What is the influence of climate change on Tanzanian protected areas?

Pangani Longclaw Macronyx aurantiigula is perhaps the best example
of a species extending west, having colonised Serengeti recently.

It's been a long time since I posted anything here - sorry! I have another common birds post in progress, but just keep failing to finish it off. In the mean time I thought I'd talk about one of my own papers that came out a few weeks ago that explores how Tanzanian bird distributions are changing (sorry, it's pay to view, but if you want a copy email me and I'll send it!). This analysis is a fairly major result of my collaboration with the Tanzania Bird Atlas and represents the combined efforts of a very large number of people, volunteers and professionals, who contribute invaluable data to Neil and Liz Baker - I know some of you read this, so firstly, thank you, and secondly, I hope you appreciate seeing how we can use these records to do interesting and (I hope!) useful research.

Indian house crows and invasive aliens

Indian House Crow, not the prettiest... Thanks to Dick Daniels

There are very few birds I don't like to see, but today's common bird is an exception - the Indian House Crow, Corvus splendens. Actually, that's probably slightly untrue, as I have been to India and I was perfectly happy to see the species there. In East Africa, however, this is not a species I'm ever happy to see. Not because there aren't interesting things to say about it, of course, but because it really belongs in India and seems to cause a number of problems elsewhere.

First though, identification is fairly simple: the house crow is a medium-large all black and grey bird, usually found in flocks in towns all along the coast and, in some areas, invading inland too. It is very loud, with a persistent "Carr, Carr, Carr" call that is the constant sound of Dar es Salaam bird life... There are few confusion species in East Africa, the only other common species of crow being the black and white Pied Crow, which often hangs about with the house crow.

Common birds: Rattling cisticola and why birds hold territories?

Rattling Cisticola, near Arusha, March 2011. Something of a birder's bird?

Returning to my recent theme of common birds, what could be more suitable as the rains begin than a look a Cisticola chiniana? Whilst small, streaked and brown might make this something of a 'birder's bird', I'm happy to think there's plenty to interest everyone in this species too.

First the identification. Let's be honest, Cisticolas can be something of a challenge to identify! It doesn't help that there are seven pages of nearly identical looking small, streaky brown birds in the fieldguide! Happily, there are better ways to identify Cisticolas than their looks - the key is always to listen. Most Cisticolas, and rattling is no exception, have fairly distinctive calls and once you know it their 'tee, tee, churrurrurr' call is a constant sound in the bush (click the link to find a recording on xeno-canto), especially during the rains when they breed. In the unlucky event that none are making any noises, you can usually be fairly confident in your identification of any moderately sized, streaky cisticola present in the drier bush regions as rattling simply because they're so common! They are surprisingly variable in size (sometimes appearing really rather small) and colour (from very grey to warmer brown - but never with bright chestnut on the wing or head) though, so don't be too taken in my any one feature if they're not calling.

Common birds: Red-billed Quelea, commonest bird in the world?

1000s of quelea at a dam on Manyara Ranch

I've been struggling to think of the next common bird to do something interesting with, until the obvious solution came to me, possibly the world's most abundant bird, the red-billed quelea.

So, first the identification. The most obvious thing about red-billed queleas are, as the name suggests, a large red beak! Apart from that feature, females and non-breeding males are rather nondescript, small sparrow-like birds. Breeding males are rather brighter, with the red bill surrounded by a black face and variable amounts of orange on the top of the head and breast, with otherwise sparrow-like brown streaks on the back and wings. Perhaps the most useful identification feature though is the fact that you almost never see just one, but flocks of tens, hundreds or thousands of busy quelea all searching for grass seeds or drinking at waterholes.

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...

Common birds: Ring-necked Dove

Ring-necked Dove (Cape Turtle Dove) in Tarangire, photo from here

Two more challenges have been set since the last one, and I'm hoping to rise to each! The first was for the African Collared Dove, however that species (Streptopelia roseogrisea) from the drier north of Africa in the Sahel and in the Middle East is not found in Eastern or Southern Africa and I suspect request was for a Ring-necked Dove Streptopelia capicola which is indeed one of the commonest birds to be seen in the bush across much of Africa.

The sound of the Ring-necked Dove  is one of the constant backgrounds to a safari in the bush (if you don't know it, the "work harder, drink lager" refrain is available here) and it's actually this distinctive song that is the easiest way to identify the species from among a number of confusingly similar species. The ring-necked dove is a medium sized, grey dove. It has a black collar around the back of its neck and is a paler grey white below, with pale edges to its tail. Unfortunately, that description is would cover just about any of the close relatives of this species, and (as well as listening to the calls) you need to look rather closer to identify the species correctly. Firstly, look at the eye: if it is dark and not obviously surrounded by bare skin, you're probably looking at a Ring-necked Dove. White (not grey) edges to the tail and a generally pale grey would confirm the identity in eastern and southern Africa. If the eye is pale yellowish, with a red ring around it and there's a warmer brownish wash to the back and neck that contrasts with a grey head, you're probably looking at an African Mourning Dove (call) and if its got a dark eye in a bare purple/red patch of skin, and is overall darker looking, with grey tail edges, you're looking at a Red-eyed Dove (call: "I am a Red-eyed Dove").

Common Bulbul and frugivorous birds

Common Bulbul nesting in Arusha

Thanks to doubtful comments from a colleague, next up in the common bird series is going to be the Common Bulbul. These birds are probably the most widespread birds in Tanzania and should be a familiar sight to everyone, with their dark blackish heads, brown back and tail, and dirty white underparts with yellow under the tail. They're typical garden birds, and often ignored. However, it is often the common birds that we know most about, because they are so easy to study. And common species, simply because there are so many individuals, often have a very irritant role to play in ecosystems - the common bulbul is no exception!

Common birds (1)

Speckled Mousebird, Arusha. Cute, and really quite interesting...

OK, I've been away from here for too long (sorry!), but to encourage me to actually get down and do something, I've decided to start a new little mini-series here on common birds. As any of you who knows me is aware, I happen to rather like birds and will happy spend hours sitting wathing birds at a pond, or even trudging through kilometers of rift valley lakes to count waders. And I have a secret theory that actually, everyone loves birds, they just down all know it. The problem is that there are a lot of different birds out there (do watch Ethan as he tries to see as many as possible this year and records his exploits over here!), they often move rather fast, and people can be easily confused at first. So I thought we'd break it down into some very simple stages and try and start with 50 of the most common / obvious birds on safari or about towns in Tanzania. For each one my challenge is to briefly describe the key features to help you identify it, and then to say something interesting about it. If all goes well, I might even expand my remit to include non-birds, but we'll start with 50 common birds and see how that goes. Rather than throw it all at you in one go (and because there's no way I could write that much in one sitting!), I think I might try three species a post. It might also get a little interactive this way, if anyone wants to help me identify the top 50 species, that would be great,a nd if you've got your own preferred 'factoids' about any of the species, please do chip in!

So, let's start today, in no particular order, with the Speckled Mousebird.

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.

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.”

Why do birds sing in the morning?

Ruppell's Robin-chat: an impressive mimic. Lake Duluti

I enjoyed a walk around Lake Duluti yesterday morning and came across a couple of wonderfully singing Ruppell's Robin-chats. These are great birds, with an amazingly varied song hat's gull of mimicry (of you want to hear one, listen here!). For me, one of the best things about camping in the bush is being able to lie in bed and listen to the birds waking up while it's still too dim to see them properly. The dawn chorus is a worldwide phenomenon and I'm often asked about bird song, so I thought it would be worth exploring some of the theories behind bird song, and - particularly - why birds sing in the morning. It's something that's interested me since I was introduced to the question by a friend of mine who did a PhD on the subject some years ago, and I know he reads the blog so I'm hoping he'll make sure I get the answers right!

Migrant bird population declines, an African perspective

Willow warbler singing in Africa - 10g but probably headed to eastern Siberia...

March is the month when northward migration of songbirds gets underway in East Africa, so this weekend I was excited to be out west of Arusha with friends and to find stacks of migrants already on the move. Driving in I noticed some really smart looking wheatears (both pied, and the very impressive northern wheatear, though many of them have already set off on their mammoth treck - perhaps as far as Alaska). But the highlight for me was the bushes alive with warblers on Saturday morning. I saw flocks of Willow Warblers, Olivaceous Warblers, Common Whitethroats and even little groups of Barred Warblers, usually a very scarce migrant around here. Some of them were even singing, in anticipation of starting breeding in a few more weeks when they get back to Europe! Having a managed a few photos I thought it the ideal opportunity to talk about bird migration.

Barred warblers are always a treat to see: headed to eastern Europe.

All these birds have been rather scarce until now, this season, and many of us have been wondering where they've got to - usually Willow Warblers and Olivaceous Warblers are one of the commonest birds in the bush from November to March, this year there have hardly been any. It's a question that will be familiar to many readers from Europe - where have the migrant birds gone? Research has suggested over the last few years that in Europe at least, migrant birds are declining faster than resident species, a change that has been attributed mainly to climate change. A number of theories have been put forward to explain why migrant birds may fare worse than resident species from the impacts of climate change - from them simply missing the peak spring food availability by arriving to late in Europe as springs get warmer (and therefore earlier), to direct effects of drought or land-use change in Africa. A recent paper (sorry, not free) has attempted to look into some of these likely causes using data on breeding population changes in the UK, and it serves as a nice bit of background to some of the remarkable things that birds do when they set off on their amazing migrations.

Why the hornbill shuts its nest

Von der Decken Hornbill nest cavity - it's tiny!

 This weekend I enjoyed a camping trip out to Simanjiro with some friends, and as well as finding some very cute new-born wildebeest, we found a number of nests. One of these, just near our campsite, was a pair of Von der Decken's Hornbill. All the hornbills of the genus Tockus have two fascinating pieces of nesting behaviour that it's well worth thinking about: firstly, after choosing (and sometimes modifying) a suitable nest cavity, the female climb inside and then plugs the nest hole with mud, faeces and other grot, sealing herself in until there's only a tiny slit through which the male feeds her and, later, her chicks. Secondly, as she's sitting there she carries out a simultaneous moult, meaning she drops all her flight feathers at once and is unable to fly. Nearly all birds moult their feathers once per year (larger birds sometimes take longer), but most do a sequential moult, meaning they drop feathers one after the other and replace them as they go, thus retaining the ability to fly throughout. (There are exceptions, of course - notably ducks and geese who also drop all their flight feathers at once.) In the case of the female hornbill, however, she goes in the nest hole, shuts the door and a little while later drops all her flight feathers. Interestingly, if she doesn't breed, she moults sequentially, just like the male, so there's some suggestion that the simultaneous moult strategy is triggered as a hormonal response to the dark interior of the nest. Now, that's the story that you'll read in all the papers (e.g. here and here), but it can't be the whole story as I was trying to find some pictures to point you to of birds inside nests looking all naked, and I couldn't. In fact, here are a few pictures that show females in the nest - this one is an African Grey Hornbill with smallish chicks, but clearly well feathered mother with fairly worn plumage - she's not just completed a moult. And here's an Asian species also with young chicks who certainly doesn't look in moult to me. I'm sure it happens though, and may be the norm, but there are obviously exceptions that haven't yet made it into the literature.

The wheatear's remarkable migration: Alaska to East Africa

A great piece of research came my way today, detailing the migration of the individual wheatears from their Alaskan breeding areas to winter territories in East Africa. We've long known this must happen, as pretty much all the world's Northern Wheatears Oenanthe oenanthe spend the winter in Africa, but now technology has allowed us to follow individual birds on their 14,600km long migration from Alaska to East Africa and back. It's a remarkable story, not least that a 20g songbird can repeatedly do this sort of movement, but that we now have devices that can be attached to such small birds and record their journey. Wheatears are also a favourite of mine, and their migration has been the subject of one of my student's research so I almost feel qualified to make a few comments!

Migration routes and wintering grounds of three northern wheatears breeding in Alaskan (AK) and one in the eastern Canadian Arctic (CN; grey dot, breeding area, blue, autumn migration, orange, spring migration, dashed lines indicate uncertainty in migration routes close to equinoxes). Fifty per cent kernel densities of winter fixes (beginning of December 2009-end of February; purple, bird AK-1; green, bird AK-2; orange, bird AK-3; blue, bird CN-1) are given depending on the sun elevation selected (with 228 for most southern and with 24.58 for most northern densities). Pie charts indicate the proportion of individuals (AK: n ¹/₄ 9, CN: n ¹/₄ 4) originating from one of the three pre-defined wintering regions (red, western; orange, central; yellow, eastern) [8] based on stable-hydrogen isotope (dD) values in winter grown feathers and the dD values within each wintering region (mean+s.d. shown); Credit: F. Bairlein et al. 'Global migration of wheatears' (doi:10.1098/rsbl.2011.1223) in Biology Letters

Why are female raptors usually bigger than males?

 A friend of ours foolishly sent me a message yesterday saying he'd got both spotted eagle owls and african wood owls in his garden at the moment. As I'm sure anyone sensible would have realised, that immediately resulted in my inviting the whole family over to his house for lunch today with the join aim of avoiding washing up and seeing some nice owls up close. I'm pleased to report success on both fronts! After the initial surprise of seeing the two species in practically neighbouring trees (eagle owls are well known predators of other owl species, making over 10% of the diet in one study), the thing that struck us most was the extraordinary degree of dimorphism exhibited by the pair of wood owls. In most birds of prey - the owls, hawks, eagles, etc - the female is the larger bird, the male being smaller which is exactly the opposite of what is normally the case in birds. Why this should be is a fairly interesting question which comes in two parts - firstly, when should there be such a large difference in body size in (particularly) birds of prey? And secondly, why should the females specifically be bigger than the males (why is it the opposite of most other species)?

Life spans of tropical birds

Admirng a White-browed Scrub Robin!

Pangani Longclaws are very impressive up close

This morning I took my children with me to go out and do some bird ringing (banding, if you're from the US or Australia!) with some friends just out of town. As is often the case when I'm ringing, I get asked lots of questions about why we ring birds, today's best was why we keep catching immature birds? There are lots of answers to this question and some of them focus on the fact that young birds are just less careful and are generally more stupid than their parents - but this bias aside it is a really good question and had me thinking again about the differences between bird lifestyles here in Africa, and those in higher latitude areas like Europe and North America. It just happened that the question came up after we'd caught two migrant birds (from Europe) and a very new baby White-browed Scrub Robin - all birds hatched within the last year. What I said at the time (and now I can look back over all the birds we caught this morning it's even clearer) was that whilst we often catch more immature than adult migrants, that's not true for the resident African birds we were catching. In fact, we only caught about 25 birds this morning, and only three of them were migrants (we were hoping for more, but this year has been surprisingly poor so far down here, the talk of all the local birds at the moment, as conditions seem good to us!), but all the migrants were young, whilst of the remaining resident African birds, only three were immature. This sample alone, of course, is of limited use: as a scientist I'd want much larger sample sizes - and I'd also want to know it wasn't just a seasonal thing - many of our local birds are only just begining to breed, so there simply aren't many babies around yet. But put our results together with many others, and start to look at the data gathered in more detail and it is indeed clear that African birds do things rather differently to their higher latitude counterparts - as described in a nice paper by Wiersma et al "Tropical birds have a slow pace of life" (get it free here!). Not unlike a lot of people living here either!

Lovebirds can live up to 20 years - they can also bite hard, so be careful extracting!

How colourful are birds?

Lilac-breasted Roller, eveyone's safari favourite! Indigo & Violet

One of the best things about birding in the tropics is the sheer brilliance of many of our bird's plumage. After a day in the field you can easily think you've seen birds of every colour of the rainbow - and you're probably right! In a paper published last year by Mary Stoddard and Richard Prum (available free to all here) they demonstrate nicely that whilst they do cover the whole rainbow (and more besides), they still don't cover even the majority of the potential colours available to them - only about 26-30% of the potential options, it seems.

Red: Scarlet-chested Sunbirds use structural and pigmented colours

To understand how anyone can ever assess exactly how many colours are availalbe to birds, you need to start by understanding that many birds (though not all) actually see more colours than us - a lot can see ultraviolet light, as well as the usual combination or red, green and blue that we humans (and most other primates) see. (By contrast, most other mammals lack even our ability to see red, so they must live in a rather dull-looking world!) So by knowing the entire set of colours that can be generated from red, blue, green and ultraviolet the authors identified the potential range of colours available to birds, and they then sat down and looked at nearly 1000 (965 to be precise) sets of feathers and precicesly measured their colour, then plotted it in the red/green/blue/uv colour space. And they discovered that despite their efforts to find feathers covering as many different colour types as they could, they only found colours in about 1/3rd of the available space. In particular, birds seem to be missing a lot of the different options of green and purple. Now, there certainly are green and purple birds out there, but not all the possible forms of green, and not all the possible sorts of purple. (They're not particularly good at pure UV either - but that might in part reflect the author's inability to identify strongly UV feather groups in their initial search - we can't see it after all!)

More amazing honeyguide discoveries!

Steel-blue Whydah, Seronera, Dec 2011.

We've featured honeyguides on the blog here before, and I wouldn't normally come back to the same species so soon, but another recent paper (available to all for free here) by Claire Spottiswoode and colleagues has grabbed my attention by demonstrating nicely some of the challenges that generalist brood parasites have to overcome. There are, of course, three groups of brood parasites (birds that lay eggs in the nests of other species to let them raise the young) in East Africa: the well known cuckoos and the less well known honeyguides and whydahs.

Greater Honeyguide, Tarangire, Sep 2011

Now most whydahs are extremely host specific - the Eastern Paradise Whydah will only lay in Green-winged Ptylia nests, whilst Broad-tailed Paradise Whydah nests in Orange-winged Ptylia. Similarly, Straw-tailed Whydah is pretty exclusive to Purple Grenadier, Purple Indigobird is perhaps best identified by listening to snatches of it's host, Jameson's Firefinch, etc. Others are slightly less specific - the Steel Blue Whydah lays in the nests of the very closely related Black-cheeked and Black-faced Waxbills and Pin-tailed will parasitise several waxbill species. Cuckoos and Honeyguides too tend to specialise somewhat, but not completely. And this is where it gets interesting. To some degree is obvious that in a species with a single host there are strong evolutionary pressures on the female to lay eggs of a similar size, colour and marking to that of the single host, a relatively simple problem. But it's less easy if you're trying to match several different species all at once as even closely related species often have differently marked eggs (perhaps as a mechanisim to make brood parasite's lives harder?). And so we find that in some of these groups some interesting evolution has taken place - in Cuckoos we've long known that females will (nearly) always lay their eggs in the nests of the same species as they were fostered in. If such differentiation happened over the long term, one might expect a new species to evolve - one that parasitises one species, another on another (which might well be what happened in the whydahs, or even among the other groups too). But the difference here is that males don't care - they'll mate with any female that looks right and is willing, so the species as a whole remains united, despite female 'races' developing. So then you have to ask whether females from one host lay eggs that differ to those of females from another host, and if so, how can they possibly have evolved such specific genes to colour and pattern the eggs in the face of complete mixing from the males? And this is (part of) the question that Claire and colleagues were interested in.

Male Greater Honeyguide, Tarangire, Sep 2011

They show very nicely that Greater Honeyguides have two main groups of host species - birds that nest in tree holes (African Hoopoe, Green Wood-hoopoe, etc.), and those that nest in earth holes (Little Bee-eater, Striped Kingfisher, etc.). The former have larger and longer eggs, the latter smaller, rounder ones. And so two forms of female greater honeyguides seem to have evolved - one specialising in the tree nesters, one in the ground nesters and as expected the females of each group lay appropriately shaped and sized eggs. So how do they do it? Well, one of the important theories that was developed as long ago as 1933 is based on another fundamental difference between birds and mammals that's important to know. In both mammals and birds the sex of a developing embryo is determined by chromosomes, the DNA containing structures that control inheritance. In mammals, everyone has one 'X' chromosome we inherit from our mothers, but from our fathers we can either inherit another 'X' chromosome (which would make us female), or - like our father - we could inherit a 'Y' chromosome, which would make us male. The 'Y' chromosome is therefore inhereted father to son, to grandson, etc., without ever finding itself in a female, and it's this pattern of inheritance that makes us male or female. Now what differs in birds is that instead of the X and Y combination making us male, it would make a bird female. Male birds have two of the same type of chromosomes, females are the ones with the different pair, and to make this distinction easier we don't use the X and Y terminology, but talk of W and Z chromosomes instead. So, unlike in mammals, it's the females of birds who have a unique chromosome that is passed one through mother to daughter to grand-daughter, without ever passing through a male. So if the information for how to colour your egg is stored on this chromosome, no information about it will ever come from a male. A neat solution to how the species as a whole can be unified by the males, but females can differ (possibly substantially) in the genes they have on their unique chromosome.Hope that's clear...

Now, Claire and her group went one step further and decided to look for differences in a special sort of DNA called mitochondrial DNA that is also only inherited from mother to daughter, and compare the degree of difference between the two groups of tree and ground parasitising females in the mitochondrial DNA with the difference in the DNA in the main part of the cell that comes from both male and females. They expected - and rather neatly demonstrated - that there might be substantial differentiation between the females in mitochondrial DNA, but that the males would mean there's little difference in the main 'nuclear' DNA. And the degree of difference in the mitochondrial DNA between the tree and ground nesters was so much that their ancestors started breeding in these two different way millions of years ago! That's pretty remarkable, and rather different from the more recent splits reported for cuckoos, probably brought on by relatively recent host changes. Why this difference? Well, they speculate that it's thanks to the greater staility of the African climate compared to the Northern one where most of the work on other brood parasites has been undertaken, but I'm not yet convinced - if we could compare similar patterns for a few local cuckoos too, that might be very interesting!

Anyway, all very impressive and a great lesson not only in the complexities of brood parasitism that is fascinating to me, but a bit on sex determination too - a subject we're sure to return to in the future...



Reference:

Spottiswoode, C., Stryjewski, K., Quader, S., Colebrook-Robjent, J., & Sorenson, M. (2011). Ancient host specificity within a single species of brood parasitic bird Proceedings of the National Academy of Sciences, 108 (43), 17738-17742 DOI: 10.1073/pnas.1109630108

Woodpeckers as keystone species

It's been a while since I posted a birdy blog and since I got some nice pictures of a Cardinal Woodpecker at the weekend, I thought I'd use it as an opportunity to talk about woodpeckers in general, since they're surprisingly important in the habitats they occupy. As usual, we'll look to answer the three questions I use to prompt me when seeing wildlife – what is it? What's it doing? And what's it's role in the ecosystem.

Female Nubian Woodpecker, Kisima Ngeda, Aug 2011

So, for identification, woodpeckers are generally fairly easy. In most of northern Tanzania and Kenya, there are four common species of savannah woodpeckers – the commonly seen Nubian, spotted all over; Bearded, the largest and with a black throat and stripy face; the rather small and neat Cardinal, with spots on the back and streaks on the front, and the very colourful Grey. Away from the dry north of Tanzania the Nubian is replaced by a number of other options – Bennett's or Speckle-throated being the obvious ones. There are plenty of other species around, of course, but they're mainly associated with forest and we'll forget about them for now. Woodpeckers in general are rather widespread, obviously similar species occur on every continent except, rather strangely, Australia. They're relatively closely related to barbets and hornbills (note the zygodactyly – two toes forwards, two-toes backwards – they share with the barbets, easily seen in some of these photos). So, that's what they are. Now what do they do?

Male Cardinal Woodpecker, Manyara Ranch, Nov 2011

Normally you'll come across a woodpecker first when you hear it, either calling – Nubians in particular are noisy – or from hearing the 'tap-tap-tap' of their beak on a tree. Calling is often done by pairs, and we can safely assume it serves the dual purpose of strengthening a pair bond and communicating to neighbours that the territory is occupied. The tapping is where it gets more interesting – most of this is exploratory, trying to find hollow bits under the bark where tasty larvae may live, some is more obviously getting at the food once they've found it, and some it again a territorial statement like calling – though this purpose seems to be less common here in Africa than in northern regions. And the most interesting of all is the hard banging they use to excavate nest holes. I'm sure (unless you're Australian!) we've all seen the beautifully neat holes woodpeckers make for their nests, often several holes in a single stem. There's two things that are particularly interesting about this to me – the first is how they do it in the first place. The speed and pressure generated in order to dig into the wood is extraordinary – the deceleration from 6-7m/sec to stationary at impact isequivalent to 1000 times the pull of gravity – the effect on humans would be similar to Usain Bolt running head-first into a brick wall at the end of his 100m sprint. Not pretty, I should think! And the adaptations they have to avoid the problems we'd get from banging out head on a brick wall are also impressive – slightly differentlength upper and lower mandibles, extra thick skull, fluid-filledshock absorbers, unusual size and shape of brain, etc., etc. Quite remarkable really!

Grey Woodpecker, Near Arusha, March 2011

But the second thing about these holes is where they get really interesting. Woodpeckers mostly use theholes they excavate only once, after which the holes are available to anything else that likes to live in holes – birds, bats, other mammals and all. In fact, there's a huge array of animals that live in holes, but can't make them themselves (though some, like barbets, may make adjustments to get the hole right for them). Over time the holes get larger and larger, allowing a whole host of species to find homes. In some northern forests, woodpeckers have disappeared (for anumber of reasons we don't need to go into), and once the holes aregone, so too do all the other species that make use of them. Thus the loss of woodpeckers has much greater impacts on the whole ecology of a woodland than the simple direct effect – the consequences cascade down through other species too. Which is exactly why some people suggest woodpeckers may be seen as keystone species – a single species that holds together a whole load of other species and have disproportionate impacts on the ecosystem. Mighty important things, woodpeckers!

This Brown-breasted Barbet is probably uing an old woodpecker hole, Nr Boma Ng'ombe, March 2011

 

Waifs and strays

Eurasian Bee-eaters at Manyara Ranch, Jan 2011

For the past fortnight or so I've enjoyed daily sight and sound of migrating Eurasian Bee-eaters whizing overhead - migration is in full flow and over the next few weeks these early bee-eaters and swifts will be joined by a whole host of other passerines and raptors. Many of these are following the movement of the rains, and will have been in Africa for many weeks already, some will stop here (like many of the bee-eaters), others will carry on further south. And among the millions of birds that get it right, we can be sure there'll be one or two that took a wrong turn somewhere, or carried on a bit too far, to turn up in unexpected places. Also moving at the moment are lots of Afrotropical species that are using the onset of the rains as a cue to move from dry season hide aways, to wet season breeding areas and with so much movement going on there too, interesting things are bound to occur. We've been in our current house for about 2 years now, but a chestnut weaver in my garden last weekend was still the first I've heard here - it's fizzing song getting going despite still being in non-breeding plumage.

Chestnut weaver in non-breeding plumage, Manyara Ranch Aug 2011

And this weekend I enjoyed a walk (in the rain - I am British, after all) around Lake Duluti where, among the regular species, a lesser flamingo was swimming around the lake in the company of this rather fine black duck. African black ducks are usually found rather rarely on highland rivers and streams, so this was quite a surprise - note it's very long body and obvious white wing marks, plus white bits on the base of the bill that separate it from other species here abouts. This and the flamingo were both new birds for me to see at Duluti, despite many visits there. The diversity of birds in Africa is truly amazing, and now, with the start of the rains, is a great time to look out for unusual things moving between their more regular locations. The forecast is for a good short rains around this part of Tanzania this year, so expect lots of breeding activing in the next few weeks too - all very exciting! Let me know if you see anything good!

African Black Duck, Lake Duluti, Oct 2011