Portland, Oregon -- The incidents have not tailed off, even since Sept. 11: a firebombing at a federal corral for wild horses in northeastern California; a fire at a primate research center in New Mexico, and back-to-back break-ins in Iowa, one at a fur farm to release more than 1,000 mink, the other to free pigeons raised for research.
All the incidents occurred in the last several weeks, and loose-knit groups like the Animal Liberation Front or the Earth Liberation Front have claimed responsibility. While many mainstream protest groups have scaled back their activism since the terrorist attacks, radical animal rights groups have not.
State and federal law enforcement officials say they are frustrated and angered by the recent acts of sabotage. Some investigators said they were worried that such vandalism could escalate because the groups involved knew that agents were already overwhelmed with reports of anthrax and terrorism.
"This is a horrible time in the nation's history," said Beth Anne Steele, a spokeswoman for the Federal Bureau of Investigation in Portland, which is looking into the incidents, "and to be adding to that with your own brand of violence just goes beyond the pale. If you look at the general public, there is even less tolerance than there might have been before for terrorism of any kind."
After the firebombing last month at a wild horse corral of the Federal Bureau of Land Management near Susanville, Calif., a radical group released a statement saying it was in reaction to the bureau's "continued war against the earth." The bombing caused about $80,000 in damage.
So far, no one has been arrested for the most recent attacks. To the degree that individuals or groups have offered any defense of the actions, they say their conduct constitutes neither violence nor terrorism.
In a statement, a Canadian-based faction of the Animal Liberation Front defended the attacks in Iowa, which took place on Oct. 17 and 18, saying that those involved were "giving these animals a fighting chance for survival."
Several other Iowa farms have been subject to break-ins and the release of animals in recent years, and the group's statement said such acts would continue until the animals' "blood stops spilling."
Several birds and mink died shortly after their self-styled liberators cut holes in fences and nets, when they were hit by cars or fell to prey, the farms' owners said. But the animal liberation group said the animals' release was preferable to the "tortures, gassings and electrocutions" they faced in captivity.
Between them, the Animal Liberation Front and the Earth Liberation Front have claimed responsibility for at least six actions since Sept. 11, and for many others in recent years, including fires at a Vail, Colo., ski resort, which they said impinged on lynx habitat, and a Long Island housing-construction site.
Several months ago, someone set fires at an Oregon tree farm and a genetics research laboratory at the University of Washington in Seattle. The Earth Liberation Front claimed responsibility.
The groups have no formal structure, but espouse philosophies, most publicly on the Internet, that support sabotage in defense of animal life or the environment. There have been few arrests in the cases.
Eco-saboteurs, as they are called, are also suspected in a Sept. 8 fire at a McDonald's in Tucson, that caused extensive damage. The initials "A.L.F." and "E.L.F." were spray- painted at the scene.
In addition, the authorities are investigating an incident last Monday at Michigan Technological University in Houghton, Mich., in which two homemade bombs were discovered at two buildings where forestry research is conducted.
The F.B.I., federal firearms agents and the Michigan State Police were called in to defuse the devices. The university said it had received e-mail threats from the Earth Liberation Front earlier this year after it received a grant for research that includes genetic manipulation of trees.
No one has been injured in the incidents, although law enforcement officials say it is only a matter of time before that happens, even if it is not the intent of the perpetrators.
In late September, vandals damaged oil-exploration equipment near Moab, Utah, leaving a postcard near the site that claimed the Earth Liberation Front was involved.
Other recent incidents include a firebombing on Oct. 15 at a corral of the Federal Bureau of Land Management, near Susanville, Calif., in protest of the roundup of the horses.
The Animal Liberation Front in Canada released a communiqué saying it was from the Earth Liberation Front, which said the firebombing was in reaction to the bureau's "continued war against the earth." It added: "In the name of all that is wild we will continue to target industries and organizations that seek to profit by destroying the earth."
One firebomb started a blaze, destroying a barn and about 250 tons of hay and causing a total of about $80,000 in damage. The vandals tore down part of a fence but failed to free the roughly 160 horses at the corral. Three other firebombs, connected to an electronic timer, did not ignite, though a nearby stretch of U.S. 395 was closed for 12 hours while the devices were removed.
While those who commit sabotage have remained anonymous, some animal rights activists have staged public protests recently. In Little Rock, Ark., on Oct. 29, animal rights protesters tried to breach a barricade at the downtown offices of Stephens Inc., a company with ties to a British company, Huntingdon Life Sciences, that conducts animal research.
Several protesters chanted "stop the torture, stop the pain" and wore animal masks, gas masks or bandanas. About 20 people were arrested on charges of disorderly conduct. The organizer, a Philadelphia group called Stop Huntingdon Animal Cruelty, says the company mistreats animals. Huntingdon Life Sciences says it complies with all government regulations on animal research both here and in Britain.