December 2017: Asian vulture population estimates lower than previously thought
Blog by Dr Toby Galligan, Senior Conservation Scientist, RSPB Centre for Conservation Science
South Asia’s vultures underwent catastrophic population declines in the 1990s and 2000s. The veterinary drug diclofenac, a cure-all for cattle, but a poison to vultures, was the cause of these crashes. Vultures were exposed to diclofenac while carrying out their ecosystem service to humans – that is, disposing of cattle carcasses. Three resident species of Gyps vulture formerly considered abundant are now considered critically endangered.
Figure 1: A slender-billed vulture (Gyps tenuirostris) with its dark grey neck and head stands in the centre. It is flanked on the left and right with an immature and mature white-rumped vulture (Gyps bengalensis), respectively. Further left and right are two Himalayan griffons (Gyps himalayensis). All these species are intolerant to diclofenac and other vulture-toxic NSAIDs and all have undergone declines in South Asia. Photograph by Natasha Peters.
The RSPB Centre for Conservation Science and our BirdLife partner in India, the Bombay Natural History Society, have monitored the population of the three resident Gyps vultures across India from before the crashes. Every three years, we repeat a survey covering approximately 15,500 km road among 154 road transects and 13 states in northern, central, western and north-eastern India. We count individual white-rumped (Gyps bengalensis), long-billed (Gyps indicus) and slender-bill (Gyps tenuirostris) vultures.
In 2007, we crudely estimated the population size for each species as 11,000 for white-rumped vultures, 45,000 for long-billed vultures and 1,000 for slender-bill vultures. In 2012, we reported a slowing in the decline for all three species and the possible first sign of recovery in the white-rumped vulture. These were encouraging findings that made the headlines.
New population estimates
Our new population trends and size estimates for these species in India were published in Bird Conservation International today. We added one more survey (2015) to the trend analysis and recalculated population size using a more sophisticated method then in 2007. This time, our findings were less encouraging.
The good news is that the positive trend for white-rumped vulture population appears to be continuing. The bad news is that the long-billed and slender-billed vulture populations continues to decline. In addition, the best estimate of population size for all three species is much lower than previously estimates. In 2015, we estimate there were approximately 6,000 white-rumped vultures, 12,000 long-billed vultures and 1,000 slender-billed vultures. These numbers are alarmingly low.
Figure 2. Population indices and trend of white-rumped vulture in India. Points show indices of population density, relative to that in 1992, estimated by log-linear Poisson regression performed on data from seven road transect surveys in northern India. Vertical lines show 95% bootstrap confidence intervals. The curve is the quadratic log-linear population trend fitted to data for the period 2000–2015. Reproduced from Prakash et al. 2017 Bird Conservation International.
Diclofenac remains a problem
Veterinary diclofenac was banned in India in 2006, but manufacturers continued to make and distribute large vials of diclofenac supposedly for human medicine. We continued to be sold diclofenac for treating cattle during pharmacy surveys and we continued to recover dead vultures that had been poisoned by diclofenac. A second ban on the large vials of diclofenac was put in place in 2015. It is hoped that this second ban will finally bring about an end to the production of diclofenac and its use in cattle.
Figure 3. Population indices and trend of long-billed vulture and slender-billed vulture combined in India. Points show indices of population density, relative to that in 1992, estimated by log-linear Poisson regression performed on data from road transect surveys in northern India. Vertical lines show 95% bootstrap confidence intervals. The line is the log-linear population trend fitted to data for the period 2000–2015. Reproduced from Prakash et al. 2017 Bird Conservation International.
Other toxic-NSAIDs present a bigger problem
Diclofenac is only one of over a dozen drugs known as non-steroidal anti-inflammatory drugs (NSAIDs) available in India. We know that one of the other NSAIDs called meloxicam is non-toxic to vultures. However, we also know that five other NSAIDs (aceclofenac, carprofen, flunixin, ketoprofen and nimesulide) are toxic to vultures, none of which are banned. We lack evidence either way for the remaining five or so available NSAIDs, but we must consider them potentially vulture-toxic until shown to be otherwise.
The use of other vulture-toxic NSAIDs in cattle could prevent the recovery of white-rumped vultures and continue the decline of long-billed and slender-billed vultures. Our paper is reminder that the vulture crisis in India is not over and more regulatory actions on vulture-toxic NSAIDs need to happen to save the countries vultures from extinction.
For more information on vulture conservation work by the RSPB, BNHS and SAVE partners visit the SAVE website.
You can find the paper here: https://doi.org/10.1017/S0959270917000545
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