· Response or an observable activity of an organism that responds to stimuli in its environment
· All organisms respond to stimuli like light, heat, chemicals, temperature, pressure, electricity, gravity etc.
· Ethology: branch of biology that deals with animal behaviour.
· Father of ethology: Khorad Lorenz
· Stimulus → Sense organs → Brain or Spinal cord → Muscles → Response

Types of Behaviour

i. Innate or Stereotyped or Instinct or Inborn behaviour
· Inborn and is genetically controlled, independent of the experience and is determined by heredity.
· Examples: reflexes, taxes, migration, courtship, mating, leadership, dominance etc.
ii. Learned Behaviour
· Acquired as a result of experiences during the lifetime of an organism to ensure better chances of survival in the changing environment.
· It is not genetically controlled so never inherited.
· Examples: dancing, singing, swimming, joking, playing, studying, painting, tailoring, cycling etc.

Reflex Action

· A rapid, automatic and involuntary action shown by a part of the body in response to a stimulus.
· The site of reflex action spinal cord. Innate behaviour
· Example: hunger, salivation, sneezing, eye blinking, knee jerk, withdrawal of hand from the hot object.
· Two types of nerves transmit messages in the form of impulses from receptors to the effectors through modulator organs (Brain or spinal cord).
· They are:
i. Sensory or afferent or ascending nerves: Transmit impulses from receptors to the spinal cord or brain.
ii. Motor or efferent or descending nerves: Transmit impulses from the spinal cord or brain to effectors.

Mechanism of reflex action (Studied by Marshall and Hall in 1883AD)
· The receptor cells receive the stimulus and the nerve signals go to the brain or spinal cord (modulator organ) in the form of wave (sensory impulse) through the sensory nerve where the sensory impulse is modulated into the motor impulse and goes back to the effectors (muscles and glands) through the motor nerve and thus forms a reflex arc.
· The reflex arc comprises reception, conduction, modulation (interpretation), conduction and effect.
· Reception (Sensory organs) → Conduction (Sensory nerve) → Modulation (Brain or Spinal cord) → Conduction (Motor nerve) → Effect (Effectors- muscles or glands)
· Examples: Rapid withdrawal of the hand when touched fire or hot objects, blinking of eyes when an object or dust approaches the eyes, knee-jerking, sneezing, salivation in mouth seeing the citrus foods etc.
· External stimuli - Receptor (Sense organs) - Sensory nerve - Modulator (Brain or Spinal cord) - Motor nerve – Effector.

Reflex Arc
· Simple nervous pathway through which an impulse travels from a receptor to an effector organ to bring about a response during a reflex action.
a. Cerebral or cranial or brain reflex - Reflex arc passes through the brain.
· Examples: blinking of eyes, sneezing, salivation etc.
b. Spinal reflex - Reflex arc passes through the spinal cord.
· Examples: Knee jerking, with drawl of hand from hot object etc.
· Hunger and cough reflexes involve both spinal and cerebral reflexes.

Types of Reflex
1. Monosynaptic reflex (Only one synapse)

· Impulses transfer from sensory to motor neuron directly.
· Example: knee jerk.
2. Polysynaptic reflex (Two or more synapses)
· Impulses transfer from sensory to motor neuron in the spinal cord or brain through interneuron.
· Examples: withdrawal of hand from a hot object, blinking of eyes.

Importance of Reflex Action
i. Minimizes damage or injury of the body by providing a quick response to harmful stimuli.
ii. Reduces the overloading of the brain, so it prevents fatigue.


· Response of an organism in a particular position in relation to a stimulus.
i. Primary orientation: Adjustment of the body in a normal balanced position in space and time.
· Examples: fishes (water), Birds (air), Terrestrial animals (land), wall lizards (wall) etc.
ii. Secondary orientation: Orientation of the body in response to external stimuli.
· Examples: Taxis, kinesis etc.

· Orientation of an organism in a certain direction with respect to the source of stimulus
· Or, Directional movement of an organism in a certain direction in response to the source of stimulus, innate behaviour
· Positive (Towards the stimulus) and Negative taxis (Away from the stimulus)
· External stimuli may be light, temperature, chemical, gravity, cold, heat, electricity etc.

· Turning movement of plants in response to external stimuli like light, chemical, gravity etc.
· Examples: phototropism, geotropism etc.
· Towards (Positive tropism) or away (Negative tropism) from the stimuli


· According to the type of stimulus received, taxis are of the following types:
a. Phototaxis: Locomotory movement of an organism in response to light.
· Examples: Euglena and moths (positive phototaxis), cockroach and earthworms (negative phototaxis)

b. Chemotaxis: Movement of an organism in response to chemicals.
· Examples: Euglena, weak acid solution (positive chemotaxis), and strong acid solution (negative chemotaxis), insects are attracted to insect attractants and avoid repellents. Antherizooids towards the Malic acid

c. Thermotaxis: Movement of an organism in response to temperature.
· Examples: Hydra in cold water (above 25°C, it disappears from the surface).
· Paramecium (optimum temperature 24°C to 28°C), avoiding reaction to the temperature lower or higher than it

d. Geotaxis: Movement of an organism in response to gravity.
· Examples: Amoeba and Earthworms show positive geotaxis and Paramecium and fruit fly negative geotaxis.
· Planula larvae swim towards the seabed while the Ephyra larva is away from the seabed.
· Burrowing and arboreal animals

e. Rheotaxis: Movement of an organism in response to the current of water or air.
· For example, birds, insects and fishes show positive rheotaxis.
· Planaria move against the water current i.e. negative rheotaxis.

f. Thigmotaxis: Movement of an organism due to touch or contact.
· Examples: Amoeba and Paramecium show negative responses when touched with solid objects.

g. Sociotaxis: It is the movement of organisms pertaining to a family or group.
· Examples: Honey bees, Ants, Termites, Wasps etc.

h. Klinotaxis: The organisms having sensory receptors but not the paired sensory organs in the body can orient themselves only when the receptors in both sides of the body are equally stimulated.
· For equal stimulation, they move their anterior ends sidewise.
· After the two sides are equally stimulated, the organisms move forward approximately in a straight line.
· Example: Euglena moves towards the source of light by continuously bending its body right and left to test the intensity of light.

i. Trophotaxis: Simultaneous comparison of stimulation by bilaterally symmetrical receptors like paired eyes, ears etc, so they show straight movement.
· Example: grayling butterfly always orients towards the sun by turning towards that position in which both the eyes are equally stimulated.

j. Telotaxis: Out of two similar types of stimuli of equal intensities, the movement of an animal shows towards only one stimulus.
· Example: Honey bees collect nectars in the morning and move towards the source of light during the evening. With a view of light, they return to their hives.
· The Hermit crab can orient itself towards either one or the other source of the stimulus but never in the intermediate direction.

k. Menotaxis: Movement of an organism towards the stimulus at a constant angle, also called as “Light compass response”.
· Example: Bees and ants change their direction in response to change in the direction of the sun.

l. Mnemotaxis:
Movement of an organism in response to complex stimuli.
· Example: Hunting wasps use light direction, landmarks and trail of chemicals left while returning to their hives.

m. Galvanotaxis:
Response of animals to electric current.
· Example: Paramecium moves towards the cathode when a weak electric current is given.

n. Aerotaxis: Special type of chemotaxis in which the movement of organisms in response to the air (oxygen).
· Motile aerobic bacteria move towards oxygen.

o. Magnetotaxis: Response of an organism to the magnetic field.
· Certain motile bacteria show a response to the magnetic field.

p. Hygrotaxis:
Movement of an organism in relation to moisture.


· Non-directional orientation of an organism in response to the intensity of the stimulus or random movement of an organism in response to the intensity of the stimulus.
· Two types are:
i. Orthokinesis: The rate of movement of an organism is affected by the intensity of stimulation.
· For example, a woodlouse moves faster in a dry region and slowly in a damp atmosphere.

ii. Klinokinesis: The rate of change of direction is related to the intensity of stimulation.
· For example, the human body louse, when adapted to favourable conditions, follows almost a straight path.
· But, when it enters an unfavourable environment, it begins to turn in search of a favourable zone.


· Innate behaviour which leads the member of a particular group by a certain leader.
· Guides the members of a particular group at the time of moving together for food, nesting, fighting etc.
· A leader may be one or a group in a flock.
· A real leader initiates, stabilizes or integrates the behavioural activities of other members of the group for maintaining attitude and fulfilling their common requirements.
· The leader should be physically strong to lead the group.
· Besides these, other qualities are freedom of action, responsibility for others and guidance to them in each activity.
· Leadership is the highest rank or hierarchy either of any sex or age.
· Leadership is determined by fighting, bluffing and treating an encounter or a series of encounters.
· When social rank is established, it is maintained by habitual subordination (inferior rank) of those in lower positions by threats and occasional punishment method by those who are in the higher rank.
· Leadership is also expressed in territoriality which is defined by males and sometimes by females.
· Both leadership and territory have obvious survival value.
· Examples of leadership found in various social animals are given below:
i. In red deer, a female called ‘hind’ acts as a leader of the herd. 
Such a herd is matriarchal. She looks after the welfare of the groups. Male deer called ‘stag’ remains away from the herd of female or hind. It only approaches during the mating time. Similarly, the kangaroo herd is patriarchal as it is led by an old male.

ii. Leadership in monkeys is well defined. Every troop has a troop leader that selects four sub-leaders which are placed in east, west, north and south directions. In Swayambhu and Pashupatinath, there are several troops of monkeys and the activity of each group is controlled by its leader. Besides leadership and dominance go together. If a leader is strongly dominant and aggressive, his group covers a wide range of territory than those of a less able group.

iii. Leadership in geese birds can be easily observed. When geese fly over the sky, the leader is always in front of the flock and he or she is old and experienced.

iv. In sheep and goats, the socially dominant individual generally takes the lead.

v. Queen is a leader in social insects like honey bees. She helps in sexual reproduction.


· Social behaviour where some individuals dominate others by aggression or threat.
· Dominant animal controls the behaviour of other animals.
· Dominant animal has more access to food, shelter, mating partners etc.
· Dominance is determined by age, experience, sex, morphological and physiological factors.
· Generally the older one dominates the younger one, bigger-smaller, male-female, physically sound to the weaker individuals.
· The different animals express their dominance in a group differently.
· Examples:
· Cattle and other hoofed mammals show a series of threats by pawing the ground, butting of heads, spring and making sounds of different sorts. Sometimes dominance is determined by the actual fighting.
· The mouse vibrates its tail when meets another mouse. Later on, one of the mice will recognize the dominant and retreat itself.
· The dogs threaten others by snoring, posing their teeth etc. The dominant one moves away by lowering the tail.
· In Rhesus monkeys and baboons, younger ones after maturation challenge the experienced ones. The newly matured songbird may dominate their fully matured songbirds.
· In lemur and dog, female dominates the male during the breeding season. An example of reverse dominance.

Advantages of Dominance
1. The dominant animals are well fed and healthy as they get priority for better food, space, mate and other requirements.
2. Dominance helps to keep the species fit, since the survivors of the fierce battles are the most vigorous, and therefore improve the species by passing the traits on.


· The periodic movement of an animal from one place to another for food, breeding and protection from the enemies or unfavourable environmental conditions is called migration.
· It is also a kind of innate adaptive behaviour of an animal.
· It is shown by newts, turtles, whales, zebra, insects, birds, fishes etc.
· Migratory animals move from one place to another but always return to the same place.

· Fishes show well-marked migration from one place to another generally from freshwater to sea or vice-versa for the purpose of food and reproduction.

Causes of Fish migration or factors regulating the fish migration
I) Physical factors
·These are light, temperature, depth, cold, pressure, water current and turbidity of water.
· Due to changes in these environments, fishes migrate to a suitable area for better survival.
· The water current influences the direction of the movement of the fish.
· Eggs and juveniles are carried passively along with the water current to their feeding ground.

II) Chemical factors
· Salinity of water, pH, smell and taste of water, pesticides etc are the chemical factors that influence the migration.

III) Biological factors
· It includes:
(i) Breeding: Some fishes need a favourable environment for spawning, so they are compelled to migrate to suitable breeding areas either in short or long distances.
· It is also called gametic migration.
(ii) Scarcity of Food: Sometimes there may be a scarcity of food where the fishes live. So they migrate to such areas where the food is available for survival.
· It is also called alimental migration.
(iii) Increase in enemies: Increase their predators viz, large fish, amphibians, reptiles in surrounding environment compels fishes to migrate into suitable protective areas.
IV) Osmoregulatory migration
· It is the migration for maintenance (balance) of the salt and minerals in their body.

Types of movement shown by Migratory Fishes
I) Drifting movement: The movement of fishes is passively carried by the water current.
· This is called drift.

II) Random movement: In this movement, fishes randomly move in any direction.
· It is also called dispersal.

III) Orientated swimming movement:
The movement of fish in a particular direction i.e., either towards or away from the sources of stimulation.

IV) Denatant and Contranatant movement: The movement of the fish in relation to water current.
· If the movement is along with the water current, it is called denaturant and against the water, the current is called contranatant.


· The migration of fish can be classified into the following types:

1. Diadromous or Spawning Migration:
· This is the migration of certain fish from freshwater to marine water or vice-versa and is mainly for breeding purposes.
· It is also of two types: Catadromoud & Anadromous.

a) Catadromous Migration
· Those fishes which spend the major part of their life in the river (freshwater) migrate to the sea (marine water) during breeding time.
· Remember as Kantipur F.M. which means Catadromous from Fresh to Marine.
· Thus, the river is served as a feeding area and the sea as a breeding area.
· During this, following changes are seen in catadromous fishes:
i) Feeding is stopped.
ii) Eyes are enlarged.
iii) Snout becomes sharper and back portion become darker.
iv) Alimentary canal undergoes degeneration.
v) Body colour changes from yellow to silver-white.
vi) Gonads becomes fully matured and so on.
· Anguilla bengalensis (freshwater eel) spends most part of its life in river water but migrates to seawater for spawning.
· Migration starts after the maturation of gonads.
· They migrate about 4800 km and reach the breeding place. After spawning, parents die.
· Eggs, after fertilization, develop into leaf-like leptocephalus larva which undergoes metamorphosis into elver larva.
· Each spring enormous number of eels come to the river and grow some years and become adults.
· The adult eels, on maturity again move towards the sea.

b. Anadromous migration
· These fishes migrate from sea to freshwater for spawning.
· Example: Atlantic and Pacific Salmons, Lampreys, Hilsa, Sturgeons etc.
· During migration, the following modifications occur on their body:
i) Body becomes weighty due to more development of gonads.
ii) Feeding is stopped.
iii) Alimentary canal undergoes degeneration.
iv) Sexual dimorphism is seen, male is characterized by enlarged front teeth.
· Male and female Salmons leave their feeding ground (seawater) and move towards freshwater and grow some years there.
· They select a suitable spawning ground and make nests where females lay eggs and males shed sperms over them.
· Females cover the fertilized eggs with gravels.
· Eggs hatch out larvae and young Salmons return to sea for feeding.

2. Feeding migration or Alimental migration

· The migration of certain fishes from spawning area to feeding area i.e., from spawning to feeding area i.e. freshwater to marine water and again from marine to freshwater for food, not for the breed.
· Example: Sharks, Carps etc.

3. Amphidromous migration
· Migration of fishes from sea to fresh water and vice-versa for completion of some stage of life cycle not for breeding and feeding is called Amphidromous migration.
· It means they are alternating their habitats at certain stages of their life cycle.
· Example: Gobies fish.

4. Potamadromous migration
· It is the migration of some fishes from freshwater to freshwater or river to river or stream to stream or vice -versa, for searching suitable place for feeding and breeding i.e. confined to freshwater only.
· Example:: Carps, Trouts etc.

5. Oceanodromous migration

· Those fishes which migrate from ocean to ocean for breeding as well as feeding show oceanodromous migration i.e. confined to sea only.
· Example: Herrings (Clupea), Tunnas (Thunnus) etc.
· They travel a long distance in the sea to deposit eggs and later return to their feeding sites.

6. Shoreward migration
· It is the temporary movement of certain fishes from water to land or seashore or bank of the river.
· Example: Anabas, climbing perch, migrates from water to land or even climbs on trees.
· The common eel travels from one pond to another through moist meadow grass.

7. Overwintering migration
· It involves the migration of some fishes from feeding to wintering ground where the fishes remain in an inactive state with low metabolic rate.
· Example: Grass carp.

8. Latitudinal migration
· The migration of fishes from north to south in spring and south to north in autumn.
· Example: Swordfish and Hammer headed shark (Sphyzaena).

9. Vertical migration
· Generally deep fishes perform daily vertical migration from surface water to deep water or vice-versa for food, protection and spawning.
· Example: Mackerels come to the surface to feed on plankton and go back into deep water after feeding.
· Swordfish normally lives in surface water but go to the deep water to feed fishes found there.
· Some viviparous fishes of the deep lakes come to the surface for giving birth to their larvae.

10. Climatic migration
· When the climate is changed, fishes migrate towards suitable places for better survival and this is called climatic migration.
· Example: migration of freshwater fishes due to turbidity of water during the rainy season.

Advantages of Migration
i) Migrated fishes get enough food, a suitable breeding place and a better environment.
ii) It ensures favourable conditions for better survival and reproduction.
iii) It also provides defence from the enemies.


· Generally many species of birds migrate from one place to another in search of food, temperature, climate, reproduction and protection from enemies Migration is a two-way journey, a yearly round trip, with seasonal ‘coming and outgoing’.
· Some birds show periodic migration between their winter and summer homes or from a breeding or nesting home to a feeding or resting place.

I) Environmental condition: Certain adverse external environmental conditions like change in temperature (increase or decrease in heat or cold), drought and scarcity of food, increase in enemies, shortening of day length, seasonal change and stormy weather etc are the causes the migration in birds.

II) Gonadial stimuli: Gonadial maturation causes physiological changes in migratory birds.
· It stimulates them to migrate to safe breeding grounds for breeding.

III) Fat deposition: Fat deposition in the body leads to changes in the metabolic processes so leads to migration.

IV) Thyroxine (Thyroid secretion): The secretion of thyroid hormone causes changes in metabolic activities which stimulates or excites the birds to migrate.

V) Antipituitary hormone: Decrease in pituitary hormone activity in winter causes migration of birds in the south plane.
· In summer, the activity of pituitary hormone becomes active and gonads are developed.
· So, the birds return northward to their previous habitat for breeding.


1) Latitudinal migration:
· The migration of birds from the northern mountainous region to the south plane area and vice-versa for breeding and another purpose.
· When the northern temperate zone is covered by ice, they migrate to the southern area for shelter and food and again they return to their original habitat during summer.
· Example: American Golden plover (Pluvialis dominica) migrates to Africa to spend winter.
· Many Siberian birds from their home areas visit the wetlands of the Terai region and so on.

2) Altitudinal or vertical migration:
· It is the migration of birds regularly up and down the slopes of mountainous regions to low land or valley area during winter and again to high mountain regions during summer.
· The Woodcock, Himalayan bush chat migrate from plains to the slopes of the Himalayas of Nepal and India during summer and return to plains with the onset of winter.

3) Longitudinal migration:
· It is the migration of birds living in the southern hemisphere towards the east to the west direction or vice-versa.
· Example: Patagonian plovers show migration to folk land and south Patagonia during the early winter season for breeding.
· Starling bird moves from the breeding area in East Europe to Asia towards the Atlantic coast.

4) Seasonal migration:
· Birds may be summer or winter visitors.
· Example: Swifts, swallows are summer visitors for they arrive in spring from the south, remain to breed and leave for the south in autumn.
· Fieldfare and Snow bunting are winter visitors as they arrive in winter, chiefly from the north, stay throughout winter and fly northwards again in spring.

5) Climatic migration: The migration of birds that occurs due to daily or seasonal climatic changes is called climatic migration.
· Example: Geese and Ducks.

6) Gametic migration: It is the migration of birds to some suitable place or environment for breeding.

7) Irregular or Vagrant migration: The movement of birds that is irregular in all directions is called irregular or vagrant migration.
· Example: Herons after breeding, the young and adults disperse in all directions over many or a few hundred miles in search of food and safety from enemies.

· The migratory birds may follow the same or different routes year after year.
· The different routes are as follows:
i) Mountain range route: It is the route of migrants crossing through the mountain range.
ii) River valley route: The route of migration crossing the rivers and river valley.
iii) Coast route: The route of migration along the coastline of different oceans.
iv) Sea route: Migration through sea or oceans.
v) Sun and stars: Some birds migrate through the position of the sun and stars.

Advantages of Bird Migration
i) It protects the birds from cold, heat, stormy weather etc.
ii) It helps in searching for suitable breeding grounds.
iii) It is a good activity to get sufficient food and better condition in comparison to their natural habitat.
iv) It helps the birds to reach a favourable environment for nesting, breeding and protection from enemies.

Disadvantages of Bird Migration
i) Due to long journeys, some migratory birds get tired and some passive or tired ones may fall into the sea.
ii) They have the risk of attack by natural enemies during migration.
iii) Due to adverse environmental conditions like heavy rain, snowfall, stormy weather etc, many migratory birds may die.
iv) Many migratory birds die by hitting Lighthouses, Mountains, Big buildings, Television towers.
v) They are also killed by hawks and bird hunters (other enemies) during migration.

Also, Read our Other Related Notes for Entrance Exams:
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