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HIBERNATION

Many mammals, such as bats and dormice, survive winter in cool

and polar lands by entering a deep sleep called hibernation. This

strategy helps to conserve energy that would otherwise be lost in

the struggle to keep warm and find scarce food.

4 SURVIVING THROUGH SLEEP

A dormouse passes the winter in

a snug ball of grass and bark in

its underground nest. Not dead

but simply saving energy, it lives

on stored fat and wakes when

temperatures rise again in spring.

HOW DO MAMMALS REPRODUCE?

All mammals reproduce sexually – sperm from the

male fertilizes the female’s egg. In some mammal

species, males establish breeding territories, where

they display to the females, showing that they are

fit and strong. In others, the males fight for the

right to mate. Many male hoofed mammals have

horns or antlers which they crash or lock together

in tests of strength.

WHAT CHANGES HAPPEN DURING HIBERNATION?

Heartbeat, breathing, and other body processes slow

right down, and the animal’s temperature drops so

that it feels cold to the touch. When the weather

warms again in spring, these processes are reversed,

and the mammal wakes up to resume active life.

WHAT OTHER TYPES OF ANIMAL HIBERNATE?

Hibernation is very common among cold-blooded

animals, such as amphibians, reptiles, and insects, that

live in cold or temperate regions. In deserts and other

barren places, some animals enter a similar state,

called aestivation, to survive drought.

WHY IS BEING WARM-BLOODED USEFUL?

Mammals maintain a constant body temperature, which

lets them stay active in all weathers. Maintaining body

temperature takes up a lot of energy, so mammals need

large quantities of food. To help reduce the amount of

food they must find, mammals in cold environments

have thick fur or fatty blubber to retain body heat.

Some go into. HIBERNATION to survive winter.

1 POLAR BEAR CUBS SUCKLING
At birth, young mammals are
fairly weak and defenceless. One
or both of the parents, and
sometimes other adults, looks
after the young until they are
weaned and able to find food for
themselves. The babies learn
survival skills from the adults and
often by playing with others of
their own age.

MAMMAL CLASSIFICATION

• Mammals make up the
  vertebrate class Mammalia.
  There are about 4,500 species
  split into three main groups.


• The first group – the
  monotremes – is also the
  smallest, with five species.
  
  
  • The second group contains
    the marsupials, with 331
    species in all.
  
  
  • The third group contains all
    placental mammals and is
    split into 17 orders. Rodents
    make up the largest order.
  
  
  
  

FIND OUT MORE. Marsupials 123 • Monotremes 123 • Primates 122 • Rodents 122

mammals