Wild pigs are perhaps the most destructive invasive species in the United States, causing an estimated $1.5 billion in damages every year to crops and property across the country, uprooting farmers' fields, degrading water quality and out-competing native wildlife for food.

In this installment of AL.com's series on invasive species, we examine the feral hog, one of the costliest non-native species in Alabama, and what landowners and wildlife officials can do to keep their populations under control.

Dennis Pillion | dpillion@al.com

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Photo by Joe Songer | jsonger@al.com.

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The hunt is on

Chris Jaworowski is a really good shot with his semiautomatic rifle, and he has plenty of experience hunting hogs.

As a wildife biologist and Regional Extension Agent with the Alabama Cooperative Extension System and former employee of the Alabama Department of Conservation and Natural Resources, he's one of the foremost experts on feral hog control in Alabama, if not the Southeast.

Still, with all Jaworowski's experience and training, with thousands of dollars worth of specialized equipment, hunting feral pigs in Alabama is not easy.

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In the dead of night in rural Autauga County woods, Jaworowski and his partner switch on their thermal night vision scopes -- which cost more than $3,000 each -- from their perch downwind of an empty cornfield where 21 hogs are doing what they do best; rooting around in the dirt, looking for something to eat and ripping up good cropland in the process.

The two experienced marksmen, with the aid of surprise and $7,000 worth of optics, are able to bring down 11 pigs. The other 10 scurry off into the trees to live and breed another day, as shown in the video above.

(Warning: video contains infrared footage of a hunt that may be disturbing to some viewers.)

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Trapping the 'most efficient' method of control

That's why, as Jaworowski describes it, hunting is just "one tool in the toolbox" of control methods for keeping hog populations down, and it's not even the most effective one.

“Trapping is the most cost-efficient and most effective way of removing large numbers in a short period of time," he said. "They will all harvest pigs, but with trapping, you can catch 20 instead of shooting one.”

Photo by Joe Songer.

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Laws of pig hunting

There is no closed season for hog hunting in Alabama, nor bag limit on the number of pigs you can harvest. There are rules, however.

Hunting at night or hunting over bait (like in the video above) requires a special permit from the Alabama Department of Conservation and Natural Resources, according to Carter Hendrix, a captain with the ADCNR's law enforcement division.

Those permits are not issued during the open deer or turkey seasons to avoid conflicts and prevent hunters from applying for pig permits to shoot deer.

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80 percent

Even though many of the pigs that got away look young and helpless, they'll be sexually mature before they're a year old, ready to bring future generations into the Autauga County woods.

That's the problem with hunting as a means to control feral hog populations. It's just not efficient or fast enough.

Mark Smith, an associate professor of forestry who specializes in wild pig damage management with the Alabama Extension, said pigs reproduce so quickly in the wild that you have to kill 80 percent of them just to stop the population from growing.

"It's not the number you kill, it's the number you don't kill that matters," Smith said.

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Rapid reproduction

Sows can regularly give birth to two litters a year, sometimes three in 14-16 months. Litters typically include four to six piglets, but range from one to 12, according to the Cooperative Extension System.

Sows can birth between 18 and 27 piglets in a year, and those piglets -- boars and sows -- will reach sexual maturity themselves in less than a year. Pigs usually live about five years in the wild, though some live to see 14 or 15. One study in South Carolina found a 14 year-old sow still capable of reproducing.

Older, larger sows tend to be more prolific breeders, with larger litters.

Photo by Joe Songer | jsonger@al.com.

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Few natural predators

In addition to being rapid breeders, wild hogs have almost no natural predators in Alabama once they reach maturity. Some alligators may be able to bring down a few mature pigs, but there's little else that is up to the task, especially males with large tushes (yes, tushes).

Photo by Joe Songer | jsonger@al.com

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Sounders off

Sows typically travel in small groups called sounders, consisting of as many as three generations of sows and their offspring. These sounders often contain 20 or more pigs.

Mature boars are more solitary and will occasionally wander searching for breeding opportunities, typically following a sounder only if attempting to mate.

In this AL.com file photo by Joe Songer, hog hunting guide Gary Daugherty watches a sounder of hogs cross a logging road in front of him.

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Males fighting males

Though the pigs have few if any natural predators, the males do sometimes fight each other over breeding opportunities. Those fights can get nasty, resulting in serious injury or death to the combatants.

The Cooperative Extension notes that "[b]ecause success in these fights is related to size, most breeding done in feral hog populations is by the larger and older males."

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Monster pigs are rare

Big pigs like this one killed by Eli MacKinnon in 2015 grab headlines, but Smith says truly wild pigs rarely get that big.

A boar weighing more than 300 pounds is considered "very big," Smith said and any pig over 500 pounds "probably had a name," meaning it was very likely kept by humans and given a steady food supply.

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Extensive damage

The U.S. Department of Agriculture calls feral swine the "rototillers of nature," citing the ability to easily uproot farmers fields with their snouts, munching on corn, spinach, peanuts or any number of planted crops.

This USDA photo shows a cornfield under attack by hogs.

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Photo courtesy Chris Jaworowski of hog damage in Alabama.

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Water quality issues

Hogs also contribute to water quality issues by muddying streams and spreading bacteria like e. Coli in the water.

Photo by Joe Songer.

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They are invasive

Feral hogs are an invasive or introduced species in the United States, even though that introduction happened more than four centuries ago.

Spanish explorers carried the first pigs to what is now the United States in the 1500s to provide food for his men on their expeditions in the New World. It worked, and the hogs have been here ever since.

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Genetic mix

The wild pigs encountered today in Alabama and other parts of the country are hybrid mixes of the original species set loose so long ago and agricultural breeds of pig that escaped from farm pens more recently. They have many different colors and color patterns, ranging from very light to almost black.

Photo courtesy Chris Jaworowski, ACES.

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They're now spreading rapidly

Though the hogs have been here 400 years, their population and range has exploded over the last 15 years or so. This USDA map shows by county how far the pig population has spread from 1982 to 2015.

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They don't travel by themselves

Hogs don't migrate and rarely leave stray too far from the area where they were born. Though they can run up to 30 miles per hour in short bursts, they're not built for cross-country travel. So why are the pigs spreading so much now, after more than 400 years?

Mark Smith, an associate professor of forestry and wildlife sciences and extension specialist with the Alabama Cooperative Extension System, said the most likely explanation is that pigs were deliberately introduced into new areas by humans looking to spread recreational hunting opportunities.

"We're pretty darn sure that pigs cannot fly," Smith said. "They're kind of homebodies."

Late last year, conservation officers arrested 16 people for illegally transporting hogs in Alabama.

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Active at night

Pigs don't sweat, so they are most active at night to avoid the midday heat. Jaworowski said peak pig activity hours are from 2 a.m. to 5 a.m., another factor that makes hunting them inconvenient.

“All the control methods except for trapping, you have to be out in the field, actively pursuing or hunting," he said. "With trapping once you have the initial outlay of setting up the trap and baiting it, you get to go home and let the trap work for you.”

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'Judas' pig

In the war between wildlife officials and pigs, some swine have been betrayed by one of their own.

Jaworowski and a team of researchers at Auburn have at times attached transmitters to so-called "Judas pigs," in order to track their movements, and to find where the sounders bed down to escape the mid-day heat. Hogs encountered midday are more sluggish and easier to dispatch and the tracking data provides researchers more information about pig behavior.

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Helicopters hunts happen

Alabama authorized its first helicopter hog hunt last year to test out the feasibility of controlling populations from the sky.

Texas, which probably suffers more damage from hogs than any other state, has been using helicopter hunts for a few years to control populations.

This photo, provided by Jaworowski, shows a helicopter used in the Alabama hunt.

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Efficient but expensive

Hunting by helicopter can be very effective. The noise and wind from the rotors will drive pigs out into the open during the day, where they are vulnerable. Alabama's first helicopter pig hunt resulted in more than 200 pigs harvested in two days.

It is expensive, however, and complicated. Flying low and slow over the terrain while a gunner opens fire requires experienced personnel to be done safely.

This Associated Press file photo shows a group of hogs from the air in Texas.

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Hogs are smart

If you're going to trap hogs, it's best to get as many as you can in one swoop, Jaworowski said, because the hogs learn to avoid traps and get skittish.

“They're pretty quick. If you're not trapping the right way, you can definitely educate them and make them harder to trap. Unfortunately when you catch two or three at a time, you educate 10 or 12 that were running with them and they don't want to go back in the trap.”

Box traps, which are smaller and can only hold one or two hogs are particularly ineffective.

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Traps are getting better

Traps are improving with the help of experience and modern technology. Modern traps should be round or oval shaped, avoiding 90 degree angles, and at least five feet high. Some pigs can jump over three-foot fencing, and in corners, they can pile on top of each other to allow some to escape.

Some traps now include video trail cameras and a smartphone app that can be used to activate the trap remotely. An alert will be sent to a cell phone when motion is detected near the trap and the user can watch the video feed and activate the trap when all the pigs are inside, as shown in this video.

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Drop-net traps

Another style trap that doesn't spook the pigs is the drop net-style traps like this one being tested out by researchers at Texas A&M University.

A newer product, the BoarBuster features a circular metal corral that can be dropped from above remotely via a smartphone app.

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Help available to landowners

Large landowners who are struggling to cope with hog damage do have options for assistance in Alabama. The USDA's Natural Resource Conservation Service will reimburse some costs for landowners to buy traps, provided they can demonstrate a significant pig problem and go through a training course on effective trapping technique.

The program can cover up to one trap per 200 acres of land for qualifying participants, and areas where multiple property owners can work together to have a larger impact are preferred to have a greater impact on larger populations.

The Alabama Cooperative Extension also has a remote-activated gate that they will rent out to farmers under similar conditions.

Landowners should contact the nearest USDA service center for more information about this program.

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More on feral hogs

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More on invasive species in Alabama