Are die-offs occurring more often?

To the casual reader, it can certainly seem that reports emerge on a regular basis of thousands of animals of a species suddenly dying.

The latest victims are common murres in the Northeast Pacific. They have been dying for months, but estimates of the toll jumped sharply when David Irons, a retired United States Fish and Wildlife Service biologist walking a beach in Whittier, Alaska, found close to 8,000 dead birds in early January.

Since then, scouting teams in boats from Fish and Wildlife, the United States Geological Survey and the Prince William Sound Science Center counted another 10,000 to 12,000 dead murres on beaches and in the open water of Prince William Sound, said Kathy Kuletz, a seabird specialist for the Alaska region with the Fish and Wildlife Service.

As with most die-offs, theories are close at hand. Murres weigh about two pounds and live in large groups, diving to feed on fish like juvenile pollock. In winter, they usually gather near the continental shelf, and they need to eat a lot to keep going, up to half their body weight in a day.

There are more than two million of them in Alaskan waters alone. But last year was not good for them.

The birds are emaciated and seem to be starving, according to the National Wildlife Health Center in Wisconsin, which has found no evidence of disease or toxins that could cause such deaths.

When there are changes in water temperature, as has been occurring in the Northeast Pacific, food fish may disappear.

Still, this die-off has surprised experts, because it has been going on for around a year and it covers such a vast area.

Most die-offs in the past have been more concentrated in time and space, said John F. Piatt, a seabird expert with the United States Geological Survey in Anchorage.

The effects of the current El Niño, a change in ocean currents, also have not yet reached Alaska. If history is any guide, El Niño means trouble to murres.

“I still don’t think we’ve seen the worst,” said Dr. Piatt, who said it was likely that 100,000 or more birds had died and speculated that if the worst happened, the deaths could reach into the many hundreds of thousands.

A tougher question for researchers is trying to understand how one population crash fits in with die-offs of other animals and whether die-offs have been increasing in recent years.

Certainly, there are remarkable recent events, like the death of half of all saiga antelope last year. And moose, bees and dolphins off the East Coast have also had die-offs in recent years.

Samuel Fey, a researcher in biology at Yale University, was moved by news media attention of die-offs to research whether they were really increasing over time. “These individual events garner so much attention,” he said. “They have shock and awe value.”

So he and Stephanie Carlson, a specialist in environmental science at the University of California, Berkeley, and a group of other researchers put together a database of more than 700 such events worldwide in 2,400 animal populations dating to the late 19th century.

Their analysis, published a year ago, showed that the magnitude of die-offs since about 1940 had increased. But in terms of frequency, all they could say was that reports of die-offs were certainly increasing.

They could not say whether the reports represented a real increase or just increased attention because, as Dr. Fey said last week after reports of the murre deaths, there is no central database of big die-offs of birds, fish, frogs and other animals.

He is, however, working to remedy this with Julie Lenoch, a veterinarian and deputy director of the National Wildlife Health Center of the geological survey in Madison, Wis.

The center does necropsies on wild animals sent to it by agencies like Fish and Wildlife and keeps track of what it finds. But, Dr. Lenoch said, “We only test samples we receive.”

And because that is their only lens on the phenomenon of die-offs, they are handicapped in trying to answer bigger questions.

“Understanding both the cause and consequence of animal die-offs is critically important,” she said, because disease may be involved, like rabies, West Nile or avian influenza, that could spread to farm animals, domestic animals or humans. Toxic chemicals may be a cause, and those can affect other animals and humans.

Or changes in climate or weather may be involved, and recognizing patterns could help prepare for future events and understand natural systems better.

Some databases exist now. The National Oceanic and Atmospheric Administration has one for oceanic wildlife. And the geological survey has a historical database of animal die-offs called Whispers that went online about a year ago. Separate databases are not adequate, however, she said. So she and Dr. Fey are hoping to have a meeting of representatives of state and federal agencies and others involved in animal care to begin work on creating a central database.

For the murres, there is nothing to be done other than observe, study and record the deaths, with an eye to understanding what they say about the effects of changes in the ocean.

The birds have a great capacity to rebound, said Dr. Piatt. From 1984 to 1985, he said, 95 percent of the common murres in the Barents Sea off Russia and Norway disappeared, apparently because of overfishing of capelin. Today, there are more of them there than ever.

On the other hand, when murres near the Farallon Islands off California had a population crash in 1983, some colonies almost vanished, and population growth was very slow after the die-off.

“Murres can rebound,” Dr. Piatt said, “But sometimes, they don’t.”