Colour Vision in Animals

  

It will come as no surprise that an animal's view of the world is different to our own, but what isn't so clear is exactly what they see. A recent exhibition at the Royal Society showed images that illustrates what our pets and other animals see when they look at each other and when they look at us. 

The fascinating insight shows the latest research into the colour vision of animals, many of which can see ultraviolet, or colours that we can't see, making their world view completely different to ours. 

Birds, for example, can see ultraviolet so a peacock looking at a potential mate would not see the beautiful rainbow of greens and blues that we behold, but a plainer yet more brightly coloured display of plumage. 

Birds have four types of cone cells in their eyes called photoreceptors (humans have three), and can see many more colours than we can. They can also see ultraviolet, which means that the 'eye' markings in a peacock's tail features looks sharper.

Purple haze: Using the ultraviolet recepters in its eyes the peacock would see a mating feather display more like the example in the above photograph.

Understanding how animals see the world could be key to understanding their behaviour. 

Animal colouration provides some of the most striking examples of evolution by natural and sexual selection. But animal colours did not evolve for our benefit; the impressive array of animal colours that we see (and can’t see) in the natural world allows animals to communicate with each other, to attract mates and to avoid predators. 

Dr Tom Pike, Senior Lecturer from Lincoln University’s School of Life Sciences, said: ‘We rely overwhelmingly on colour vision in our everyday lives, and tend to assume that what we see represents the limits of the visual world. 

'However, colour vision in animals, and their resultant perception of the visual world, often differs considerably from our own. The eyes of cuttlefish evolved separately from humans and are completely different from ours - they can't see colours, but can discern the polarisation of light, which lets them pick out contrasts better.  The colourful spots are designed to fend off predators - what the butterflies themselves see is quite different ‘Many, for example, can see ultraviolet light, some can see polarised light, and a good number can see many more colours than we can,' says Pike. 

'Having said that, certain animals see far fewer colours than us – something that anyone who is colour blind can sympathise with.' 

‘Because animal colours evolved for the benefit of animal - and not human - eyes, understanding the visual world from an animal’s point of view can explain why some animals are bright while others are dull. Some are highly patterned and others plain. This allows us not only to shed exciting new light on the animal colours we can see, but also to understand the importance of colours that we can’t.’ 

Red Wattled Lapwing

The Red-Wattled Lapwing is a bird commonly found around Tiruvannamalai. Probably the most uncommon and distinctive thing about it, is its amusing and easy recognisable call, which sounds like a scolding, did-he-do-it; often uttered throughout the night.

In the below photograph you can easily see another curious thing about this bird which is its white V-shape wingbar prominent only while in flight.

This bird which is a large wader is often found at the banks of reservoirs and water catchment areas, and is in great numbers around the Samudram Lake area here at Arunachala.

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Emerald Dove

STATE BIRD OF TAMIL NADU

Emerald Dove
Chalcophaps Indica
Green-winged Pigeon, Bronze-winged Dove

Main features: Medium (25cm), metallic green mantle, wings; head, underparts rich pink.

Male: Forehead, eyebrow, shoulder white; crown and nape greyish; bill red; feet crimson.

Female: Same as male but duller; forehead, eyebrow grey; crown, nape brown; white shoulder patch absent or indistinct.

Call: Described as a low cu-oo or tik-oo, repeated monotonously; soft deep tu-hoop.

In flight: Green wings and mantle contrasts strongly with reddish underparts; two distinct black and white bars on lower back.

World distribution: India across to China and the Philippines, Southeast Asia to eastern Australia.

Classification: Family Columbidae. World 310 species.

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The beautiful Emerald Dove is the official State Bird of Tamil Nadu. It is quite common but as its very shy and secretive, is rarely seen.

Emerald Doves feed on fallen fruit and seeds (including grass seeds, figs and bamboo). They also eat tidbits like termites. Unlike some fruit-eating birds, however, Emerald Doves destroy the seeds that they eat and don't appear to play a major role in plant dispersal.

This bird usually forages on the ground, mostly under tree cover. Sometimes, they cautiously venture out onto open grassland to forage, but will scuttle back into the undergrowth at the slightest hint of danger. They fly low and quickly, zipping in and out among trees and undergrowth. They also visit mineral seeps in the forest.

Unlike other doves, Emerald Doves forage alone, or in pairs. When several are drawn to a food-rich areas, each maintains a small feeding territory.

Pigeons and doves do not have well-developed oil glands, which in other birds are used to waterproof their feathers. Instead, pigeons and doves have special plumes scattered throughout their body which disintegrate to produce a powder which cleans and lubricates the feathers.

Breeding: Emerald Doves appear to have a limited breeding season from April to September. Like other pigeons, the nest is a flimsy platform, often simply leaf litter that gathers naturally in a palm frond, stabilised by a few twigs. A nest may comprise a large leaf lying on a tangle of creepers. They only nest in the forest or closed-canopy woodland, 1-5m above the ground. Males perform a bobbing dance during courtship.

1-2 white eggs are laid, but usually only 1 chick survives. Only the female incubates. The eggs hatch in about 2 weeks and the young fledges in 12-13 days.

Migration: Although Emerald Doves may travel long distances to forage for food and are somewhat nomadic (following fruiting seasons), they are not migratory. They are found in lowland and montane forests, secondary growths, mangroves; also in cultivated lands.

Status and threats: Although Emerald Doves have adapted to feed in parks and agricultural land, they still require natural wooded areas to nest in. Because of their beautiful colouration and soothing call, Emerald Doves are often trapped and sold as cage birds.

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Pigeon's Milk
The most fascinating feature of pigeons and doves is their ability to produce crop milk. During breeding season, special glands in the crops of both males and females enlarge and secrete a thick milky substance.

The chicks drink this milk by poking their bills into the parent's throat. Thus, pigeons and doves can feed their young without having to incessantly hunt or forage for food. Instead of laying many eggs, they lay one or at most two eggs.