What is behaviour? Stimulus and response
Behaviour is anything an animal does: moving, eating, calling, hiding, building a nest.
A stimulus is a change the animal senses. An external stimulus comes from outside (light, a smell, a predator, cold). An internal stimulus comes from inside the body (hunger, thirst, hormones in the breeding season). The response is what the animal does. The nervous system and hormones link the two.
Scientists ask two kinds of question: how does it happen (causes: senses, nerves, hormones, genes, experience) and why does it exist (function: how it helps survival and reproduction).
Innate behaviour: instinct and reflex
Innate (inborn) behaviour comes from genes. It appears the first time, without practice, and is the same in every member of the species.
- Reflex: a fast, simple response of one body part, like blinking.
- Instinct: a chain of actions, like a spider spinning a web, a bird building its first nest, or a baby turtle running to the sea.
- Taxis and kinesis: simple animals move towards or away from a stimulus, like woodlice moving to damp places.
Innate behaviour is quick and reliable, but it cannot change if the world changes.
Learned behaviour
Learned behaviour changes with experience. It lets an animal fit a changing world.
- Habituation: the animal stops reacting to a harmless stimulus that keeps coming (birds ignore a scarecrow).
- Imprinting: in a short sensitive period just after birth, a young animal learns who its parent is and follows it. Goslings that first see a person will follow that person.
- Classical conditioning: the animal links a signal with something that happens next (a dog drools at a bell rung before food).
- Operant conditioning (trial and error): an action that brings a reward is repeated; one that brings pain is avoided.
- Insight: solving a new problem in one go by putting earlier experiences together (a chimpanzee stacking boxes, a crow bending a wire hook).
- Copying (social learning): young animals learn songs, routes and tool use by watching adults.
Most real behaviour is a mix: a bird has an inborn urge to sing, but learns the exact song from adults. This is how behaviour develops as an animal grows.
Function: behaviour in groups and populations
Behaviour helps an animal survive and pass on its genes. Natural selection keeps useful behaviour.
- Living in groups: herds and schools give many eyes and make it hard for a predator to pick one.
- Division of labour: in bee and ant colonies, queens lay eggs while workers find food and guard.
- Communication: calls, colours, smells (pheromones) and dances. A honeybee dance tells the direction and distance of flowers.
- Territory: animals defend an area with food or nest sites, often by song or scent marks instead of fighting.
- Courtship: displays (a peacock's tail, a bird's dance) help choose a healthy mate of the same species.
- Hierarchy: a pecking order decides who eats first and cuts down on fights.
- Parental care and migration also raise the chance that young survive.
Animals as sentient beings
Sentience is the ability to have feelings: to feel pain, fear, comfort or pleasure, and to care what happens to you.
Signs of sentience: the animal has a nervous system with a brain, avoids pain, learns from it, and changes its behaviour when hurt (limping, guarding a wound). By these signs, mammals and birds are sentient, and so are fish, octopuses and many other animals.
Non-sentient living things, such as plants, fungi and bacteria, respond to stimuli (a plant bends to light) but have no nervous system, so they are not thought to feel anything. Because animals can suffer, many countries have laws on animal welfare: proper food, space, care, and no cruelty.
Key formulas and definitions
- Stimulus → sense organ → nervous system/hormones → response
- Innate = inborn, same in all, no practice (reflex, instinct)
- Learned = from experience (habituation, imprinting, conditioning, insight, copying)
- Function = helps survival and reproduction
- Sentient = can feel pain and pleasure
Worked examples
1. A newborn kangaroo crawls into its mother's pouch with no help. Innate or learned? Why?
Innate (instinct). It does it the very first time, without practice or a teacher.
2. Snails on a table pull into their shells when tapped. After many taps they stop pulling in. Name this.
Habituation. The tapping is harmless and repeated, so the snail stops wasting energy on it.
3. Ducklings raised in a lab follow a toy train. Explain.
Imprinting. In the sensitive period after hatching, the train was the first moving thing they saw, so they learned it as 'parent'.
4. A rat learns to press a lever to get food. Which type of learning is it?
Operant conditioning (trial and error with a reward).
5. Give one cause and one function of a robin singing in spring.
Cause: longer days raise hormone levels. Function: the song defends a territory and attracts a mate.
6. A crow drops stones into a jar to raise the water and drink. Why is this called insight?
The crow solves a new problem quickly by putting earlier knowledge together (stones take up space), not by slow random trying.
Common mistakes
- Saying all bird songs are instinct. Many birds learn the exact song from adults.
- Mixing up habituation and conditioning. Habituation is learning to ignore; conditioning is learning a link.
- Thinking a plant bending to light is behaviour from feelings. Plants respond, but are not sentient.
- Giving only a cause when asked for the function. Function = how it helps survival or reproduction.