A pair of grownup African Oystercatchers within the surf zone at Robben Island, the place the species is prospering. Photos: John Yeld
- The iconic African Oystercatcher has made a dramatic restoration from its ‘Near Threatened’ standing on the Red Data List.
- The Robben Island inhabitants of the species has elevated four-fold over the previous 20 years.
- But the species is extremely vulnerable – a single storm surge can successfully wipe out a season’s breeding effort.
Conservation success tales are sometimes eclipsed by harrowing accounts of organic catastrophe and environmental tragedy – however one southern African chicken species is offering a contented exception, to the delight of organic scientists and the conservation neighborhood.
This is the putting African Oystercatcher, an iconic coastal chicken whose shiny black plumage, shiny orange-red eye-ring and dagger-like invoice make it immediately recognisable within the slim inter-tidal zones of South Africa and Namibia the place it lives.
Bucking a staggering downward pattern in chicken numbers globally, the good-looking oystercatcher has recorded a considerable inhabitants progress over the previous a long time – a lot in order that its IUCN (World Conservation Union) Red Data List standing has been downgraded from Near Threatened to Least Concern.
This enhance is confirmed at a key breeding web site on Robben Island, the place the outstanding success story of Haematopus moquini (named by Napoleon Bonaparte’s nephew Charles in 1856) is being carefully documented by researchers, assisted by passionate volunteer citizen scientists in a research operating since 2001.
The venture – began as a joint initiative of UCT and the Robben Island Museum heritage unit – now falls below the Rondebosch-based Biodiversity and Development Institute (BDI). The BDI is an impartial, non-profit firm staffed by lecturers and designed to foster analysis and neighborhood motion within the fields of biodiversity conservation and social improvement.
BDI founder and director Professor Les Underhill, a retired professor of statistics at UCT, is a life-long, extremely embellished birder with a specific curiosity in coastal and wading birds, chicken ringing, and selling citizen science in biology whereas fixing environmental issues.
Karis Daniel (left), coordinator of the Biodiversity & Development Institute’s African Oystercatcher analysis venture on Robben Island, and volunteer Robyn Smith, study an egg from a nest on the northern aspect of the island.
In the early Eighties, the general African Oystercatcher inhabitants had plummeted to solely about 4,800 grownup birds, largely due to human interference in its very slim coastal breeding habitat. The scenario remained dire into the Nineteen Nineties.
Researchers discovered that within the 1996/7 season, for instance, breeding success on this species’ key West Coast vary was solely about 15% of what was wanted to keep up a secure inhabitants. On 60km of its Eastern Cape coastal habitat – an roughly 40-metre broad strip across the high-water mark – they discovered no proof of profitable breeding by any means.
But a multi-disciplinary, nationwide oystercatcher conservation programme was initiated in 1998, and it quickly achieved success.
One of the principle causes for the species’ sharp inhabitants restoration was the 1979 native look after which fast unfold of the alien Mediterranean black mussel. Since the invasion, these mussels represent greater than 90% of the oystercatchers’ weight loss program.
A second key issue was the nationwide ban on seashore driving, launched in December 2001.
A 3rd issue was more practical conservation administration on the breeding islands.
A typical African Oystercatcher nest, little greater than a scrape amongst shells and seaweed. The non-permanent quantity helps researchers re-locate the nest throughout monitoring over a number of weeks.
Underhill was in a position to report that the oystercatcher inhabitants was estimated at 6,670 birds within the early 2000s – a rise of 46% for the reason that early Eighties – and was persevering with to rise. Also, its breeding vary had prolonged northwards alongside the KZN shoreline.
On predator-free islands, oystercatcher pairs now efficiently elevate on common one chick each two to a few years – nowhere close to as fecund as many different chicken species, however however adequate to keep up these island populations and to supply some “surplus” birds.
African Oystercatchers mate for all times and don’t migrate, being strongly territorial and counting on native shellfish provides year-round. Some surplus birds not in a position to obtain a territory of their very own go away the island and head for the mainland, however breeding success right here is proscribed.
An African Oystercatcher within the air over Robben Island, the place researchers have recorded a four-fold enhance in numbers of this species in 20 years.
Robben Island, simply lower than 10km in circumference, holds some 8% of the worldwide African Oystercatcher inhabitants, making it a vital breeding web site.
In 2001, Underhill and his BDI colleagues initiated a long-term research of the species right here, assisted by volunteers. Since then, the island’s oystercatcher inhabitants has elevated four-fold and the variety of nests has almost doubled.
The major causes for this big enhance was the elimination of feral cats, which have been predating greater than 80% of oystercatcher nests, in addition to the elimination of European rabbits and the sharply elevated provide of alien black mussels.
The researchers’ report rely got here within the 2019/20 breeding season (November to March). During monitoring of oystercatcher breeding efforts each six days, they counted 550 birds and recorded 158 nesting makes an attempt, thought to have been made by 133 nesting pairs. (Oystercatchers can lay a second time in a season if the primary clutch is misplaced.) An additional 300 or so non-breeding oystercatchers have been additionally current.
Of the 158 clutches, 47% produced a number of hatchlings, and of a complete of 288 eggs laid, 38% hatched.
In 2021/22, complete of 176 nests have been discovered on the island – an additional 11% enhance.
Although full statistics are nonetheless being gathered for this present 2023/24 breeding season that’s now drawing to an in depth, some 450 grownup birds and between 15 and 20 juveniles have been recorded through the two most recent weekly counts, in addition to 130 to 140 nests.
“But a lot of those nests are actually re-nesting attempts after the eggs were washed away or predated, and then the adults tried again in the same spot,” explains present venture co-ordinator postgraduate scholar Karis Daniel.
Amaia Sagarzazu (left) and Ángela Colina, interns from the Basque Country in Spain, monitoring African Oystercatchers’ breeding efforts on Robben Island for Biodiversity & Development Institute’s analysis venture.
While oystercatcher chicks go away the nest inside about 24 hours after hatching (they begin to fly at about 40 days), they’re nonetheless fed by their dad and mom for about 100 days whereas their payments develop robust sufficient to prize shellfish off the rocks for themselves.
“So it’s quite good to have this many juveniles this early in the breeding season,” says Daniel.
Although this season’s numbers look like barely down from the pre-Covid peak, this isn’t essentially trigger for concern, she provides.
“It could just be natural fluctuation as part of a long-term pattern. We have to look at it in the context of all the other years, and the population on Robben Island does seem to be doing well.”
Underhill confirms that African Oystercatchers have executed properly in recent a long time, however he’s involved about what he phrases “their crazy vulnerability”.
“They breed about a metre from the spring high tide level, and nests have to survive two spring tides before they hatch. So a single storm surge event in the breeding season can wipe out all nests with eggs from Saldanha Bay all the way to Cape Agulhas,” he explains.
And if these occasions enhance in frequency because of local weather change, as is predicted, the oystercatchers “may once again be in trouble”, he warns.
A newly hatched African Oystercatcher chick on Robben Island. In the background (proper) is its unhatched ‘twin’. Photo: Karis Daniel
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