angels in CAMOUFLAGE An appreciation of larks
arks have inspired poets as glorious as William Wordsworth, John Milton and Percy Bysshe Shelley, yet most birders consider them only as bothersome LBJs. Much maligned, they are often viewed Las little more than a boring identification chore. However, larks have a history as old as Africa itself. Some members have the most remarkable survival techniques in the avian world, and they sing and display like angels. So is there more to these sombre brown birds than first meets the eye? Shelley thought so, and so do I, writes KEITH BARNES.
albert froneman arks are a massive identification validity of geographical races is not ost birders in southern It isn’t just the casual birder who has problems challenge and, together with pip- orthodox. Having been a sinner myself, Africa are familiar with the its and cisticolas, they wear the I can expiate my indiscretions without Spike-heeled Lark. A short- distinguishing between larks. Ornithologists have unwelcome mantle of ‘Africa’s exultation and in repentance.’ Conversely, tailed, upright lark found in LLBJs’. Most species use open habitats in Gordon Maclean wrote, ‘It is doubtful Ma wide variety of open-country habitats, been arguing about them for more than 100 years desert, semi-desert and grasslands, and are whether the matter [of lark systemat- its white outer-tail tips, stocky frame and characterised by a great deal of morpho- ics] will ever be satisfactorily resolved.’ sociable behaviour render it one of the its finder. As the bird is highly resident Above In the course of one of the more logical convergence. This is because the Maclean’s cautious view was in strong most easily recognisable and identifi- and non-dispersing, it is likely that at elaborate displays in the family, the environments they exploit are very simi- contrast to Meinertzhagen’s self-assured able of all larks. In 1965 John Beesley some stage in the past this population Rufous-naped Lark leaps, calls and claps lar, so the species often end up looking and somewhat misguided statements. discovered a small population of this must have had a contiguous distribution its wings. confusingly alike. To exacerbate the prob- The truth of the matter probably lies species near Mt Meru, Tanzania, some with the Spike-heeled Larks in southern lem, differences in plumage and form are somewhere between the two great lark 2 000 kilometres from its closest neigh- Africa. The rumblings of the Rift Valley Opposite Gray’s Lark is restricted to frequently as great within species as they men’s perspectives. bours. A short paper describing the bird and rise of Mt Kilimanjaro and Mt Meru gravel plains in the Namib. Although are between them. The advent of molecular techniques to was published and nothing more was some five million years ago seem to it strongly resembles the Ammomanes It isn’t just the casual birder who has assess the status of races and species has really thought of it. There was a theory have created a bizarre microclimate on larks of North Africa and southern problems distinguishing between larks. aided us immeasurably. Good recent work that the ice ages that dominated 100 000 the western side of Mt Meru. With rains Asia, it is in fact closely related to the Ornithologists have been arguing about involving genetics has been able to show years ago may have been responsible for being pushed in from the Indian Ocean Spike-heeled and Long-billed larks of them for more than 100 years, with many convincingly that the Long-billed Lark of the appearance of this population at the coastline, the dual rainshadows created southern Africa. inconsistent and controversial taxonomic southern Africa, once regarded as a single, ‘wrong’ end of the continent. In 1997, by these two massive mountains result treatments being proposed in the last highly variable species, is better treated as Tanzanian ornithologists Liz and Neil in a rainfall gradient that shifts from century. Two of Africa’s specialists in lark five distinct species. And it has revealed, Baker invited a team to the area to study 3 500 millimetres on the wetter, eastern taxonomy ventured vastly differing opin- for example, that the rare and highly the bird. Genetic investigation revealed side of Kilimanjaro to about 500 mil- ions on the matter. In his A Review of the localised Ethiopian endemic Degodi Lark, that this tiny population had been sepa- limetres on the dry western slopes of Alaudidae, perhaps the most flawed taxo- only described in 1971, is simply a race of rated from other Spike-heeled Larks for Meru. It is apparent that a mini-desert nomic treatise on the family ever the more widespread Gillett’s Lark. These far longer than previously appreciated, has persisted on the western slopes of produced, Richard Meinertzhagen are good instances of just how problem- probably more than two to three mil- Meru as the surrounding habitats have flamboyantly stated, ‘I make no atic the taxonomy of this group can be. lion years. It differed morphologically become wooded and moist over the past peter ryan apology for my methods, for I Without getting too caught up in the too, having a particularly short tail and three million years. As the world around believe that they correctly inter- mind-numbing world of molecular tax- smaller bill. it has changed, Beesley’s Lark has been pret the facts and that posterity onomy, let’s explore what these birds can It was clearly a different species and trapped within a micro-habitat: its global will concur. My view on the tell us about Africa and its history. was named Beesley’s Lark in honour of range extends only some 40–65 square
50 larks africa – birds & birding august/september 2009 larks 51 kilometres and probably no more than 100 individuals remain. It is literally on the brink of natural extinction. But many larks have incredibly small ranges and persist in minuscule patches of Larks offer us a unique snapshot of habitat. The genus Heteromirafra, compris-
r ing South Africa’s Critically Endangered o d Africa’s history, as they are an ancient i r The hypothetical arid corridor that may Rudd’s Lark, Ethiopia’s Sidamo Lark and r o c Somalia’s Archer’s Lark, is the most obvi- have persisted during the ice ages and at d i group of birds that can trace some of the r ous group. With ranges scattered widely A other periods during Africa’s history obvi- across the continent, each of these spe- ously impacted on the evolution of some continent’s earliest geological events cies occupies an exceptionally small glo- larks. However, its effect was limited for bal range. Genetic work has revealed other groups, which seem to have evolved that Heteromirafra possibly represents more in situ. an ancient lineage that is slowly being martin benadie replaced and outcompeted by more the arid corridor for dispersal and there dominant larks. are closely related species that occur at Larks offer us a unique snapshot of opposite ends of it, such as the Foxy Lark Africa’s history, as they are an ancient in the north and the Fawn-coloured Lark group of birds that can trace some of the in the south. continent’s early geological events. They are dominant in Africa’s rangelands and, hile the study of larks is of all the bird families adapted to this able to reveal intriguing habitat, they are also the most species- patterns about the evolu- rich group, with the most complex dis- tion of Africa’s arid zones, tribution patterns. All of these factors theseW hardy little birds also have an array assist researchers’ investigations into the of features that enable them to master poorly studied rangelands. the dry country. Of the 96 species of larks in the world, Feathers are the first. Larks are dull- some 78 are found in Africa. They are coloured birds that have conservative concentrated in two main areas in par- plumage coloration and patterns. There ticular: the south-west (South Africa, is a good reason for this: they require Botswana and Namibia) and the north- camouflage. In some larks, the colour of east (Ethiopia, Kenya and Somalia), with their plumage is linked to that of the soil, 26 and 23 species respectively being and their streaking pattern is related to Opposite, top The Dune Lark has endemic to these zones. Some theories vegetation density. As rangeland special- plumage that matches almost exactly the propose that over many millions of years ists, these birds are placed under severe substrate on which it lives in the Namib these two areas were connected (maybe pressure from aerial predators, with sand-dune sea. It can survive without nancy bell a number of times) by an arid corridor, falcons, kestrels and sparrowhawks fre- freestanding water and derives its water and that in the process larks dispersed quently overhead. When a lark is alarmed requirements from its food. and speciated across this corridor. by a distant threat, it freezes, relying on Genetic research has turned up some its cryptic plumage to best effect. Only Opposite, middle, left The Spike-heeled fascinating evidence in this regard. It when a threat is extremely close does the Lark is a species of open grassland and seems that true desert larks did not dis- bird flush. semi-desert in southern Africa. Unusually, perse via the arid corridor. Instead, they There are two main types of lark cam- it breeds cooperatively and uses aardvark appear to have evolved from neighbour- ouflage plumage: generalised and spe- burrows for shelter in hot climates. ing larks and have undergone radical- cialised. Generalised plumage comprises ly divergent morphological evolution. a mixture of colours with dark streaking Opposite, middle, right The Sidamo A good example from southern Africa or spotting on the feathers. This offers Lark belongs to Heteromirafra, a genus is Gray’s Lark. For many years it was crypsis anywhere and is particularly use- apparently in ecological retreat, with all its thought to be closely related to the ful in a wide range of vegetation back- members having minute ranges scattered Ammomanes desert larks of North Africa grounds. Because of their varied habitat across Africa. because of their uncanny morphological use, almost all migrant and nomadic similarity. However, Gray’s Lark’s clos- larks (for example, the Somali Short-toed Opposite, bottom Gillett’s Lark, a scarce est relatives are other southern African Lark) have generalised camouflage. local resident in arid country in north- larks, including the very dissimilar Spike- Specialised camouflage tends to be eastern Africa, is related to the Karoo heeled and Long-billed lark complexes. uniform and involves a very close col- and Dune larks of southern Africa – a Unlike true desert larks, semi-desert and our match with the tones of the bird’s good example of speciation along the grassland larks do seem to have used favoured habitat. An excellent example arid corridor.
august/september 2009 larks 53 keith barnes (2) is the Dune Lark, which is resident in the to use less energy during summer by Opposite, top A Karoo Lark performing open terrain of the Namib sand-dune sea. lowering their metabolic rate by up to its energy-sapping display flight. Upon Despite lacking cover, the Dune Lark can 30 per cent. At this time of year their food landing, it uses its specialised camouflage virtually vanish from sight when it is sta- demands are lower and they reduce the to blend in with the sand and vegetation Of the 96 species of larks tionary on bare sand. In an experiment, size of their internal organs (including of its habitat. an ornithologist tried to chase an individ- liver and kidneys) to suppress their energy in the world, some 78 are ual lark with specialised plumage onto a requirements. As there is virtually no Opposite, middle The sexes of Raso nearby substrate that would make it more free-standing water in the deserts where Lark (male, left; female, right) have bills found in Africa conspicuous. The bird refused to remain some of these species live, how do they that differ so markedly in their size and on the adjoining substrate, preferring to survive? These larks lose water through shape that the birds are able to forage take flight and land where its plumage evaporation at a rate much lower than as separate species. This is just as well, coloration matched the ground. that expected from similar-sized birds because the resources on the tiny islet When larks take flight, their camou- in other families. They are also capable on which this species survives are under peter ryan flage often breaks down. Many species of reabsorbing a considerable amount serious pressure. have red or white patches in the wings or of water in the intestine when water is tail that act as signals for communication scarce. Several species are so efficient Opposite, bottom The Greater Hoopoe and, frequently, for display purposes. The at retaining water that they have never Lark has a hefty bill designed for digging white outer-tail feathers, for example, are been observed drinking. It is thought in the Sahara’s soft sands and long legs often more noticeable from below, where that some species gain all their water that enable it to run great distances. a female might be watching, than they requirements through their food, by It is a remarkable bird, with a highly are from above, whence a predator may eating moist insects or the fleshy parts adaptive physiology that helps it survive approach. of plants, or through the oxidation of in its desert world. seeds. In extreme desert conditions, the s a family, larks have arguably birds actively seek out items that would the most variable bills of any improve their water balance, and have African passerines. Those spe- even been seen drinking dew. cies using softer substrates have With so much effort invested in longer,A down-curved bills for digging retaining water, staying cool and keep- and tend to be insectivorous. Seed-eating ing their metabolic rates in check, larks larks have smaller, finch-like bills, and the have had to adopt a number of unusual Thick-billed Lark has a massive, chunky behaviours. Some species, such as Gray’s bill more befitting a grosbeak. This Lark, specialise in displaying only in the
EDWIN WINKEL (2) immense variability helps larks exploit pre-dawn and post-dusk light to reduce virtually any food source available in their energy expenditure. All larks try to rest meagre environments. Even within spe- during the hot and parched midday. cies, bill proportions can differ extraord Perching on bushes to avoid the hot inarily; in the Raso Lark they diverge so ground and increasing their exposure significantly that the males and females to a breeze is one way of staying cool. can practically forage as different species. In Saudi Arabia, larks are known to rest The longer-billed males dig and probe for on the leaves of plants in the cucumber food while the females use their smaller family, as they have deep roots that reach bills to flip pebbles. The completely differ- the water table and are considerably ent foraging strategies help this Critically cooler than the surrounding environ- Endangered species to exploit more fully ment. Spike-heeled Larks use burrows of the limited resources on its minute, two- ground squirrels and Hoopoe Larks those square-kilometre Raso Islet home. of lizards to avoid the extremes of the Larks can tolerate massive environmen- midday environment. By going under- tal extremes. The Greater Hoopoe Lark ground to a depth of 30 centimetres and can exist in an environment that receives remaining there for five hours, a Hoopoe less than 50 millimetres of rain a year and Lark may reduce its water loss by some reaches temperatures of more than 50 °C 80 per cent. in summer. Conversely, the Horned Lark Larks are amazing and they encapsulate survives in the Atlas Mountains, where the lost art of birdwatching, but only if temperatures plummet below -15 °C on you are prepared to stop and study them. mid-winter nights. So the next time you see a lark, don’t just Desert-dwelling larks have developed dismiss it as an LBJ avoiding identifica- several impressive physiological adap- tion. Instead, watch it for a while and see tations that enable them to survive in if in it you can discover a survivor, a song- parched lands. Individual larks are able ster or a storyteller.
keith barnes 54 larks africa – birds & birding august/september 2009 larks 55