BOGOTA, Colombia (AP) _ Once Louise Augustine decided to visit Colombia on a bird-watching expedition, there was no dissuading her.

Friends tried, warning the 63-year-old retired teacher and former nun about rebel and drug-related violence. She was excited, and a State Department travel advisory wasn't going to change her mind.

Ms. Augustine, from Chillicothe, Ill., spent her fifth day in captivity Saturday with three other American bird-watchers, an Italian and several Colombians. All were kidnapped by leftist guerrillas in rugged mountains south of the capital, Bogota.

``They knew the risks and they were cautioned not to go there,'' her brother, Jerome, told The Associated Press in a telephone interview from his Peoria, Ill., home. ``Several birders refused to go with them.''

Along with Ms. Augustine, the Revolutionary Armed Forces of Colombia, or FARC, abducted Peter Shen of New York City and Tom Fiore and Todd Marks, whose hometowns were not available. The Italian, who was not with the group, was identified as Vito Candela, a Bogota business owner.

The FARC commander holding the group, Comandante Romana, told the AP that rebels were evaluating the foreigners' wealth to decide how much ransom to demand. On Friday, he had said that anyone having more than 1 billion pesos _ $735,000 _ must pay a 5 percent ``peace tax.''

Romana, a man with a $75,000 bounty on his head who grinned for photographers Saturday at his mountain compound near El Calvario, would not allow journalists to see the captives. He said they were being held at a site about four hours away.

The foreigners, including Ms. Augustine, were in good shape and would not be harmed, he said, but negotiations could take six months to a year.

Romana, a bearded 29-year-old wearing green military fatigues and a dark beret, also defended the killing of four people during Monday's hostage-taking at a highway roadblock 35 miles south of the capital, Bogota.

``Those are four dead paramilitary fighters,'' he said.

He said he released nine Colombians on Friday because they were not linked to paramilitary death squads, the rebels' enemies, and were not wealthy enough to make a ransom demand worthwhile. Originally, about a dozen Colombians were kidnapped Monday.

Leftist guerrillas have been fighting the state since the 1960s and increasingly have relied on kidnapping for ransom and extortion to fund their insurgency. As a result, Colombia has the world's highest kidnapping rate, with about four abductions a day.

Colombia also has the greatest diversity of birds in the world, with some species found nowhere else on the planet.

Yet bird-watching in a known guerrilla stronghold is dangerously naive, said Juan Mesa, assistant director Pais Libre, a Bogota-based kidnapping research group.

``If you come to a country in conflict in the middle of a civil war without really knowing what areas are dangerous ... you are really putting yourself in danger,'' Mesa said.

Foreigners long have been prized quarry because they fetch the highest ransoms, and Mesa said being of modest means won't make much of an impression.

``One must think like a rebel soldier who doesn't have much outside contact,'' said Mesa. ``They have a very basic outlook on the world. To them a foreigner is a 'gringo' and has money.''

Gen. Manuel Jose Bonnet, the armed forces commander, said he lacks the resources to protect intrepid tourists.

``We do what we can to safeguard foreign investments and to protect people,'' he said. But ``we don't have enough troops to cover the entire country and all the highways.''

Ms. Augustine was at least somewhat familiar with the country _ her brother said she'd spent three months in Colombia once before _ and her passion for birdwatching had taken her all over the world.

She and the others apparently wandered by chance into the rebel roadblock, on a highway notorious for guerrilla activity where two weeks earlier rebels held up traffic for five hours and killed a policeman.

Last year a Brazilian construction company pulled out of a $34 million highway-improvement contract on the same stretch of road after two of its engineers were kidnapped by rebels. The company paid $1.8 million to free the men, who were held for seven months. It pulled out after rebels demanded more money to let the project continue.

Rebels rarely kill their captives, with one notable exception being three American missionaries missing since their 1993 abduction and feared dead. Mesa described the rebels as tough negotiators because of their willingness to wait as long as necessary to get a high ransom.

The average kidnapping in Colombia lasts more than four months, but Jerome Augustine said he was hoping his sister would be freed sooner because of her age and a foot infection that was still mending.

``Louise could have some problems if they keep her too long,'' he said. ``We're all worried about her, but she's a survivor.''