldwide are considered to be obligate brood parasites.[19]

Synodontis multipunctatus, the cuckoo catfish.

The only vertebrate species to practice brood parasitism other than birds is the cuckoo catfish.[21] These fish prey specifically on mouthbrooding cichlids. When the female cichlid lays her eggs on the ground the cuckoo catfish will lay her eggs among the clutch and a male will fertilize them before the cichlid picks her eggs up in her mouth, causing her to also pick up the cuckoo catfish's eggs.[21] The cuckoo catfish eggs hatch before the cichlid eggs and the cuckoo catfish is able to eat the cichlid eggs and reside within the protection of the cichlid's mouth until they are spit out.[21]