Who is on the night shift?
Even when we are asleep many kinds of animals are out and about. We know less about them than species that are active during the day because they are difficult for us to study.
| Word | Definitiion |
|---|---|
| Diurnal | Animal is active during the hours of daylight (eg blackbird, lizard) |
| Nocturnal | Animal is active during the hours of darkness (eg tawny owl) |
| Crepuscular | Animal is active primarily during the twilight period. Some crepuscular animals may also be active by moonlight or during an overcast day |
Nocturnal animals have evolved physical traits that let them roam and feed in the dark more effectively.
Sight adaptations
The eyes get bigger and the pupils widen. Owl eyes, for example, are so big that they can’t move in the socket, but their wide pupils help them collect more light. To compensate owls turn their heads to fix their stare on their prey. Tawny owls can famously turn their head through 270 degrees and are able to look behind them.
Many nocturnal animals appear to have glowing eyes if they are seen in car headlights or with a torch. These animals have a special layer of tissue in the eye called the tapetum lucidum which gives them superior night vision. Lying immediately behind the retina, it is a retroreflector. It reflects visible light back through the retina, increasing the light available to the photoreceptors.
In 1934 Percy Shaw registered the patent for the ‘Cats eye’ reflective road stud which we see on our roads today. He got the idea after seeing a cat in his headlights by the side of the road on a foggy night.
Smell
Most nocturnal animals have a keen sense of smell, many times more sensitive than ours. Hedgehogs for example largely hunt for insects and grubs by smell.
Hearing
Many nocturnal animals have very large ears. In owls one ear is positioned slightly higher than the other which helps the animal to correctly assess the distance to a sound source – a small vole in the grass perhaps. The stiff feathers that make an owl’s round “face” also help to direct sound towards the ears.
You can find out more about tawny owls here.
Echolocation
This is a very specialised system of sonar which has evolved in bats.
You can find out more about pipistrelle bats and echolocation here .
Touch
Whiskers are modified hairs that form specialised touch organs.
As whiskers brush an object, irregularities in the surface are translated into movements of the whiskers; those, in turn, are detected by hundreds of motion sensors inside a specially adapted hair follicle – rats and cats have 100–200 nerve cells per whisker. These nerves relay detailed information allowing the animal to detect the precise location, size, texture and other details of the object. Many nocturnal animals have very long whiskers to help them move and hunt in the dark.
A couple of good websites introducing nocturnal creatures for children are here (RSPB) and here (BBC Bitesize).