CULIACAN, Mexico -- "They're innovative, these people," says Mexican Col. Ricardo Alvarez.

Alvarez was at the Culiacan airport looking over one of the most curious air forces ever assembled: scores of planes confiscated from drug runners resting wing-to-wing on the tarmac.

The planes are among the 400 aircraft Mexico has seized in the past five years: a fleet bigger than the Mexican air force. They are a virtual case study on how smugglers have been adapting their fleets to counter President Felipe Calderon's crackdown on the drug cartels, say Mexico authorities.

Alvarez says the planes are a window into how traffickers always find ways around the crackdown, from ultralights that can skim across the U.S. border to satellite-driven tracking equipment that helps smugglers locate drug shipments.

"They'll try anything," he says.

Finding new places to land

Gone are the days when twin-engine planes could fly drugs directly from the fields of Colombia to northern Mexico for delivery across the border via couriers. Those long-range flights raise too much suspicion on radar.

Now, cocaine shipments arrive in Guatemala and are brought into Mexico by land or boat, the Mexican Attorney General's Office says. Small planes move the drugs northward to avoid the army checkpoints that have sprouted on Mexico's highways.

Drug pilots are having to land in more rugged areas because the government has destroyed 2,086 unregistered airfields since 2006. As a result, almost all of the seized planes at the Culiacan airport are single-engine Cessnas that can haul a lot of weight and have high wings ideal for landing on dirt roads or desert washes.

"They're like a Volkswagen Beetle -- they take a lot of abuse," Alvarez says.

Many planes have modified wings so they can take off from short strips, or metal plates attached under the nose to protect the engine from gravel. Some have homemade extra fuel tanks behind the seats or extra-big tires for landing on rocky terrain.

One homemade plane with folding wings is painted to look like a federal police aircraft, with blue-and-white markings and the Mexican government crest on the sides.

Most of the planes were caught bringing drugs to the border in Mexico for eventual shipment to the United States. At any given time, the army has about 100 seized planes at the airport that are auctioned off or given to government agencies to use.

Smugglers have begun using ultralights, simple aircraft made from aluminum tubes and fabric to carry drugs directly across the border. Ultralights are harder to detect on radar and can land and take off on strips of land as short as 100 feet.

Three ultralights have crashed in Arizona since late 2008. On Oct. 6, a Border Patrol agent spotted an ultralight fly over the border near San Luis, Ariz., drop 176 pounds of drugs, then fly back into Mexico. It was not caught.

The USA has pledged millions of dollars to help Mexico better track drug flights as part of the Merida Initiative anti-drug package. It's upgrading Mexico's Cessna Citation chase planes with better sensors, buying four CASA 235 patrol planes for the Mexican navy, and giving as many as 16 helicopters to the Mexican army and Federal Police.

The Mexican government claimed a key victory against drug planes in February with the arrest of Jose "Wild Boar" Vazquez Villagran, who police say was the main dispatcher for the airplanes of the Sinaloa Cartel.

"We've cut a lot of their capacity to move around," Alvarez says.

Market expands overseas

Even as authorities claim progress in grounding drug planes in Mexico, the cartels are using aircraft to exploit new routes.

Drug flights between South America and the Caribbean nations of Haiti and the Dominican Republic have been rising since 2006, the U.S. State Department says. And smugglers from South America are crossing the width of the Atlantic Ocean to move cocaine into Europe by flying it into West Africa first. The market for cocaine in Europe has been expanding at the same time that cocaine use in the United States has declined from its peak in the 1980s, according to the United Nations Office of Drugs and Crime.

"For a while, they've been pushing small amounts (across the Atlantic) to test the system and see how it works. But they seem to have reached a breakthrough," says Douglas Farah, an expert on drug trafficking at the International Assessment and Strategy Center, a Washington think tank.

In September, U.S. prosecutors said they had uncovered a smuggling ring dubbed "The Organization," which was flying cocaine from Venezuela to countries in West Africa. There is no radar over the ocean so such flights are virtually undetectable. Pilots were paid up to $300,000 per trip, the Department of Drug Enforcement said in an affidavit, citing informants and agents.

On Nov. 2, tribesmen found the burned-out hulk of a Boeing 727 in the sand in the Gao region of Mali. Investigators believed the plane came from Venezuela and was used to smuggle drugs, Alexandre Schmidt of the U.N. Office on Drugs and Crime said.

In December, Antonio Maria Costa, the head of the U.N. office, called the 727 discovery "a new example of the links between drugs, crime and terrorism."

"Drug trafficking in the region is taking on a whole new dimension," Costa told members of the U.N. Security Council.

Hawley is Latin America correspondent for USA TODAY and The Arizona Republic