African Oystercatcher monitoring on Robben Island : 2025 to 2026

Introduction

We have been monitoring the breeding of the African Oystercatchers Haematopos moquini on Robben Island since the summer of 2001/02. We have also monitored their abundance. This blog aims to describe the fieldwork we are doing in the summer of 2025/26. Our target interval between trips is six days, but that sometimes gets adjusted by the weather and other commitments. So this blog ought to be updated at roughly six-day intervals. The most recent visit is on top! Our objective for the summer is to find every oystercatcher nest on the island. At the end of the blog is a list of some of the publications that have emerged from this fieldwork. The papers give more background to the science and conservation objectives.

Fieldwork 3 : 27 and 28 November 2025

We found 14 new nests (S07 to S12, and N06 to N13), so the total number of nests found with eggs for the breeding season so far is 25. Nest S05, which had one egg on the previous trip, now has two! All nests found with eggs on previous trips still have the same number of eggs (or more!), so there have been no losses due to predation, or any other cause. In addition there is one pair which has two chicks, and a second pair suspected to have at least one chick.

Our study species, the African Oystercatcher. The bird on the left has been ringed.

Diane is measuring and weighing the eggs at nest S08. The process takes a few minutes, and is only done once. We have never had a desertion.

Nest S09, with two eggs, is in the centre of this photograph. There is also an arrow on the flat rock which points to the eggs.

Team 3 at work in the office.

Photogenic species!

The final stage of production of an oystercatcher egg is done in the paintshop. Every egg has a unique pattern.

Bird species 27–28 November

This is our list of bird species, in the order in which they were recorded for the bird atlas project (SABAP2, pentad 3345_1820, Robben Island). The first bird seen after we started atlasing was a Chukar Partridge. There are some surprising omissions. We didn’t see a Cape Wagtail, although, between the four of us, we covered the entire coastline. We failed to see sparrows, neither Cape nor House. Pied Crow is missing. We looked for White-throated Swallow as we waited about 20 minutes at Murrays Bay Harbour for the ferry, but didn’t see them. The Bank Cormorant is the final species on the list; there were nests of breeding birds on the short arm breakwater as we left the harbour.

There were lots of Chukar Partridges.

African Penguin was low down on the list at 17, i.e. the 17th species to be recorded. That is scary low. Most of these are juveniles doing their first moult. They moult into adult plumage, even though it is likely to be several years before they start to breed.

Cape Cormorant with chick. The number of Cape Cormorants breeding this spring seems much smaller than in previous years.

White-fronted Plover.

Other species

This big male Cape Fur Seal was one of three seen on the shore a couple of hundred metres south of the Faure Jetty. It has a nasty open wound on its right flipper.

We found this piece of shed mole snake skin at these coordinates along West Perimeter Road. The snake had clearly used a big piece of chipboard as den.

Cricket.

Sea urchin.

Abalone shell.

A lighter note, but actually dark!

73 lighters found on 2 km of shoreline by three observers! Robben Island sits alongside busy shipping lanes into the port of Cape Town, and also in the dispersal fan of the trash that washes out to sea from 214 square kilometres of the city of Cape Town via the Black River. See Industrial biodiversity 2 : Black River in Paarden Island : stormwater drain.

Fieldwork 2 : 18 and 19 November 2025

This was the second trip of the breeding season. Rene Navarro did the monitoring single-handed. He found nine new nests (S03 to S06 and N01 to N05). The two eggs in N01 are both pipped, so they were laid about a month ago! S01 and S02 (see Fieldwork 1, below) are still going strong.

S03. First nest of the Fiedlwork 2 trip. Minimalist approach to nest architecture.

Both eggs in nest N01 were starred. The chicks will gradually turn the fine cracks into a bigger and bigger hole in the eggs, and will hatch within a couple of days.

Fieldwork 1 : 10 and 11 November 2025

We started the African Oystercatcher monitoring on Robben Island on 10 and 11 November 2025. The focus of this phase of the monitoring is on the 2025/26 breeding season.

Theoretically, it is exceptionally early in the breeding season. The African Oystercatchers should be right at the start of their breeding season. To our astonishment we found that one pair were the proud and noisy parents to two recently-hatched fluffballs:

The chick at the bottom of the photo is not yet completely dry, so had hatched in the previous couple of hours. The nest, i.e. the place where the eggs were incubated. is the shallow depression immediately to the left of this fluffball.We knew there were chicks because the parents were going absolutely ballistic. They are totally blasé when there are eggs. But the moment they hatch, there is a radical change in behaviour.

One of parents did an Oscar-winning performance of the “rodent run“, a distraction display in which the bird pretends it is injured to lead you away from its chicks. As in the video below!

The video failed to capture the more determined parts of the display.

One of the parents was ringed:

The ring has six characters. The left photo shows: K50 _ _ _ ; the right photo gives _ _ _ 313. Therefore K50313. It had been ringed, as a breeding adult, on 4 January 2019. Potentially, we can read a more ring numbers by taking lots of photographs. Say, 30. Then you can hope to get an in-focus photo of each digit!

We saw lots and lots of scrapes, some of which will have eggs added over the next weeks and months. We found two nests with eggs: S01 and S02. Both had two eggs. Here are photos of the nests.

S01 is a scrape that has been neatly line with shell fragments.

S01, the “Traffic Beacon Nest”. The big marker is a few metres away from the nest. Close to the nest there are arrows on the rocks to point to the nest. If the nest gets destroyed, by a predator, or worse, a storm (which moves stuff around), we can then work out where the eggs actually were. We need to do this, because the African Oystercatcher takes a minimalist approach to nest architecture.

S01 is a nicely concealed nest, above the spring high tide level.

S02 is a little depression, lined with fragments of shells and little stones, just on the seaside of a small ridge of kelp. The incubating oystercatcher can see over it, but its body is concealed.

The “Box Nest” has a series of markers, starting at the road around the perimeter of the island.They get more subtle closer to the nest.

The final marker is the little piece of white plastic (there is lots of debris washing up on the shore) halfway between the box and the nest, just at the thin line of kelp.

In addition to the Little Egret, find four birds.

Species lists 10–11 November

The bird list has 41 species. Those with links in red have structured species texts on the BDI website.

Reptiles: Mole Snake (two), Cape Girdled Lizard, Angulate Tortoise

Mammals: Cape Golden Mole (fresh runs), Humpback Whale (three together, including a small calf, just outside Murrays Bay Harbour on 11 November), Steenbok.

Butterfly: Cabbage White

A Sunfish was seen during the trip back to the Waterfront.

Papers

We have done a fair amount of science over the years resulting from this monitoring. Here are some of the Open Access papers.

Braby J, Underhill LG 2007. Was poor breeding productivity of African Black Oystercatchers on Robben Island in 2004/05 caused by Feral Cats, Kelp Gulls, Mole Snakes or the Sumatra tsunami? Wader Study Group Bulletin 113: 66–70.

Calf KM, Underhill LG 2002. Productivity of African Black Oystercatchers Haematopus moquini on Robben Island in the 2001/02 breeding season. Wader Study Group Bulletin 99: 45–49.

Quintana I, Button R, Underhill LG 2021. African Oystercatchers on Robben Island, South Africa: The 2019/2020 breeding season in its two decadal context. Wader Study 128: 209–219.

Underhill LG, Calf KM 2005. How far is an egg through incubation? Wader Study Group Bulletin 106: 39–41.

There are papers to be added. It will take a while to find the online versions.

Acknowledgements

We are grateful to the Robben Island Museum for a vast amount of logistical support for the African Oystercatcher monitoring project. This has been provided over a period of 25 years; we started in the summer of 2001/02. This fieldwork is done with ethical clearance and a research permit.