When a species experiences catastrophic population declines as high as 99.9 percent, any bit of good news is cause for celebration—even if the news isn't exactly great. India’s vultures now have some.

The birds were almost completely wiped out by a veterinary drug called diclofenac, but a new study finds that the number of deaths have declined by nearly two thirds since 2006. Unfortunately, the study confirms what we already knew: Despite the fact that diclofenac was banned in India in 2006 it remains heavily used, as does another drug, ketoprofen, one of several treatments that were brought in to replace diclofenac.

Both drugs treat inflammation in livestock, such as cattle (which are raised for milk but not eaten in Hindu culture), but they are fatal to vultures. When the birds eat carcasses of animals treated with the drugs, they experience acute kidney failure and die within days. India’s introduction of diclofenac in the 1990s proved immediately calamitous to the country's vultures. One species, the Indian white-rumped vulture (Gyps bengalensis), declined by 99.9 percent. The Indian vulture (G. indicus) and slender-billed vulture (G. tenuirostris) experienced similar declines. All three species were classified as critically endangered in 2000.

The loss of the vultures had a cascading effect. Without the scavengers to eat fallen cows the number of feral dogs increased, as did incidents of human disease. One religion, Zoroastrianism, whose members leave their dead for the vultures, also had to build $5-million worth of vulture aviaries to maintain their tradition.

The good news arrived in a study published October 13 in Philosophical Transactions of the Royal Society B. It says the ban has started to do some good. Researchers from the Royal Society for the Protection of Birds (RSPB) and other institutions studied vultures and fallen cattle carcasses from 2006 to 2010. In 2009 alone the number of carcasses of cattle treated with diclofenac had dropped by 49 percent. The researchers extrapolated this to conclude that, based on vulture feeding behaviors, diclofenac-related vulture deaths had declined by 65 percent.

Of course, with the populations of all three species already devastated, 65 percent doesn't add up to all that much, but it is a step in the right direction.

Here's the bad news: "Indian pharmaceutical companies are manufacturing diclofenac for human use in vials large enough to treat livestock," RSPB conservation scientist Toby Galligan noted in a press release. "Some veterinarians and livestock owners continue to choose diclofenac over the vulture-safe alternative, meloxicam." Their tests found that 6 percent of livestock carcasses are still contaminated with the deadly drug. This, Galligan said, "equates to one in 200 vultures dying from diclofenac poisoning every time they feed." During the period of catastrophic decline, that rate was three in 200, not much higher.

Galligan has an interesting idea for making more progress: continue to allow diclofenac to be sold for human use (it's good for arthritis) but limit it to vials no larger than three milliliters. This will make it harder to use in veterinary settings.

The paper makes no suggestions about ketoprofen but notes that it is not as widely used and breaks down quickly in deceased cattle. The drug was detected in less than 1 percent of carcasses tested in 2006. Other diclofenac substitutes—such as meloxicam, which appear to be safe for vultures—have achieved wider usage. Ketoprofen remains legal in India.

Vultures need more intervention—and quickly, if they are expected to survive. And not just in India. Last month BirdLife International warned that European and African vultures are also at risk from the drugs and other intentional poisonings, and could all disappear within a generation. The organization called vultures "one of the most threatened families of birds on the planet."

Photo: Indian white-rumped vulture by Lip Kee Yap via Flickr. Used under Creative Commons license