Why behaviour matters
Behaviour is everything an animal does in response to its surroundings and its internal state: finding food, avoiding predators, finding a mate, caring for young, resting. Behaviour helps an animal survive and reproduce, so it is shaped by natural selection just like body structures. Biologists ask both how a behaviour works (the stimuli, nerves and hormones involved) and why it evolved (how it helps the animal leave offspring).
Instinct and learning
| Type | What it is | Examples |
|---|---|---|
| Innate (instinct) | Inherited; performed correctly the first time; similar in all members of a species | Egg-rolling in geese, a spider spinning a web, a newborn mammal suckling |
| Learned | Changed by experience during the animal’s life | Avoiding bad-tasting prey, a dog coming when called, birdsong dialects |
An instinct is often triggered by a simple sign stimulus, such as an egg-shaped object near the nest. A fixed action pattern, once started, runs to completion even if the stimulus disappears. Instincts are useful when there is no time or chance to learn: a newly hatched turtle must head for the sea at once. Learning lets an animal adjust to its own particular surroundings. Most behaviour combines both: songbirds inherit a template for their song but must hear adults to learn it properly.
Kinds of learning
- Habituation: learning to ignore a repeated, harmless stimulus, like birds that stop fleeing from a scarecrow.
- Imprinting: rapid learning in a short sensitive period early in life. Goslings follow the first moving object they see, usually their mother.
- Classical conditioning: linking a neutral stimulus with a reward or punishment, as in Pavlov’s dogs that salivated at a bell.
- Trial and error (operant conditioning): learning from the results of one’s own actions, like a bird that avoids striped caterpillars after tasting one.
- Insight and social learning: solving new problems, or learning by watching others, as young chimpanzees learn to crack nuts with stones.
Foraging and predator avoidance
Foraging is searching for and handling food. An animal must gain more energy than it spends, so cold weather, which costs energy, and scarce food both make animals spend more of their time feeding. Every moment spent feeding in the open is a risk, so animals balance food against safety: they stay near cover, feed in groups where many eyes watch for danger, freeze, flee to shelter or use camouflage. Being active at a time of day when predators are not is another way to stay safe.
Communication and territories
Animals communicate with sounds, scents, colours, postures and even dances. A bird’s alarm call warns the whole flock of a predator; honeybees dance to tell others where food is; wolves howl and scent-mark. Many animals defend a territory, an area with food or nest sites. In spring, male songbirds sing from high perches to advertise their territory to rivals and to attract females, and chase out intruders. Displays and song usually settle disputes without dangerous fights.
Migration and seasonal cues
Migration is a regular, often seasonal, journey between places. Warblers and swallows fly from Europe to Africa for the winter, caribou follow fresh grazing, and salmon return from the sea to the river where they hatched. Animals need a reliable calendar to time these journeys. Temperature changes from day to day, but day length (photoperiod) changes in exactly the same way every year, so many animals use it to time migration, breeding, moulting and preparing for winter. Migrating animals find their way using the Sun, the stars, the Earth’s magnetic field and landmarks.
Daily rhythms
Most animals divide the day into active and resting periods. Diurnal animals, such as squirrels, most songbirds and humans, are active by day and rely mainly on vision. Nocturnal animals, such as mice, owls, bats and hedgehogs, are active at night, avoiding many predators and, in deserts, the heat. They often have large eyes or rely on hearing and smell. Crepuscular animals, such as rabbits and deer, are most active at dawn and dusk.
The biological clock
These daily rhythms are not just reactions to light and darkness. An animal kept in constant darkness still sleeps and wakes in a regular cycle, so it must have an internal circadian clock (from Latin circa diem, “about a day”). The clock is not exactly 24 hours long, so in constant darkness the rhythm slowly drifts: itfree-runs. In nature, light at dawn and dusk resets the clock every day, keeping it in step with the 24-hour day; this is entrainment. If the light schedule suddenly shifts, as when you fly across time zones, the clock can move only an hour or so a day, so it takes several days to adjust: jet lag. In mammals the master clock sits in a small part of the brain that receives signals directly from the eyes.
Common misconceptions
- “Birds migrate because it gets cold.” Many leave while it is still warm, triggered by shortening days and their internal annual clock; food shortage is the deeper reason.
- “Instinct and learning are completely separate.” Most behaviours involve both.
- “Nocturnal animals are active at night because they cannot see in daylight.” Their rhythm is set by an internal clock and has evolved to suit their way of life.
- “Animals behave for the good of the species.” Behaviour evolves because it helps individuals, and their relatives, survive and reproduce.
- “Habituation is just tiredness.” A habituated animal still responds fully to a different stimulus.
What the model simplifies
This is a simplified, rule-based model. Each bird follows a short list of rules in order of priority, and the thresholds (for example, migrating when days are shorter than 10.5 hours, or breeding when they are longer than 13 hours and above 5 °C) are illustrative, not measured. Real birds also respond to hormones, their body condition, their internal yearly clock and each other in far more complex ways. A whole day passes in under a minute, nights pass faster than days, and the hawk’s success rate is arbitrary. In the rhythm view, the activity patterns, clock periods and how quickly the clock resets are typical illustrative values. The learning experiments show the overall pattern of real results, not data from a particular study.
Key takeaways
- Behaviour helps animals survive and reproduce, and it evolves by natural selection.
- Instincts are inherited and need no practice; learned behaviour changes with experience.
- Habituation, imprinting, conditioning, trial and error and insight are kinds of learning.
- Animals balance foraging against predator risk, communicate with calls and displays, and defend territories.
- Day length is a reliable seasonal cue for migration and breeding.
- Diurnal, nocturnal and crepuscular rhythms are driven by an internal circadian clock that daylight resets each day.