How come there are no blue or green mammals?

Have you ever thought about this? Think about it for a minute. If you were to list 10 mammals off the top of your head – perhaps animals like your dog, cat, an elephant, rat, zebra, skunk, raccoon, opossum, bobcat, or even a coyote – you would quickly realize that the colors of these mammals lack blue and green hues. There are a couple of reasons as to why this is, and why other animals like insects, birds, amphibians, and reptiles exhibit these colors quite often.

The reason has to do with chemistry primarily. First off, let’s talk about what produces colors in living things. Pigments are chemical compounds that are responsible for producing color in the biological world. When pigments absorb light, they reflect back certain wavelengths, producing colors our eyes can perceive. Plants, for example, have many different kinds of pigments with all kinds of peculiar names, such as carotenoids, flavonoids, and anthocyanins. Thousands of these chemicals have been identified by scientists and this is the reason why plants can produce a vast array of colors – from the dominant green leaves, to different shades of bark on trees, to the orange color of a carrot, the colorful fruits and flowers there are and the beautiful foliage colors we see during autumn in temperate latitudes.

When it comes to animals however, things are a bit different. The vast majority of animals simply do not have the variety of pigments that plants do. Specifically, they are not able to genetically produce blue and green pigments. Then how come we still see animals that are those colors? There’s blue butterflies, green frogs, and peacocks are well-known for their blue feathers! Most of these animals produce this color through a phenomenon known as structural coloration, which is the optical illusion of a color, essentially. Small structures of the skin scatter and reflect back light in a way so that only the blue wavelengths reach our eyes. But, in reality, there is no blue pigment doing that. When it comes to green, usually there is a yellow pigment involved with a structural blue coloration.

For instance, when a rough green snake (Opheodrys aestivus), a common River Legacy snake, dies, it turns blue because the yellow pigment is no longer being produced but the structural color is still there. Another way animals are able to produce vibrant colors is by obtaining pigments from their environment, typically their diet. This is how flamingos develop their typical pink to red hue, by eating foods like algae, shrimp, and crabs that have these pigments in them. A similar phenomenon occurs with the northern cardinal (Cardinalis cardinalis), another River Legacy common sight.

Now, let’s go back to mammals. Mammals have not been able to evolve or have lost the ability to implement pigments obtained through their diet to the same extent as other animals have. It happens but not to the same degree. This is why eating something like beets can turn the toilet a certain color when we go to the bathroom but it does not turn our skin purple. When it comes to naturally-produced pigments, mammals really only produce one kind – melanin. Melanin is an important pigment that provides protection against the sun’s damaging UV rays but it also is responsible for the majority of colors in mammalian skin. It comes in two kinds – eumelanin (responsible for black and brown colors) and pheomelanin (responsible for yellow or reddish to brown colors). Very few mammals, like mandrills (a type of African monkey), are able to produce small amounts of blue color through structural coloration.

But, how come no other mammals can? Scientists are not really sure but it may have had to do with the evolutionary history of mammals. Early mammals survived during the Mesozoic era, the golden age of the dinosaurs, by basically not being around them too much in order to avoid becoming food or by not trying to compete with them for the same resources. It is believed that most dinosaurs were active during the day so it is most likely that mammals had to turn to a largely nocturnal lifestyle. This meant that mammals did not have the need to develop adaptations that were not necessary in the night, such as the ability to see a wide range of vibrant colors. If there was no selective pressure (i.e. need) for either evolving structural coloration, pigment formation, or the ability to obtain pigments through diet, then the genes that allowed for those traits disappeared from the mammalian gene pool. The majority of animals today, with the exception of most mammals, have stellar color vision. On the other hand, as a result of their evolutionary history, mammals tend to be color-blind when it comes to blue and green colors. The big exception to this are primates – the group to which humans and mandrills belong. Therefore, it is hypothesized that as a result of all of this, the vast majority of mammals lack green or blue colors on their skin or fur.

What an incredible and fascinating subject to be sure. Next time you take a hike in the River Legacy trails and you come across a mammal – whether it be a squirrel, bobcat, or rabbit – you will know why those creatures are not flashing blue and green at you!

Recent Bobcat Sightings

Bobcats (Lynx rufus) are well-known inhabitants of our woods! These cats are usually very secretive but, every once in a while, they are spotted walking openly on our paved trails where people can see them. Unlike most mammals, bobcats are still active despite the increasingly colder days. During fall and winter, they become more diurnal as their prey (rabbits and rodents, mainly) is more active at daylight during those seasons. So, it is possible that more bobcats are going to be seen in the next coming weeks and months. Bobcats, in general, are not aggressive species. It is incredibly rare for bobcats to present danger to people. Nevertheless, here are some things you should know if you happen to encounter a bobcat:

  • Stay within a reasonable distance of the bobcat. If you start getting too close to it, it might think you present a threat. Naturally, it would want to defend itself.
  • If the bobcat starts to walk toward you, which is incredibly rare, slowly start backing away. It is important that you do not run as this might scare the bobcat.
  • Do not touch or attempt to feed the bobcat. Bobcats are wild animals and you always want to minimize opportunities for them to bite. As it is the case with most wild mammals, wild bobcats may be rabid at times. Feeding any wild animal can cause harm to the animal, and there are plenty of food resources in River Legacy Park.
  • If a bobcat decides to walk by you, as long as you do not try to kick it or make sudden movements, the bobcat will just continue on its way.
  • Always have your pets on a controlled leash. The last thing you want is any altercation between a wild bobcat and your dog.
  • Be sure to take a picture and/or video of your bobcat encounter from a safe distance!

Seeing bobcats is a neat experience and if you find yourself in that situation and, as long as you follow these precautions, you will be able to enjoy being in the presence of these wonderful cats!

 

Bobcat (Lynx rufus) seen near the entrance of River Legacy Living Science Center last Saturday, November 10th, 2018!