Levels of parental care and commitment vary hugely in the animal kingdom but what are the most extraordinary ways the natural world uses to try and ensure the next generation survives?

Individual animals rely on the commitment of their parents to keep them healthy and safe until they reach independence.

We think of a good mum as someone who unselfishly dedicates lots of time and effort to the care of her children, yet some animal mums do very little and still produce a thriving new generation.

Bonobos, like other apes, provide entire lifetimes of support for their young, which may seem to make them perfect for the job. However species that appear to have less maternal instinct in human terms may simply be balancing their offspring's requirements with their own need to reproduce again.

BBC Earth asked scientists what makes a good animal mum and for some of their more surprising examples.

“Animal mothers are always trying to have their cake and eat it too – they want their current babies to grow and survive, but they also want to save some of their energy for their next baby or babies,” says Kirsty MacLeod, from the Department of Zoology at the University of Cambridge.

“So the best mums might simply be the ones that are able to do that most successfully, either by being in good physical condition, or being socially dominant in groups where other individuals also help to bring up the babies.”

Ms MacLeod has studied meerkats (Suricata suricatta), where dominant females enlist the help of their subordinates to look after and feed their pups.

Such good parenting comes at a high cost to the other females in the group, they face being evicted or having their pups killed to avoid any competition for child care.

Different animals require different levels of input from their mums

But Ms MacLeod argues that successful animal mothers are those that don’t bring up baby on their own.

Elephants and orangutans usually top lists of brilliant mums in the animal kingdom for having to wait the longest for their offspring to grow up. Yet Ms MacLeod says their long life-spans allow them to be such dedicated parents and the dependency it creates in their infants makes long periods of care essential for survival.

“Long-lived species that have many years to reproduce are the ones that are able to be a good mum in the way we see it – by taking a long time over gestation and infant care,” she says.

“These species may look like they’re better mums because they look after them for longer but that’s not really the case.

“It’s in everyone’s best interest for the offspring to survive, and different animals require different levels of input from their mums.”

A record-breaking feat of mothering endurance was reported in July when scientists observed a female deep-sea octopus brooding her eggs for four and a half years.  

It is the longest brooding time ever seen in the animal kingdom and more than quadruples the usual brooding periods of shallow-water octopuses.

The female kept up a remarkable vigil next to her eggs, keeping them clean, oxygenated and protected from predators, leaving her no time to hunt for food for herself.

“Virtually all octopus mothers are very dedicated, very devoted,” says lead researcher Dr Bruce Robison from the Monterey Bay Aquarium Research Institute (MBARI), US.

Most octopuses have only one reproductive period during their life and after mating, laying and brooding the eggs to hatching, the female dies.

“The longer the brooding period, the more time the babies have to develop. The more developed a hatchling is, the better its chances of survival,” Dr Robison adds.

“For this deep-sea species the strategy is to produce a relatively small number of eggs, but to give them a very long time to develop so that when they hatch the hatchlings are like miniature adults, ready to face the challenges of life.”

Another species with a very rare brooding behaviour is the southern yellow-billed hornbill (Tockus leucomelas), the female adopts the risky strategy of relying on the male to keep her alive.

Females nest in holes in trees and block themselves in with mud in order to protect their offspring from predators. They then lose their feathers and are entirely dependent on their mate to bring them food while they incubate the eggs.

“If their partner dies, or just isn’t very good at providing for them, their survival and the survival of their brood would be compromised,” Ms MacLeod says.

“That kind of risk is rare and shows total commitment to their babies.”

Other animals are able to make judgments on whether the risk to their own life is worth it.

Female sea otters find child-rearing particularly exhausting, they spend about half of every year of their adult life feeding at least one pup and are so weakened by the process they may succumb to minor wounds or infections.

Adult sea otters have to eat around a quarter of their body weight every day to survive. Recently researchers found that raising a pup nearly doubles these daily energy demands, and therefore the amount of food mum needs to find.

Good investments

Co-author Nicole Thometz, from the University of California at Santa Cruz, US, says this explains why mothers are often weak and skinny as their pups near weaning and why they may abandon pups before they are fully grown.

A female's decision whether or not to keep their pup depends on her own condition and environmental factors such as the availability of prey.

Abandoning a pup may give her a better chance to successfully rear a pup the following year.

“Individual strategies can be vastly different and can depend on lots of things. In some bird species females put in a little extra bit of investment in their eggs if they are paired with a particularly sexy male,” explains Ms MacLeod.

“In this case the brood are already likely to be good quality so the female can afford to expend a little extra on what is guaranteed to be a good investment.”

Hormones can also influence how caring animals are and scientists are becoming increasingly interested in personality traits in animals and how they could have consequences for whether they perform well as mothers or not.

Yummy mummy

But some new mums are simply unflinching in their devotion to the survival of their offspring.

In this particular category Ms MacLeod nominates female Australian crab spiders (Diaea ergandros), who actively encourage cannibalism in their young.

“The spiderlings suckle nourishing juices from her leg joints, the way mammals suck milk from their mothers, but in this case they literally suck her dry and she dies,” Ms MacLeod says.

“She allows them to eat her so that they don’t eat each other, that way her genes are still passed on.

“These spiders only have one breeding attempt so she can afford to give them all the energy she can, as she doesn’t need to save any for a future attempt.”

A similar behaviour was filmed in a black-lace weaver spider (Amaurobius ferox) for the BBC series Wildlife on One, first shown in 2003.

“Darwin’s theory of natural selection says “stay alive at all cost” because dying at the expense of others is very rarely an adaptive thing to do," says Ms MacLeod.

“But if it increases the likelihood of many of your offspring surviving then it can be beneficial genetically as many copies of your genes are then running off to reproduce themselves.”

Watch Parenthood, the final episode of Life Story, on Thursday 27th November at 21:00 GMT on BBC One.