Is one of nature’s finest clean-up crews under threat from the drugs administered to Europe’s livestock?

The Eurasian griffon vulture (Gyps fulvus) fills an important ecological role by feeding on the carcasses of wild and domestic animals. Although not the most attractive of species, their role in naturally removing dead animals from farmed land has been shown to cut down on greenhouse gas emissions associated with disposing of livestock that can’t be used for human consumption. In recent years, two veterinary drugs containing an ingredient known to be toxic to vultures have been approved for use in livestock in Spain, which is home to 95% of the European breeding population of griffon vultures. A recent study by conservation biologists based both in the UK and Spain has looked at the potential impact this could have on populations of Europe’s vultures.

Diclofenac is a non-steroidal anti-inflammatory (NSAID) used to treat the symptoms of a number of common livestock disorders, including mastitis. Unfortunately, the standard veterinary dose that benefits livestock is bad news for vultures – it results in kidney failure and often a rapid death for the birds when they feed on the bodies of treated animals. Diclofenac use in livestock has been shown to be responsible for the Indian vulture crisis, which resulted in a >90% decrease in the numbers of three species of vulture between 1993 and 2002, with catastrophic consequences. Dogs and rats have increasingly stepped in to fill their role as scavengers, and their numbers have risen in India in parallel with vultures’ decline. This is significant given that vultures are often a ‘dead-end’ for diseases which could affect humans, whereas dogs and rats are more likely to carry and transmit diseases to the people around them. Carcasses left to rot rather than being naturally removed can themselves also pose a health risk, and their safe removal costs farmers time, energy, and money.

So why is diclofenac currently approved for veterinary use in Spain, and what is its impact on the Eurasian griffon vulture likely to be? The Eurasian griffon vulture is currently not a threatened species, but legislation in Spain allows dead livestock on farms to be made available to scavengers, so it could well be under threat.

The scientists investigating have predicted the annual number of vulture deaths and the impact on Spanish vulture population that could result from diclofenac use. They based these predictions on estimates of vulture food requirements, what we currently know about the mortality rate of diclofenac in Gyps vultures, and estimates of vulture reproductive success. Worryingly, they estimate that diclofenac use in livestock will result in a decline in the vulture population of between 0.9-7.7% per year. These estimates are higher than those previously calculated by Spain’s medicines agency and agriculture ministry, and are significant given that this species live for a long time (up to 40 years in captivity) but reproduce relatively slowly – each pair produces no more than one chick per year. This is a combination of traits that makes their population particularly sensitive to anything that could increase the adult mortality rate.

No large declines in the Spanish vulture population have been reported so far, since the veterinary use of diclofenac was approved in 2013, and these new estimates suggest that the impact in Europe is likely to be less catastrophic than in India. However, given how valuable vulture populations are, not just to biodiversity but also public health, it would be wise to be cautious. The researchers propose that a precautionary ban on diclofenac use in Spanish livestock would be justified. Instead, they encourage the use of meloxicam, another NSAID which does not harm vultures at commonly used veterinary doses. In this case, for Europe’s vultures, it would be better to be safe than sorry.

references

Green, R. E., Donázar, J. A., Sánchez‐Zapata, J. A., & Margalida, A. (2016). Potential threat to Eurasian griffon vultures in Spain from veterinary use of the drug diclofenac. Journal of Applied EcologyDOI: 10.1111/1365-2664.12663

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