MONTELIBANO, Colombia — On a November morning, several drug runners sat down at a bar in the quiet hamlet of El Palmar. They had told the bar’s owner, Pedro Tapias, who doubled as an operator of the town’s boat, not to allow river crossings after 6 p.m.

The armed men demanded music and beer, said several residents. Shortly after 3 p.m., they got up, and pumped Tapias with no fewer than 13 bullets. Then, they slit his throat, turned up the music, locked the door and left town. The song played on. It was a vallenato — a traditional ballad often about loss and longing.

The next day, Tapias’ wife and 16 other families fled. In three months, El Palmar had lost a quarter of its population. “This was a big village, but now many houses are alone,” said Marelis Tapias Lopez, a niece of the murdered boat operator.

Across the northern department of Cordoba, residents are leaving en masse as drug gangs murder villagers and issue death threats. Drug violence is growing across the country, and has reached particularly alarming levels in Cordoba.

This latest incarnation of drug-trafficking groups has emerged following the demobilization of paramilitary soldiers. Between 2003 and 2006, after striking a peace deal with the government, more than 32,000 fighters belonging to the paramilitary group called the United Self-Defense Forces of Colombia (AUC) put down arms.

But many mid-ranking paramilitary commanders either never demobilized or slipped back into drug trafficking, starting up new gangs and recruiting ex-AUC fighters.

By 2006, the national police estimated these paramilitary successor groups numbered 4,000 across Colombia. Today, that number is about the same, despite 2,765 arrests of their members last year alone — a sign that their ability to replace killed or arrested members is outpacing increased police efforts.

“These groups are constantly renewing themselves,” said Col. Luis Eduardo Herrera, police commander of anti-drug gang operations for a wide swath of Cordoba. The Nuevo Arco Iris research organization estimates they number at least 10,000.

Perhaps nowhere is their presence more acutely felt than in Cordoba, a key battleground for several drug gangs fighting for control of trafficking routes to the Atlantic Ocean on Cordoba’s coast. Last year, the number of homicides in Cordoba reached 575, more than double from 2006.

Towns on the border of contested territory are often the worst off, such as El Palmar. It sits in Los Paisas’ turf, but on the other side of the San Pedro river lies the territory of the Black Eagles. Los Paisas’ men started coming here last year. Murders and disappearances followed.

They call town meetings to lay down rules. They offer residents $500 a month to snitch on a rival gang or the army. Anyone with a small business or several heads of cattle who fails to pay a “protection tax” can face death or expulsion. Anyone suspected of collaborating with their enemies can become a target — collaboration can be as simple as selling food to a rival gang or giving a boat ride to the military.

With no choice in the matter, residents say they are caught in the middle. “You have to take whoever comes,” said Dairo Ramos, who operated the town’s boat until his colleague’s murder. “If it’s the military, or that [armed] group or another, you can’t deny anyone crossing.”

Residents say living under today’s drug gangs is even worse than living under the AUC. Though the AUC paramilitary fighters were ruthless and violent, they operated within a hierarchical military structure.

Now, civilians face a confusing chaos of competing drug gangs who are often nameless and constantly re-structuring. “Today, there is no organization nor structures … Each boss does what he wants in each region,” said Father William de Jesus Guzman, whose parish is in El Palmar.

Military soldiers are now stationed in El Palmar and the drug gangs have retreated — for the moment. Inhabitants fear as soon as the army troops move elsewhere, the armed men will return with vengeance. “The day the military leaves, we leave too,” Father Guzman said.

Guzman fears El Palmar could soon be empty. While Colombia continues to have extremely large numbers of internally displaced people, the mass displacements that were characteristic of the AUC’s era subsided in recent years.

Now, in Cordoba, they’re starting back up — but this time due to the paramilitary’s successor groups. Those working with displaced populations in Cordoba can list town after town where groups of 50, 100, 150 people are up and leaving. Accurate numbers are hard to find however, because government statistics are incomplete.

Villa Carminia sits on the banks of the San Jorge river, an important drug-trafficking route. It’s easy to see how this small village of thatched-roof homes once known for its fine crops of watermelons was picturesque. But now, rubber boots and children’s sandals lie strewn in dirt streets overgrown with grass. The sparse furniture that remains in homes is tossed about.

There is little left but silence. Armed men started coming here in 2009. Sometimes, they sought out a villager to threaten or kill. Other times, the sound of gunshots between rival gangs sent residents hiding under their beds. Following a massacre last June in a neighboring settlement, rumor spread the drug gangs would hit Villa Carminia next. The next week, the town’s 350 inhabitants fled. Later, the village was ransacked.

Residents traveled two hours downriver to the city of Montelibano. Many have dispersed, but 19 families still take refuge in the city’s former slaughterhouse. Norma Ojeda Guerra doesn’t know where else to go, and she is still in shock over the fate of her community. “Villa Carminia lasted 22 years and 41 days, and never, never, did we see something like this,” she said from the passageway she now sleeps in where cattle were once herded to slaughter.

Villa Carminia is the first village known to be entirely displaced by the paramilitary’s successor groups. But it is likely not the last.

Active in about 150 to 250 municipalities, neo-paramilitary groups have become a major national security issue. They dropped in number from 33 in 2006 to seven today, according to police, but without a decline in their membership numbers, that may point to their consolidation rather than their weakening.

Police have boosted resources and efforts to fight the drug gangs. “We will see what is more decisive,” said Mauricio Romero, a conflict researcher at the Nuevo Arco Iris think-tank. “The pressure of the armed forces or the re-organization that is happening among these groups.”