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Causes of declines
Following the identification of the declines, a number of hypotheses were proposed about the possible causes, including contaminants, infectious disease and food shortage. The geographical pattern, extent and spread of declines, along with results from analyses of blood from sick birds, and tissues from dead birds in India, initially suggested infectious disease as a likely cause of the declines. However, research by The Peregrine Fund in Pakistan discovered that the major cause of the population decline was diclofenac, an non steroidal anti-inflammatory drug (NSAID) used widely in veterinary medicine across South Asia (Oaks et al. 2004, which can be accessed from this web page of The Peregrine Fund). Research by Vulture Rescue has confirmed that diclofenac is the cause of vulture declines across the rest of the Indian subcontinent (Shultz et al. 2004), and population modelling has shown that less than 1% of carcasses need to contain a lethal quantity of diclofenac for this drug to be the main, or only, cause of the decline in vulture numbers (Green et al. 2004).
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