DFW Urban Wildlife

North Texas Mammals come in a variety of different colors. For some species their coloration is meant as camouflage, for others it is intended to be a warning, and for others still, the reasons behind their hues are harder to discern. Whatever the case, it can be certain that a mammal’s coloration is intended to help the animal to survive in a complicated environment full of predators, wary prey, and other challenges.

In this article we are going to take a closer look color and camouflage strategies in general, and how they apply to various mammal species living in North Texas. We will explore the ways in which behaviors and active hours influence the effectiveness of different colors and patterns, and we will examine the physiological aspects of coloration in our area mammals.

North Texas Mammals

Let’s begin by first compiling a list of mammal species that can be expected in the North Texas area. The ledger is surprisingly short, and consists largely of varying types of bats and rodents, with a few other more commonly known species thrown in for good measure…

Rats Mice Voles	Squirrels Gophers	Rabbits Hares	Carnivores
Black Rat	Eastern Fox Squirrel	Black-tailed Jackrabbit	Bobcat
Cotton Deermouse	Eastern Gray Squirrel	Eastern Cottontail	Coyote
Eastern Harvest Mouse	Southern Flying Squirrel	Swamp Rabbit	Gray Fox
Eastern Woodrat	Thirteen-lined Ground Squirrel	Ungulates	Red Fox
Fulvous Harvest Mouse	Black-tailed Prairie Dog	White-tailed Deer	Raccoon
Hispid Cotton Rat	Baird’s Pocket Gopher	Wild Pig	Ringtail
Hispid Pocket Mouse	Plains Pocket Gopher	Bats	Skunks Weasels Otters Badgers
House Mouse	Large Rodents	American Peri-myotis Bat	Badger
Lacey’s White-ankled Deermouse	Beaver	Big Brown Bat	Long-tailed Weasel
Merriam’s Pocket Mouse	Common Muskrat	Brazilian Free-tailed Bat	Mink
North American Deermouse	Nutria	Cave Myotis Bat	River Otter
Northern Pygmy Mouse	Porcupine	Eastern Red Bat	Eastern Spotted Skunk
Norway Rat	Shrews Moles	Evening Bat	Hog-nosed Skunk
Plains Harvest Mouse	Least Shrew	Hoary Bat	Striped Skunk
Southern Plains Woodrat	Southern Short-tailed Shrew	Silver-haired Bat	Other
Texas Deermouse	Eastern Mole	Seminole Bat	Nine-banded Armadillo
Texas Marsh Rice Rat		Southeastern Myotis Bat	Opossum
White-footed Deermouse
Woodland Vole

This list, of course, is just a baseline. I compiled it mostly for fun and for your information. We’re not going to discuss all of these mammals, but instead we are going to address a short list of some of our more commonly encountered species. Fortunately, the general concepts should apply to many, if not most, of the species on the long list as well.

Fur Color and Pigmentation

Mammals are typically fur covered, so any discussion about coloration has to begin with the nature of their hair. Most–but not all–mammals in the above list make use of a hair coloring known as agouti. Agouti occurs when each shaft of hair has two or more bands of pigmentation.

Pigmentation in mammalian hair is due to a group of proteins called melanins. Dark bands on the hair shaft consist primarily of eumelanin, and mute bands are made of the paler pigment, pheomelanin. Lack of pigment presents as white fur, and black fur results from a dominance of eumelanin.

The overall appearance of an agouti coat will be a brown, red, gray, or muted yellow. Spots and stripes are also possible. In general, there are three factors that determine the overall appearance of an agouti pelage. The color and order of the individual bands on a shaft of hair is important. The relative size of each band of color contributes to its composite appearance. And the distribution over the animal’s body of hairs consisting of different band combinations creates patterns and disruptions.

The most prominent band of color on each hair shaft has the most influence on the animals general coloration, but the other bands work together to give the pelage an impression of texture. Further, an agouti coat can present differing appearances depending upon the animals relationship to a viewer.

Color and Camouflage Strategies

My investigation on the internet led me to a handful of articles describing camouflage theory. In these articles I gleaned the names and description of several different techniques and strategies for concealment with camouflage. I found a number of these to be broadly applicable to North Texas mammals, and collected those into the list below. There is one other–non-camouflage coloration–called Aposematism that is worth mentioning as well. I added it to the bottom of the list.

• Background Matching – When coloration and/or patterns are designed to match the background typical of the animal’s habitat.
• Disruptive Coloration – Randomized high contrast marking intended to break up an animal’s outline, thus helping disguise its silhouette to aid blending with the background
• Distraction – High contrast marking that are intended to attract a predator’s attention in an effort to confuse
• Changeable Coloration – With North Texas mammals this strategy involves molting fur of one color and/or length with a new coat of fur more appropriate for the new season. Usually associated with season change.
• Countershading – Intended to flatten an animal’s appearance by counteracting dark shadows with lighter colored fur on the animal’s underside. Countershading is very common across the entire animal kingdom.
• Motion Dazzle – Often seen in herd animals. Intended to cause confusion and make targeting a single animal more difficult. For instance, Zebra stripes may give impression of inverted motion, similar to the appearance of counter-rotation of car and wagon wheels in motion pictures.
• Aposematism – Unusual coloration meant to advertise that an organism maybe dangerous to attack or eat. Not camouflage.

Behaviors of Activity

Let’s next take a look at the time-of-day habits that are common among North Texas mammals, so that we can discuss their influence on coloration. Many local species can be active at any time of the day–if the need arises, but science recognizes three basic behavior pattern with regards to the day-night cycle: Diurnal, Nocturnal, and Crepuscular. Diurnal animals are typically active during the day and inactive at night. Nocturnal reverses that pattern, with the organism being most active during the darkness of night, an at rest during daylight hours. And finally, Crepuscular animals are most active in the twilight of dawn and dusk.

It’s not hard to imagine how–over the course of a day–differing light conditions can have an impact on the effectiveness of some colorations and patterns as camouflage. During the day there is usually an abundance of light; colors should appear bright and vivid except in places where they are washed out by overexposure or muted by shadow. On gray overcast days colors can also appear dull and muted.

The low light at dusk and dawn can produce similar effects to those of an overcast day. But when the sun is located very near the horizon, its light has a much longer journey through the atmosphere than when the sun is overhead. As a consequence, particulate matter in the atmosphere filters out a sizeable part of the spectrum, allowing only longer wavelength light from the red end of the spectrum through. Without much green light, the color of vegetation can appear muted and even brown at these times of day.

On moonless nights it can be very dark, but a near-full moon can be bright enough to cast shadows. In urban areas light pollution can be a major consideration. When light pollution is reflected off of a low overcast, visibility can be even better than when there is a full moon. However, even on the brightest nights, colors remain muted and are very difficult to discern in these kind of lighting conditions.

Select North Texas Mammals

Eastern Cottontail – Coloration Strategies: Background Matching, Disruptive Coloration, Countershading

Eastern Cottontails are primarily nocturnal and crepuscular. Their brown and gray coloration is especially effective in disguising the animal in low light–particularly in the reddish light of dawn and dusk. At these times, green light is limited, muting the colors of vegetation. As a consequence, the brown and gray of the cottontail’s coat tends to background match much better.

The Cottontail’s namesake white tail works as a flag for pursuing predators to follow in order to encourage them to anticipant the rabbits next move. At a critical juncture during a chase, a lucky rabbit will tuck its tail and abruptly change direction, momentarily confusing the predator and buying the bunny some extra time to escape.

Gray Fox – Coloration Strategies: Background Matching, Disruptive Coloration, Countershading

The Gray Fox has a gray agouti coat with red and white countershading, and red and white disruptive coloration. It is thought that this coloration pattern supports the Gray Foxes semi-arboreal lifestyle. The coat of the Gray Foxes is also effective when the animal is on the ground. Gray foxes tend to be nocturnal and crepuscular in their behavior, and the textured appearance of their agouti pelage provides adequate camouflage under the lighting conditions typical of these time periods.

Fox Squirrel – Coloration Strategies: Background Matching, Disruptive Coloration, Countershading

The Fox Squirrel gets its name from it similarity to the Gray Fox in general coloration, which may be motivated by many of the same factors that influence the Gray Fox’s appearance. Fox Squirrels are diurnal in their behavior. They are largely arboreal, but they also spend significant time on the ground. Their camouflage can be quite effective when they are laying flat against a tree branch.

Raccoon – Coloration Strategies: Background Matching, Disruptive Coloration, Countershading, Motion Dazzle

Raccoons are typically nocturnal in their activities. Their agouti coats in gray or cinnamon are effective camouflage along the intersection of mud and vegetation that often borders the bodies of water where Raccoon prefer to forage. The Raccoon’s striped tail is more difficult to explain. Some suggest that the striped tail can be used to distract predators toward the least vulnerable part of the Raccoon. Others see the varying bands of dark and light stripes as helping the Raccoon to match the pattern formed by branches and sky when the Raccoon is perched in a tree.

Armadillo – Coloration Strategies: Background Matching, Disruptive Coloration

The nocturnal Nine-banded Armadillo has very little hair on its upper surfaces. Its overall gray coloration is created by the Armadillo’s armored shell made up of keratinized epidermal scales. This armor provides effective protection for adult Armadillos, and as a consequence these animal make very little effort to avoid being seen. Nonetheless, the mottled appearance of the Armadillo’s armor provides effective camouflage against areas of forest floor detritus in which the Armadillos spends much time rooting.

Striped Skunk – Coloration Strategies: Aposematism

Striped Skunks are active from dusk to dawn; that makes them nocturnal and crepuscular. Their starkly contrasting pelage of black white white stripes has little camouflage value. Instead this distinctive coloration is meant to draw attention to the animal in a aposematic way, warning of the skunk’s powerful defense. Striped Skunks want to be seen!

Bobcat – Coloration Strategies: Background Matching, Disruptive Coloration, Countershading

The crepuscular Bobcat is most active at dawn and dusk. Their tawny agouti coat can be highly variable between different individuals. Some Bobcats have uniformly tawny coats with no well defined spots, while other Bobcats will sport vividly spotted pelages. Regardless of the number of spots present, the Bobcat’s coloration is highly effective camouflage for the woodland and wetland area they prefer to haunt. The coat’s ability to help the Bobcat blend with a background of leaf litter is especially remarkable.

Coyote – Coloration Strategies: Background Matching, Disruptive Coloration, Countershading

Coyotes can be active at any time of the day. Their pelage has a very subtle coloration that includes a gray or tan agouti with black, red, and white disruptive colorations, and white counter shading. There are a number of habitats where the Coyote’s camouflage works well, but it is particularly effective in areas of tall, dry grass. The Coyote’s camouflage may aid in the predator’s attempts to approach potential prey animals, but it is also valuable in efforts to hide the Coyote from larger and aggressive competitors–like the Gray Wolf.

White-tailed Deer – Coloration Strategies: Background Matching, Countershading, Changeable Coloration

White-tailed Deer are crepuscular in their behaviors. Their pelage is general very uniform in color. Their fur tend to be reddish in summer and more gray during the winter months. It is thought that the deer’s red coloration background matches much better with the lush green vegetation of summer, while the gray coat blends better against the barren landscape of winter. Some speculate that the darker color of the winter coat may absorb more heat from sunlight, thus helping to keep the deer warm when the weather turns cold.

As their name implies, the underside of these deer’s tails are starkly white. When alarmed, White-tailed Deer will flash their tails as an alert to any other deer that may be in the vicinity.

Fawns are born with white spots that are used to mimic dappled sunlight such as can be found streaming through tree leaves in the forest. Because fawn must be left alone for long stretches of time, laying still and trusting in the effectiveness of their camouflage is key to their survival strategy.

Virginia Opossum – Coloration Strategies: Background Matching, Disruptive Coloration, Countershading

The nocturnal Virginia Opossum is a highly successful animal. They are very common all throughout North Texas in both rural and urban areas. The secret of their success, however, is hard to define. These animals are not particularly fast or agile. They are not commonly though of as being cunning or aggressive. The Virginia Opossum’s fur color runs the gamut from a dirty shade of white to gray to black. Often a mix of these colors located on different areas of the animal’s body will contribute to disruptive coloration and countershading, giving the opossum some level of camouflage. Opossums are accomplished climbers, and their camouflage strategy may be most effective high in the branches of trees. At the end of the day, the Virginia Opossum’s habit of playing dead when under stress may be its most effective defense against predation.

Wild Pig – Coloration Strategies: Background Matching, Disruptive Coloration

Wild Pigs are nocturnal and crepuscular. Because these animals are feral domestics, many come with domestic coloration and patterns. Wild Pig coats may be black and white piebald, Red and white piebald, solid red, solid brown, or solid black. Most Wild Pigs are dark in color, and that may help them stay unseen at night. But Wild Pigs are big, powerful animals with few nature predator once they reach adult size. The need for camouflage may not be of great importance to these animals.

Beaver – Coloration Strategies: Background Matching, Countershading

The nocturnal and largely aquatic North American Beaver benefits from having a dark coat. Their dark brown pelage makes Beavers less noticeable at night when they are most active. When on the land in search of food or trees to fell, Beavers are easily disguised by the dark and shadows of night. In a watery habitat, they are well hidden when viewed from above, and even more so when the water is murky.

River Otter – Coloration Strategies: Background Matching, Countershading

North American River Otters are nocturnal and crepuscular. Much in the saw way as with the Beaver, an otter’s pelage provides background matching in the low visibility waterways these animals frequent. From above looking down, the Otter’s dark fur will help conceal it in murky water, while its lighter ventral coat will be more difficult to notice from below looking up.

Why No Green?

For mammals that are inclined to spend time in lush vegetation, the expectation might be that green coloration would be the go to strategy for camouflage. Many animals do use green in this way to great effect. There are a number of examples of reptiles, amphibian, insects, spiders, other invertebrates, fish, and birds successfully using the color green in their efforts to remain unseen.

But there are no green mammals. Why is this?

Its hard to imagine an adaptive reason for mammals not to have developed green coloration. Mammals are certainly capable of producing the color green. Some mammals–people included–can have green eyes, for instance. Mammals are also capable of produce vivid reds and blues skin coloration, but these are generally used for signaling not camouflage. And while these kinds of bright colors are present in mammalian skin, they do not occur in mammalian hair–not even when it might be useful for warning signaling, such as with a skunk or a porcupine.

Searching the internet, I found a number of possible explanations for why mammals do not produce green fur or skin. Since most mammal are covered in fur, the color of their skin is only important–in this context–where it is exposed. In most cases where exposed skin is pigmented in an unusual way (such as with red and blue), the displayed colors are meant for signaling, not camouflage. And since green is a color most appropriate for use as camouflage, it would have little value as a signal.

The most compelling reason for lack of green fur that I found is the idea that mammalian hair is just not capable of making the pigments that are required to appear green. But, more than that, the structure of hair also gets in the way of the color green. In nature the color green is typically produces as the result of the mixing of yellow and blue colors. There IS a pigment that appears as yellow, but blues are created differently. Instead of a blue pigment, most animals use a refraction effect called Tyndall Blue to produce shades of this color. The refraction technique for creating blue requires that refractive particles be distributed through a transparent medium in a uniform way. Eyes, skin, scales, and feathers have the needed uniform texture, but hair does not.

Fortunately, color may not be the most important elements of camouflage. Full range color vision is not common in the wild kingdom. Breaking up the outline of an animal against its background is at least as important as color matching, and maybe even more so.

Before I close, let me touch on one more point. There is always an exception to the rule. While no North Texas mammal can claim to have green fur, there are a couple of mammals species that have found a clever way around the limitations of hair to produce the color green. Some species of tree sloth that live in the rainforest of South America that have specially adapted hairs that contain grooves or channels. These groves facilitate the growth of algae on the hair follicle which give the animal a subtle overall green coloration.