1 1 2 2 3 3 4 African Black 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 ’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 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 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, 100 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 ’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 , 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 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 . 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 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 , 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 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. times the rate of mainland limpets!). and provide the birds with a rich source they lose a clutch, they can still only 5 6 The consequence of this is that the Because the limpets are kept at low den- of food not available on the mainland. rear one brood of young in a season; 6 7 shallow waters around the island’s edge sity on the islands, they have super- the reason for this being the way they 7 8 become nutrient-rich, and these nutri- abundant food and grow very fast. Very Danger time – the breeding season care for their young. Whereas the 8 9 ents are used by the algae growing on small limpets are not worth an - African Black Oystercatchers are long- young of are truly precocial, 9 10 the shore. Algae respond to the nutri- catcher’s while to eat, and very large lived and faithful to their territories and and can feed themselves from the day 10 11 ents in the same way as a lawn responds ones are too big for the birds to dislodge. their mates: some pairs are known to they hatch, the young of oystercatchers 11 12 to fertilizer – they grow faster and repro- The limpets themselves are therefore have been together in the same place for are fed by their parents, one food item 12 13 duce faster, producing millions of tiny only vulnerable for a certain stage of nearly 20 years. At the approach of the at a time, until well after fledging. This 13 14 spores which settle on the rock surface. their life: if they grow beyond a certain summer breeding season, however, there is because the young have neither the 14 15 It is these spores that provide the food size, they are safe. Some limpets spend are some movements. Some pairs move apparatus nor the strength to tackle 15 16 for limpets, one of the main prey of the their lives in sites inaccessible to birds – away from rocky mainland coasts to shellfish on the shore. 16 17 oystercatchers. Because they are living in deep cracks or on tall, steep rock faces breed on nearby sandy beaches or, if Because they are long-lived, a pair of 17 18 in such pastures of plenty, the limpets – and others simply escape being eaten they can find room, on offshore islands. oystercatchers does not need to breed 18 19 also grow and breed rapidly, providing by good luck. It is these very large lim- The islands are obviously the prize – successfully every year in order to 19 20 food for oystercatchers. Because there pets that are the key to maintaining some pairs manage to find a spot to replace themselves: if a pair succeeds in 20 21 are so many oystercatchers, however, numbers. A very small percentage of the breed on islands, but are unable to estab- fledging one chick every three years, 21 22 these fast-growing limpets are being total limpet numbers (the very large lish a feeding territory on the island this should be sufficient. On predator- 22 23 eaten at a prodigious rate. If all the oys- ones) produce most of the limpet off- shore. Instead, they fly to the mainland free islands, pairs on average achieve 23 24 tercatchers were removed from the spring. Thus, the limpet population is to feed. This may not be too much of an somewhere between a chick every two 24 25 island, the balance between algae and constantly replenished by breeding indi- ordeal during the incubation period but, and every three years – enough to main- 25 26 limpets would be disrupted and the lim- viduals that are in no danger of being when they are feeding chicks, they must tain the island population and perhaps 26 27 pet populations would grow to the point eaten themselves. On the mainland, work hard to balance the energetic provide some surplus. What happens to 27 28 where they eliminated most of the algal where nutrient levels are lower and algal books because food items are brought to this ‘surplus’, if indeed it exists, is not 28 29 beds, with the result that there would be growth is slower, limpets do not grow to the young one at a time. clear. Although more than 1 500 chicks 29 30 far fewer mature algae to provide the such a size that they are safe from oys- The reason that birds move to poorer- have been ringed on the islands since 30 31 supply of sporelings. By keeping the lim- tercatchers, so the shore cannot support quality feeding situations in order to 1980, and several have subsequently 31 32 pet populations in check, the birds the same high density of birds. breed is almost certainly the risk of pre- been found breeding as adults on their 32 33 (albeit inadvertently) ensure a rich food By keeping limpet numbers down on dation. Like almost all other waders, island of birth, not one has ever been 33 34 supply for the remaining limpets. the islands, oystercatchers are instru- oystercatchers breed on the ground, lay- found breeding on the mainland. 34 35 But this is not the end of the story. In mental in maintaining algal beds; it is ing their one or two in a shallow 35 36 scrape. They do their best to site the A looming crisis? 36 37 Because their feeding is confined to a small area, oystercatchers can have a major impact nest scrape so that it is either camou- African Black Oystercatchers are rare: 37 P.A.R. HOCKEY 38 on the structure of the shore community. Here, one of the author’s hand-reared birds stands on flaged (for example, next to a stone or they are approximately twice as com- 38 39 the pile of limpets that it ate in one month. shrub) or raised, so that they can see an mon as black rhinos, but are rarer than 39 P.A.R. HOCKEY approaching predator from afar. Outside southern right whales. Their rarity is not 40 the breeding season, one of the ways in easily appreciated because they are so 41 which they avoid predators is to form conspicuous – it is a lot easier for a black 42 communal roosts at high tide – when rhinoceros to hide than for an oyster- 43 they are breeding, this option is no lon- catcher to do so. Because their entire 44 ger open to them. lives are confined to the coast, they are 45 The potential danger that predators potentially at risk from all sorts of 46 can pose was well illustrated in an human factors, ranging from pollution 47 unfortunate ‘natural’ experiment in and coastal development, to straightfor- 48 Saldanha Bay in 1976, when Marcus ward disturbance by man, his pets and 49 Island was connected to the mainland his toys. For example, there is an inter- 50 by a causeway. During the breeding esting and alarming correlation between 51 season, adults were killed on an almost a decrease in the breeding success of 52 daily basis by terrestrial predators such oystercatchers and an increase in the  53 as foxes and genets which could now 54 reach the island, and the population of Above right When their young are threat- 55 about 60 pairs was producing almost no ened, oystercatchers indulge in noisy and 56 young. Indeed, the rate at which they conspicuous displays to lure danger away. 57 were rearing chicks was only one-tenth Right Oystercatcher chicks are very crypti- 58 of the rate needed to maintain a cally coloured. When danger threatens, 59 stable population. Construction of a they respond to their parents’ alarm calls 60 ‘predator-proof’ wall across the causeway by remaining motionless, crouched among 61 helped to a small extent, but breed-  rocks or beach debris. 62 P.A.R. HOCKEY 63

32 african BLACk OYSTERCATCHER africa – birds & birding 1997 – volume 2, number 5 AFRICAN BLACK OYSTERCATCHER 33 

 1 sales of 4x4 vehicles in South Africa. Shellfish Poisoning, the other to an out- THE OYSTERCATCHER 2 Similar trends have been noted else- break of avian cholera. Taken together, CONSERVATION PROGRAMME (OCP) 3 where – oystercatcher numbers around these statistics do not bode well for the 1998–2000 4 Hobart in Tasmania have decreased by species’ future. Need for the OCP 5 some 40 per cent in the last 30 years, South Africa and Namibia between The African Black Oystercatcher is the only 6 and human use of the shore in the them hold the global responsibility for oystercatcher species breeding in Africa, 7 Canary Islands undoubtedly contributed the conservation of this species – the only where it is restricted to the coasts of Namibia 8 to the of the islands’ endemic oystercatcher breeding in Africa. In addi- and South Africa. It is the third rarest oyster- 9 oystercatcher. tion to its own intrinsic value, this species catcher in the world, with a global population 10 In the breeding season of 1996/97, a is an excellent barometer of coastal only twice that of the black 11 survey of oystercatcher breeding success change, both for the better and the worse, rhinoceros. Because it is resident and territo- rial, it is very susceptible to disturbance and 12 was organized by Cape Nature Con- simply because it must find all that it coastal degradation; it is therefore an excel- 13 servation and the Percy FitzPatrick needs within a relatively small area. lent barometer of the health of the coast. 14 Institute. In the core of the species’ west Because of increasing concern over the Recent surveys suggest that its mainland 15 coast range, it seems as though breeding future of southern Africa’s coast in gen- breeding success is dangerously low and it is 16 success was about 15 per cent of that eral, and the African Black Oyster- catch- clear that a strategic plan for its conservation 17 needed to maintain a stable population: er in particular, the Percy FitzPatrick is a high priority. 18 we recorded a ratio of 500 adults to nine Institute will be spearheading an Aims of the OCP 19 fledglings. On 60 kilometres of the Oystercatcher Conservation Pro- gramme • To assess oystercatcher population trends on 20 Eastern Cape coast, there was no evidence (OCP), involving governmental and non- the South African coast over the past 20 years. 21 of successful breeding at all. It seems governmental conservation bodies. The • Where changes (positive or negative) have 22 unlikely that it was just a poor breeding first phase of the programme will run occurred, to investigate why these changes 23 season, because it was ‘business as usual’ from 1998–2000. have taken place. • To develop a model of oystercatcher pop- 24 on the west coast islands. The main aim of the OCP will be to ulation dynamics which can be used to 25 Superimposed on the human impacts provide a conservation strategy for the predict future changes in the oystercatcher 26 are episodic mass mortalities from natural species: if we can cater for the needs of population under different development/ 27 causes. Twice in the past 20 years, this special and charismatic bird, the conservation scenarios. 28 oystercatchers on the Saldanha islands spin-off benefits to other species along • To develop a conservation strategy for the 29 have experienced such events, which the coastline will be considerable. oystercatcher which will also benefit other 30 may kill 30–50 per cent of the popula- coastal species. • Through practical demonstrations of 31 tion. One die-off was due to Paralytic  successes, failures and their causes, to 32 develop awareness of the conservation 33 Because oystercatchers nest in the open, they often site their nests next to objects which break needs of South Africa’s coast. 34 up the outline of the incubating bird. How you can participate in the OCP 35 P.A.R. HOCKEY Information gathering 36 The success of the OCP is very dependent on 37 public participation in the data-gathering 38 phase. We need volunteers who can help in 39 monitoring breeding success, collecting chick 40 feeding-piles at the end of the breeding 41 season, and recording the size and age- 42 structure of winter roosts. All the information needed is easy to collect, and every additional 43 piece of information will help us improve the 44 final conservation strategy. 45 46 Sponsorship 47 The project is currently being sponsored by the Mazda Wildlife Fund, the Cape Bird 48 Club, the Endangered Wildlife Trust, Cape 49 Nature Conservation, the Tony and Lisette 50 Lewis Foundation, and MTN. However, what 51 we can achieve will, to a large extent, depend 52 on the total sponsorship. 53 How to get involved 54 If you are keen to participate in, and/or 55 sponsor the OCP (either privately or as a 56 corporate sponsor), please contact Prof. Phil 57 Hockey, Oystercatcher Conservation 58 Programme, Percy FitzPatrick Institute of 59 African Ornithology, University of Cape Town, Rondebosch 7701, South Africa. 60 Tel. (021) 650-3293; fax (021) 650-3295; 61 e-mail [email protected] 62

34 AFRICAN BlacK OYSTERCATCHER africa – birds & birding