Reproduction and Survival Strategies
3. Parental Care
Learning outcomes
- I can define parental care and explain its importance.
- I can compare different parental care strategies.
- I can explain the relationship between parental care and offspring survival.
- I can identify examples of parental care in different animals.
- I can evaluate the costs and benefits of parental investment.
What Is Parental Care?
Producing offspring is only part of reproductive success. In many animal species, parents also perform behaviours that increase the probability that their offspring will survive.
Parental care is any behaviour by a parent that increases the survival or future reproductive success of its offspring, usually at some cost to the parent.
Parental care can include:
- Protecting eggs.
- Building nests.
- Keeping eggs warm.
- Providing food.
- Carrying offspring.
- Defending young from predators.
- Cleaning or grooming offspring.
- Teaching or assisting young in finding food.
- Helping young learn important behaviours.
However, parental care requires time, energy, and resources. Different species therefore show very different levels of parental investment.
Why Does Parental Care Matter?
Young animals are often particularly vulnerable.
They may:
- Be unable to find enough food.
- Have difficulty regulating body temperature.
- Be unable to defend themselves.
- Have limited mobility.
- Lack experience.
- Be vulnerable to predators.
- Be susceptible to environmental changes.
Parental care can reduce these risks.
In species where young depend heavily on their parents, successful parental care can have a major effect on the number of offspring that survive to adulthood.
Parental Investment
Parental investment refers to the time, energy, and resources that a parent devotes to an offspring in ways that can improve that offspring's chances of survival and reproduction.
Investment can begin before birth or hatching.
Examples include:
- Producing nutrient-rich eggs.
- Pregnancy.
- Building a nest.
- Selecting a safe nesting site.
- Incubating eggs.
It can continue after birth or hatching through:
- Feeding.
- Protection.
- Transport.
- Teaching.
- Grooming.
Parental Care Before Hatching
Parental care does not necessarily begin when offspring emerge from an egg.
Many animals protect their developing embryos.
Birds commonly:
- Build nests.
- Incubate eggs.
- Defend nests.
- Turn eggs.
- Maintain suitable temperatures.
Some fish guard nests containing eggs.
Some reptiles guard nests or remain near eggs.
These behaviours can increase the probability that embryos survive until hatching.
Nest Building
A nest provides a controlled location for eggs or young.
Nests can provide:
- Protection from predators.
- Protection from wind and rain.
- Insulation.
- A suitable temperature.
- A place where parents can locate and care for offspring.
Nests can range from simple depressions in the ground to elaborate structures requiring considerable time and energy to construct.
Incubation
Bird embryos require suitable temperatures for normal development.
Many birds therefore incubate their eggs.
During incubation, a parent sits on or otherwise warms the eggs.
This helps maintain a suitable developmental temperature.
However, incubation has costs.
A parent spending long periods incubating eggs may have:
- Less time to find food.
- Increased energy requirements.
- Greater exposure to predators.
- Fewer opportunities to reproduce again.
Parental care therefore involves trade-offs.
Feeding Offspring
Many young animals cannot obtain enough food independently.
Parents may provide food directly.
Examples include:
- Birds bringing insects to chicks.
- Mammals producing milk.
- Predators bringing prey to their young.
- Some insects supplying food to larvae.
Providing food can increase:
- Growth rate.
- Development.
- Survival.
- Ability to resist disease.
- Probability of eventually reaching reproductive age.
Protection from Predators
Predation is a major cause of mortality among young animals.
Parents may protect offspring by:
- Guarding them.
- Hiding them.
- Attacking predators.
- Giving alarm calls.
- Moving offspring to safer locations.
- Keeping young together.
Protection can greatly improve offspring survival, but it may also place the parent in danger.
Carrying Offspring
Some animals physically transport their offspring.
Examples include:
- Kangaroos carrying young in pouches.
- Primates carrying infants.
- Crocodilians carrying young in their mouths.
- Some frogs carrying tadpoles.
- Some spiders carrying egg sacs or young.
Carrying offspring can provide protection and help young reach suitable feeding or developmental areas.
Parental Care in Mammals
Mammals typically show substantial parental investment.
One defining mammalian characteristic is the production of milk by mammary glands.
Milk provides young mammals with:
- Water.
- Energy-rich nutrients.
- Proteins.
- Minerals.
- Other substances that support development.
Many mammals also provide:
- Protection.
- Warmth.
- Grooming.
- Social interaction.
- Opportunities for learning.
In some species, parental care continues for years.
Learning from Parents
In animals with complex behaviour, parental care may involve more than feeding and protection.
Young animals may learn important behaviours by observing or interacting with adults.
These can include:
- Hunting techniques.
- Food selection.
- Migration routes.
- Predator recognition.
- Social behaviour.
- Communication.
- Use of tools.
This can be particularly important in animals with long developmental periods and complex nervous systems.
Parental Care in Birds
Birds display an enormous range of parental behaviours.
These can include:
- Nest construction.
- Egg incubation.
- Egg turning.
- Nest defence.
- Feeding chicks.
- Removing waste from nests.
- Teaching young to locate food.
In many bird species, both parents contribute to care.
Sharing parental duties can increase the amount of food and protection available to offspring.
Altricial Young
Some birds produce altricial young.
Altricial offspring hatch in a relatively underdeveloped condition.
They may be:
- Nearly helpless.
- Unable to fly.
- Poorly insulated.
- Unable to obtain food independently.
These offspring require extensive parental care.
Many songbirds follow this strategy.
Precocial Young
Other birds produce precocial young.
Precocial offspring are relatively well developed at hatching.
They may:
- Have feathers or down.
- Walk soon after hatching.
- Follow their parents.
- Feed more independently.
Ducklings are a familiar example.
Precocial offspring may require less direct feeding, although parents can still provide protection, guidance, and warmth.
Parental Care in Fish
Although many fish provide little care after spawning, others show sophisticated parental behaviour.
Some fish:
- Build nests.
- Guard eggs.
- Fan water across eggs.
- Defend young.
- Carry eggs or young in their mouths.
Mouthbrooding occurs when a parent carries eggs or young inside its mouth for protection.
This can dramatically reduce predation but may interfere with the parent's ability to feed.
Parental Care in Amphibians
Amphibian parental care varies enormously.
Many frogs lay large numbers of eggs and provide little additional care.
Other species may:
- Guard eggs.
- Keep eggs moist.
- Carry tadpoles.
- Transport tadpoles to small pools.
- Provide unfertilized eggs as food.
This demonstrates that closely related animals can evolve very different reproductive strategies.
Parental Care in Reptiles
Parental care among reptiles also varies.
Many species provide relatively little care after laying eggs.
Others show extensive parental behaviour.
Crocodilians, for example, may:
- Guard nests.
- Assist hatchlings leaving the nest.
- Carry young toward water.
- Defend young after hatching.
Parental care is therefore not restricted to mammals and birds.
Parental Care in Invertebrates
Some invertebrates also provide remarkable parental care.
Examples include:
- Spiders carrying egg sacs.
- Insects guarding eggs.
- Beetles preparing food for larvae.
- Octopuses guarding eggs.
A female octopus may guard and ventilate her eggs for an extended period, often eating little or not at all during this time.
This represents an extremely high reproductive investment.
Maternal Care
When the female provides most or all parental care, this is called maternal care.
It is common in mammals because pregnancy and milk production already create a strong biological connection between mothers and offspring.
Maternal care can include:
- Nursing.
- Protection.
- Carrying.
- Grooming.
- Teaching.
- Maintaining warmth.
However, parental-care patterns vary greatly among mammal species.
Paternal Care
In some species, males provide substantial care.
This is called paternal care.
Male care can include:
- Guarding eggs.
- Incubating eggs.
- Feeding young.
- Carrying offspring.
- Defending offspring.
Male emperor penguins provide a famous example. The male incubates the egg on his feet beneath a fold of skin while experiencing extremely harsh Antarctic conditions.
Biparental Care
In biparental care, both parents contribute to raising offspring.
This occurs in many birds and some mammals, fish, and other animals.
Potential advantages include:
- More food for offspring.
- Greater nest defence.
- Shared incubation.
- More effective protection.
- Reduced workload for each parent.
However, both parents must devote resources to the current offspring.
Cooperative Care
Parental care does not always involve only the biological parents.
In some social species, other members of the group help care for young.
This is sometimes called cooperative breeding or cooperative care.
Helpers may:
- Feed offspring.
- Guard them.
- Carry them.
- Protect them.
- Teach them.
This occurs in animals such as some birds, meerkats, and certain primates.
Little or No Parental Care
Not all animals care for their offspring.
Many species produce eggs or young and then leave them.
Examples occur among many:
- Fish.
- Marine invertebrates.
- Amphibians.
- Insects.
These animals often compensate by producing large numbers of offspring.
If hundreds or thousands are produced, some may survive even if mortality is high.
Number of Offspring and Parental Care
A broad reproductive trade-off exists between:
Number of offspring ↔ investment in each offspring
Animals producing many offspring generally cannot provide intensive care to every one.
Animals producing relatively few offspring can potentially invest much more in each.
This is not an absolute rule, but it is an important general pattern in animal reproductive biology.
Worked Example: Cod and Elephant
Imagine comparing two very different reproductive strategies.
A large fish may produce enormous numbers of eggs.
An elephant normally produces one calf at a time and provides years of care.
The fish strategy depends partly on:
Very many offspring × low probability of survival for each
The elephant strategy depends more heavily on:
Few offspring × high parental investment × relatively high survival probability
Both strategies can result in successful reproduction.
Benefits of Parental Care
Parental care can provide many benefits to offspring.
These include:
- Increased protection from predators.
- More reliable food supply.
- Improved temperature regulation.
- Reduced exposure to environmental extremes.
- Protection from competitors.
- Opportunities to learn.
- Increased growth.
- Increased probability of reaching adulthood.
The ultimate evolutionary benefit is increased probability that offspring survive and eventually reproduce.
The Costs of Parental Care
Parental care is not free.
Parents have limited amounts of:
- Energy.
- Food.
- Time.
- Body reserves.
Resources invested in current offspring cannot be used for other purposes.
Potential costs include:
- Increased energy expenditure.
- Reduced feeding time.
- Increased exposure to predators.
- Increased risk of injury.
- Delayed future reproduction.
- Reduced number of additional offspring.
- Reduced parental survival.
This creates an important biological trade-off.
Current Versus Future Reproduction
Imagine an animal has limited energy.
It could invest heavily in its current offspring.
This may increase their probability of survival.
However, extremely high investment could reduce the parent's condition and decrease its ability to reproduce again.
Alternatively, the parent could provide less care now and preserve resources for future offspring.
Natural selection therefore acts on a balance between:
Current reproductive success ↔ future reproductive opportunities
Worked Example: Feeding Chicks
Suppose two parent birds are feeding four chicks.
Every feeding trip requires energy.
It may also expose the adults to predators.
If the parents make more trips:
- Chicks receive more food.
- Chicks may grow faster.
- Chick survival may increase.
But:
- Parents use more energy.
- Parents may experience greater predation risk.
- Parents may lose body condition.
The optimal amount of parental care therefore involves both benefits and costs.
Offspring Competition
When several offspring are raised together, they may compete for parental resources.
Competition can involve:
- Food.
- Space.
- Warmth.
- Parental attention.
In a bird nest, chicks may beg loudly or position themselves closer to the parent.
Parents may respond to these signals when distributing food.
Parent-Offspring Conflict
Parents and offspring do not always have identical interests.
An individual offspring can benefit from receiving more resources.
However, a parent must divide resources among:
- That offspring.
- Its siblings.
- Future offspring.
- The parent's own survival.
This can produce parent-offspring conflict.
For example, offspring may continue begging for food even when reducing feeding would help preserve the parent's condition.
Care and Offspring Development
The amount of parental care required often depends on how developed offspring are at birth or hatching.
Altricial offspring generally require more intensive care.
Precocial offspring can often perform more behaviours independently.
However, even highly developed young may still benefit from:
- Protection.
- Guidance.
- Social learning.
- Access to food.
Developmental strategy and parental-care strategy are therefore closely connected.
Care and Learning
Long periods of parental care can create opportunities for learning.
Young predators may need time to learn how to hunt.
Young primates may learn:
- Food selection.
- Social relationships.
- Communication.
- Tool use.
Young elephants may learn:
- Migration routes.
- Water locations.
- Social behaviours.
In animals with complex behaviours, learning can be a major benefit of prolonged care.
Parental Care and Survival
The effect of parental care can be understood as a probability.
Suppose two hypothetical species each produce 100 offspring.
Species A provides no care, and 5 offspring survive.
Species B provides extensive care, and 60 offspring survive.
Species B does not necessarily need to produce as many offspring to maintain its population.
This helps explain why species with extensive parental care often produce fewer offspring.
Environmental Conditions Matter
The value of parental care depends partly on the environment.
Parental care may be especially valuable where:
- Predation risk is high.
- Food is difficult for young to obtain.
- Temperatures are challenging.
- Suitable nesting sites are limited.
- Young require complex learned behaviours.
In other environments, producing many offspring with relatively little care may be successful.
Parental Care and Predation
Parental behaviour can affect predation in different ways.
Guarding can reduce the probability that offspring are eaten.
However, parents moving repeatedly to and from a nest might attract attention.
Parents therefore face a balance between:
Providing resources ↔ avoiding detection
This demonstrates why parental behaviour is often highly adapted to local ecological conditions.
Parental Care and Natural Selection
Parental-care behaviours can evolve when they increase overall reproductive success.
Imagine a genetic or behavioural characteristic that causes parents to protect their offspring slightly more effectively.
If those offspring are more likely to survive and reproduce, the characteristics associated with effective care may become more common over generations.
However, care that is excessively costly could reduce parental survival or future reproduction.
Natural selection therefore acts on both:
- Benefits to offspring.
- Costs to parents.
Evaluating Parental Investment
When evaluating a parental-care strategy, it is useful to ask:
- How many offspring are produced?
- How vulnerable are they?
- How much care does each receive?
- How much does care increase survival?
- How much energy does care require?
- Does care expose parents to danger?
- Does it reduce future reproduction?
- Do offspring need to learn complex behaviours?
- How predictable is the environment?
There is rarely a simple "best" strategy.
The effectiveness of a strategy depends on the animal's biology and environment.
Worked Example: Sea Turtle
A sea turtle lays many eggs.
The mother invests considerable energy in:
- Producing eggs.
- Migrating to nesting areas.
- Digging a nest.
- Depositing and burying the eggs.
However, after nesting, there is generally no prolonged parental care.
Many hatchlings die, but producing numerous offspring increases the probability that some survive.
Worked Example: Emperor Penguin
Emperor penguins use a very different strategy.
Only a small number of offspring are produced at one time.
The egg and chick receive substantial parental investment.
Parents:
- Incubate the egg.
- Protect it from extreme cold.
- Provide food.
- Protect the chick.
Each offspring represents a large investment, so protecting that offspring can have a major effect on reproductive success.
Worked Example: Poison Dart Frog
Some poison dart frogs show surprisingly extensive parental care.
Depending on the species, parents may:
- Guard eggs.
- Keep eggs moist.
- Carry tadpoles on their backs.
- Transport tadpoles to suitable pools.
This increases offspring survival but requires considerable parental time and energy.
Worked Example: Octopus
Some female octopuses invest heavily in a single reproductive event.
A female may:
- Guard her eggs.
- Clean them.
- Move water over them to provide oxygen.
- Defend them from predators.
During this period, she may eat very little.
This represents a dramatic example of the cost of parental investment.
Comparing Parental Care Strategies
| Strategy | Typical Offspring Number | Care per Offspring | Possible Survival of Each Offspring |
|---|---|---|---|
| Little or no care | Often high | Low | Often relatively low |
| Maternal or paternal care | Variable | Moderate to high | Often increased |
| Biparental care | Often lower | High | Often relatively high |
| Cooperative care | Often lower | Potentially very high | Can be high |
These are broad patterns rather than universal rules.
Animal reproductive strategies are highly diverse.
Parental Care and Reproductive Success
The goal of parental care, in evolutionary terms, is not simply to keep offspring comfortable.
Parental care can increase the probability that offspring:
Survive → mature → reproduce
If parental behaviour increases the number of surviving descendants, it can increase reproductive success.
However, the benefits must be considered alongside the costs to the parent.
Common Mistakes
Saying All Animals Care for Their Young
Many animals provide little or no care after eggs or offspring are produced.
Thinking Parental Care Begins at Birth
Nest building, egg guarding, incubation, pregnancy, and provisioning eggs can all represent investment before birth or hatching.
Saying More Parental Care Is Always Better
Care requires energy and time. Excessive investment in one reproductive event could reduce parental survival or future reproduction.
Assuming Only Mothers Provide Care
Maternal, paternal, biparental, and cooperative care all occur in animals.
Assuming Animals With Little Care Are Unsuccessful
Producing many offspring with little care can be a highly successful reproductive strategy.
Confusing Parental Care With Parental Investment
Parental care usually refers to behaviours that benefit offspring. Parental investment is broader and includes resources devoted to producing and supporting offspring.
Assuming More Offspring Means Greater Reproductive Success
What ultimately matters is how successfully genetic information is passed into future generations through surviving, reproducing descendants.
Check Your Understanding
1. Define parental care.
2. Give four examples of parental-care behaviour.
3. Explain how parental care can increase offspring survival.
4. What is parental investment?
5. Compare maternal, paternal, and biparental care.
6. Explain one advantage of biparental care.
7. Why do altricial offspring generally require extensive parental care?
8. Explain the relationship between offspring number and parental investment.
9. Give one example of parental care in a fish, amphibian, reptile, bird, or mammal.
10. Explain why guarding offspring can create both a benefit and a cost.
11. Why might feeding offspring reduce a parent's future reproductive success?
12. Explain why learning can make prolonged parental care especially useful in animals with complex behaviour.
13. Compare the parental-care strategies of a sea turtle and an emperor penguin.
14. Why might environmental conditions affect how useful parental care is?
15. A bird can either spend additional energy feeding its current chicks or preserve that energy for future reproduction. Explain the biological trade-off involved.
Key Terms
- Parental care – parental behaviour that increases offspring survival or future reproductive success.
- Parental investment – time, energy, and resources devoted to offspring that can improve their chances of survival and reproduction.
- Maternal care – care provided primarily by the mother.
- Paternal care – care provided primarily by the father.
- Biparental care – care provided by both parents.
- Cooperative care – care in which additional group members help parents raise offspring.
- Incubation – maintaining suitable conditions for developing eggs, particularly temperature.
- Altricial – relatively underdeveloped and dependent at hatching or birth.
- Precocial – relatively well developed and mobile at hatching or birth.
- Mouthbrooding – carrying eggs or young in the mouth for protection.
- Reproductive success – success in passing genetic information to future generations through surviving descendants.
- Trade-off – situation in which increasing investment in one biological function reduces resources available for another.
- Parent-offspring conflict – differences between the amount of parental investment that benefits an individual offspring and the amount that best balances the parent's overall reproductive interests.
Key Takeaways
- Parental care includes behaviours that increase offspring survival or future reproductive success.
- Care can occur before or after birth or hatching.
- Nest building, incubation, feeding, guarding, carrying, grooming, and teaching are forms of parental care.
- Animals show enormous variation in the amount and type of care they provide.
- Care may be maternal, paternal, biparental, or cooperative.
- Parental care can protect offspring from predators, starvation, environmental extremes, and other dangers.
- Extended care can provide opportunities for young animals to learn complex behaviours.
- Species producing relatively few offspring often invest more resources in each offspring.
- Species providing little care often compensate by producing larger numbers of offspring.
- Parental investment requires time, energy, and resources.
- Caring for current offspring can reduce resources available for parental survival or future reproduction.
- Parental-care strategies therefore involve important cost-benefit trade-offs.
- Extensive care is not automatically superior to limited care; different strategies can succeed under different ecological conditions.
- Natural selection can favour parental behaviours when their benefits to reproductive success outweigh their costs.
- Ultimately, parental investment is successful when it contributes to offspring surviving, reaching reproductive age, and producing descendants of their own.