High Plains Anteater

Every time I travel away from home, I make a point of looking at the ground. The main reason for this seemingly odd behavior is to make sure I detect traces of whoever else might be living in my temporary neighborhood. This ichnological practice came in handy last month while I was doing field work in the high plains of central Montana. Located just east of the front range of the Rocky Mountains, this area – which happens to have some lovely Late Cretaceous trace fossils – is also prime real estate for grizzly bears.

Grizzly-Bear-Scat-Montana-Ants-1Had we found this in the woods, it would have answered just one specific question. But because it was in the high plains of Montana, it generated a lot more questions than answers. (Photograph by Anthony Martin, taken in central Montana.)

Grizzly bears (Ursus arctos) are the largest land carnivores in North America. The earliest written records describing grizzly bears came from Meriwether Lewis and William Clark, who traipsed through this part of Montana with their expedition in the early 19th century. After several encounters, they soon verified that this species was much tougher than they had presupposed, often taking more than ten shots from then-modern rifles to kill. To make matters worse, it had a low tolerance for upright bipeds traipsing, skipping, sashaying, or dosey-doeing in its territory. Moreover, these bears possessed the means to enforce their you-no-go-here zones. There’s something about weighing 300+ kg (700+ lbs), having powerful limbs ending in huge claws, big teeth, an ability to run more than 50 kph (30+ mph), and an aggressive attitude that persuasively argued for people to avoid them whenever possible.

Bear-Treeing-PersonLewis and Clark thought they were badasses because they carried boom sticks, but Mr. Chocolate soon showed them why grizzlies were the Mongos of the animal kingdom: shooting them sometimes got them mad. (Image is originally from Sargent Patrick Gass’s journal and borrowed from Frances Hunter’s American Heroes Blog, co-written by Mary and Liz Clare.)

So although the area where I did field work in Montana is world famous for its dinosaur nests and other fossil evidence, modern grizzly-bear traces there also mean I associate this place with these animals. For instance, I’ll never forget my first morning there in 2000, when – while walking to an outcrop I’d be studying by myself for the next six days – I encountered fresh grizzly tracks in one of the arroyos. These traces readily explained why I heard a pack of coyotes making a racket the night before, while also invoking mild anxiety in this petite paleontologist once I realized the surrounding environment lacked any trees or other means of escaping an angry grizzly.

Grizzly-Bear-Tracks-MontanaLeft rear-foot track of an adult grizzly bear, left in the muddy sand of an arroyo next to a Cretaceous outcrop where I did field work in 2000.  Notice the length of its claws, which left marks well in front of its toes. Photo was taken about four days after I had seen them freshly made my first day in this area of Montana. (Photograph by Anthony Martin.)

This time, with 14 more years of tracking experience behind me, I felt a little more confident about detecting grizzly-bear tracks and other sign, and looked forward to seeing these traces, but not their tracemakers. Thus I was pleased when my field companions and I found several-weeks-old evidence of a grizzly during my first morning there. Yet these traces were not tracks. Instead, they consisted of scat bearing (sorry) some never-before-seen items (for me, anyway), accompanied by nearby feeding signs that directly connected to another trace made by another animal.

So let’s first talk feces. Based on its size alone, we quickly determined that this deposit was from a grizzly bear, as the two pieces collectively were about 15 cm (6 in) long and about 5 cm (2 in) wide. Nearby coyote scat nearby gave some perspective: although 20 cm (8 in) long, it was only 2 cm (0.8 in) wide, indicating a much smaller anal diameter. However, that wasn’t the largest grizzly scat I’d ever seen, which made us think that maybe it was from a young bear.

But was really puzzled us was the contents of the scat: it was full of ants and grass stems. Despite none of us being entomologists, let alone myrmecologists, we recognized the red-and-black ant parts in the scat were from an ant common there in the high plains, and probably some species of Formica. Colonies of this ant built nests with prominent domes at the ground surface, which are composed of a mixture of soil and grass stems. Hmm, ants and grass stems: what could it mean?

Grizzly-Bear-Scat-Montana-Ants-2See all of those orange and black bits in this scat? Those are ant parts that passed through the digestive tract of a grizzly bear. Notice these pieces are accompanied by lots of plant fibers, which must have provided some healthy roughage. (Photograph by Anthony Martin, taken in central Montana.)

OK, you already got it: this scat was evidence of a grizzly bear that ate ants. But the grass also showed that this grizzly ingested a lot of plant debris along with these yummy insects. This implied that it must have been chowing down on the top of an ant nest, scooping up insects and grass stems indiscriminately, like it was dining on an ant salad. Furthermore, knowing how ants tend to defend attacks on their nests, they probably swarmed upward in great numbers and straight into this grizzly bear’s mouth, unwittingly aiding its efforts. (Incidentally, an insectivorous member of our field crew had been tasting these ants just minutes before we found the scat and independently confirmed their delectable qualities.)

Montana-Ant-Nest-2Ant-nest mound in the field area composed mostly of grass stems, and probably made by a species of Formica. Scale is a size 8 1/2 (men’s) boot. (Photograph by Anthony Martin.)

Montana-Mound-Nest-Ants-CloseupClose-up of the ants in the colony moving in and out of a nest entrance, in between all of the grass stems. Also, check out those black abdomens and reddish-orange thoraxes and heads, which we now know don’t change color much after spending time inside a grizzly bear. (Photograph by Anthony Martin, taken in central Montana.)

So how did we know that the grizzly was “scooping” (using its paws) instead of simply mashing its face into the nest like it was competing in an ant-eating contest at a grizzly-bear fair? Ah, that was the other trace evidence. Only a couple of meters away from the scat were two big pits. These pits showed exactly where the ant-eating grizzly had used its big-clawed paws to rip into a couple of nests. While taking into consideration the needed residence time of ants in a grizzly gut, we figured this bear had already raided a nest somewhere else and pooped here, or it came back to this place for seconds the next day. Either way, it left a little calling card for us bipeds and any other mammals in the area, warning us to stay away from its ant stash.

Grizzly-Bear-Ant-Predation-PitsEver wonder what a grizzly-bear-ant-eating pit looks like? Wonder no more, here’s two of them. The one on the left was about a meter (3.3 ft) across, whereas the one on the right was closer to 1.5 m (5 ft) wide. (Photograph by Anthony Martin.)

What was very gratifying about these traces is how they reflected the same sort of insectivorous bear behaviors I had discerned in black-bear traces in forests of Wyoming and Idaho. The big difference, though, was in the types of insects and substrates. Insect-eating bears in forests rip open rotten logs for their fodder, which mostly would hold wood-eating beetle grubs; this behavior leaves huge gouges and scatters wood chips around the feeding site. Without trees, the same behavior means digging into the soil, and after different insects, such as  moths and ants, and the traces will be large pits like the ones we saw.

So how would traces like these look in the fossil record? Better yet, how would our knowledge of these grizzly-bear traces help us to test whether any dinosaurs did similar behaviors, such as tearing into Mesozoic ant or termite nests and feasting on these little protein-rich treats?

Well, you’re lucky that I’m the person asking such rhetorical questions, because I just happened to have talked about about this in my most recent book, Dinosaurs Without Bones. Based on their anatomies, dinosaurs accused of ant- or termite-eating behaviors include a few unusual theropods, such as alvarezasaurs and therizinosaurs. Very simply, dinosaur trace fossils of insectivory would be analogous to what we saw with these grizzly-bear traces in Montana. Lacking dinosaur skeletons with insect parts in its gut region, trace fossils might include coprolites containing abundant ant parts, accompanied by sediments or plant debris from their nests. Even better would be a fossil ant or termite nest with visible damage matching the claws or other body parts of these suspected dinosaurs.

Have paleontologists ever found such two-for-one ichnological specials? Not yet, but given an awareness of modern insect-eating animals and the traces – some of which are next to Mesozoic rocks – I have every confidence that we’ll discover find them some day.

Going Hog Wild on the Georgia Barrier Islands

(The following is the third part of a series about traces of invasive species of mammals on the Georgia barrier islands and the ecological effects of these traces. Here is an introduction to the topic, the first entry about the feral horses of Cumberland Island, and the second entry about the feral cattle of Sapleo Island.)

Anytime I hear someone refer to a Georgia barrier island as “pristine,” I wince a little bit, smile, and say, “Well, bless your heart.” The truth is, nearly every island on the Georgia coast, no matter how beautiful, is not in a pristine state, having been considerably altered by humans over the past 4,500 years, whether these were Native Americans, Europeans, or Americans. These varying degrees of change are sometimes subtle but nonetheless there, denoted by the loss of original habitats and native species or the addition of non-native species.

Still, one Georgia barrier island comes close to fulfilling this idealistic label: Wassaw Island, which during its 1,000-year geologic history somehow escaped commercial logging, agriculture, animal husbandry, and year-round settlements. Partially because of this legacy, Wassaw is designated as a National Wildlife Refuge, and is reserved especially for ground-nesting birds. One of the ways this island works well as a refuge for these birds is – as of this writing – its “hog free” status, a condition that can be tested with each visit by looking for the obvious traces of this invasive species.

The interior of Wassaw Island, with maritime forest surrounding a freshwater wetland created by alligators, the rightful owners of the island. On Wassaw, there are no tracks or signs of feral hogs, qualifying it as a “pristine” island. (Photograph by Anthony Martin.]

Contrast this with Cumberland Island National Seashore, where hogs run wild and freely. The huge pits here are in an intertidal zone of a beach on the northwest corner of the island. Naturalist Carol Ruckdeschel (background) for scale. (Photograph by Anthony Martin.)

Feral hogs (Sus scrofa) have a special place in the rogue’s gallery of invasive mammals on the Georgia barrier islands, and most people agree they are the worst of the lot. Hogs are on every large undeveloped island – Cumberland, Sapelo, St. Catherines, and Ossabaw – and they wreak ecological havoc wherever they roam. The widespread damage they cause is largely related to their voracious and omnivorous diet, in which they seek out and eat nearly any foodstuff, whether fungal, plant, or animal, live or dead. Their fine sense of smell is their greatest asset in this respect: every time I have tracked feral hogs, their tracks show head-down-nose-to-the-ground movement as the norm, punctuated by digging that uses a combination of their snouts and front hooves to tear up the ground in their quest for food. In other words, they generally act like, well, you know what.

Most importantly from the standpoint of native animals that try to live more than one generation beyond a single hog meal, feral hogs eat eggs. Hence ground-nesting birds and turtles are among their victims, and hogs are quite keen on eating sea turtle eggs. Mothers of all three species of sea turtles that nest on the Georgia coast – loggerhead (Caretta caretta), green (Chelonia mydas), and leatherback (Dermochelys coriacea) – dig subsurface nests filled with 100-150 eggs full of protein and other nutrients, making tempting targets for any free-ranging feral hogs. Similarly, hogs also threaten another salt-water turtle, the diamondback terrapin (Malaclemys terrapin); this turtle lays its eggs in shallow nests near the edges of salt marshes, which hogs manage to find. Conservation efforts to save diamondback terrapins from human predation have mostly succeeded (it used to be a tasty ingredient in soups), but hogs can’t read and don’t discriminate when it comes to eating eggs. Here is where feral hogs are particularly dangerous as an invasive species: unlike feral horses or cattle, which “merely” degrade parts of their ecosystems: feral hogs can contribute directly to the extinction of native species. As I often tell my students, if you want to cause a species to go extinct, stop it from reproducing.

Sea-turtle nest on Sapelo Island, marked by a stake and protected by plastic fencing to prevent feral hog and raccoon depredation of its eggs. An individual raccoon would only eat about 1/3 of the eggs in a sea-turtle nest, whereas pigs would just keep on eating. (Photograph by Anthony Martin.)

As an ichnologist, though, what astounds me the most about these hogs is the extremely wide ecological range of their traces. I have seen their tracks – often made by groups traveling together – in the deepest interiors of maritime forests, in freshwater wetlands, and crossing back-dune meadows, high salt marshes, coastal dunes, and beaches. If their traces became trace fossils, paleontologists would refer to them as a facies-crossing species, in which facies (think “face”) are the identifiable traits of a sedimentary environment preserved in the geologic record. Based on their tracks and sign, they are ubiquitous in terrestrial and marginal-marine environments. Oh, and did I mention they are also good swimmers? Swimming across a tidal channel at low tide is an easy feat for them, enabling hogs to spread from island to island, without the assistance of humans.

Run away, run away! Feral hogs in a St. Catherines Island salt marsh, consisting of two juveniles and an adult, do not stick around to see whether humans are going to shoot them; they just assume so. This sighting, along with their widespread tracks and other traces, show how feral hogs can occupy and affect nearly every environment on a Georgia barrier island. (Photograph by Anthony Martin.)

So to better understand why feral hogs are such successful invaders of the Georgia islands, it’s helpful to think about their evolutionary history. As expected, this history is complicated, just like that of any domesticated species in which selective breeding narrowed the genetic diversity we see today. About 15 subspecies of Sus scrofa have been identified, making its recent family tree look rather bushy. Based on genetic studies, divergence between wild species of Sus scrofa (so-called “wild boars”) and various subspecies may have happened as long ago as 500,000 years ago in Eurasia, although humans did not capture and start breeding them until about 9,000 years ago.

Depiction of a European wild boar from 1658, in The History of Four-Footed Beasts and Serpents by Edward Topsell. Original image from a woodcut, digital image in Wikipedia Commons here.

The closest extant relatives to these hogs native to North America are peccaries, which live in the southwestern U.S., Central America, and South America. However, peccaries are recent migrants to North America, and only one Pleistocene species (Mylohyus nasutus) is known from the fossil record of the eastern U.S. This means that the post-Pleistocene ecosystems of the eastern U.S., and especially those of the Georgia barrier islands, have never encountered anything like these animals. Also, unlike the feral horses of Cumberland Island and the feral cattle of Sapelo Island, the feral hogs of the Georgia barrier islands were likely introduced early in European colonization of the coast, and may have started with the Spanish in the 16th century.

Unfortunately, part of the selective breeding of Eurasian hogs was for early sexual maturity and large litter sizes. Female feral hogs can reach breeding age at 5 months, and litters typically have 4-8 piglets, but can be greater than 12; females also can produce three litters in just more than a year. Do the math, and that adds up to a lot of pigs in a short amount of time. Furthermore, on Georgia barrier islands with few year-round human residents, the only predation pressures young piglets face daily include raptors (no, not that kind of raptor) or alligators. This means young hogs reach sexual maturity soon enough to rapidly overrun a barrier island.

Feral hog trackway in a sandy intertidal zone of Cumberland Island, showing a typical gallop pattern (four tracks together –> space –> four tracks together), symbolizing how they are running roughshod over this and other islands. (Photograph by Anthony Martin.)

Yet as we have learned in North America, and particularly on the Georgia barrier islands, feral hogs rapidly revert to their Pleistocene roots. Similar to the feral cattle of Sapelo Island, these hogs are rarely seen by people, especially on islands where humans regularly hunt them. Every time I have spotted them on Cumberland, Sapelo, St. Catherines, or Ossabaw, they instantly turn around, briefly flash their potential pork loins and ham hocks, and flee. As anyone who has raised hogs can tell you, pigs are smart and learn quickly. Hence I imagine that after only one or two shootings of their siblings or parents, they readily associate upright bipeds with imminent death, especially if these bipeds are carrying boomsticks.” (Speaking of which, I know of at least one sea turtle researcher who does his part to decrease feral hog populations – while also feeding the local vultures – through his able use of such a baby-sea-turtle-protection device.)

Hence much of what we learn about these free-ranging pigs and their behaviors in the context of the Georgia barrier islands is from their traces. Among the most commonly encountered feral hog traces are:

• Tracks

• Rooting pits

• Wallows

• Feces

Feral hog tracks are potentially confused with deer tracks, as they both consist of paired hoofprints and overlap in their size ranges, which are about 2.5-6 cm (1-2.5 in) long. Nonetheless, feral hog tracks are less “pointed,” have nearly equal widths and lengths, rounded ends, and the two hoofs often splay. Two dew claws – vestigial toes – frequently register behind the hoofs, especially when hogs step into soft sand or mud or are running. Trackways normally show indirect register of the rear foot onto the front footprint in a diagonal walking pattern, but can also display a whole range from slow walk to full gallop patterns. With repeated use of pathways, trackways become trails, although I’m not sure if hogs are merely using and expanding previously existing whitetail deer trails, if they are blazing their own, or a combination of the two. (I suspect the last of these is the most likely.)

Feral hog tracks, showing nearly equal lengths and widths, rounded ends, and splaying of hooves, all three of which help to distinguish these from whitetail deer tracks. Scale in centimeters. (Photo by Anthony Martin, taken on Sapelo Island.)

Feral hog trackway on upper part of a sandy beach (moving parallel to shore), showing slow diagonal walking pattern, verified by hoof dragmarks between sets of tracks. Scale = 10 cm (4 in). (Photo by Anthony Martin, taken on St. Catherines Island.)

Rooting pits are broad but shallow depressions – as much as 5 m (16 ft) wide and 30 cm (1 ft) deep – that are the direct result of feral hogs digging for food. In most instances, I suspect they are going for fungi and plant roots, but they probably also eat insect larvae, lizards, small mammals, and any other animals that live in burrows. These pits are typically in maritime forests and back-dune meadows, but I have seen them in salt marshes and dunes, and, most surprisingly, in the intertidal areas of beaches. What are they seeking and eating in beach sands? I think anything dead and buried that might be giving off an odor. I have even seen their tracks associated with broken carapaces of horseshoe crabs (Limulus polyphemus), a menu item that never would have occurred to me if I had not seen these traces.

Rooting pit in back-dune meadow on St. Catherines Island. Former student, who answers to the parent-given appellation of “Andrew,” for scale. (Photograph by Anthony Martin.)

Evidence of feral hog feeding on a horseshoe crab (Limulus polyphemus). All I can say is, it must have been really hungry. (Photo by Anthony Martin, taken on St. Catherines Island.)

Wallows are similar in size and appearance to rooting pits, but have a different purpose, which is to provide hogs with relief from both the Georgia summer heat and biting insects that invariably go with this heat. These structures are often near freshwater wetlands in island interiors, but I’ve seen them next to salt marshes, too. If these wallows intersect the local water table, they also make for attractive little ponds for mosquitoes to breed, meaning these hog traces indirectly contribute to the potential spread of mosquito-borne diseases.

Wallow in maritime forest, Sapelo Island, with a standing pool of water indicating the local water table at the time. (Photo by Anthony Martin.)

Hog feces may look initially like deer pellets, but tend to aggregate in clusters. Most of the ones I have seen are filled with vegetation, but the extremely varied diets of feral hogs means you should expect nearly anything to show up in their scat.

Feral hog feces on Sapelo Island, which is more clumped than that of whitetail deer. Scale in centimeters. (Photo by Anthony Martin, taken on Sapelo Island.)

Which of these traces would make it into the fossil record? I would certainly bet on at least some of their tracks getting preserved, based on the sheer ubiquity of these traces in nearly every sedimentary environment of a Georgia barrier island. Other likely traces would be their pits and wallows, although their broad size and shallow depths would make them difficult to recognize unless directly associated with tracks. Feces would be the least likely to make it into the fossil record as coprolites, unless these contained a fair amount of bone or other mineralized stuff, which could happen with hogs.

What to do about these hogs, and how to decrease the impacts of their traces? Well, as most people know, pigs are wonderful, magical animals that were domesticated specifically for their versatile animal protein. So one solution is more active and year-round hunting of hogs, and using them to supplement breakfasts, lunches, and dinners of local residents on the Georgia coast, a neat blend of reducing a harmful feral species while encouraging a chic “locavore” label on such food.

However, the sheer numbers of hogs on some of the islands would likely require a more systematic slaughter to make a dent in their numbers, an approach that would probably deter any ecotourism unrelated to hog hunting. (Let’s just say that firearms and bird watching are an uneasy mix.) The introduction of native predators is another possible solution. For example, Cumberland Island has a population of bobcats (Lynx rufus) that was introduced primarily to control the whitetail deer population, but these cats probably also take a toll on the feral hogs (although how much is unknown). I have even heard suggestions of reintroducing red wolves (Canis rufus) to a few of the islands. These pack-hunting predators were native to the southeastern U.S. before their extirpation by fearful European settlers, and probably would reduce feral hog populations, but just how much of an impact they would have is hard to predict.

In summary, the feral horses, cattle, and hogs of the Georgia barrier islands have significant effects on the ecology and geology of the Georgia barrier islands, and will continue to do so until creative solutions are proposed and implemented to reduce and otherwise manage their numbers. In the meantime, though, these invasive species present opportunities for us to study their traces, learn more about their unseen behaviors, and compare these behaviors with their evolutionary histories. More science is always good, and in this respect, the Georgia barrier islands are the gifts that keep on giving.

Traces of feral mammals on Sapleo Island: feral hog tracks strolling past a piece of feral cattle scat in a sandy road next to a maritime forest. What is the fate of these invasive species on the Georgia barrier islands, and how will these environments continue to change because of their presence? (Photo by Anthony Martin, taken on Sapelo Island.)

Further Reading

Ditchkoff, S.S., and West, B.C. 2007. Ecology and management of feral hogs. Human-Wildlife Conflicts, 1: 149-151.

Giuffra, E., Kijas, J.M.H., Amarger, V., Carlborg, Ö., Jeon, J.-T., and Andersson, L. 2000. The origin of the domestic pig: independent domestication and subsequent introgression. Genetics, 154: 1785-1791.

Mayor, J.J., Jr., and Brisbin, I.L. 2008. Wild Pigs in the United States: Their History, Comparative Morphology, and Current Status. University of Georgia Press, Athens, Georgia: 336 p.

Taylor, R.B., Hellgren, E.C., Gabor, T.M., and Ilse, L.M. 1998. Reproduction of feral pigs in southern Texas. Journal of Mammalogy, 79: 1325-1331.

Wood, G.W., and Roark, D.N. 1980. Food habits of feral hogs in coastal South Carolina. The Journal of Wildlife Management, 44: 506-511.