Phenotypic Variability in Feral Hogs

By: Aaron Sumrall, PhD 

I have the honor and privilege to extensively travel, meeting new people and cultures in the pursuit of researching feral hogs (Sus scrofa) and educating people about the biology and necessary management of the animal. Seems to be that every time I get to a new location or a new audience, I get the same statement:  “My feral hogs are different.” When I get that statement, I follow it up with a question of my own:  “As compared to what feral hogs?” That question is typically followed by a period of silence before an answer that varies about as widely as the terrain feral hogs cover. 

Land managers/owners begin to describe their feral hogs in a very accurate manner almost exclusively from a phenotypic observation. According to the region, descriptions will vary in color from black, white, red, spotted, belted, striped, to even tri-colored. These observations continue with descriptions of feral hogs with short legs to those with very long legs and even some with curled tails. Many say the shape of “their” hogs’ heads is similar to a yard dart and, if thrown hard enough, would stick in one of the huge, majestic oaks of the South. Others state head shape is compact and very robust. Descriptions of feral hogs frequently include animals ranging from a frail, thin-boned animal that has a traveling gait similar to that of a coyote, to a deep-bodied, heavy-boned lumbering animal bulldozing through obstructions rather than going around them.  

Let’s take a look at the aforementioned explanations of how feral hogs vary with a foundation that all of us were exposed to in biology and that many were introduced to in animal science and wildlife classes. Biology 101 introduced us to the Punnett Square, with animal science classes expanding on this by covering the topic of hybrid vigor, or heterosis. Both animal science and wildlife classes cover several rules of nature, with Bergmann’s Rule explaining several descriptions of feral hogs.

Early on in biology classes, we were exposed to the Punnett Square, which explains traits passed from one generation to another. Through the combination of upper-case and lower-case letters placed on a chart, one could get some level of probability as to what offspring could resemble. The complexity of the square is near limitless in what one could plug into the process to see what would result. Simple analysis could plug in color and, say, height at the shoulder and roll the dice. Combinations would result with the probabilities of offspring of different color and shoulder height options. One thing tough to assess is the likelihood of ancestral traits rearing their little heads. An example of this is a red male and a black female producing a white offspring. Where the heck did that come from? Somewhere in the lineage of the individuals, that white trait was there, much like finding feral hogs with curled tails and uncommon colors due to a historical origin as a domestic livestock species.

Feral hogs come in 3 flavors: Russian/Eurasian boar, domestic-turned-feral, or a combination of Russian/Eurasian and domestic lineages. Pure lines of breeding will consist largely of a very common appearance, while crossing lineages can, and often does, produce offspring that may not look much like either parent. This crossing we learned about initially in biology, animal science, and wildlife classes is referred to as heterosis or hybrid vigor. About 60% of all feral hog litters have multiple sires. The promiscuity of the female and the determination of the males will result in litters that could have multiple colors or even racing stripes in the same litter. 

Head shape is explained through this combining of genetics. Long, yard-dart looking heads are common in strains that have been extensively removed from domestic breeds. Feral hogs exhibiting this trait are commonly referred to as Piney Woods Rooters. Why? I don’t know, because you can find this same look in pigs in arid landscapes as well. Compact, robust head structure is common to the Russian/Eurasian boar and can also be found across an ever-increasing landscape. The combination of the two will result in any variation in between. Many folks have made an accurate note that phenotypic changes have happened over a relatively short period of time. This quick shift in phenotypic appearance can be placed largely on illegal transportation. Individuals trucking in new blood to release on the landscape is the equivalent of a rancher with a cross-bred cattle herd. Offspring look a bit different. The other feral pig fall-out is that, with heterosis, litter size will likely increase.

We have all heard of Murphy’s Law, and some of us would like to put hands on ole Murph. Wildlife science also has laws to explain why things happen the way they do or why things are the way they are. Earlier mentioned explanations of feral hogs ranging from thin, frail individuals to these short, thick, heavy-boned individuals can also be explained by wildlife law. To sum up Bergmann’s Rule, structure and conformation of the population will be determined by the environment. Have you ever wondered why White-tailed deer are so much bigger in the North as compared to those in the South? Why do southern deer typically have larger ears and longer legs proportional to body size when compared to their northern counterparts? Well, if a species has long legs and large ears, that increases the time that blood is close to the surface of the body, thus cooling the body more easily. It is simple thermoregulation. Feral hogs quickly spreading and occupying Provincial Canada must deal with long periods of very cold temperatures and are doing so quite well. As with deer, feral hogs in colder climates (the name Russian can explain the climate of origin) are going to be short-legged, thick-bodied bulldozers, while their counterparts to the south must have the ability to regulate temperature with a different body conformation of longer legs and tubular bodies since hogs can’t sweat. 

Let’s take this discussion now to the landscape and look at a few things that have an affect on phenotypic characteristics. Let’s say you live in an area that does not have much food or water. If your body structure is like mine, you need calories to maintain it and even more to grow.  So if you are a strain of a species that is a heavy-boned lumbering animal that is slow moving, you are not going to do well in areas that require you to travel great distances in pursuit of very limited resources. If this is the case, Mother Nature is going to favor those animals that are slower-growing, thinner-boned, capable of long-distance travel, and don’t need much to stay alive. If water sources or food resources are miles apart, if available at all, the species will need to evolve a gait that will allow them to travel long distances while burning minimal calories. This requirement does not bode well for strains exhibiting strong Russian traits. 

So, back to the coat of many colors worn by feral hogs. Why such and array in the color palette of feral hogs? There can be many thoughts and arguments around this topic, but let’s consider something that is a bit more inclusive than just the collateral of the Punnett Square. The Square can, and does, explain well why we have the likelihood of a wide array of colors in a single sounder, but where does predator management factor into phenotypic appearance? We are very aware that once a piglet is weaned, predatory take is cut to nil. However, every species on the planet that has meat in its diet likes pork. Take a given litter of six pigs. The sow is not completely concerned with rearing all of them.  She will do her best, but piglet mortality is high. In that litter of six piglets, there are three black, two red, and one white. Let’s say you are a coyote. Which piglet will stand out most to you? Yes, the sore-thumb white one. I bring this up because, in the instances where predator management is high on the management list in livestock operations, what will be a result? Every action has a reaction, and the extensive removal of piglet predators will result in the increased survivability of piglets. With fewer predators, more color variability in piglets could occur, resulting in more color variability to put into the Punnett Square, resulting in more phenotypic combinations. 

Stating “My feral hogs are different” is a very accurate statement when looking from the phenotypic stance. Beyond that, all feral hogs are the same. Feral hogs are a scourge on the landscape, negatively impacting native floral and faunal species, domestic livestock system, water body, golf courses and new subdivisions, and EVERY pocketbook, either directly or indirectly. Feral hogs, by definition, cannot be rehabilitated or persuaded to perform differently. You will have to make the decision to accept the destruction to all that is natural and good or to do something about it. Choose wisely. Our native species and water quality are depending on it.  

By: Aaron Sumrall, PhD 

Director of Research and Outreach

Field Engine Wildlife Research and Management 

Pig Brig Trap Systems