Hotsome Like It
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some like it hotAFRICA’s deserT BIRDS Text by Andrew McKechnie o the average inhabitant of a sprawling 21st-century metropolis, the arche- typal desert is the one portrayed in films – a sun-blasted world of sand Tdunes and intense heat, devoid of water and life, and thoroughly inhos- pitable to any creature unfortunate enough to find itself stranded there. It may therefore come as a surprise to many to learn that the world’s deserts are home to diverse and fascinating communities of animals and plants. Rather than the barren, lifeless expanses they are often perceived to be, deserts represent some of the most unique ecosystems on the planet, where birds and other animals bend the rules of physics and chemistry to survive and reproduce. SHEM COMPION DESERT BIRDS 37 species follow similar patterns. For instance, the White-backed Mousebird Colius colius and Scaly-feathered Finch Sporopipes squamifrons are the south- ern counterparts of the White-headed Mousebird Colius leucocephalus and Speckle-fronted Weaver Sporopipes fron- talis of the deserts of north-eastern Africa and the Sahel region. These striking avifaunal similarities between two far-flung desert regions reflect events that occurred in the dis- tant past. Although today the deserts of south-western and north-eastern Africa are separated by thousands of kilome- tres of savanna and forest, palaeon- tologists believe that an arid corridor linking the two regions developed in the past, during recurring glacial events that saw vast areas of North America and Eurasia covered by massive sheets of ice. This corridor, which is thought KEITH BARNES to have passed between Lakes Malawi and Tanganyika, allowed desert spe- Above The Greater Hoopoe Lark, like Birds of the African deserts cies to move between these corners of several other species, makes use of bur- Deserts are generally harsh environ- Africa, establishing the similarities that rows to avoid searing midday surface ments where rain often doesn’t fall for we see today in birds, mammals and temperatures in the Sahara Desert. years (or even decades) at a time and other organisms. where sweltering midday temperatures Opposite, top The massive nests of contrast with freezing conditions at Behaviour – the key to survival PETER RYAN (2) Sociable Weavers provide a spectacular night. Scarce and unpredictable rainfall Many species that live in deserts rely on example of how birds can manipulate means that water and food are almost ingenious behaviour patterns to avoid soar in summer or drop below freezing these tiny desert-dwellers with cosy their thermal environments. always in short supply. excessively harsh conditions. In the in winter. The nest-chambers provide surroundings and protection from the Despite their unforgiving nature, the Sahara Desert of North Africa, Dunn’s the birds with the avian equivalent of biting cold. By roosting together in Opposite, bottom The Cream- deserts of Africa, like those of other Lark Eremalauda dunni, Bar-tailed Lark air-conditioned apartments – cool in this fashion, the finches probably save coloured Courser Cursorius cursor, a continents, are home to a surprising Ammomanes cinctura, Black-crowned summer and warm in winter. around 60 per cent of the energy they resident of the North African desert plains. number of bird species. These include Sparrowlark Eremopterix nigriceps and They also provide another key benefit would otherwise have used to keep the world’s largest extant bird, the Greater Hoopoe Larks spend the hot- in habitats that can go for months, or warm. Some birds combine physiolo- Common Ostrich Struthio camelus, sev- test periods of the day underground, even years, without a drop of rain, fol- gical changes with the use of sheltered eral species of sandgrouse, the archi- in burrows excavated by the large, her- lowed by a single, massive downpour. roosts to reduce their energy require- tecturally inclined Sociable Weaver bivorous Egyptian spiny-tailed lizard Whereas most birds need to go through ments even further. In the 1980s, Colin Philetairus socius, and species like the Uromastyx aegypticus. By resting in these a busy nest-building period before they Sapsford found that Pygmy Falcons Greater Hoopoe Lark Alaemon alaudipes burrows, the larks avoid the brutal sur- can breed, Sociable Weavers can rapidly employ an energy-saving mechanism that can eke out an existence on even face temperatures of up to 60 degrees lay eggs and raise chicks during the known as torpor (see Africa – Birds & the most barren gravel plain. There Celsius. They also save a considerable first flush of vegetation that follows a Birding 10(3): 14), and lower their body are several families of African birds percentage of the water and energy that storm. Their nest-chambers are regular- temperatures by around 10 degrees while whose evolutionary histories are closely they would otherwise have expended ly taken over by other species, includ- roosting in Sociable Weaver nests. linked to desert habitats, with bustards to keep cool, thus reducing the resourc- ing Pygmy Falcon, Red-headed Finch (Otididae), sandgrouse (Pteroclidae) es that they have to obtain from their Amadina erythrocephala and Rosy-faced Desert nomads and larks (Alaudidae) most clearly asso- inhospitable environment. Lovebird Agapornis roseicollis, which Another approach to avoiding unfa- ciated with these environments. A par- Another way in which some desert obtain much the same benefits as the vourable conditions is simply to fly ticularly interesting distribution pattern birds avoid harsh conditions is by build- original inhabitants. away. Many desert birds, like desert- among African desert birds concerns ing shelters, with the Sociable Weaver Many other desert birds construct dwelling humans, are highly nomadic species such as the Kori Bustard Ardeotis of southern Africa being the undis- nests, albeit on a much smaller scale, and range across large areas. Nomadic kori and Pygmy Falcon Polihierax semi- puted champion in this regard. The with similar motives. On bitterly cold lifestyles are common among desert torquatus that occur in the deserts of investments of time and energy these nights in the Kalahari Desert, Scaly- birds, and heavy rainfall events in the both south-western and north-eastern birds make while building and main- feathered Finches roost communally in deserts of southern Africa are often the Africa, but nowhere in between. In taining their massive nests are returned insulated nests that trap the heat gen- prelude to the sudden appearance of other cases, pairs of closely related with interest when air temperatures erated by the inhabitants, providing large numbers of species such as 38 DESERT BIRDS AFRICA – BIRDS & BIRDING AUGUST/SEPTEMBER 2007 DESERT BIRDS 39 Namaqua Sandgrouse Pterocles namaqua Cutting-edge science and Eremopterix sparrowlarks. A highly The past decade has seen a new wave mobile way of life allows these birds of research on desert birds, spearheaded to track water and food resources, and by the work of Irene Tieleman and Joe to breed in regions where food and Williams. Their research has revealed water are, for a while at least, in suf- that several fundamental differences ficient abundance to sustain them and exist between desert birds and their non- their offspring. Many nomadic species desert counterparts. Desert birds, as a are granivores, and their movements rule, require about half as much energy are dictated by seed production by and water in 24 hours as other birds. This desert plants in response to patchy and economy comes about largely through unpredictable rainfall. Because of the conservative behaviour patterns – desert large proportion of desert birds that birds spend less time indulging in energy- are nomadic, the number of species and water-demanding activities and more occurring in any given area may vary time resting, often in the patchy shade dramatically from year to year, with provided by a shrub or grass tussock. an explosion of avian diversity during However, their research has also revealed occasional wet periods. that desert and non-desert birds differ more fundamentally. Over the millen- nia, desert birds have evolved several physiological characteristics that make them well suited to their environments. These adaptations involve slower rates of metabolism, equivalent to a lower ‘idling speed’, and the ability to make carefully regulated increases in body temperature P. wagnER/PHOTO ACCESS during very hot weather. There is also evidence that parenthood birds require and may well prompt cata- them and on their edges. These plant Climate change is expected to cause is approached very differently by desert strophic mortality events during future communities provide the food, shade major habitat transformation in some birds. Among larks, desert species tend to heatwaves (see Vol.10(2): 12). and other resources that allow many bird desert areas. Their on-the-edge existence lay fewer clutches and a smaller number Even more worrying, climate change is species to survive in this harsh environ- will make desert birds particularly of eggs per clutch than non-desert spe- expected to drive major habitat transfor- ment. If wind speeds in the Kalahari vulnerable to such changes. cies, and hence invest less energy and mation in some desert areas. Research by Basin increase over the next few dec- water in breeding. Differences are also a team from Oxford University (Thomas ades, as is predicted by most climate evident in the nestlings of desert species, et al. 2005 Nature 435: 1218–1221) has models, a frightening scenario is set which grow more slowly than those revealed the devastating effects that to unfold. The stable dunes of today’s Burchell’s Sandgrouse of non-desert species and thus require climate change is likely to have on Kalahari Desert will be remobilised, less energy and water per unit time. several African deserts, most notably and the shifting sands will bury most However, the flip side is that the chicks the Kalahari Desert of southern Africa.