Department of Statistical Sciences
University of Cape Town
| Avian Demography Unit
Department of Statistical Sciences University of Cape Town |
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Six members of the staff of the Avian Demography Unit went to Robben Island on the afternoon of 29 November and stayed overnight in the Marine and Coastal Management (MCM) house on the island. Three additional members of staff joined them early next morning. We compiled bird lists for the island for each of the two days (Table 1). These bird lists were for BIRP, the Birds In Reserves Project of the ADU. Although Robben Island is not formally a "nature reserve" or "protected area", it is an Important Bird Area, and is therefore in the list of BIRP sites. Rather few bird lists for the island have been submitted to BIRP. Probably our most interesting ornithological "discovery" was to find the first nests of Kelp Gull on Robben Island. Although Kelp Gulls have always been common all along the shoreline of the island, it is not at all clear why they have not previously bred on the island. We found four nests, three empty, and one with three newly hatched young in the quarry in the northeastern corner, and one nest with three eggs on the western shoreline.
We made a count of all the waders and other waterbirds along the shore of the island (Table 2). The previous published count of the waterbirds of the island was made on 9 December 1980, 20 years ago. That count was part of a Western Cape Wader Study Group survey made in summer 1980/81. The results of that survey are also presented in Table 2. The total number of migrant waders had decreased from 1021 in 1980 to 430 in 2000, with large decreases in numbers of three common species, Sanderling, Curlew Sandpiper and Turnstone. Numbers of African Black Oystercatchers had increased by 52%, from 89 to 135. Sacred Ibises, which were absent from the island in 1980, were commonly seen feeding on rocky shores in the intertidal zone. We did not count the "waterbirds" in the interior of the island. These included Blacksmith, Crowned and Kittlitz's Plovers, and Spotted Dikkops. The Blacksmith Plovers occur wherever there is short vegetation, including fields and lawns in the village. During the day time, most of the several hundred Spotted Dikkops on the island shelter under the alien vegetation. Robben Island has a remarkably high density of this species. Crowned Plovers and Kittlitz's Plovers occur in the northwest of the island, between the runways of the airfield and the shore.
We made a survey of the large heronry on the island. The existence of a heronry on the island was discovered during the 1980 survey of the island. At that time the heronry was situated in the mixed pine and eucalyptus "forest" in the northeastern corner of the island (where African Penguins now breed); it is now in the southwestern part of the island, in a dense and impenetrable stand of alien Port Jackson scrub. The notes made by the late George Underhill on 9 December 1980 estimated about 30 nests of Little Egret, most with large clambouring young, about 300 nests of Cattle Egret, most with young able to leave their nests either by climbing into branches or flying short distances, about 25 nests of Blackcrowned Night Herons, with large young, and 86 nests of Crowned Cormorant, with young of varying sizes, but mostly containing two small downy chicks. At that time the colony contained no Sacred Ibises. In 2000, James Harrison and Sue Kuyper reported about 750 nests. They estimated that there were 530 nests of Cattle Egret, 120 of Sacred Ibis, and 80 of Crowned Cormorant. In addition there were perhaps 10 Blackcrowned Night Heron nests and a similar number of Little Egret. Most nests contained large young, although some Cattle Egret nests still contained eggs. The Cattle Egret and the Sacred Ibises commuted to the mainland to feed and gather food for their young. Birds were seen returning to the island, flying against a very strong southeasterly wind, at least until darkness fell on the 29 November, and resumed flights early next morning. Doug Harebottle put up two mistnets close to the MCM house, targeting Cape Weavers. We caught only one bird, a Cape Francolin! This bird now features in the staff picture of Doug on this website. The purpose of ringing small passerines on the island is to try to determine whether the island populations are isolated from the populations on the mainland. Cape Weavers are particularly mobile, with a substantial proportion of recoveries and retraps for this species at distances exceeding 20 km from the place of ringing. We thank Rob Crawford and Leshia Upfold for allowing the Avian Demography Unit the use of the MCM house, and Mario Leshoro, Environmental Officer of the Robben Island Museum, for arranging transport.
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