African Black Oystercatcher

In 1648 Ettiene de Flacourt, the governor general of Madagascar, visited Saldanha Bay and wrote the following: “There are birds like blackbirds, with a very shrill and clear cry, as large as partridges, with a long sharp beak and red legs; they are very good to eat and when young, taste like Woodcock”.  As far as we know, this is the first description of the African Black Oystercatcher, Haematopus moquini, South Africa's bird of the year for 2018. The first description of the bird's ecology dates only from the late 19th century and a lot of that knowledge was based on what was known about the European Oystercatcher, a bird with totally different habits - so most of that knowledge was wrong ...

The OYK, as the African Black Oystercatcher affectionately is called in Birder dialect, had a confused past and for long its future looked bleak.  The OYK numbers have grown from 4800 in 1980 to today's about 6700.  In the blog “project Oystercatcher” we talked about the numbers and statistics. Today I want to tell you more about these wonderful creatures of God.

OYKs live on both rocky and sandy coasts and to a lesser extent in estuaries and lagoons.  The distribution of this endemic of southern Africa is far from even.  Densities are usually between one and four birds to a kilometer of coastline.  The highest mainland densities (2,6 per kilometer) are reached between St Helena Bay and Cape Point.  Densities on island shores are at an average of 1,2 birds a hectare and can be as much as 112 birds per kilometer (Malgas Island). The highest densities are found around Saldanha Bay, especially Malgas, Marcus, Jutten and Dassen Islands.  These island populations have increased 83-156% between early 1980s and 2003 due in part to the invasion of the coastline by the alien Mediterranean Mussel Mytilus galloprovincialis which increased the food supply.

OYKs are long-lived and faithful to their territories and their mates: some pairs are known to have been together in the same place for nearly 20 years.

More than 50 prey species, including 31 mollusk species have been identified in the diet of the  African Black Oystercatcher.  They obtain their food from a narrow strip of the coast between the land and the sea – the inter-tidal zone.  Consequently all their feeding must be crammed into the low tide period.  Like many waders, they are adapt at foraging at night.

The diet consists primarily of sand mussels and occasionally sandhoppers on sandyshores, and tellins, pencil bait, mud prawns and crabs on estuarine mudflats.  A greater diversity of prey species is hunted on rocky shores.  This includes polychaetes, whelks, various crustaveans, turbans, chitons, false limpets, periwinkles, abalone, barnacles, clams and especially mussels (up to 6cm) and limpets.

The shapes of male and female African Black Oystercatchers` bills differ. The male`s is a relative short, chisel-ended bill, the female`s longer and more pointed.  This difference enables males and females to exploit different prey types – although there is much overlap – and so may have the effect of reducing the size of the feeding territory a pair needs to defend.  Males take a higher proportion of gastropods, especially limpets and whelks, while the female concentrate more on mussels and polychaetes.

Limpets are dislodged with a sharp blow to the edge of the shell – the blow is usually directed at the edge away from the limpet`s head.  The flesh is neatly scissored out from the shell and swallowed.  Mussels require a quite different approach.  The oystercatchers wait until the mussels themselves are feeding and slightly open to filter microscopic food particles.  By quickly inserting the bill between the gaping valves, the strong adductor muscles can be cut.

At the approach of the summer breeding season some pairs move away from rocky mainland coast to breed on nearby sandy beaches or, if they can find room, on offshore islands.  The islands are obviously the prize.  Some pairs manage to find a spot to breed on islands, but are unable to establish a feeding territory on the island shore and fly to the mainland to feed. 

Picture credit: Oystercatchertracking.com

OYKs breed mainly from December to February.  The nest is a scrape in the sand on an exposed beach or rocky area, often next to dried black kelp or among stones.  On sandy mainland shores nests are usually unlined, but on the offshore islands almost all are completely lined with fragments of mussel and other shells, probably because there are many aerial predators of eggs on the islands, particularly Kelp gulls.  Some nests are raised so that they can see an approaching predator from afar.

Normally two eggs are laid (80%) at two day intervals.  The eggs are greenish or a buffy stone colour, spotted and scrolled with blackish brown and purplish grey.  The incubation time is anything from 27-39 days.  Most chicks are independent of their parents within two or three months of fledging, but some continue to be fed, at least occasionally, for up to six months.

Picture credit: Pintrest.com