Mimicry and Protective Coloration in the Road Fauna
In pursuit of species survival, natural selection has produced many animals that resemble inanimate parts of their habitat. There are caterpillars that, at rest, look exactly like dead twigs, tigers whose stripes disappear in the sun-shadowed pattern of bamboo stalks, and insects that look like leaves, thorns, or flowers. We may question whether such mimicry exists among the animals on the road. For most of the flattened fauna, the analysis of mimicry is difficult at best, since neither the mimic nor the object of mimicry will blow its cover by moving. Whether the flattened sod clump mimics the flattened porcupine or vice versa is a moot point for the student of road animals, interesting thought it may be for the evolutionary biology (see Yoram Yom-Tov, “The Evolution of Two-dimensional Vertebrates”). The issue for the road naturalist is what non-animal objects on the road look like animals, and how we can tell them from one another.
The most extensive professional treatment of mimicry on the road to date appeared in the October 3, 1983 New Yorker. However, the author treated only the limited set of mimics represented by pieces of rubber tires that are so common along major highways. For those particular residents of the road he coined the word “recaptoids,” and included among the animals only the “curving reptile,” the “modified tarantula,” and a “spectacular spiny crustacean.” A spiny crustacean seems unlikely to appear on most roads, although I do have in my file of flat creatures a fine, two-dimensional sea star found on the Oregon Coast Highway. The recaptoid mimics are of limited interest in this guide. Only the curving reptile is likely to be among the common road fauna, and a genuinely flattened recaptoid is extremely rare. Most curl significantly above the road surface and are immediately distinguishable from any properly flattened animal, none of which retains any residual capacity to rise from the road. Although it is true that the wing of an occasional bird or the tail of a squirrel will lift and flap in the slipstream of large trucks, only totally black birds and black squirrels could be confused with any recaptoid.
Since exhaust systems parts are common along any road, an inexpensive short muffler, properly flattened, may at first glance resemble an armadillo. Coloration and segmentation are important distinguishing features in this case (armadillos have segments, mufflers do not), and few mufflers, even after long road residence, develop the gentle curves and tapered tail characteristics of the days-old flat or nearly flat armadillo.
A rusted hubcap looks enough like a painted turtle to confuse even the longtime student of road artifacts. Evidence of feet or a tail is the only certain way to distinguish the turtle from its mimic.
A chuck of recently cut sod fallen from a flatbed truck during dry weather will follow almost the same pattern of flattening and spreading as an equivalent-sized mammal. The green sod will bleach to pale tan, and the whole thing will look much like a prairie dog (Cynomys ludovicianus), which fortunately is rare near newer subdivisions where the sod may be common. Or the sod may resemble an upside-down yellow-bellied marmot (Marmota flaveventris), which is uncommon outside the mountainous regions of western North America. Sod chunks are also a good deal more solid than even the sturdiest mammal. I don’t usually encourage driving over a specimen to help with identification, but if you suspect that the pale tan lump is a sod chunk mimic, drive over it. Two loud thumps from the tires will help confirm your suspicions. Yoram Yom-Tov reports in his examination of flat creatures that driving over them causes no change in shape or size.
Both tree branches and pieces of tree bark can resemble flattened fauna. Long, thin branches are probably the road objects nearest in shape to a road snake. But branches are always more resilient than snakes and will fray at the edges over time. Snakes almost never fray before total disintegration, and usually remain firmly fixed to the road at all points. Bark fragments of the right size present more of a puzzle than branches. They can be almost any shape, and as frayed edges develop they can look like some of the longer-furred small- to medium-sized mammals. Redwood bark and red squirrels are often confused, as are darker colored barks and uniformly colored mammals like the Norway rat (Rattus norvegicus), or a yellow-bellied marmot right-side up. Careful reference to the silhouettes in the guide will help, but at highway speeds, some mimics will escape proper identification.
Many mammals and birds in their off-road habitat remain totally stationary as protective behavior. However, both road fauna and the mimics are more or less permanently immobile, even while exposed on the highway. Once the animal is firmly on the road, only the tips of birds wings and the tails of squirrels tend to move much.
Food on the Road
Most animal habitats provide plants for the resident herbivores. The road is a peculiar habitat in that it provides almost no growing plants for food. Plant food on the road (all imported) consists of seeds blown from passing grain transports, occasional bits of badly wilted lettuce from a discarded McDonald’s carton, or a few potato chips from a littering child. Animal food for the carnivores is produced in abundance right on the road—from the flattened animals themselves. An ecologist’s dictum states, “Everything is food for something,” and this certainly applies on the road. Everything organic that finds its way onto the road is likely to be used as food by something else that finds its way onto the road. Road carrion is among the major reasons why flesh-eating mammals become part of the flattened fauna. Ground squirrels nibble on bats, opossums on ground squirrels, and skunks on opossums, providing a fine two-dimensional example of food chains and the balance of nature.
It is safe to say that many of the animals on the road are or were seriously addicted to fast food—fast food is almost the only kind you can get on the road. For most of us, the only serious hazard likely from fast food on the road is indigestion if we eat too fast. For potential road fauna, not eating fast enough may carry a more permanent penalty: becoming the next course.
1 No domestic animals are included in this book because their habits are governed by their responses to people rather than to their habitat. The death of a pet may well be a tragedy, the death on the highway of a squirrel can be both interesting and informative.
2 See H. Elliot McClure. 1951. An analysis of animal victims on Nebraska’s highways. Journal of Wildlife Management 15:410–420.
3 The Snapping Turtle report is a personal communication from John Tjostem, a colleague, who was citing his grandmother’s diary.
4 Scott, Thomas G. 1938. Wildlife mortality on Iowa’s highways. American Midland Naturalist 20:527–539.
5 Simmons, James R. 1983. Feathers and fur on the turnpike. Boston: Christopher Publishing House.
6 McClure, H. Elliott. 1951. An analysis of animal victims on Nebraska’s highways. Journal of Wildlife Management 15:410–420.
chapter 2
The original edition of this guide concerned itself only with the road fauna of North America. Interest in that book became worldwide, and correspondence with Flattened Fauna aficionados on all continents except Antarctica has continued to the present time. While the particular creatures involved may vary from place to place, the principles outlined in Chapter 1 apply universally. The road fauna will crop up, or rather lie down, anywhere in the world that has roads and traffic. Antarctica would appear to be the only continent excluded.
While interest in the road fauna is almost universal, or at least multinational, objective, scientific information about the number, frequency, and species of two-dimensional animals is sadly lacking for areas outside North America. Even Europe is poorly represented. What follows constitutes something close to the sum of direct information about non–North American road fauna.
Unpublished correspondence about flat animals from personal communications has begun to establish part of the international picture. A 1989 report from what was then extreme eastern Zaire included not just information, but that rarest of artifacts, an actual road specimen. Paul Pena, who was a Peace Corps volunteer in the area of Lake Kivu near the Rwandan border, provided the
first African specimen on record. The animal, Chamaeleo dilepsis, the African flap-necked chameleon, which is in the live condition already somewhat flattened laterally was near perfect, down to the clockwise curl of its tail. Road chameleons show no color change under any circumstances, although from the written description of the location, this particular specimen did nearly match in color its immediate highway environment. More such specimens and descriptive locality information would be most valuable.
The other African report is a published work from Tanzania which concerns primarily baboon mortality on highways. Apparently even animals smart enough to function as substitute goatherds are susceptible to the hazards of the road. Africa will clearly provide a rich environment for the road fauna as highway networks expand.
The most complete professional examination of European road fauna comes from Ireland. Sleeman, Smiddy, and Sweeney published papers in the Irish Naturalist Journal during the late 1980s documenting stoat and other mammal fatalities. An additional paper on badgers (Meles meles) on the roads of Denmark (J. Aaris-Sorenson) from 1995 contributes additional European information. More up-to-date data seems to be lacking. Sometimes obscure professional journals are the best source of real information. So far as I am aware, nothing on the subject has ever appeared in the international journals Nature or Science.
Tropical America should be a rich field for measurement of highway impact. As roads spread into the tropical forests of the Americas, literally thousands of new animals and birds may become part of the developing international road fauna. David Campbell in his 2005 book A Land of Ghosts, details both the development and the demise of the Transamazon Highway in the far eastern portions of the Amazon. The highway was built and then disintegrated within 20 years, from 1970 to 1990. Campbell’s interest was in the botany and the sociology of the area and he made no recorded observations of highway animal mortality, although the impact of the highway on indigenous people was dramatic and tragic.
A magnificent contribution to the tropical American road fauna has come from Julian Monge-Najera of the University of Costa Rica. Professor Monge-Najera’s work might well serve as a model for other investigators. In examining more than 10,000 kilometers of Costa Rican highways, a large number of species never before a part of the road fauna were added. Traffic volume is low by contrast with most North American highways, and total density of animals was 0.027 specimens per mile if domestic dogs and cats were included and only 0.019 per mile for wild reptiles, birds, and mammals. This contrasts with a value of 0.429 animals per mile for 1938 Iowa roads (see T. G. Scott, 1938).
While there are few animals in common between North America and Costa Rica, the basic principles helping to define the road fauna apply. The behaviors of animals that are found most frequently on the road are consistent regardless of the particular species or geographic area involved. Central American porcupines and skunks are important elements in Costa Rica as are the North American porcupines and skunks. Opossums are found on the highways of Central America for the same reason they are found in Alabama, even though the species of opossum are different. That two-toed sloths, with their much reduced metabolic rate, could not make it across the road is no surprise, but the common presence of a small, arboreal anteater permanently on the highway cries out for further investigation of its habits.
Twenty species of mammals were found in Professor Monge-Najera’s study, along with six species of birds, four of reptiles, and a single amphibian species. The much smaller number of total organisms found in Costa Rica is attributed to the lower traffic volume and slower speeds as compared with North American highways.
Australia should be a fine source of road fauna information. However, I am not aware of any published work from Australian highways. Correspondence and other personal communications suggest that interest is high. Aussies commonly refer to “making smart kangaroos” (the smart kangaroos are those that either make it across the road or do not attempt the journey) or thinning the wallaby numbers, but critical quantitative work is up to now missing. Since Australia represents a remarkable array of climatic and geographic areas, such information would be of great value in interpreting the international implications of road flattening.
The best solution to the paucity of information on the international scene is not to wait for professional biologists to develop interest, but to begin immediately the collection of information from dedicated amateurs. A sample form is included on this page of this volume that could be duplicated and used to forward information about the flattened fauna of all corners of the globe. The headquarters of the International Simmons Society will maintain the central data bank, and serve to coordinate this international effort.
How and Where to Study the Road Fauna in North America
Interstate highways are a good place to begin your examination of the road fauna. Most miles of travel occur on such roads, and vehicle speed is sufficient to maintain interest in the beginning student. These highways tend to be more uniform from one part of the country to another than do secondary roads, so there are likely to be fewer regional differences in the number and variety of animal inhabitants on the interstates. For the beginner, the number of potential identifications more than makes up for the reduced diversity. Highway speeds also reduce the probability of seeing and identifying the smaller members of the road fauna. On the fast road, look for the larger specimens. The most common road fauna mammals include skunks, raccoons, porcupines, and marmots. Birds disappear from high speed roads so rapidly that it is rare to find a good one on an interstate. But the brighter colored woodpeckers and an occasional herring gull in coastal regions will develop your ability to spot birds. This skill will become more valuable as you extend your study to less-traveled routes with their more varied offerings.
Surveys by both professionals and amateurs have shown that the most varied and numerous specimens of the road fauna are likely to be found on less busy highways. Infrequently traveled roads, even those without asphalt or concrete surfaces, are often the most productive place to look for that relatively rare specimen to add to your life (or properly, death) list. I well remember finding an almost perfectly flat specimen of the Least Weasel (Mustela nivalis), one of the world’s smallest carnivores, in northern Iowa in the outside wheel track of a little used rural asphalt road that must have had total traffic of less than one car per hour.
The keys and descriptions in this guide are meant to be used at highway speeds. However, situations with less traffic allow you to briefly slow to 30 mph and examine the specimen in a more leisurely fashion.
Secondary roads bordering marshes or wetlands are probably the best places for seeing the widest and flattest variety of species. Roadside vegetation is often a critical part of the effective habitat of road fauna, especially for those species that do not live directly on the road or road edge. A variety of turtles, snakes, frogs, marsh birds, and muskrats are commonly part of the flattened fauna near a marsh. Any marsh-edged road in late summer will be the best possible place to rapidly expand your “death” list.
Lakeside roads are less interesting than those near marshes, but an occasional gravity-stricken gull may make up for the lack of more familiar flat birds. Fish are so rare among the road fauna that I hesitate to mention them at all, but if you seek the thrill of that one rare, flat, finny specimen, you might spend some time on lake roads. The June-July 2005 issue of National Wildlife Magazine has a remarkable photograph of a large spawning salmon crossing the center-line of a partially flooded roadway in Oregon, and I have photographic proof of a medium-sized guppy, flat as a sheet of paper, found on a small town street in northern Michigan.
Lonely roads with forest on one side and open fields or meadows on the other are prime locations for seeking out the less common flattened fauna, but see the following section on dangerous road animals before beginning that portion of your study. Birds (especially woodpeckers) and some mammals are described as “edge animals,” living most commonly on the margin of forest
s. The occasional presence of some of the rarer road species, such as the flying (actually non-flying) squirrel (Glaucomys species) and the bushy-tailed wood rat (Neotoma cinerea) of the far Northwest, makes woodland and field-bordered roads with only moderate traffic loads a good choice for the novice, as well as for the expert.
Any road that you follow repeatedly while commuting to work or traveling to the local shopping area provides the opportunity to observe seasonal changes in species and abundance. Many of this guide’s descriptions include information on seasonal presence. It’s a good idea to keep written records of sightings and identifications along oft-traveled routes (see the final pages of the guide for record sheet format). As your death list grows, it is important to report rare specimens or dramatic changes in numbers to the International Simmons Society headquarters. Widespread sharing of information through the society will stimulate further interest in the road fauna and will increase general understanding and appreciation for this up to now poorly known class of creatures.
While parking lots are not the best parts of the road habitat (they might be described as the deserts of the road), the occasional presence of a specimen of commonly flattened urban animals (such as the Norway rat or the house mouse) will provide a unique opportunity for the relatively safe, close-up examination of flattened fauna. Although close viewing or even collecting may be safer in parking lots than anywhere else (see following section on the collection of specimens), it is usually best to leave examples in place where they can be observed easily by other interested persons. Federal laws and many state laws prohibit the collection of any non-game animal without special permission. We can all help by refraining from collecting or disturbing the flattened fauna so that the animals can continue to educate the general public about the road’s natural wonders. Let us not repeat the over-collecting errors of nineteenth-century naturalists and dilettantes; leave parking lot specimens in place. If you find something of exceptional interest, you might even encourage your local school’s biology teachers to take the class on a field (or rather, road) trip. The urban environment is often all too poor in providing easily accessible examples of dead, two-dimensional things.
Flattened Fauna, Revised Page 2
