Pharmaceuticals introduced into the animal food chain merit consideration when we look at the recent spate of bird and mammal deaths.

A case in point is the killing of millions of vultures in India and Pakistan five or six years back:

the drug, diclofenac, has been used in human medicine for decades, it has only recently been introduced for veterinary use in India and Pakistan. Vultures appear to have been exposed to the drug while scavenging livestock carcasses.

Further, it is reported that

In 2006 India banned the production and sale of diclofenac, an important step in halting the extinction of slender–billed (Gyps tenuirostris), Indian (Gyps indicus) and white–rumped (Gyps bengalensis) vultures. Each of the three species had declined by as much as 97% in 15 years.