Thursday, 25 August 2011

Human influences in national parks

Maasai Paintings at Moru Kopjes, Serengeti NP
Gong Rocks, Moru Kopj
Quite a few people are surprised that one of my 10 things to talk about is people - we're on safari, we've come to wonderful wilderness, and you want to talk about people?! Must be crazy...  But I don't think so, and it shouldn't be surprising once you remember that people evolved in Africa and have been here a very, very long time. Their influence is everywhere, despite the fairly recent notion that we must separate people from wildlife in strict protected areas.

Some things are obvious - such as the paintings featured above at Moru Kopjes in Serengeti. These are relatively recent Maasai paintings, but despite their recent history I can't find anything particularly informative about them - some speculation here, and some hints they may be a circumcision site. Anyone with any better information to share (if you know a source, even better, but I suspect the stories must still be available in living memory...)? Such sites obviously provide an opportunity to talk about how the idea of wilderness areas and safari sites as being without people are a moden (mostly colonial) myth - people have been present in wildlife areas in Africa for as long as there have been recognisable 'people'. I think this is an issue that can generate debate, but I think a lot of visitors to these areas are willing to engage and learn and I think a lot of people are interested to know that what they might have thought of as a 'pristine wilderness' and 'unchanged Africa' is very much a modern invention.

'Managed' fire in Tarangire NP, June 2011
Even today, the influence of people is obvious in many parks - and I don't mean simply the negative aspects of queues of cars, roads, poaching and all the rest. Fires, already established as a favourite topic of mine here and one of the big four of savanna ecology, are actively set by people as the one major land-management practice carried out in much of East Africa's savannah. And they're pretty much all set by man (I understand from Grant Hopcraft that there isn't a single recorded incidence of natural fire in the Serenegeti ecosystem - though I suspect that's mainly a consequence of an inappropriate management regime, rather than an indicator that there wasn't any pre-hominid fire) - and before modern men were around, they were set by earlier hominids, perhaps as long ago as 1.5 - 2 million years ago. Now, that long ago there were some pretty odd beasts inhabiting the savannahs, as anyone visiting the Olduvai museum will know (if you ahven't been, check the photo here!). So the modern fauna of the savanna have all evolved under conditions of regular, hominid induced, fire - our influence is massive and pervasive, and fires are still a good opportunity to talk about people in the savanna today.

Hadzabe hunter shooting doves, Eyasi, Jan 2011
Handzabe baobab peg ladder, Mongo wa Mono, April 2011
It's not just that though. Until relatively recently (and in some areas, still today, even with parks!) people were one of the top predators. And hopefully we already know how top predators are important at maintaining a functioning ecosystem - we've talked a lot about lions creating a landscape of fear, people too must have done the same in many areas until relatively recently. And in a few pockets, of course, they still do (let's ignore poaching!) - the Hadzabe are a hunter-gatherer tribe who maintain a traditional lifestyle and although now limited in distribution to a few pockets around Lake Eyasi they were relatively recently spread much more widely. You can still find evidence of their (or similar people's) occupation in many parks today. Baobabs are probably the best places to look - you'll often see old pegs from honey-gatherers embedded in the trunk, and when watching the Hadza use these ladders today I find it amazing to think that their ancestors may well have been running up the same tree 1000 years ago, for exactly the same purpose - that's sustainaility! These hints of a (recent) but different way of life are always fascinating I think.

And your conversations about people can be wider than that too - you can point out the berries you can eat (feed people them too!), the uses people have for many of the plants (and animals!), and all the rest. These little pointers about how people still use nature are great and to be exploited - I hope we'll be able to feature some of these stories in more detail on the blog in time (let me know your favourites in the comments, as I love to learn too!).

Tuesday, 23 August 2011

Lilac-breasted Rollers

Lilac-breasted Roller, Mwiba Ranch, Aug 2011
Lilac-breasted Rollers are one of the few birds that catch the eye of even the most die-hard mammal obsessed tourist and offer an ideal opportunity to open people's eyes to the fantastic world of birds. [BTW I have a theory that everyone is actually a birder, most people just don't know it yet. Though I confess that some are harder nuts to crack than others...] As you can't do a drive in much of the bush without encountering one of these beauties, I'm often asked by guides if I have any stories they can use to talk about the birds and until recently, I had to confess that I didn't. They're ecology is fairly straight-forward, they feed on a variety of invertebrates (which they'll often pick up squashed from game-viewing tracks) though they'll also take the odd vertebrate if something suitable stumbles past – a lizard, perhaps, chicks in a poorly hidden nest. They nest in holes and usually have two or three eggs and they're mostly resident (though there's a race breeding in Somalia that is a migrant into Kenya and – very, very rarely, Tanzania).

But thanks to Marcus from Oliver's Camp I was at last given a story about the birds that could make them just a little bit more interesting (though, given the colour, I'm not sure they need much more...). You might (or might not) know that they're the national bird of Botswana (and according to at least one web site also of Tanzania, but I'm not certain about that!), and it's not so surprising that such a pretty bird would have acquired some cultural value. These values probably reached their peak in the culture of the Ndebele people of Zimbabwe and neighbouring parts of South Africa, who had a complex system of uniforms to denote hierarchy, the peak of which was (obviously) the king, who's crowning glory (literally) was a headdress made of Lilac-breasted Roller feathers. Only the king could wear these feathers, and I suspect he looked rather fancy in it too! (Thanks Marcus for the pointer! Be with you this weekend, btw...)

There's also a story I came across (I've no idea of the original source though, I found it here) that suggests that during the act of creation the lilac-breasted roller was first in line for God's attention. So he took the very best of colours, but was so proud of his new paint-job that he forgot to ask for a voice and by the time he realised and got back to God, all the best voices had been used up leaving him with what can only be described as a rather poor effort, considering... (If you want to hear it, there are several recordings here, which is also a fantastic resource for many African bird noises that I thoroughly recommend.)
Armoured Ground Cricket, in my towel, Mwiba Ranch, Aug 2011

As a final note, I've also recently discovered that they rather like eating these beasties (each ridge in the pic is c. 1cm...), which I think most visitors to Tanzania would agree can only be a good thing! It's some form of Armoured Ground Cricket, probably genus Acanthoplus (family Tettigoniidae - the bush-crickets to English folk, the Katydids if you're American), but I'm not sure which species. If you know, do please leave details!

Monday, 22 August 2011

They're back! The swifts return...

Eurasian or Common Swifts, Apus apus, are not the most exciting of birds to look at (nor, here in Africa are they one of the easiest to identify, given their similarity to both African Black swifts and Nyanza Swifts), but they arrived back over Arusha at the weekend (and I'm told100s arrived back in Serengeti at the same time) and are real signs of the changing seasons. They're also absolutely fascinating things.
Common Swift (from Wikipedia)

Unfortunately, I've not got a photo of my own to share, so I've had to borrow this from Wikipedia. Firstly, you want to identify the thing. Swifts and swallows are often confused, but they're actually fairly simply to separate. Swifts are (usually) larger, have have long, stiff wings which they hold out sideways and only flap from the base of the 'arm', whilst swallows are (usually) smaller and have active flapping flight bending the wing at the 'elbow' quite a lot. With a bit of practice you can easily spot a swift and a swallow. Then you've got to identify the species and this gets tricky - Common Swift is best identified by being pretty much back everywhere, except a small white patch under the chin. Both the other common confusion species in most of East Africa have paler secondaries that you can see when you get a good vew - Nyanza is a bit browner, Black is otherwise similarly black. Range and season will also help - black is a highland species, Nyanza a Westhern Kenyan and northern Tanzanian - all back swifts elsewhere are almost certainly Common. Between May and early August you can be pretty sure you're not seeing a Common  too, as these are wonderful migrants.  Still, that's pretty advanced identification and I recommend visiting some well known colonies before you try and identify the other species confidently. Anyway, why do I like them so much?

Well, these are one of the most arial of any birds. They feed, sleep (like dolphins, one half of the brain at a time, flying ino the wind) and mate on the wing, and their wings are so long that they struggle to fly if they accidently lando the ground - they have to drag themselves using their tiny feet up a rock or tree to get enough height to take off again. That, in itself, is pretty remarkable. But common swifts are even more impresive than that. Feeding on small arial insects, if the weather is wet it's hard to find suitable food. During the non-breeding season, this isn't a problem - the birds just keep flying  and may cover huge distances to find suitable foragine areas. In fact, they often forage just in front of storms - a flock of swifts rushing across the plains in front of a big storm is a common indicators you're about to get wet! When they're nesting, this is a problem though - such trips take days and days. So the chicks have to survive without food for days at a time, and to do so they essentially switch off the major bodily functions and enter "torpor". Here (instead of a usual avian body temperature of around 40 degrees C), they settle on about 21 degrees and are unresponsive to external stimuli, taking several minutes to return to 'life' when a parent returns with food. The cost of this is that development is very slow - they weight about 44g, similar to a Yellow-vented Bulbul. But incubation takes about 20 days, and fledging varies from 37 days (when there's little torpor) to 57, if the chicks are in torpor a lot. That friendly Yellow-vented Bulbul, by contrast, takes a much more efficient 12-14 days to hatch and a similar period to fledge.

So, when the young birds are finally ready to fledge, they don't wait several days for their parents to return, but most set off immediately on their first flight, after sunset (there's less chance of being caught by a Hobby or similar if they make their first flight at night), which takes them straight, non-stop, to Africa. Of course, that sudden shift from being stuck in a nest, to constant flight is hard work - the young swifts prepare themselves for this insane flight by exerising: using press-ups where they push their wings down and hold their bodies completely off the ground for as long as possible - initially, only a second or two, later for longer periods. And so begins what must be one of the longest, continuous flights of any bird. On fledging, the birds leave for Africa (so these first birds might well be young ones, with adults following in a few days time), they eat and sleep on the wing the whole way down. Then once here they drift about following food, still not landing. And then come March or April, they decide to head north, back to Europe. But most don't breed in in their first year, so they keep flying up there too, perhaps checking out suitable breeding colonies. And then, come August they head back here and keep flying through the northern winter, before finally returning to Europe two years old. This time, most still don't breed, but there's some evidence they might settle in a colony and at least some of them come down to roost in their chosen nest site for the follow year. So those first flights of a young bird straight out of the nest likely lasts practically 2 years, and involves two trips to Africa and back - quite remarkable for anything I think, and sure makes up for the rather non-descript plumage! Look out for them near you, right now!

Friday, 19 August 2011

Parasitic plants - a Commiphora mistletoe

Plicosepalus meridianus growing on Commiphora, Mwiba Ranch, Aug 2011

In the middle of the dry season out here there's precious little colour to break the greys and browns, but look closely at the Commiphora and you might be surprised. Not only do they flower themselves in the dry season - a small rather unexciting flower, but many of them (I think mainly C. schimperi, but it's tricky for me without leaves!) around Mwiba had been parasitised by Plicosepalus meridionalis, a shockly pink flower that on first glance appears to grow straight out of the tree's bare branches. (I don't know a common name, I'm afraid.)

So, how would we interpret this 'wildlife' sighting? Start by identifying it - I'm fairly sure this is what I've photographed (certainly this genus), but some of you are probably better botanists than me and might correct me. It belongs to the family Loranthaceae, most of which are parasites and which also includes all the African mistletoes (though not the European and North American ones). It's worth pointing out it's only growing on Commiphora too - like many, it's a pretty host specific parasite.

Note how it grows all along the host!
Then explain what it's doing. You probably don't need to say it's flowering - that should be obvious! But have a close look and you should spot a little green at the base, and have a fiddle with the Commiphora bark and you might find some more where the plant holds tight to it's host. It's green because, like most mistletoes, it can photosynthesize a bit - though it does get most of it's nutrients from it's host. So its also (probably) photosynthesizing and stealing nutrients and water from the Commiphora - though probably not much at the moment, as the host is in a dormant phase for the dry season. Find the plant in the wet season and the story is different - mistletoes use both active and passive mechanisms to tap into and extract nutrients and water from their hosts. This is clearly not to the hosts' advantage, but the impacts probably aren't so strong that it threatens the health of the host - a closely related species P. acacia (guess what it's host is!) has been found to only thrive when the host itself is thriving, a sick host means a sick parasite with few flowers and low growth.

That's what it's doing, but what about my third question, what's the role in the ecosystem? Well, in this case we can speculate a bit. The obvious thing it's doing right now, is flowing in the middle of a period where there are few other flowers available. (It can probably do this and remain active during the dry season because it has a ready source of water from it's host, the succulent Commiphora.) And the flowers are pink. So stick around a few minutes and see what happens - you'll almost certainly see a sunbird nip in to feed. Pink, red, orange and yellow flowers are often signals for birds (which have good colour vision), and during the dry season there are precious few flowers around. Some sunbirds move away for the dry season - Coppery Sunbirds are a well known migrant, for example - but many stay and make use of the few specialised flowers available during this lean season. And those few flowers that are available, of course, must get visited very regularly, with excellent pollination chances. So you could argue the plant is helping to maintain the pollinator community during the lean period - certainly if there weren't a few species during this, all the sunbirds would have to migrate to greener areas during the dry season.

Scarlet-chested Sunbirds (here Arusha, March 2011) require dry season flowers
Even more interestingly, we could talk about some of the general impacts of parasitic plants on biodiversity at large. As we've mentioned, parasitised plants aren't (usually) killed by other plants, but they are weakened. And if you were going to be a parasite you'd probably want to parasitise something fairly vigorous and strong that there's lots of, to ensure the next generation can also find some hosts to parasitise. Now, if you have one particularly strong and domiant plant in an ecosystem, it's likely to out compete all the others and you'll end up with a rather low diversity system. But if parasites are more common on these strong plants because it's in their interests to do so, then they'll weaken that dominant plant and allow other species that aren't usually able to compete to survive too, boosting the biodiversity of the ecosystem - a pattern that has been demonstrated experimentally in grasslands, using grass parasites. So although I don't know it happens with this species and Commiphora, you can certainly wheel the story out again in April when the Cycnium are flowering everywhere (you know them, the little white and pink flower that love short grass, I've not got a photo though, I'm afraid. You'll have to look here for one if you don't know it!), as these are also hemi-parasites (hemi-parasites being parasites that don't steal all the requirements they need from their hosts, but also make some nutrients themselves) on grass. Certainly plant parasites are interesting things with important impacts!

Wednesday, 17 August 2011


Moru Kopjes, Serengeti, Jan 2011 - stacked boulders form by erosion around cracks
One of the prettiest things about Mwiba is the large number of kopjes (pronounced 'kopees') found down here. Massive and ancient, the rocks that form kopjes are great added value in many safari destinations. They also form an important part of the landscape and should never be seen simply as a photogenic backdrop, or a great place to enjoy the sunset! 

Mwiba kopjes give a good view! Jan 2011
In fact, geology is one of my 10 things to talk about, and there's no more obvious prompt to talk about geology than when sitting on a kopje. But if you're going to do that, it's important you know something about them before plunging in. If you want a really good overview of the soils and geology of the Serengeti ecosystem, you'd do no better than looking here, this is more of a general overview and whilst mostly focussed on the Serengeti ecosystem, the processes involved are similar across Africa and it shouldn't be too hard to find out the location specific details once you understand the process if you want other areas. 

So, what is a kopje, geologically? Essentially, it's a pile of ancient rocks that protrude through the more recent soils and surface rocks – that's what gives them their other name of inselbergs: 'mountain islands'. In Serengeti they're either gneiss [pronounced 'nice'] (a metamorphic rock that looks rather like granite but doesn't have the little flat crystals of mica or similar – some gneiss has originally been formed from granite) or diorite/granite. And they're all OLD! The kopjes of the north west are the oldest and those of the western corridor the youngest, but all are Precambrian, which means over 500 million years old. Compare that to the volcanic ash deposits they poke through on the Serengeti plain, which are only 3million years old, and you see how different they are. All originally formed under the surface of the earth from volcanic activity that didn't make it to the surface, cooling below ground, and then over the ensuring millions of years the surrounding softer rocks have eroded, leaving the harder metamorphic or igneous rocks to become exposed as they are today.
Figs on a Mwiba kopje, Aug 2011
Horned Rockdweller, Bradinopyga cornuta, perhaps a surprising rock specialist!

Gloriosa superba the Glory lilly are common on kopjes: Naabi, Jan 2011

Klipspringer, a kopje specialist. Kruger May 2011
So, that's what they are and it's a good start on geology (though there's much more to talk about there too). But what about the role they play in the savannah ecosystem? In thinking about this it's first of all good to remember that they're a pretty unique habitat, with a specialised group of animals and plants. Kopjes are the place to find klipspringer and hyrax, they're also the only place to find one or two more esoteric bird species like rock-loving cisticola. Rock figs, as the name suggests, are common on kopjes but not many other places. As well as these really rather specialised species, there are a number of species here that are more often associated with riverine vegetation: there's a range of figs, you'll often see tamarind on kopjes and plenty of the animals often found by rivers are there too – both kopjes and rivers are great places to find leopard, for example. Why's this? Well, we need to think about the savannah 'big four' again, and how kopjes affect them.

(1) Water availability: you might think kopjes are dry barren places, but not at all – whilst the rocks are definitely dry, there are often hollows and cracks within them that keep the water for a long time. Figs are particularly good at sending roots over rocks to find the damp pockets and grow really well in such wet places. Animals and birds often know about the puddles too and will use them throughout the dry season, allowing water-dependent species to utilise areas of savannah that would otherwise be too dry for them.

(2) Grazing/browsing: ever seen an elephant on top of a kopje? A giraffe? No, me neither. Whilst there is a specialist browsing community of bush hyrax and klipspringer, for example, the huge impacts of mega-herbivores are minimal on kopjes, allowing plants that are poorly defended to thrive in a way that they can't manage on the flatter plains.

Bush hyrax and Mwanza Agama share this kopje! Moru, Serengeti, Jan 2011
(3) Fire (my favourite of course!): Yes, kopjes are fire breaks – large areas of bare rocks obviously can't burn and plants growing in the gaps in the rocks are safe from fires. As we know fire can be the main process determining whether there's forest or savannah in the wetter areas, it should be no surprise that the fire refuge offered by kopjes should have a forest type vegetation.

(4) Nutrients: just as the bare rocks allow water to concentrate in hollows and cracks, so nutrients from hyrax dung, baboon dung, leaf litter and all the rest concentrate in the cracks too, providing a relatively nutrient high (though thin) soil for those plants that can get to it. What's more, several animal species (like leopards hunting the plains, but bringing their kills back to the trees on the kopje, or eagles nesting on the crags but foraging over a wide area) use the kopjes at certain times of day or night and the plains at other times, but bring their food (and/or dung) back with them to the kopjes, further concentrating nutrients on the kopjes and resulting in a net flow of nutrient out of the surrounding plans, onto the kopje on a truly grand scale.

So, with all of the big four savannah processes being substantially different on a kopje from the surrounding landscape, it should be obvious that there's going to be a big difference in the ecology of the kopje, just as we see. And as the differences are mostly fairly similar to those in a healthy riverine area, it's not surprising that some of the elements are shared between the two otherwise rather different habitats.
Simba on Simba Kopjes, Serenegti. Jan 2011

As one last thought to leave you with, I've already mentioned how kopjes can be seen as a large-scale nutrient pump, pulling nutrients out of the plains and focussing them on the rocks, but there's one other big way in which they alter the ecology of the surrounding plans: predators. Just as leopards like kopjes, so too do lions. They're great places to warm up in the morning or evening sun, and provide an ideal viewpoint to survey the plains for food. Moreover, the rocks and thicker vegetaion make it much easier to sneak out and ambush your prey. So kopjes have a real impact on the 'landscape of fear' if you're a tasty antelope. Out on the short grass plains you've got a great view and it's tough for lions and the like – the plains prides of Serengeti have a home range over 200km2, compared to only 15km2 in the woodlands around Seronera (no wonder they're easy to find there!). So if you're a wildebeest, zebra or kongoni, you'd be wise to avoid the immediate area of kopjes – just as they do a lot of the time. And removing that grazing pressure from the plains around the kopjes, of course, is going to result in a changed ecology of the grasslands there too. So the impact of kopjes spreads out far wider into the landscape than just the rocks themselves. All very interesting – and easy to see whilst sitting about waiting for the sun to set!
Mwiba sunset from a kopje, Aug 2011

Monday, 15 August 2011

Burning Mwiba

Back from my trip now, I thought I'd make a few posts based on the things we've seen on safari. As I've been writing up my thoughts about one place already today, I thought I'd use that as the basis for this first post.
Buffalo are a major grazer in Mwiba, note the relatively short grass.

Mwiba Game Ranch is a new private game reserve within the Serengeti ecosystem. I've been before when I put together a bird list for the area. This time it was a trip to see the place in the dry season with a view to including it within my big Serengeti Fire experiment. For those who know Serengeti , Mwiba is squeezed into the corner between NCA and Maswa GR, right down in the south of the ecosystem. (NB, we usually define the Serengeti/Mara ecosystem as the area that encompasses the wildebeest movements - Mwiba includes some of the calving grounds, particularly important during drier years.) This puts it right in the driest region of the ecosystem, with around 400mm of rain per year and as you'd expect at that end of the gradient it's largely Acacia-Commiphora woodland, though there's a surprising number of nice Albizia in there too. It's also interesting because it's got a number of interesting mammals not found or not easy to see in the rest of Serengeti - we saw both Greater Kudu and Roan Antelope again this trip. Anyway, I was there to talk fire, but knowing that we're in a low rainfall part of the ecosystem is important, because water availablity is one of the big four drivers in the savannah (fire, grazing/browsing and nutrients being the other three, of which we'll visit two more shortly). Low rainfall means low productivity - the grass even on the highest nutrient soil never grows tall and thick like in other parts of the Serengeti, but what does grow tends to be nutrient rich annuals, so pretty good grazing, even if it isn't plentiful.
Zebra are the other big grazer - the grass here has already been grazed a bit

Rich grass means plenty of game, with the main dry-season grazers being large populations of buffalo and zebra thanks to the numerous perrenial springs around the ranch. Already, only half way through the dry season the grass in the areas around the waterholes and by the denser thickets is heavily grazed - by October it seems unlikely there'll be much left at all as the grazing impact spreads further from the water points. A lot of the area is pretty dense bush though, with some good thickets in places along the (seasonal) rivers.
Nearby areas with many cattle are already completely denuded, what will they do until the rains come?
 In recent years this area (as with most of Serengeti) has been subject to an early burning management regime - fires being set as soon as the vegetation starts to dry in June. Fires are important in the savannah for a number of reasons we've gone into elsewhere, but the two most important issues to bear in mind here are bush control - there were lots of seedlings in the grassy areas of Mwiba that have been prevented from forming to thick bush by regular burning - and grazing management, maintaining and encouraging new growth of nutritious grass. The early burning policy that has become the norm in Serengeti and most other Tanzanian protected areas ensures fires are controlled and generally are rather cooler than fires set at the end of the dry season when the fuel is drier.  But here in the drier areas with lower water availability it also means the fires burn regularly - you can be fairly sure there's enough fuel to burn early in the dry season, whilst later on all those animals will have eaten so much there might not be anything left to burn. That's good if you want regular firest to control bush encroachment, but isn't so good if you happen to be a buffalo wanting to eat during the dry season and all the nice grass gets burnt at the start. In fact, the ranch manager is of the impression that this year, when for the first time in a long time no fires have been set during the early season, there are lots more animals on the ranch than last year thanks to the availability of unburnt grass.
There's a sand river that forms a firebreak between the grass and the bush - frequent early burns have removed thicket vegetation from the upwind side of the river.

Mwiba's springs attract a lot of wildlife (and reflect sunset)
So, what to do? Maybe late burns will be possible at a lower frequency - give the land a few years to build up sufficient fuel reserves left over at the end of the dry season to allow a fire to take with regular enough frequency to control bush encroachment. Or maybe early burns are the only option to allow fires in these low rainfall areas to carry - though they probably don't need setting each year, balancing fire options against forage loss. The only real way of finding out will be through a big experiment, of course, which is exactly what I intend to do! Watch this space for the answers...

Thursday, 11 August 2011

Why is Africa so full of thorns?

Assorted browsers and browse lines, Selous GR, June 2010
I'm actually away this week, but left this to post itself whilst I'm off and keep people interested! One of the places I'm headed to is Mwiba Ranch, south of Serengeti and, as you might know, mwiba is swahili for 'thorn'. No doubt I'll have some specifics to talk about when I'm back, but one of my 10 things to talk about topics is thorns. Why? Well, many visitors from the north live in places where tere aren't lots of thorny trees, so going to a walking safari and discovering that just about every bush and tree is covered in massive needles is a bit of a shock, even if those of us lucky enough to live here barely notice them (until they get infected, of couuse...).

Giraffe (and shorter!) browse line, Arusha NP, June 2010
So, why should Africa, or at least African savannahs in particular, be so thorny? The answer, of course, is fairly simple - why do tourists visit the savannah? To see the animals, and what do the animals eat? Well, rather a lot of them like to eat bushes, which is no fun at all if you happen to be a bush. In fact, in many places the grazing pressure is so heavy, very distinct browse-lines form and the plants take on structures as if someone was pruning them into interesting sculptures. So, defending yourself against Africa's abundan browsing animal population is a very good idea, and I've always thought thorns must be pretty nasty things to eat. But, you say, if the thorns are a defense against browsing, how come I still see impala and giraffe and all the others happily choping on thorn trees? Obviously the defence doesn't work? That's a good point, and allows me to introduce one of the many ways in which nothing in biology makes sense except in the light of evolution. Imagine living in an Africa before there were any thorns - all the bushes are undefended, and equally appealing to a browser. Now imagine there's a little mutation in one of the offspring of those bushes, that means it grows small spines - all the other bushes are still nice and undefended. If you were an impala, which bush would you eat? I suspect you'd go for any of them, except the one with the small spines. Which, of course, means that the spiny bush is going to do very well and will produce lots of babies, also with spines. In time, all the bushes will have little spines and the poor impala, if he wants any lunch, just has to tuck into that thorny bush. But, of course, one bush might have a mutation making it's spines a little harder, a little longer, a little nastier - and you can see immediately what's going to happen now - bigger spines evolve.
Greater Kudu, carefully nibbling around thorns, Kruger NP, May 2011.

Of course there might also be heritable variation in the impala browsing technique or mouths - maybe for thicker skin, or a narrower nose that can squeeze between the thorns. Giraffe, of course, have evolved a huge long sticky tongue so they practically lick the leave out from between the thorns, rather than have to go to close. But both species certainly are aware of the thorns, even though they have no choice but to eat the prickly trees, of course - imagine what would happen to the poor thorn tree that, though some mutation, had no thorns. Ooops, poor thing! So clearly the thorns do have an impact - what's interesting to me to look for in places with very heavy browsing is evidence that the thorns do work, even though the plants get eaten.
Heavily browsed yellow-barked Acacia, Arusha NP, June 2010

To see this, you need to look at the shapes of trees and bushes. Here's a nice Vachellia xanthophloea (see, I'm trying to get you used to the new names!) that's been very hevily pruned - a favourite with the girafe. So how's it ever going to make the leap from heavily pruned bush to fully fledged tree? The secret is to grow wide, before growing tall. While the bush is still short and relatively narrow it doesn't stand a chance - any giraffe will bend down, and chew off the top bits. But if it can get wide enough the giraffe don't like the thorns on their skin, and they'll just nibble to top bits within easy reach - leaving a tuft in the centre to break away. And once that is done, those short, wide branches at the base of the tree are no longer important and soon die back, in favour of the taller tree. Not clear? She here's a little diagram showing how to escape giraffe broswing pressure...
Bushes escaping browsing. Honest!

Nearly there! This bush behing the giraffe has started to escpe from the centre, Lake Manyara NP, April 2010
Not the most artistic ever, I admit - but I'm an ecologist, not an artist... (It's a giraffe bending down on the left, not a funny, long-necked kangaroo). So on the left you have a tiny seedling been chewed by a giraffe. This makes the bush grow flat, like in the photo above. Then, when the plant is wide enough, the throns around the edge stop the animals from being able to reach the centre and in the third part of the diagram a new shoot is escaping browsing, and finally in the last picture a mature tree has grown, with just a little whisp of the original short, fat bush that had to escape browsing remaining as evidence.

Made it! Just a few whisps of short left, West Kili, April 2010
So, that all sounds very nice, but why, you ask, do some plants get away without thorns, even in the savannah? Both Terminalia and Combretrum are fairly thorn-free, but a typical savannah plants. So how do they do it? Well, the difference here is the nutrients. Remember that Acacias (or whatever we're going to start caling the group now) are legumes and are absolutely full of nutrients, whereas these other two species live on the nutrient poor ridges and represent pretty low-quality browse. So, if you're a tasty plant growing in nutrient rich areas, you're going to be browsed much more than those specialising in nutrient poor environments, and here you want to invest more in defence.

And that, for now, is that. Hope you're having as much fun as I will be having in Mwiba!

Wednesday, 10 August 2011

Have you seen this duck?!

Not very common any more, we were pleased to see a couple of White-backed Ducks here at Kisima Ngeda yesterday. It's usually a bird of clean wooded ponds, with lots of water lillies, but this is the second record for the area here. Have you seen it anywhere? We've no real idea aut why it may be declining, but perhaps there's a shortage of clean ponds that don't get cattled? It's also a mystery why Maccoa ducks are decling (even faster!), so if you've any thoughts do let us know! These two are probably just dispersing  and found a nice place to break their search for new water as the more usual ponds dry out.

White-backed Duck, Eyasi 2011

 This one was just too cute not to post! You can see he's a very young juvenile from the large gape which makes the bill a wider target for the parents to post insects into. After a month or two he'll still look juvenile with the dull cap and pale-edged wing feathers, but the gape will have gone and his beak will look normal.
Juvenile Wire-tailed Swallow, Kisima Ngeda, Aug 2011

Tuesday, 9 August 2011

Egrets (and other birds) at Lake Eyasi

I'm at Eyasi at the moment, and busy having fun. But I've taken a few pictures and though it might be worth posting some egret shots, since these species often confuse people - white, heron-like birds. So, here are a few examples with the key pointers (unfortunately no intermediate egrets around at the moment, so I can't complete the inland set!):
Cattle Egret, Lake Eyasi, Aug 2011
This one's easy. That brown thing is a cow, so it must be a cattle egret! Unfortunately they don't always do that... Still, the beak is pretty short and yellow with a steep forehead and the neck is short and fat. THe only inland confusion should be with Intermediate (or Yellow-billed if you prefer that name) Egret, which has a longer beak, less sloped forehead and different gape - where the pale line goes up to the beak. You might also make out yellowish legs on this picture.
Great White Egrey, Kisima Ngeda, Eyasi, Aug 2011

Next up a great white egret. Note here the gape goes right behind the eye and it has a really long, strongly curved neck. Intermediate would have a much shorter gape (not as short as cattle though) and a shorter neck (not as short as cattle). It's also got black legs when it's not breeding.

Little Egret, Eyasi, Aug 2011

And finally a Little Egret - inland this shouldn't be too tricky - it's got a long black beak with just a little yellow by the eye, and black legs (with yellow feet if they're not too muddy).

If I find an intermediate I'll post that too to complete the inland set!

Monday, 8 August 2011

Mating Millipedes

Mating Millipedes, Ushongo Beach, July 2011
Whilst we were down at the beach we enjoyed seeing rather a lot of gian millipedes up to all sorts of things. Several decided it was definitely the mating season and thought's they'd show us some of the interesting things it takes to create a new generation of millipedes. So, here we go with some more wildlife interpretation...

What is it? Well,a giant millipede of some sort - I'm not exactly sure which one, but quite possibly a variety of Epibolus pulchripes, the Giant Red-legged Millipede. If you know better, please do let me know! And what are they doing? Well, that's certianly mating! As you can see, the male starts off by climbing on the back of the female and giving her a good tickling (at least, that's what it looks like). . In fact, he's busy preparing to mate - it's not easy with all those legs and, what's more, he keeps his genetalia in interesting places. In fact, his 7th pair of legs (millipedes have two pairs of legs per body segment, except for the first 7 segments where there's only one) are modified into what we call gonopods - gono, relating to gonad, and pod for leg. But the genitals themselves are in the 3rd segment (some species of millipede have two penises, which seems excessive), so the first thing the male has to do is depost a little package of sperm (the spermatophore) onto his gonopods.

Mating Millipedes, caught int he act.
Then once he's done that and the female is ready, she turns around and they go face to face for the finale (right). He now accesses her genital pores, as they're known (and on the female 3rd segment) and uses his gonopods to push the spermatophore into place. She then stores this sperm to fertilise her eggs, which in these giant species get laid in a nest in the moist soil under the leaf litter. She probably lays several hundred eggs, all fertilised from this one encounter, which in time hatch into baby millipedes, most of which are rather short and have just three pairs of legs, but will moult as they grow, each time adding more segments and more pairs of legs until they're mature.

Saturday, 6 August 2011

Water skaters

Larval Water Strider, Usa River, Aug 2011 They can move like lightening!
Here's a little guy that doesn't get much attention. Just about every pond or stream has them, but have you ever looked closely at what they're doing? These ones were on a stream and just keeping themselves in the sunniest spot, each time a little leaf or twig floated down steam (often provided by my daughter!) they'd wizz off like lightening to check if it was some small invertebrate to eat. On ponds they're not easily fooled - their feet pick up all the vibrations on the surface of the water from struggling insects and immediately know the difference between a still leave and a moving item of prey, but that's obviously not so easy on a flowing stream.

Water Strider, Usa River, Aug 2011

So, let's try the three things I ask about when interpreting wildlife - what is is? That's easy to a certain level, it's a pond/water skater of some description. These insects (check the body structure and 6 legs - the front two are short and used to capture prey, the others are long and used to propel the animal across the surface of the water) are actually true bugs - order Hemiptera. Now, I think these one are probably family Gerridae (maybe even genus Gerris), the typical pond skater (though they usually have a long thin body), and not family Veliidae, but I'm not sure - unless you're an expert the only certain way to ID them seems to involve dissection of the genitalia. Nice (what is it with entomologists and dissecting genitalia?). Still, pond skater or water strider is probably enough for most people anyway, and knowing it's a true bug might be a little bit interesting too. Look at the picture below, however, and you'll see something more - there are no wings, yet true bugs (usually) have wings? In fact, this tells us we're looking at one of the larval forms - just as juvenile grasshoppers don't have functional wings, nor do juvenile Gerrids, which suggests we know something about the age of these little guys too. But even more interestingly, this is a group where in some species developing animals in low population densities never develop wings, but when growing up in higher density populations, the adults do grow wings - a phenomenon known as phenotypic plasticity, when the same genes under different envorinmental conditions (high or low population density) result in different body plans.
Larval water strider, Usa River, Aug 2011

What's it doing? Well, obviously, it's looking for food, but rater remarkably it's doing that by walking on water! How? Well, you probably remember being told that water has a high surface tension - water-molecules rather like to cling to one another. If you're small, that means that it's as though the water has a skin, and by having very long legs that spread it's weight out neatly over the water,  the bug can exploit that skin to stand on the surface aided by one further adaptation - tiny hairs on the legs that are hydrophobic - that repel water. These three things allow the critters to take up their life on the water surface.

And what impact does it have on the ecology of the world it lives in? Well, here I'm not to sure, whilst there's quite a lot fo research into the group, not much has focussed on it's ecology or role inthe ecosystem. Certainly they get eaten by lots of things and eat lots of others (they're also very successful as a group, with over 1700 species), but no-one seems to have speculated aout how the world - or even the pond - would be different without these creatures. There's a project for someone...

Thursday, 4 August 2011

Waterholes and dams

A nice waterhole never did any harm, did it? Sasakwa Dam, Grumeti GR July 2009
I often hear questions about the impacts of artificial waterholes and I've spent some of today writing about this issue in a paper we're working on about management practices in the savannah enviornment, so I thought that whilst it was fresh in my mind I'd share those thoughts here. The topic usually comes up when we talk about South Africa, and the far more intensively managed parks that exist down there, but it's also often an issue that crops up when talking to managers of lodges and camps who are, understandibly, keen to have a nice waterhole infront of their property.

Grazers love artificial waterholes - the migration reaches Seronera, Nov 2010
Certainly, waterholes and perrenial rivers are a fantastic place to find wildlife, especially during the dry season. You only have to sit by a water hole for a few minutes and the animals (and sometimes clouds of birds!) start trickling in for a drink. And, of course, the predators know this too, so theyll just sit and wait until lunch laks up to them! So what's the problem? Everything loves a waterhole, it's great for tourists to see animals, let's dig them everywhere! And that's what has happened in some places in southern Africa - both in National Parks like Kruger, and even more in private grame reserves people have dug waterholes and pumped water. In some of the private reserves waterholes were dug every 2km, so even the most sedentary of animals could always have access to water. And, as expected, this made a huge difference to the distribution and populations of animals - particularly Zebra and other grazers, animals that are very strongly dependent on water and don't like to walk far to find it. So, everyone's happy, right?
Lions wait for thirst animals by a waterhole, Selous GR, June 2010

Roan Antelope, Mwiba Ranch, Jan 2011. Declines have been related to water provision
Wrong. Zebra are also pretty much the favourite food of lions, so if you increase the zebra population and let them go to areas they couldn't use before, you also increase the lion population and let them spread further afield in their hunt for zebra. That might sound good too - but it's not if you happen to be an animal that deals with predation risk by hiding away in areas predators don't go - like Roan and other large, slow antelope. In fact, mainly in recognition of the damage that has been caused by making water available throughout the landscape there has been a recent policy within Kruger and some other areas of closing (some of) the artificial waterholes to allow such sensitive species spaces where they can survive.
Elephant near dam, Kruger NP, June 2011 - and look at the invasives on the dam!

But that's not all artificial waterholes do, they also attract elephants. Now, there's a long running discussion between East and South Africans about elephant impacts (dare we say damage?) in protected areas that I'm not going to go into here. But impacts they certainly do have, especially in areas near waterholes as they're another species that doesn't like to travel far from water if they don't have to. So spreading waterholes across the landscape means elephants can easily get everywhere, especially during the crucial dry season when they are feeding on bushes (grasses during the wet season, remember) and have bigger impacts on the habitat. So providing waterholes for elephants everywhere means the vegetation never gets a chance to recover from browsing impact, and can easily start to cause problems throughout the landscape. So, another thing to be aware of.
Zebra drinking, Manyara Ranch, Sep 2010. Note how heavily grazed the land is around the dam.

Now, the last thing you might want to argue with me about, of course, is what happens in a dought? If you don't provide water for the animals, surely they die? And that's true, of course - but it turns out that if you do maintain artificial waterholes everywhere, the animals still die - not of thirst, but of starvation. During a drought there far less food around, especially in areas where everywhere is usually accessible to most animals because there are waterholes everwhere. If there are fewer waterholes and things get tough, animals (even those lazy zebra!) will make the decision to walk further to feed in areas they don't normally go and there'll be enough food to go around. So in a serious droung in the 1980s in southern Africa, one private game reserve with lots of waterholes where studies were made lost nearly 90% of grazing animals, whilst the next door Kruger, with fewer waterholes, only lost 35% of animals. So, no, I don't think waterholes are essentially a good idea, even during drought.

The unifying process at work here, with the lions, the elephants and the drought stress, is a loss of heterogeneity - variability in the landscape. With waterholes everywhere, lion predation risk was the same everywhere, elephant impact is the same everywhere, grazers are the same everywhere. Without artificial waterholes, there are refugia from lions, elephants and heavy grazing that can be used by other species and at other times when needs are greatest. Heterogeneity, as we'll see time and time again, is a key issue in maintaining functioning ecosystems.
Birds like waterholes too! This is a Black-winged Stilt near Ndutu, NCA. Jan 2011
 So, do I always think artificial waterholes are bad? In an ideal world, I'd say yes. But we don't live in an ideal world, so to be realistic I have to say usually. Some protected areas - such as Hwange in Zimbabwe - would once have only been wet-season dispersal areas, with no permanent waterholes. But here the seasonal movements have been blocked by people, so waterholes are needed to enable any of the ecosystem to survive. That said, I don't think they should be spread all over the park - rather, groups of pools in one or two areas would maintain the heterogeneity that is needed. And if climate change and human water abstraction continues to increase aroudn parks, we'll start loosing perrenial rivers, in which I'd I'd advocate maintaining some limited pools of permenant water along these routes artificially if necessary. Finally, of course, if there's already a nearby source of perrenial water, another waterhole nearby will probably have little additional effect (good news for lodge owners who are near rivers, but didn't negotiate the view!). But interferring with savannahs is not easy, and should never be attempted without considering all the impacts you might have. Let's keep waterholes natural!