Most mammals are a pretty boring when it comes to their colours but the giant panda is another story. Tim Caro, Nick Scott-Samuel and Ossi Nokelainen explain why this may be
一世n contrast to the many flamboyant species of birds, most of the 5,000 species of 哺乳动物 are drab browns or greys. But there are a small number of well known and intriguing exceptions – most notably zebras, skunks and orcas.
Perhaps the most famous of all, 然而, 是 giant panda秒. We already had a preliminary idea why they had their markings but wanted to confirm the reason for its mysterious pattern.
Viewed up close in a zoo, the giant panda is a striking, conspicuous mix of a white bear with black forelegs, shoulders and hind legs and an extraordinary face with black fur around the eyes and ears. By comparing these different parts of the body with the coloration of other carnivores (contrary to popular belief pandas are officially classified as carnivores) and also with bears, we already knew that carnivores with white backs are found in snowy environments and those with dark legs and shoulders are found in shady habitats. This suggested that the fur was an adaptation to be camouflaged in different environments.
Nowadays, giant pandas are confined to isolated forests in western China, where there are relatively few predators. But we needed to confirm that the camouflage was effective against the giant pandas’ former predators: tigers, leopards, Asiatic black bears and dholes (a wild dog) from the days when they ranged right across China into Vietnam.
The breakthrough came when we linked up with colleagues in the Chinese Academy of Sciences, Yong-gang Nei and Fu Wen Wei. They work with giant pandas in the field and had rare photographs of wild giant pandas. Crucially, the photos in their natural habitat were taken at a distance.
We used state-of-the art image analysis to demonstrate that the unique colourings do indeed work to disguise the giant panda.
By matching reflectance (the amount of light reflected) from the giant panda’s fur with natural objects in the background, we discovered that their black fur patches blend in with dark shades and with tree trunks, whereas their white patches match bright foliage and snow when present. 还, infrequent, muddy-coloured pale brown fur matches the colour of the ground. This provides an intermediate colour which bridges the gap between the very dark and very light visual elements in the natural habitat.
These results are consistent whether viewed by humans, feline or canine vision models. Domestic dog and cat visual systems are well known and are good surrogates for the visual systems of the giant panda’s natural predators such as tigers and wild dogs.
下一个, we examined a second form of camouflage – something termed disruptive colouration – in which highly visible patches on an animal break up its outline by blending in with patches in the background.
We found that giant pandas show this form of defensive coloration, especially at longer viewing distances of at least 60 码. At these distances, the outline of the giant panda becomes difficult to recognise as the black fur patches blend into the background of dark rocks and tree trunks.
最后, we used a novel colour-mapping technique to compare how well various animals including the giant panda merge into their background. This comparative analysis confirmed that the background resemblance of the giant panda fell solidly within the group of other species that are traditionally considered as very well camouflaged, right next to shore crabs and jerboas (desert rodents).
所以, although giant pandas in zoos or other captive settings are highly conspicuous to us, it is because we see them up close and surrounded by artificial backgrounds but when in the wild and at a distance, our research shows that they are beautifully camouflaged, using two different mechanisms to avoid detection.
Giant pandas are a much-loved species and doing better now in the wild thanks to extraordinary conservation efforts. So the future of this species is cautiously optimistic.
Tim Caro is a professor at the School of Biological Sciences, University of Bristol. Nick Scott-Samuel is a professor of experimental psychology at University of Bristol. Ossi Nokelainen is a postdoctoral researcher at the University of Jyvaskyla, 芬兰. This article first appeared on 谈话.