Tuesday, 3 April 2012

African Vulture Declines

I saw this hooded vulture in Tarangire this weekend, so they are still around!
I've spent a bit of time over the last few days analysing some of the data from the Tanzania Bird Atlas project on vulture declines in advance of a workshop happening soon in the Maasai Mara. The Asian vulture decline is quite possibly the fastest decline in any bird species ever recorded, with more than 95% of the Indian population of Oriental White-backed Vultures dying between 1988 and 1999, from one of the commonest large raptors in the world to one of the rarest. It's now well know that the cause of that decline with the veterinary use of a drug called Diclofenac which, happily, isn't in quite the same usage here in Africa - sick o dying cows tend to be eaten here, not treated with drugs and then left for the vultures. But although the declines haven't been as steep and there are still plenty of vultures in places here in East Africa, there's still a problem.

Changes in Egyptian Vulture distribution (after accounting for observer effort) from 1980/1990s to 2000s.
Red are where the change has been observed, black is where the models fill in observer gaps.
Juvenile Egyptian Vulture (note tail shape) on the Mara River,
only recent evidence of breeding in TZ Sep 2011

In the Maasai Mara, studies are suggesting around 60% decline in vulture numbers, whilst in South Africa and west Africa the problem is even greater, with near total loss of vultures in many areas. Monitoring in Tanzania isn't our strongest point, but the data that the Tanzanian bird atlas have produced show some obvious patterns here too. Look at these maps above I generated today of Egyptian Vulture, for example, showing the changes between the earlier records from 1970 and 1980s to post 2000 records. It's clear that until 1980 you had a chance of seeing this species across much of northern Tanzania. Since 2000 you've only really stood any chance at all in the Serengeti Ecosystem, and to be honest more recently it's extremely rare, with just a handful of records each year from this area. Whilst this is far and away the most extreme decline, my analysis today suggests there's also something happening with Ruppell's and White-backed in Tanzania, so we shouldn't be complacent.
Ruppell's Vulture, Serengeti, Sep 2011
So, what's going on? Well, most of the declines are probably due to poisoning. There's no shortage of meat in the parks of East Africa, so we can rule food out (although this isn't necessarily the case with declines in West Africa, where large mammal populations are virtually zero on many areas too). Poisoning occurs for all sorts of reasons, deliberate or accidental: people leaving poison out to (illegally) kill lions are likely to kill vultures too. In the past poachers are said to have diliberately have targetted vultures, since their movements may give anti-poaching teams an idea of where recently killed carcasses lie. And more recently, there's evidence that killed animals are being used to supply traditional medicine demand from elsewhere in Africa: if it weren't so damaging, I'd find it fascinating to learn that because vultures have such good eyesight, practitioners of juju in South Africa have attributed them with foresight and use their body parts to divine football results! One question we haven't really managed to address yet, though, is why the smaller species (Egyptian Vulture and Hooded Vulture) seem to have been declining first and fastest? Are they simply more exposed to poison, being rather more closely associated with humans? Or what? Any ideas gratefully received!

Lappet-faced Vulture, Serengeti, Sep 2011
Some, of course, might think it doesn't matter and we shouldn't care. But, as I've already said on this blog when talking about how to identify the various east Africa vulture species, vultures are really important ecologically as keystone scavengers. Take them away and other animals (and potentially people) suffer: populations of other scavengers such as dogs can increase, leading to increases in rabies (and the potential for infected animals to bite people, or spread this and other canine diseases to wild dogs, etc.). Human anthrax case increases are also attributed to vulture declines in some places. They also show other scavengers the way to dead animals, enabling a lot of opportunistic scavengers to benefit too. So I suggest we should be concerned. And if you're in Tanzania, do let us know where you see some of the rarer species - and in September I'm expecting there'll be a vulture counting day organised, so keep looking here and see how to get involved!

Main reference:
ResearchBlogging.orgVirani, M., Kendall, C., Njoroge, P., & Thomsett, S. (2011). Major declines in the abundance of vultures and other scavenging raptors in and around the Masai Mara ecosystem, Kenya Biological Conservation, 144 (2), 746-752 DOI: 10.1016/j.biocon.2010.10.024

1 comment:

  1. That very interesting, I didn't know that vultures were declining. I believe it does have to do with poisoning and the smaller species are declining faster because the poison affects them more. In the USA the use of the pesticide DDT causes rapid decline in our bald eagle, peringrine falcons, ospreys and other raptors so I can defiantly see that poison might be affecting the vulture population. It also might have to do with climate change here in Colorado summers have been longer but also dryer this is affecting our bird population. Maybe something like this could be happening in Africa. Another idea is an external problem. Maybe habitat outside of the birds feeding areas is being destroyed like roosting and nesting sights or even wintering grounds. I know that many of our bird are being affected by this. These are some ideas I have for the vulture decline.