Common Birds: the case of the Baglafecht Weaver and missing forests

Male Baglafecht Weaver, Mt Kilimanjaro

 If you live on or near an East African mountain, you're very likely to have Baglafecht Weavers in your garden. Like most of the other true weavers, they're a basic black and yellow colour. The first thing to look at in weavers is usually the colour of the eyes and legs: in Baglafecht weavers you'll always see a yellow eye (easy to see against the surrounding black feathers) and pink legs. Males and females differ slightly: males in the population in northern Tanzania and Kenya have only a black mask on the face, with yellow on the top of the head right down to the (black) beak. Females have an all dark head. In northern Tanzania the back of both sexes is essentially black, with some yellow wing edges, in other areas of Tanzania the back is greenish/grey and not as strongly contrasting. Juveniles of all forms are rather greener and lacking in black, but still have the yellow eye. Like other weavers, they weave their nests from grasses in colonies of 5-15 pairs (not usually in very large groups) and males in the breeding season are pretty noisy with their rather scratchy and squeeky song!

Baglafecht weaver nests aren't the neatest of affairs...

Revising climate impacts on African vertebrates

A few weeks ago I wrote a piece on climate change and African vertebrates. As I usually do, and especially in this case as Raquel had pointed the paper out to me, I let her know that I'd written something and asked her opinion. After quite a few emails back and forth we confirmed that I'd misunderstood a figure in the paper that I'd thought was the crux of the matter, but it turns out to have been not as useful at all.In light of these discussions, Raquel and colleagues have now produced an addendum to their paper that contains the figure I thought I was looking at and, although I still have some issues with the work, it makes much more sense to me now! In the interests of getting all this information out there, as well as my pointing out the mistakes in the original post and Raquel posting a comment there, I thought her ideas were valuable enough to reprint in full from the comment as a new post, with some more discussion here. So, here's what she has to say:

Distribution of Ethiopian Bush-crow and the nature of explanations

Yesterday I was sent a link to a press release from the excellent BirdLife International (read it here). It's talking about some research by an international team to try and explain the remarkably restricted range of the Ethiopian Bush-crow (cute picture here, since I've never actually been there to take my own), and in it, Paul Donald the lead author makes some interesting comments:

“The mystery surrounding this bird and its odd behaviour has stumped scientists for decades – many have looked and failed to find an answer.  But the reason they failed, we now believe, is that they were looking for a barrier invisible to the human eye, like a glass wall. Inside the ‘climate bubble’, where the average temperature is less than 20°C, the bush-crow is almost everywhere.  Outside, where the average temperature hits 20°C or more, there are no bush-crows at all.  A cool bird, that appears to like staying that way.”

The reason this species is so completely trapped inside its little bubble is as yet unknown, but it seems likely that it is physically limited by temperature – either the adults, or more likely its chicks, simply cannot survive outside the bubble, even though there are thousands of square miles of identical habitat all around.

BirdLife International’s Dr Nigel Collar is co-author of the study. He added “Whatever the reason this bird is confined to a bubble, alarm bells are now ringing loudly.  The storm of climate change threatens to swamp the bush-crow’s little climatic lifeboat – and once it’s gone, it’s gone for good.”

Climate change and African vertebrates

Last year I spent a very happy evening in Cape Town enjoying some of the local specialities with a colleague and a visiting student. Or at least, that's what I thought - poor Raquel now tells me I was giving her a hard time... Still, good practice for her eventual defence of her thesis I hope. Anyway, she pointed me in the direction of the paper she was writing at the time that's now out and attempts to describe what's going to happen to some 2723 species of African vertebrates as the climate changes over the next several decades. Now, despite climate change being a huge conservation issue and one of my main research interests (and climate/weather being one of my 10 things to talk about), we've not talked much about it here on the blog before, so the chance to discuss what might happen to 2723 species across the continent as a whole is an ideal opportunity to start!

TAWIRI Conference discussions

I've spent most of this week at the Tanzania Wildlife Research Institute (TAWIRI) conference here in Arusha. This is an event that happens every two years and involves a very high proportion of researchers active across Tanzania, so it's always a good place to hear about interesting things going on in these areas. I thought I'd give a few of my highlights today. The two talks that most exicted me were from two different aspects of ecology - one by Dr. Grant Hopcraft on the Serengeti and how climate change might impact wildlife there, the other also related to Serengeti, but this time by Dr. Dennis Rentsch from Frankfurt Zoological Society on the economics of the bushmeat industry. I know both of these folk fairly well, so was able to press them for lots of extra information about both talks, and what I'm going to descibe here represents both their presentations and some of the other stuff we talked about - I hope they don't mind me putting this information out before it's all polished and published!

Wildebeest and zebra migrating through Grumeti Reserves, Feb 2010

Grant knows rather a lot about Serengeti and, in particular, the herbivores of the system. His work has focussed on how nutrition impacts herbivores and his talk fitted well into the overall theme of the conference on climate change, by asking how climate change will affect the nutrient content of the grasses and how this might impact the animals that feed on them. You might think it's crazy to suggest that climate change impacts grass quality (i.e. nutrient content), but actually it can have some pretty profound impacts indeed. Grass growing in high rainfall areas gets very tall very quickly, but also tends to be poor in nutrients - it might be that the grass can only collect the same amount of nutrient from it's roots, but in wet years it grows faster, so there's less nutrient per leaf than in dry years when the plants can't grow as much and pack all the nurients into a smaller volume. So more rain means lower quality grass, but more of it, less rain would mean less, but higher quality grass. In fact, lots of people showed plots of rainfall in Serengeti and demonstrated that the area is getting wetter (though I also suspect there might be shifts in the dry season length which could be even more significant, but no-one really talked about that), so we should be seeing more, lower quality grass. What is the consequence of this? Well, according to Grant, perhaps it means different things for different species, since all the herbivores prefer slightly different combinations of nutrient quality and grass quantity. In particular, hind-gut fermenters like zebra are happy with lots of relatively low quality food, whilst wildebeest are typically selective ruminants and need higher quality grass. Now, Wildebeest in Serengeti are food limited, not predation limited or anything else, so a decline in food quality might be bad for them - but they are, of course, interested in quantity too, particularly during the dry season when any rain is going to provide grazing which is clearly better than no rain at all. So a wetter Serengeti, if it impacts the dry season too, is probably going to mean more food at this crucial dry-season food shortage period, and we can expect that even in a wetter dry season the rain will still be scarce, so the grass will be relatively nutritious. So on the one hand poorer-quality forage during the wet season might be bad news, but more grass in the dry season is certainly going to be good news - which effect wins out isn't yet clear. My money will be on the dry season effects, but we'll wait to see! On the other hand, it seems pretty unambiguously clear that a wetter Serengeti will be good news for zebra, provided again that the dry season remains at least a bit wet too. So more zebra will always be good - though how that will affect everything else is also tricky to forsee. Does more zebra mean better facilitation for the wildebeest? Or might there be more competition? Who knows, as usual, more research needed (and if you want to fund Grant on his next project, do let him know - he's searching for money right now!).

The migration reaches Seronera, Nov 2010. Don't get eaten!

Spot the snare: many animals are poached in Serengeti. Moru Jan 2011

Meanwhile Dennis has been working on bushmeat trade on the western side of Serengeti for many years now. His approach to studying what is, after all, an illegal activity has been to deal not with the hard end in the park of finding and apprehending poachers and trying to get them to tell him how many animals they hunt (they're very unlikely to give an honest answer in such circumstances!). Instead he's focussed mainly on trying to work out how much bushmeat is being consumed in the villages around the Serengeti by asking them about the various protein sources they eat during the week. Although there might still be some resistance to tell the absolute truth in this context, it's likely his numbers are underestimates of the full impact of the harvest (especially as it doesn't include any of the meat that gets exported from the region commercially). Underestimates they might be, but the numbers are still staggering. In the villages surveyed, the average number of meals of wildebeest eaten per family per week was 2.4. Obviously that goes up during the period when the wildebeest are migrating through the particular village, and down when they're far away, but 2.4 meals per week is the average for the villages immediately around Serengeti NP. And knowing the number of households in each village, plus the number of villages Dennis estimates that somewhere between 90,000 and 100,000 wildebeest are harvested (illegally) from Serengeti each year. To put that into context, it's equivelant to a harvest greater than the entire wildebeest population of South Africa each year!

At between 500 and 1500TSh / kg (depending on seasonal availablity), and assuming a conservative 100kg of meat per animal that gives a a total market value of $2.5 - $8.5 Million per year. Compare that to TANAPA income from Serengeti gate fees 10 years ago (the latest I can find online) at about $5.23 Million, and we're talking the same size economy. (Bear in mind that these TANAPA fees are used throughout the national park system to subsidise less well visited parks, so Serengeti NP actually has an opperating budget of only around $2Million per year.) That's a pretty remarkable figure on it's own, but Dennis went on to talk about how consumption is related to price of other meat in the area - if the price of beef goes up, more wildebeest is eaten. Which suggests that it might be possible to reduce the amount of wildebeest eaten, if you bring the price of beef down. Now unfortunately I wasn't quick enough to get all the figures off Dennis's slide to do the calculation here, but I think I'm right in saying that if you want, say to halve the wildebeest harvest, his figures suggest you need to bring the price of beef down by about 3 times as much - so 50% of 50% of 50%, which is an 87.5% reduction in price. That's probably going to be tricky to achieve, unless you fill Serengeti with cattle, which is hardly going to help! So you're rather stuck there. Instead, the only effective solution is to make the wildebeest more expensive - and Dennis suggested you can do that either by giving poachers alternative employment and dry up the supply of meat, or by even more strictly enforcing the regulations within the park. But bear in mind that this is a sustainable harvest - there's no impact of this level of poaching on the wildebeest population overall. The problem is the bycatch - people want to trap common wildebeest, but instead their snares catch resident game sometimes and have had a missive impact. So instead of strictly enforcing current regulations, perhaps TANAPA should be looking at ways to encourage sustainable use and minimse the negative off-take. Perhaps making a few million $$ in the process. What do you think? Should we go this way? Or how should we feed these people?

East African climate

One of my 10 things to talk about that I haven't touched on very much so far is the weather, which is a bit of a surprise as I'm British, and apparently talking about the weather is the top thing that identifies us Brits. Even more so, as studying the impacts of climate change on the savannah is what pays my salary at the moment. So, it's about time that was rectified a bit and our recent trips to northern Serengeti and Tarangire have given me the ideal inspiration to do so.

Southern Serengeti is dry whilst the north is already green: Mwiba August 2011

Why do I think that the weather (or more generally, the climate) is something worth talking about (apart from because I'm British, of course)? Well, firstly it makes a huge difference to the ecology of the system - we've already talked a lot about how water availability make a huge difference, and most (though not all) of that is due to differences in rainfall. So understanding the seasons will help make sense of what's happening throughout East Africa. But also because the climate in East Africa is completely different to the climate where most of your clients come from - visitors from the north are mostly used to four seasons of different length and severity depending on quite where they live. There's winter, from about Dec - Feb, when it's cold wet (or snowy), the days are short (seriously, before I moved out here we lived in Aberdeen and in the December the sun would rise at 8.45 and set at 3.30pm) and trees loose their leaves and wildlife finds it tough. Then there's spring, March - May, when the days start to lengthen, the temperature warms up, rainfall declines somewhat, the trees grow leaves and there's a flush of invertebrate life. Summer arrives June - August, with long days (Aberdeen sunrise at 4am, set after 10pm) and madly busy breeding season for wildlife, with lower rainfall (and very little in more southern areas). Then the days start shortening, the temperature falls and September - November is Autumn (or Fall if you're not in UK), the leaves start to fall, rains pick up and the migrants all head south.

Wildebeest enjoy the green in northern Serengeti, September 2011

Wildebeest endure the dry, Tarangire September 2011

Here, of course, things are very different - in nothern Tanzania and through Kenya, there are two rainy seasons and two dry seasons with very little variation in day length (none on the equator, of course). Southern Tanzania has a single rainy season, running from November to May (or there abouts). In general, our rain comes from a process called the Inter-Tropical Convergance Zone (ITCZ) which is global band of rain that sits more or less under the sun as the eath tilts on it's axis. Essentially, wherever the sea is directly below the sun, evaporation is highest and winds bring the clouds inland to fall as rain - but as the year passes the earth tilts and so different bits of sea are closest to the sun at different times - close to the equatior the sun passes directly overhead twive a year, bringing two rainy seasons, further away (but still within the tropics) the sun is directly overhead only once a year, bring a single rainy season. Hence when the north pole is tipped towards the sun the sahel region get's it's rainy season (June - August), and when the south pole is tipped towards the sun in December - Feb), Southern Africa get's it's rainy seaon. In between, there are two rainy seasons as we have here. (lots more details here on Wikipedia if you really want to understand it). But Lake Victoria confuses the issue greately by generating its own local climate, which means that even in August and September when the rest of the region is dry, northern and western Serengeti are green and wet. What's more, these parts of Tanzania are rather far from the coast where most of the rain comes from and they show the opposite patterns to the rest of the place - in years of good rains elsewhere the coastal winds are strong, bringing rain inland. But the same wind blows the Lake Victoria rainfall further west into Uganda, and this side of Lake Victoria is drier than normal. But when the winds fail and the rains don't come to the rest of the region, Serengeti enjoys all that Lake Victoria rainfall too.

Total rainfall (from here), but seasonality might be more important

There's more variation too, of course - mountains tend to catch rain and be wetter places, whilst the areas on the inland side of the mountains tend to be drier (we say they're in the 'rain shadow'). But in general for East African ecology, I think it's the length of the dry season, rather than the total amount of rainfall, that's most important. Lots of water all at once isn't particularly helpful, but a small amount of dry season rainfall can make a huge difference to the ecology of an area - think of the coastal forests growing in areas not that different to many savannah areas, but getting enough dry season rainfall to keep things green. Which, in turn, keeps the fires out, meaning forest wins over savannah and showing yet again how the big four processes interact with one another to shape the ecology of East Africa.

Now, not only is it good to be able to chat about these seasonal differences with clients, (especially at this time of year when they might well go from somewhere dry like Tarangire straight to somewhere in wet and green in northern Serenegti) but it's impact is massive. Why do you think the Wildebeest are up in Northern Serengeti and the Mara at this time of year? That dry season rainfall is critical for providing good grazing for such large numbers of animals. In fact, the Serengeti ecosystem is a great place to explore the impacts of climate on the savanna, because it has such different seasons across relatively small areas - dry season rainfall in the north is actually equivalent to total annual rainfall in the south, where the crater highlands catch most of the rain coming from the coast, but I think I'll leave a more detailed analysis of Serengeti's climates for another post, as this is long enough already.

Now might be a good time to talk weather! Grumeti GR, July 2009

Last thing though - it's worth thinking about how you might actually impart this sort of knowledge to clients in an interesting and relevant way. It might, of course, come up easily enough if their ask you directly (and of course, if their British, they're bound to...). But otherwise it might be something to chat about when you're watching a big thunderstorm brewing on the horizon, or when your are about to take clients from a dry place to a wet one (putting them on the plane to go from Tarangire to northern Serengeti at the moment would be a good time!) or vice versa. Or even, of course, as you watch the migration unfolding in Serengeti, just to explain some of the processes involved in why they're even bothering to make these dangerous trips!