1 A deadly game of 1 2 2 3 3 4 4 5 5 6 and 6 7 hide seek 7 8 8 9 Nesting in the Karoo 9 10 10 11 Upon reaching adulthood, birds experience fewer 11 12 attempts on their lives, mostly because they are so much 12 13 Umore mobile than their predators. Their evolution of 13 14 feathers, flight and warm-bloodedness set them apart 14 15 from their dinosaurian ancestors, and allowed them to 15 16 flourish in a niche virtually devoid of animals longer in 16 17 tooth and claw. But one feature of their reptilian ances- 17 18 try still ties them to the earth – the very immobile egg 18 19 within which birds begin their lives. Rich in nutri- 19 20 20 21 21 22 22 23 23 24 24 25 25 26 26 27 27 28 28 29 29 30 30 31 31 32 32 33 33 34 34 35 35 36 36 37 37 38 38 39 39 40 40 41 41 42 42 43 43 44 44 45 45 46 46 47 47 48 48 49 49 Text and photographs by Penn Lloyd 50 50 51 51 52 52 Above A Double-banded Courser’s egg in typical 53 ‘nesting’ habitat, illustrating how exposed but nonetheless 53 54 cryptic the egg is. 54 55 Right The Double-banded Courser, a champion at 55 56 predator avoidance, with its chick whose downy plumage 56 57 is also an effective example of crypsis. 57
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1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9 10 10 11 11 12 12 13 13 14 14 15 15 16 16 17 17 18 18 19 19 20 20 21 21 22 22 23 23 24 24 25 25 26 26 27 27 28 28 29 29 30 30 31 31 peter steyn 32 32 33 A Black-eared Finchlark nest showing the rim packed with sand-encrusted buckspoor spider webs to camouflage it in the A male Black-eared Finchlark feeding its chicks. The species has the ability to breed before reaching full adult status – 33 34 sandy nesting substrate. another way of increasing fecundity during the short periods of plenty. 34 35 35 36 ents for the early stages of development, eggs are a nesting period of any bird in the world: its eggs hatch, on ators are left with very few cues to find the superbly camou- methods of camouflage were thwarted by the industrious 36 37 choice target for roving predators. The greatest chal- average, after just 10 days of incubation, and the chicks are flaged egg and only 20 per cent of courser eggs are found birds: as fast as I packed pebbles around Black-eared 37 38 lenge that parent birds face is preventing their vulnera- fully feathered and can leave the nest within seven days of and eaten. The incubating bird is assisted in this strategy by Finchlark nests in sandy habitat, the birds packed new 38 39 ble eggs and nestlings from becoming just so many hatching. An incubation period of 9–10 days is probably its partner, which loiters nearby, acting as a sentinel to warn webs on top of the pebbles! Buckspoor spiders spin a small 39 40 more links in the food chain. pushing the physiological limit, for finchlark chicks that the sitting bird of approaching danger. This behaviour of disc of sticky web on the soil surface above the entrance to 40 41 The windswept, sun-bleached expanses of the Great hatched after just eight days were small, weak and died ‘abandoning’ the eggs can be far more effective than sitting their underground tunnel-home. This web becomes 41 42 Karoo flatlands in the arid west of southern Africa have an within hours. tight in the hope of evading detection. The Namaqua encrusted with the surrounding sand particles. Because the 42 43 unusually diverse band of predators for such a seemingly The ‘broken-wing’ distraction display, where the bird Sandgrouse (see Africa – Birds & Birding 1(6):26–32), which birds collect webs close to their nest sites, the web and 43 44 barren landscape. The searching eyes and noses of a variety flutters ahead of a predator to entice it away from the nest, nests in very similar situations to the Double-banded nesting substrates usually match, one of the prerequisites 44 45 of snakes, mongooses and larger mammals commonly find is a familiar behaviour that adults adopt as a last resort. But Courser, adopts the latter strategy and loses over 90 per cent for effective camouflage. 45 46 seven or eight of every 10 nests with eggs or nestlings. The there are other, more discrete behaviours that can be of its nests. Predators either scent the bird or flush it off the The insectivorous birds of the Karoo tend to be resident 46 47 Lark-like Bunting seems to fare particularly badly, with employed to hide the nest and avoid the close approach of nest accidentally when they trot past too close, and use this and territorial, whereas most of the seed-eaters are 47 48 sometimes fewer than five nests in every 100 escaping predators. The Double-banded Courser arguably rates as one as a cue to find the eggs. nomadic, moving about widely in search of dense patch- 48 49 detection. In the face of such an extreme selection pres- of the champions at predator avoidance. Because it ‘nests’ For birds that must construct a nest, camouflaging the es of seed which appear following localized thundershow- 49 50 sure, it is hardly surprising that the birds living there have in such open and exposed situations, one might expect it to site is of the utmost importance. Species such as Sclater’s ers. These divergent life-styles have a significant influ- 50 51 evolved a wide variety of intriguing behaviours to reduce be very visible to predators. In fact, the opposite holds true and Stark’s larks, as well as the Grey-backed Finchlark, ence on the outcome of the deadly game of nest hiding 51 52 their vulnerability. – the predators are more visible to the incubating bird, surround the protruding twigs and bits of nest lining with and nest seeking. Because residents patrol the same 52 53 The longer the eggs and chicks remain immobile in the which runs off the ‘nest’ well before the predator gets any- a rim of pebbles from their gravelly nest environment. The restricted beat every day of the year, they develop 53 54 nest, the higher the risk of them eventually being found. where near. I use the term ‘nest’ because this bird does not Black-eared Finchlark prefers slightly sandier substrates and a detailed knowledge of predator activity within their 54 55 To shorten their time in the nest, several species have accel- have a nest as such, but simply lays its single egg on bare it has the extraordinary habit of collecting dozens of sand- relatively small territories. This enables them to select 55 56 erated the rates of egg and chick development. The Grey- ground. In an apparent paradox, the complete absence of a encrusted webs of buckspoor spiders (Seothyra spp.) to pack safer sites for their nests. On the other hand, nomads are 56 57 backed Finchlark, for example, has the shortest bird at the nest lowers predation risk considerably, for pred- around the rim of its nest. My efforts to test the different continually on the move and have to take pot-luck in 57
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1 their choice of nest site. They consequently lose twice as But when the rains are good and the sandy plains are 2 many nests to predation as do their resident counter- transformed into a sea of waving grass, insects abound and 3 parts. Nomads are able to compensate for these losses, to the birds increase their clutch size accordingly, laying as 4 some extent, by avoiding areas experiencing drought and many as five eggs. For as long as the favourable conditions 5 following the thunderclouds to greener pastures where last, the birds will also raise several broods in quick succes- 6 conditions are more favourable for breeding. sion so that in bumper years they quickly make up for 7 The unrelenting aridity of the Karoo ensures that plant population reductions during years of drought. 8 growth is very dependent upon rainfall. Plants directly or 9 indirectly fuel the populations of all animals, from arthro- Author’s acknowledgements 10 pods to aardvarks. To breed successfully, birds generally These insights into the breeding behaviour of arid-zone 11 need an abundance of food to produce eggs and to appease birds were gained during a study of the ecology of the 12 the insatiable appetites of their chicks. Thus the breeding Namaqua Sandgrouse supported by the FitzPatrick 13 seasons of most birds in the Karoo are fine-tuned to coin- Institute (University of Cape Town), AGRED and De Beers 14 cide with the pulses of increased food supply following Consolidated Mining Ltd. 15 rainfall. But the amount of rain that falls varies consider- 16 ably from shower to shower and from season to season. 17 Furthermore, conditions may be suitable for breeding for Bird species mentioned in the text, 18 only short periods of time before the blazing sun dries up listed in the order in which they appear 19 the landscape again. Birds therefore have to make the most Lark-like Bunting Emberiza impetuani 20 of whatever opportunities they can get, particularly if they Grey-backed Finchlark Eremopterix verticalis 21 are residents and cannot follow the patches of high pro- Double-banded Courser Smutsornis africanus 22 ductivity like the nomads do. The Spike-heeled Lark is one Namaqua Sandgrouse Pterocles namaqua 23 such resident. In a drought year, I observed this species Sclater’s Lark Spizocorys sclateri 24 building nests and laying eggs within one week of a mere Stark’s Lark Spizocorys starki 25 six-millimetre rain-shower. In times of poor rainfall the Black-eared Finchlark Eremopterix australis 26 birds lay a clutch of only two eggs because there is not Spike-heeled Lark Chersomanes albofasciata 27 normally enough food to raise a larger brood. 28 29 Grey-backed Finchlark chicks, fully feathered at the age of seven days, in their pebble-rimmed nest. Finchlark nests are near- 30 ly always placed on the south to east side of small plants to gain some shade during the heat of the day. 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57
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