Tigers generally appear orange to humans, but to mammals like deer and boars, that constitute the tiger’s common prey, they appear green, according to a new study.
The tiger, the largest feline species and one of the most fearsome predators in the world, is known for its very recognizable striped orange (and black) fur. But who knew this coloration could be useful for camouflage to stalk its hoofed prey in a mostly green environment?
Of course, when the surroundings are made up of dry undergrowth, tigers’ coloration allows them to be hardly visible even to keen human eyes. But, according to a new study by researchers from the University of Bristol, their bright orange fur makes them almost invisible even in a predominantly green forest – at least for most mammals other than humans.
Deer, boars, and other ungulates that constitute tigers’ favorite prey, are, like most mammals, dichromats, which means they only have two types of functioning color receptors in their eyes. For this reason, they are actually red-green blind, which makes it almost impossible for them to distinguish between green tones and red-orange tones. So to them, an orange-colored tiger will match the surrounding forest pretty well, with all the unfortunate consequences that can bring.
The human eye, on the other hand, has three color receptors which makes us trichromats – we can reliably differentiate between orange and green, so for us tigers appear orange.
The research team used a machine learning algorithm to simulate what the world looks like to dichromats, allowing the scientists to figure out the optimal colors for camouflage of different animals. They concluded that as long as a prey animal cannot distinguish between orange and green, there’s no need for their predator to develop a green-colored fur to hide in the forest.
“Based on our results and given that most non-human mammals have dichromatic color vision that is unable to reliably differentiate orange and green, it seems that there is little benefit to actually become green if the receiver is dichromat,” the researchers explained. “Hence predators (eg tigers), whose main prey is other mammals (eg deer), experience little evolutionary pressure to evolve green coloration from a trichromatic perspective.”
But then why hasn’t evolution pushed prey mammals towards becoming trichromats, like us and other apes? The researchers aren’t sure but are keen to find out. Anyway, until that evolutionary jump happens, tigers have no reason to change their distinctive orange color.