NIGHT LIFE: This weeks article deals with the animals that are active by night. They are called nocturnal animals. There are some animals that are active both by day and night like the Leopard, Jackal etc.
The intermediate activities that are between the day and the night i.e at twilight or dusk, is called crepuscular. There are many animals that fall into this category.
With darkness setting upon the land, there are many denizens of the forest and some outside forest areas, which come out and start their activities.
These activities are mainly centered round finding sufficient food for themselves and their young, and going through the process of reproducing their species.
Those species that are predated upon also have to make sure that they stay alive by avoiding their predators. In other words the hunter has to make sure that he finds its prey, whilst the hunted has to ensure its survival.
Nocturnal animals sleep during the day, often in a burrow or den. When their ‘day’ begins, they move out slowly from wherever they have been spending the daylight hours and with the disappearing shadows, the forest comes alive with footfalls, scuttles, the soft beating of wings and screeches etc.
Why are some animals nocturnal?
A rule of nature is that all species need to obtain the resources necessary for their existence. One method of avoiding competition among the animals that use the same resources is to confine their activities to different times of the day.
Take the flying foxes and the birds for example. Both these animal groups have the same dietary habits in that they are fruit eaters. Flying foxes cannot compete with the birds in terms of speed of flight and also the maneuverability that birds have when flying at speed amongst the trees.
Therefore the flying foxes have adopted a nocturnal life style when they can fly and feed at their own pace with no competition from the birds.
Some species have taken to a nightlife to avoid their predators that forage during the daytime. Long ago, mammals moved about in darkness in order to escape predators such as dinosaurs. Some developed adaptations such as increased night-vision or hearing that suited their nighttime activities.
Today several of the smaller mammals have remained nocturnal, and it has become necessary for their predators to also be active at night in order to catch them.
On the other hand some animals make use of this change in activity times to their advantage by hunting for food during the night.
For example most of the rat species have adopted a nocturnal life. With this owls have now included rats as prey species. All these changing process of the struggle between predator and prey is subjected to continuous refinement by the process of evolution.
Many animals, like animals in the desert, are nocturnal in order to escape extreme daytime heat.
Most nocturnal animals have been subject to convergent evolutions. Convergent evolutions can be described as an evolutionary process in which organisms not closely related, independently acquire some characteristic or characteristics that are common.
This usually reflects similar responses to similar environmental conditions. This is the same as across species adaptations- like the fin of the fish and the whale, they are two different animal groups but have the same structure-fins for an aquatic life
Certain senses available to a diurnal animal, where the advantage of daylight plays an important role, is not of use to a nocturnal animal. Therefore if it adopts a nightlife, it has to evolve certain capabilities that would be of use in the night.
This happens along the line of evolution. Sharp senses are absolutely necessary for most nocturnal animals to find food in the dark, to escape from danger, or just to find their way back home, they must have senses that are extremely good
Many nocturnal animals, like owls, lorises and cats, have special eyes that see well in the dark. The most notable feature is the size of their eyes. The eyes are larger, with wider pupils. This enables them to collect more ambient light.
The loris has big round eyes with bigger irises. An owl’s eyes fill over one half its skull.
Likewise, some species have evolved tubular eyes as a means of increasing their size. Many nocturnal animals cannot move their eyes within the orbit. Instead, they have evolved an extraordinary rotational ability in the neck.
Some animals of the night have a spherical lens, which projects an equally clear image regardless of the incoming direction of the light. This increases the animal’s field of view allowing the head and eyes to remain motionless. Nocturnal animals have virtually no color vision.
Most nocturnal animals are largely inactive during the day in order to avoid over-stimulating their highly sensitive eyes. They have specialised pupils to shut out damaging bright light. In the dark when you flash a bright light at your dog or cat’s eyes, as if by magic, their eyes glow in the dark.
It is the tapetum lucidum (meaning “bright carpet”), which is an adaptation for night vision. It is a thick reflective membrane, located directly beneath the retina. It collects and re-emits light back to the retina a second time, giving the rods a second chance to absorb the image information. As this light is reflected off the tapetum, the animal’s eyes appear to glow.
If you shine a flashlight on a grassland during the night you will see thousands of small glimmering dots which one often mistakes for dew drops, these are the eye shines belonging to grasshoppers, spiders and other numerous tiny creatures.
Eye shines are also used to locate larger night animals by wildlife watchers. A sudden flash of bright light shocks birds like nightjars making them freeze on the spot enabling one to get very close.
Some nocturnal animals, like bats, use echolocation, where the animal emits a high-pitched sound, which bounces off objects. The sound is then received by that animal, which gives it information about the shape of the object, direction, distance, and texture.
Some species, like rabbits, have developed sensitive ears to be able to detect even the slightest sounds in the darkness and thus have very good hearing.
There are some nocturnal animals that have developed a keen sense of smell to enable them to seek out food in the darkness. In nocturnal birds there are sensory bristles, which help the bird to detect insects in flight.
I have listed most of the nocturnal animals in their various groups, but since I have written about some earlier, I will deal in detail only with the nocturnal animals that I have not described so far.
Moths: A moth is an insect closely related to the butterfly. Both are of the order Lepidoptera. Most species of moth are nocturnal but there are crepuscular and diurnal species as well. Moths can be distinguished from butterflies in a number of ways.
The most obvious difference is in the feelers, or antennae. Most butterflies have thin slender filamentous antennae which are club shaped at the end. Moths, on the other hand, often have comb-like or feathery antennae, or filamentous and unclubbed.
Most moth catepillars spin a cocoon made of silk within which they metamorphose into the pupal stage. Most butterflies on the other hand form an exposed pupa which is also termed a chrysalis.
Nocturnal moths are usually plain brown, grey, white or black and often with obscuring patterns of zigzags or swirls which help camouflage them as they rest during the day. However many day-flying moths are brightly-coloured, particularly if they are toxic.
Moths tend to have a stout and hairy or furry-looking bodies, while butterflies have slender and smoother abdomens. Moths have larger scales on their wings which make them look more dense and fluffy. Butterflies on the other hand possess fine scales.
This difference is possibly due to the need for moths to conserve heat during the cooler nights whereas butterflies are able to absorb solar radiation. Moths usually rest with their wings spread out to their sides. Butterflies frequently fold their wings above their backs when they are perched.
Hawk moths visit night-blooming flowers, which they find first by smell and then by sight. Many night-blooming flowers have a strong, sweet smell and a white or pale green color. Hawk moths have antennae that can pick up flower scent from as much as 300 feet away.
They fly towards the scent, and when they get close to the flowers, they find them by sight in the dim light of the moon and stars. Moths depend on the moon and stars for more than just to see the flowers.
They use this light to asses the direction and position of their flight. This is called celestial navigation. They fly toward moonlight and starlight, keeping it at a certain angle to their bodies.
Animals are active at various times of the 24-hour day and experience different pressures arising from the predators they encounter during those times.
Being active at night exposes insects to predators that rely more on hearing and smell to detect their intended prey, and some of the most studied of these are insectivorous bats, ecologically diverse mammals that inhabit almost every terrestrial habitat on the planet.
Aerially foraging bats or substrate-gleaning bats prey on flying insects by locating them using ultrasonic echolocation calls. Some of these bats hunt by flying close to the ground or vegetation while listening for prey-generated sounds. As explained earlier, insects like moths use these ultrasounds as a way of detecting that the predator is close.
There are a few birds that are active by night. They are the owls, nightjars, the Night Heron (Nycticorax nycticorax) etc.
Owls: Owls are nocturnal birds of prey with similar behaviour and looks but have some anatomical differences. The diurnal raptors are not related at all although sharing behavioural and body similarities due to convergent predatory evolution.
Owls have a dark coloured plumage with different shades of streaks and bars, which help them to stay concealed in the daytime. Owls are characterised by their round heads with flat faces and ear-like feathers.
Their large eyes are set in rigid sockets, which do not allow much movement and thus the owl has to turn its head to be able to look sideways.
A long and flexible neck allows it to turn it 270ø and therefore it is able to look backwards. Barn Owls (Tyto alba) have a heart shaped face with smaller eyes and lack the ear tufts. In owls the females are larger than the males.
Birds like the Barn Owl have also adapted to soft feathers and sound deadening filaments for silent flight. The common adaptation increases the nocturnal birds ability to locate the prey and food in the darkness.
When an owl hunts, from a perch, it listens for sounds that betray a creature’s presence. They may move about from tree to tree to get a better fix on the source of the sound. Once they pinpoint the sound, the owl silently swoops in, spreads its talons wide and pounces on its prey – known as the “perch and pounce” hunting method.
Owls have an incredible sense of hearing, a trait that allows them to hunt at night. Their ears are located on the sides of the head, but are off-set, not symmetrical like human ears. The openings of the ears are slightly tilted in different directions – often the right ear is longer and set higher up on the skull.
Plus, owls have soft feathers that surround the openings, which they can spread to make a funnel for sound to enter the ear.
This enables the owl to use triangulation to pinpoint the source of a sound, when the prey cannot be seen. By tilting or moving their head until the sound is of equal volume in each ear, the owl can pinpoint the direction and distance of the sound.
Night Heron: Night Herons are about 64 cm long. They have a black crown and back with the remainder of the body white or grey, red eyes, and short yellow legs. These are short-necked and stout herons. The breeding habitat is fresh and salt-water wetlands.
These birds stand still at the water’s edge and wait to ambush prey, mainly at night. They eat small fish, crustaceans, frogs, aquatic insects, and small mammals. During the day they rest in trees or bushes.
Nocturnal mammals share many adaptations with other animals like being elusive, a dark body coloring, good vision, acute sense of smell etc.
Mouse Deer: The Mouse Deer or the Chevrotian (Tragulus meeminna) is neither a mouse or a deer. All deer are in the genus Cervidae whereas the mouse deer is in the genus Tragulidae.
The mouse deer has a three-chambered stomach more like cattle, sheep, etc instead of the four chambers found in a true deer. It is found in all parts of the island in small patches of jungle and on the edge of the larger forests, generally close to water. They are nocturnal and rarely seen.
Both the Black-naped Hare (Lepus nigricollis) and mouse deer have been forced to use the nighttime for their activities because of predation by larger mammals.
Flying Squirrels: Flying squirrels live in tall forest trees. In the day they are in the hollows of large trees and emerge only at night. All other squirrels are diurnal. The appellation ‘flying’ is a misnomer because these squirrels cannot actually fly.
They have fairly thick membranes, extending between the front and back legs on both sides, which they use as a parachute to glide down from the tall trees to another tree lower down.
To suddenly encounter a silent flying object, just above your head, in the forest at night is quite disconcerting. Since there is no flapping of wings, the glide is silent.
Civets: The Civet Cat (Viverricula indica mayori) is found in most parts of the country but abound in the tea plantation regions. It is also encountered in urban areas. They are nocturnal and can be seen loping across the roads with their prominent ringed tail.
During the day the civet cat holes up in a small shrub or crevice in a rock. At night it feeds on small mammals, fruits etc. It is also a scavenger in gardens. Civets, like the mongoose, attack snakes.
Slender Loris: Lorises are small bodied mammals. They only come out at night, and move in silence, making them difficult to detect, if one is not specifically looking for them. Finding them, even after looking for them carefully, is difficult.
Sometimes the whistling sound they make gives them away. They specialise in consuming small insects etc. They do not seem to eat any leaves, flowers or fruits. Lizards and Geckos are consumed with obvious relish.
Jackals: The Jackal (Canis aureus) is both diurnal and nocturnal. However it comes out during the day only when and where it feels safe. The Jackal is omnivorous and a scavenger.
As Phillips says ‘few edible things, either live or dead, come amiss to the jackal; he is a scavenger by instinct and a thief by opportunity’. The jackal is found all over the island wherever there is food for it to eat.
Wild boar: The wild Boar is found all over the island and most of us are familiar with it. Wild boar are seen during the day in our protected areas but is nocturnal elsewhere in the island.
In the jungle it serves a role as a garbage cleaner whilst it is a pest when in human habitations in that it destroys cultivations. Wild boar feed early in the day and in the nights. When raiding crops it is active only under the cover of darkness.
Pangolin: The pangolin (Manis crassicaudata) is another nocturnal mammal that is rarely seen. The diet of the pangolin consists almost entirely of burrowing social insects such as ants and termites and their eggs.
Porcupine: Porcupines are rodents. Porcupines are found in all parts of the country. They are nocturnal and are an agricultural pest. They keep digging for yams, which they relish and being omnivorous, looking for all types of food. Porcupines are not seen regularly on moonlight nights.
Leopard and other cats: The four species of wild cats are nocturnal but they are also active by day if they are not frightened by human activity. Cats have an acute sight, hearing and smell.
Most big cats prefer to hunt at night or at dawn and dusk, but their daily activities vary, depending on the weather, and the periods when prey are usually active. The structure of the cats eye shows various adaptations for increased night vision.
Bats: Bats are the only mammals that have wings and can fly. The other mammals like the Flying Squirrel can only glide. Bats belong to the order Chiroptera. The larger bats are called fruit bats and the bats with smaller bodies are insect bats.
The insectivorous bats eat insects and small animals. The fruit bats eat fruit and plant. Fruit bats are species that roost in cities, towns and villages. Many species of bats eat fruit and suck the nectar from certain flowers. Bats find their way and insect prey by echolocation.
Bandicoots: They dig, with strong, clawed feet, to excavate long, complex burrows. They also dig underground dens that are quite deep and long. The size of a Bandicoot ranges from 11-32 inches long with an 8-inch tail. They have powerful clawed hind legs.
The bandicoot is an omnivore, eating both plants and animals. It eats insects, like termites, lizards, mice worms, snails fruit seeds and some plants. Bandicoots need very little water. They get the water they need from their food. They forage mostly at dusk and dawn but are also active throughout the night.
Snakes: A number of snakes are nocturnal. The Russell’s Viper (Vipera russelli), all the other pit vipers, the Kraits and the Europeltids are nocturnal. Their prey, in the case of the vipers and the kraits are rats and mice, which are active at night. The Europeltids feed on earthworms, which too are more active by night. There is also a lot of snake activity at dusk.
Frogs: Frogs are sticky-tongued amphibians that are generally nocturnal and are particularly active on moist, warm nights. Frog fauna occupies a range of habitats from deserts, to alpine areas, to tropical rainforests. But these croaking creatures live mainly in moist, coastal areas and are generally found in burrows, streams, rotting vegetation, and trees.