An automatic behavior in animals is instinct. Whereas reflexes are
common to different animals, an instinct is special to each species of
animal. Also, it is inborn and does not have to be learned. It just
happens, as we say, by instinct.
Mating Instinct
One
example is called the mating instinct. This usually takes place in
spring, especially among birds. It is believed to have something to do
with the increase in hours of daylight as the days lengthen. This causes
chemicals called hormones to circulate in the body, and to bring the
reproductive organs into breeding condition. Male birds colour up and
start to sing. They fight rivals and court the females until mating
takes place. What is so remarkable is that a bird can build its nest
without any training. When the babies hatch, the mother feeds them with
the correct food. Her mother instinct is so strong that she will even
sit on imitation eggs made of stone. What seems very sad is that she
ignores a baby if it falls from the nest—it is no longer part of the
family. All this is done by instinct.
Some very interesting
studies have been made on this kind of animal behaviour, showing how
animals do things by instinct. There is one elaborate mating story which
is easily watched—the breeding behaviour of the stickleback. This
common little fish is easy to find.
The Stickteback
To
reproduce its natural habitat artificially an aquarium would be
required, containing water plants in a layer of aquarium sand, so as to
represent a miniature pond. The male comes into breeding condition in
late spring, and colours up with red on its throat. It then selects a
gap in the water plants and guards this territory from all intruders,
especially a rival male. Battles take place in which the owner
stickleback nearly always wins. By placing model stickle-backs in the
aquarium, some with red throats and some without we know that the colour
is important. This is the warning signal—red for danger.
Meanwhile
a nest is built by the male. He collects bits of debris and pulís off
pieces of plants and pushes them into the sand. This is bound together
with a sticky substance from his kidneys. Also, mouthfuls of sand are
picked up and deposited on the nest to hold it down. If a female
approaches she is recognised by her dull colours and the shape of her
swollen body full of eggs. The male will then perform the 'zig-zag'
dance, swimming backwards and forwards and moving towards the nest so
that the female can follow. She enters the nest and lays her eggs. The
male then fertilises them. From that moment on he takes charge and even
drives away the female. The nest is now protected vigorously as the
plucky little male fights off all invaders. Extra care is needed when
the eggs hatch. If a baby strays too far away, the male will pick it up
in his mouth and put it back into the shoal. When old enough to fend for
themselves the young scatter, and the male takes no further interest in
them.
This remarkable performance by a small fish is only one of
the many ways in which animals behave by instinct. But first, they have
to be put'in the mood', as it were. This is where the hormones play
their part. One of these is called the 'fear' hormone which works when
an animal is angry, tensed up or frightened. In man this hormone comes
from the adrenal gland near the kidneys, passes through the blood, and
releases sugar from the liver. It gives us added energy, and sometimes
leads to a sweet taste in the mouth. The energy helps us to run from
danger, or to stand up to an enemy. This is what might give a soldier
courage in wartime.
