Nocturnal Adaptations

Animal Spotlight

May 2003

Nocturnal Adaptations

This month's spotlight is not specifically about any animal. Instead, we have compiled some valuable information from one of Kit Sun's lectures on the above topic. The lecture has helped us gain a better understanding of nocturnal creatures and hence we wish to share them with everyone.

The following are the summaries of the main points taken during the lecture. Let us look at the nocturnal adaptations of the following 5 main groups of creatures:

1) Bats

Mega-bats

i) Excellent sense of smell for location of food (fruit).

ii) Good eyesight to navigate in the dark.

iii) Longer faces - larger surface area to absorb molecules to interpret the scent.

iv) Can echolocate when it is too dark but their echolocation is not as good as those of insect-eating bats.

E.g. flying fox, dog-faced fruit bat

Micro-bats

i) These bats literally scream constantly throughout the night. They can 'close' their ears while 'screaming' to prevent resulting deafness and can open them again soon after to listen for returning echos.

ii) Their mouths or flower-like noses produce sonar signals to detect prey (e.g. insects). The large ears can act as radar dishes to receive the echos.

iii) They have small eyes and are rather short-sighted but their eyesight is still good enough to navigate. Can rely on echolocation as a back-up tool if visibility is very poor.

iv) Micro-bats can modulate their call frequencies to detect moving objects. If the insect is moving away, the bat increases the frequency of its calls. If the insect is coming closer, the bat will lower the frequency of its call. The resolutions of the echos are also very good.

v) Some moths can 'absorb' the active sonars released by the bats and subsequently use stealth to avoid detection. Certain moths have even evolved to send back active sonars to the bats, thus confusing their predators into thinking that the moth is another bat. See Moth Defense Systems.

2) Owls

i) Facial disk that resembles a radar dish to direct sounds into the ears.

ii) Binocular vision like all predators. The eyes of owls are so large that they cannot move them at all but to make for it, the neck can turn up to 270 degrees!

iii) Owls can catch their prey in complete darkness just by using their acute hearing.

iv) For some owls, one ear is higher than the other and hence one ear can receive sounds faster than the other.

v) When an owl moves its head from side to side, it is trying to pinpoint the exact source of a sound.

vi) When a sound is detected, the owl will turn its head and face directly at the source of the sound. Once it determines the location of the prey, the owls takes off and flies silently towards it. Just before striking, the owl stretches its legs forward until they are in a 'straight line' between its eyes and the prey. This will confirm the final exact location of the prey before the talons lash out and grasp. Split-seconds before striking, the owl closes its eyes to protect them.		vii) Most nocturnal creatures that the owl preys on, e.g. mouse can also hear extremely well so to keep one step ahead, the owl has developed stealth. There are microscopic ridges at the leading edges of the primary wing feathers to help muffle out friction with the air (reduce normal turbulence into micro-turbulence and eventually to silence). The prey can smell the owls at very close range but by then, it is too late.

3) Reptiles (e.g. Pythons)

i) Good eyesight that can see some color.

ii) Can also smell well using their forked tongue. Pythons mainly use smell to detect their prey.

iii) They switch to infra-red when the prey is within closer range. Pythons have heat sensing pits along their upper lips for detecting warm-blooded prey (pit vipers have them too).

iv) Pythons tend to be active after rainfall, especially on nights after afternoon showers. The rain would have cooled the soil and this means that warm-blooded prey are relatively easier to detect.

4) Cats

i) Sight - Cats have good eyesight and see in monochrome. Their eyes contain both rods and some cones and hence they also possess limited color vision.

ii) Hearing - In low light, cats rely on their excellent hearing. Their ears are set far apart and can swivel forward to increase baseline of incoming sounds. They can also turn their heads and face the sound to hear better.

iii) Whiskers of the cat are tools use for short range navigation (e.g. to avoid knocking into objects). Facial muscles can help to 'move' the whiskers for better navigation.

iv) Smell - Their sense of smell is not as good as those of dogs because of their flatter muzzles/faces. However, cats can recognise a variety of smells, especially those of other cats. Hence they often use urine to scent mark their territories.

v) Stealth - Cats have soft touch pads beneath their paws so that they can move as silently as possible without alarming their prey.

5) Dogs

i) Smell - This is the most crucial sense of a dog and a large part of their brains is devoted to just interpret smells. The nose is wet all the time because water is a good solvent for molecules to get sucked into the nasal passage. Hence, dogs often lick their noses to keep them moist. The dog's nose is very sensitive and if they get hit on the nose, it can be very dreadful for the dog.

The dog's sense of smell is so keen that drug dogs have been known to detect heroine hidden among gasoline.

Dogs also have infra-red in their nose that can detect cancer growth in humans.

ii) Hearing - though not as good as cats but definitely better than humans and they can even detect low frequency sounds.

iii) Sight - Dogs are a little short-sighted and they see in monochrome.

iv) Whiskers - same as in cats.

Extra notes on Dogs:

Dog Behaviour - Only the dominant male dog in the pack can urinate with its hind leg lifted up. All other subordinate males must urinate in squatting posture like female dogs. A sub male that attempts to urinate with its hind leg up is issuing a challenge to the dominant dog for the leadership position.

Only the dominant dog of the pack moves around with its tail up. All other members must keep their tails down or face the wrath of the leader.

Acknowledgements - Facts of the above were purely taken down during Kit Sun's lecture of "Nocturnal Adaptations" on 25 May 2003. Pictures from an Animal Drawings CD-Rom.

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