1 1 2 2 3 3 4 African Black Oystercatcher 4 5 5 6 6 7 7 8 Between 8 9 9 10 10 11 the tides 11 12 Text by Phil Hockey 12 13 13 14 he African Black Oystercatcher’s 14 15 15 first entry into the scientific ‘led- 16 16 17 ger’ happened only 141 years 17 18 T 18 19 ago, when a specimen collected at the 19 20 Cape of Good Hope was described by 20 21 21 22 Bonaparte. Bonaparte named the bird 22 23 moquini after the French botanist, 23 24 24 25 Horace Benedict Alfred Moquin Tandon, 25 26 director of the Toulouse Botanical 26 27 27 28 Gardens. Its first entry into the litera- 28 29 29 ture, however, predates this by more 30 30 31 than 200 years. 31 32 32 33 In 1648, Étienne de Flacourt, the 33 34 Governor-General of Madagascar, 34 35 35 36 visited Saldanha Bay. He wrote: ‘There 36 37 are birds like blackbirds, with a very shrill 37 38 38 39 and clear cry, as large as partridges, with 39 40 40 a long sharp beak and red legs: they are 41 41 42 very good to eat and when young they 42 43 43 44 taste like Woodcock’. The first descrip- 44 45 tions of the bird’s biology date from the 45 46 46 47 late 19th century – much of what was 47 48 written then was culled from knowledge 48 49 49 50 of the European Oystercatcher, and much 50 51 51 of it was wrong! 52 52 53 Now, at the end of the 20th century, it 53 54 54 55 seems as though this striking bird may 55 56 be moving from a confused past into an 56 57 57 58 uncertain future. 58 59 59 60 60 61 61 62 PHOTOGRAPH: PETER STEYN/PHOTO ACCESS 62 63 28 AFRICAN BLACK OYSTERCATCHER 1 like bill and powerful neck muscles are prey on the shore change, oystercatchers 100 limpets per day, and the birds are 1 2 put. Limpets are dislodged with a sharp change their diet in response. Over the rearing chicks on the territory, how, you 2 3 blow to the edge of the shell – the blow past 20 years, there have been major may ask, can the food supply possibly 3 4 is usually directed at the edge away changes in oystercatcher food on the support this density of birds? And it is 4 5 from the limpet’s head. (Try removing a west coast because of the invasion of the not only oystercatchers that are so com- 5 6 limpet from the rocks yourself to appre- shore by an alien Mediterranean mussel, mon along the shore; migratory shore- 6 7 ciate the skill and strength involved.) Mytilus galloprovincialis. birds, especially Turnstones, occur at 7 8 The flesh is then neatly scissored out Scientists at the Percy FitzPatrick much higher densities on the islands 8 9 from the shell and swallowed. Institute at the University of Cape Town than on the adjacent mainland. The 9 10 Mussels require a quite different have been able to monitor this invasion answer is not immediately obvious, and 10 11 approach. The oystercatchers wait until by comparing the diet of oystercatchers much careful research was needed to 11 12 the mussels themselves are feeding. from year to year. At the peak of the unravel the web of ecological interac- 12 13 Mussels feed by drawing water into their invasion, the alien mussel made up tions that maintain the system. 13 14 bodies and filtering out microscopic more than 90 per cent of the birds’ diet, The web was not a simple one involv- 14 15 food particles, such as spores from giving a good indication of just how ing just the oystercatchers and their 15 16 marine algae. To do this, they have to successful an invasive it has been. food – also included were algae, seabirds, 16 17 open their otherwise tightly clamped and even the geology. 17 18 valves. This is the oystercatcher’s chance A web of interactions The islands are important roosting 18 19 and, with a swift jab, the bird drives its The small islands around Saldanha Bay and breeding places for tens of thousands 19 20 bill between the gaping valves, cutting support perhaps the highest breeding of seabirds. Seabirds, as anyone who has 20 21 the strong muscle that holds the valves densities of any oystercatcher species ever visited a colony will know, produce 21 22 together. Once incapacitated, the meal anywhere in the world. On the tiny a lot of guano. So much, in fact, that 22 23 can then be dealt with at leisure. eight-hectare island of Malgas, for exam- until recently guano was mined on the 23 24 The choice of what to eat is deter- ple, there are more than 60 breeding islands as a source of agricultural fertiliz- 24 25 mined largely by the abundance of pairs. The pairs’ feeding territories are er. This guano is rich in nutrients, espe- 25 26 different potential prey on the shore, packed, side by side, along the shore. cially nitrogen and phosphorous, but 26 27 the birds concentrating on prey that are Given that a fully-grown oystercatcher what is particularly important is that the 27 28 common. Should the composition of may require up to the equivalent of seabirds feed at sea and roost on land. In 28 29 29 30 Oystercatchers bathe regularly: this helps maintain plumage condition and probably also keeps down parasite loads. 30 31 P.A.R. HOCKEY 31 H.P.H. PHOTOGRAPHY/PHOTO ACCESS 32 32 33 Although they can fly rapidly and strongly, African Black Oystercatchers, unlike their European relatives, do not migrate. 33 34 34 he African Black Oystercatcher 35 the ground, but south of here numbers Life at the ocean’s edge 35 36 THaematopus moquini is not only one pick up rapidly. On slightly more than African Black Oystercatchers obtain all 36 37 of the world’s more range-restricted 1 000 kilometres of coast between the their food from a narrow strip of the 37 38 oystercatcher species, it is also one of Olifants River and Mossel Bay, some 53 coast between the land and the sea – the 38 39 the rarest. In the early 1980s, the world per cent of the world population can intertidal zone. Consequently, all their 39 40 population was estimated at about be found, and about 30 per cent of feeding must be crammed into the low 40 41 4 800 birds – enough to earn it the these birds are on the offshore islands, tide period. When there is a strong swell 41 42 dubious honour of a place in the mostly in and around Saldanha Bay. running, or barometric pressure is low, 42 43 International Red Data Book as ‘near- East of Mossel Bay, there are about 950 this gives them little time to satisfy their 43 44 threatened’. The Variable Oystercatcher birds. The African Black Oystercatcher food requirements. But, like many other 44 45 is slightly rarer (2 000–3 000 birds), and is a vagrant north of the Kunene River waders, they are adept at foraging by 45 46 the Chatham Island Oystercatcher, with and east of the Bashee River, with night, almost invisible under even a full 46 47 a population numbering less than 150, extreme records being from Lobito in moon as they move silently across dark, 47 48 is one of the rarest waders in the world. Angola and Inhaca Island wet rocks. 48 49 The distribution of African Black in Mozambique. They live on both rocky and sandy 49 50 Oystercatchers around the south-western coasts and, to a lesser extent, in estuaries 50 corner of the continent is far from even. ❍ 51 ❍ and lagoons. When feeding in soft sedi- 51 52 Despite the continent’s long coastline, ments, such as sand, their diet is not 52 53 oystercatchers only breed on the rela- very varied, consisting almost entirely of 53 54 tively small section of coast between the sand mussels. On rocky coasts there is a 54 55 Hoanib River in northern Namibia and much greater variety of food on offer 55 56 Mazeppa Bay in the Eastern Cape ❍ and the birds make good use of the more 56 Province. Namibia supports about ❍ 57 ❍ diverse cuisine. Even here, though, there 57 25 per cent of the total population, split ❍ 58 ❍ are some staple food items, principal 58 roughly evenly between the mainland ❍ 59 ❍ among which are limpets and mussels. 59 60 coast and the offshore islands. Between ❍ Within even a short time of watching 60 61 the Gariep (Orange) River and the these birds feeding, it becomes obvious 61 Olifants River, oystercatchers are thin on 62 to what use the long, straight dagger- 62 63 30 AFRICAN BLACK OYSTERCATCHER AFRICA – BIRDS & BIRDING 1 this way, they transport nutrients from a order for the limpet supply to support these beds that explain the high densi- ing success is still very low and the adult 1 2 marine environment to a terrestrial one. the high densities of oystercatchers, they ties of other shorebirds. Many small population is barely half of what it was 2 3 Some of these nutrients are washed back too must have a very high reproductive invertebrates settle in these algal beds – 15–20 years ago. 3 4 into the sea by rain, and blown, as dust, rate (island limpets are eaten at about 60 whelks, mussels, shrimps and others – Although oystercatchers can re-lay if 4 5 by the wind.