Why are so Many Mammals Black and White
By Steve Harris – Why do so many mammals – from pandas and zebras to badgers and porcupines – have black-and-white coloration? It seems counterintuitive for both predators and prey.
First we need to ask two more questions: why are animals colored at all? And do they see colours?
Coloration can be important for appearance (signaling to, or concealment from, others) or physiology – for example, helping to control body temperature.
But animals see colours very differently to us. Two basic types of light receptors are found in the vertebrate eye: rods, which work best in low light, but do not give good definition; and cones, sensitive to colour and very good for detail. Only some primates and marsupials see an extended range of colours. Humans have red, green and blue cones, whereas most other mammals have only one or two types, limiting colour vision. About two-thirds of mammals are nocturnal; some, such as opossums, have only rods, providing excellent night vision but no colour vision.
Many birds, meanwhile, have ultraviolet vision – so though birdwatchers may struggle to tell male blue tits from females, parts of their plumage look very different under ultraviolet light.
These examples highlight why understanding coloration can be tricky: particular hues or patterns may be conspicuous to us but not, for example, to other mammals, which possess only two types of cone. Conversely, coloration that seems cryptic to us may be conspicuous to avian predators sensitive to ultraviolet light.
The role coloration and pattering plays in concealment is also not dear. Mammals are active foragers, so sporting colours that are ostensibly cryptic may not be useful, especially for diurnal herbivorous species – movement would soon give them away. So coloration may be less important in concealment than patterning – a general brindled or agouti coloration may be more effective than hues that actually resemble background habitat.
Young herbivores that lie hidden for the first few weeks of life often have spotted coats: roe kids, for example, are hard to pick out among vegetation in dappled woodland sunlight. Cryptic patterning is also common in carnivores: spotted species such as ocelots and margays tend to be arboreal, while striped species such as tigers hunt in grassland.
But coloration or patterning that seems cryptic may serve other functions. Many pale species live in deserts, dark ones in dense or tropical forests. But is this camouflage? Pale fur reflects light, an aid in hot environments, while dark fur in tropical environments may enhance water evaporation and help protect an animal against ultraviolet radiation.
The fact that so many mammals sport sharply contrasting colours and, particularly, defined patterns indicates functions other than camouflage. Cetaceans are essentially colour-blind, so the conspicuous black-and-white patches on many dolphins may help signal to other pod members.
Contrasting colours may also serve to warn predators of defensive tactics. An example is the noxious emissions from the anal glands of small black-and-white predators such as the skunk. Quills and spines are often black and white, as in porcupines (though, interestingly, not in echidnas); no one would want to argue with a honey badger, and black-and-white face masks are common in many other species with powerful bites.
When a muntjac raises its tail, the white underside tells a predator that it has been spotted, so it would be a waste of time continuing to stalk it; similarly, white or black tail tips on small predators such as stoats may distract swooping birds of prey, which focus their attacks on the tail rather than the stoat”s body.
And there are still other possible functions. Many nocturnal species have black face masks, probably to reduce glare. Similarly, the panda’s black eye rings may help to reduce glare from snow.
So, though we now know in which habitat and in which type of species particular patterns are most likely to occur, we are yet to fully understand the benefits.