|Avian Demography Unit
Department of Statistical Sciences
University of Cape Town
Seabird Sites of Namibia
Bird Rock: the Walvis Bay Guano Platform
Avian Demography Unit
The guano platform built over Bird Rock near Walvis Bay is a remarkable structure. The rock over which it is built is about 400 m offshore, about 7 km north of Walvis Bay on the way to Swakopmund. The rock is exposed only at low tides.
The platform was built during the depression years of the 1930s by Mr KHA Winter, who was a carpenter in Swakopmund. The following account of the construction of the platform, written by Mr Winter himself, is quoted from an article published in 1975 in Bokmakierie, which described itself as the "general interest magazine of the South African Ornithological Society". The article was written by Dr Hu Berry, of the Division of Nature Conservation and Tourism of the then South West Africa Administration. Hu Berry made a pioneering contribution to ornithology in Namibia, especially for seabirds and their breeding localities. Mr Winter wrote:The very first time when I went to Walvis Bay by train, which runs along the coast, I saw Bird Rock during low tide; it was covered with hundreds and thousands of birds. A few hours later when I returned to Swakopmund, everything had vanished and there were only seething waves to be seen above the submerged rock. In the following years I saw and pondeered over the waste of guano which was daily taking place.
In 1930 I hired the rock from the South African Railways and Harbours for five yedars and paid 24 pounds (=R48) rent yearly. In March 1930 I built a table or platform with four legs 4x4 m by 3 m high. Five minutes after I left this platform the first bird alighted on it. Two months later, after it had proved that the platform had stood against the strong seething waves, I increased the platform to 8x8 m and in March 1931 to 16x16 m. In 1931 I received an inheritance of 800 dollars from the United States of America, with which I brought from Germany some specially made iron alloy. At about the same time the Kuiseb River had overflowed the town of Walvis Bay and the timber yard of a dealer in building material was heavily flooded. I bought from this firm for 400 pounds some water-damaged timber. In August 1931 I finished the extension of the platform to 1600 square metres.
I had become, however, the laughing stock of the town and even the Mayor did his best in jeering. That alone, however, would not have worried me, but the result was that I lost my credit and I had to borrow money under hard conditions and had to pay 10% interest, and the depression in these years made things go from bad to worse for me, and I nearly went bankrupt. I was in such straits that my wife took a post as a saleswoman in a shop for 10 pounds monthly salary. Formerly I had six men employed in my big joinery shop and now I had only two apprentices. The monthly turnover was sometimes below 20 pounds. Only the strong belief which I had in my platform gave me the power and courage to bear all the calamities.
From 1934 to 1937 during the period of the collection of guano I built every year an extension of the platform of a few hundred square metres to bring the total size of the platform to 3300 square metres by 1937.
The average price I received for guano was up to 5 pounds 10 shillings (=R11) per ton. In 1938 it was 7 pounds 10 shillings (R15). I sold the guano so cheaply in ignorance of the high percentage of nitrogen and of the real market price.
In December 1938 a shipload of timber from Sweden arrived and a part of this timber we used to increase the 3300 to 17 000 square metres, the work being finished two months before the outbreak of war.
I personally had to do the hardest work from the beginning right from 1930 to 1939. In 1942, however, the platform was beginning to show good return and in 1943 I finally could pay all my debts.
The whole platform is built on stilts; the stilts are not fastened to the ground, but are standing lose on the submerged rocks. My technical idea was to give to the sea current and waves as little resistance as possible and to construct the platform in such a way that it should not be too expensive.
Perhaps it is not surprising that the alternative name for Bird Rock given on some official survey maps is "Winter's Folly".
Hu Berry, in his article in Bokmakierie explains that the guano produced on the platform is particularly valuable, because its nitrogen concentration is almost double that found in guano from the offshore islands. The platform guano is 16% nitrogen, 9% phosphoric acid and 4% potash. Island guano averages about 9% nitrogen. The quality of the guano on the platform is so high because the area is particularly dry, so little leaching takes place, and because the guano from the platform is not mixed with any sand, as happens on the offshore islands. The project ultimately became an economically successful venture, and was followed by similar platforms at other suitable sites in Namibia, for example at the pans near Cape Cross. The platform at Walvis Bay is the only one actually constructed in the sea.
The thickness of the guano on the platform varies between years, due to fluctuations in numbers of breeding and roosting seabirds, which in turn are due to changes in the amount of fish available to the birds. On average, the guano is about 5 cm thick, and then delivers a yield of 650 tonnes. Even though guano scraping has ceased on South African offshore islands, and is erratic at Namibian ones, guano production continues on the platforms. Unlike on the islands, there are no conservation issues. The guano is removed from the platforms at the end of summer (February-March), after the end of the breeding seasons of the species that use the platform.
About 99% of the birds that occur on the platform are Cape Cormorants, and they are responsible for producing most of the guano.
From a conservation perspective, the population of Great White Pelicans which breed here probably give the platform its greatest value. The number of breeding pairs is usually in the range 150-200. They were observed breeding on the platform for the first time in 1949. Prior to this, the pelicans bred on sandy islets at Sandwich Harbour, about 60 km farther south. The islands on which they bred there become linked to the mainland, allowing access to predators. It is fortuituous that the guano platform existed, because the pelicans would have had difficulty breeding elsewhere along this section of the Namibian coastline. The pelicans feed at wetlands such as Walvis Bay Lagoon and Sandwich Harbour. They also feed offshore; during a survey conducted in summer 1977/78, 60% of the 5-km count sections along the shoreline recorded at least one pelican. Both adult pelicans, and young birds close to fledging, consume the eggs and nestlings of the Cape Cormorants with which they share the guano platform. A pelican nestling, ringed on the platform on 20 December 1972, was recorded breeding there in several years, most recently in 1999, 26 years later (SAFRING ring H01008). The guano platform is one of three sites where pelicans breed annually in southern Africa, the others are in South Africa: Dassen Island, Western Cape, and Lake St Lucia, KwaZulu-Natal. Breeding inland in southern Africa occurs sporadically after heavy rains at large wetlands in Botswana and Namibia. It is not known if there is any interchange between these populations.
The secondmost numerous species of cormorant breeding on the platform is the Whitebreasted Cormorant Phalacrocorax carbo lucidus; about 700 nesting pairs have been recorded. This is the largest Whitebreasted Cormorant colony in the world; the coastal breeding distribution of this subspecies of the "Cormorant" Phalacrocorax carbo is from Inhaca Island in southern Mozambique through South Africa and Namibia to Ilha dos Tigres in southern Angola.
About 100 pairs of Crowned Cormorants nest at the gauno platform; this is the northernmost breeding colony of this species along the west coast of Africa; the next nearest colony is at Oyster Cliffs, some 250 km farther south. This species breeds and roosts on the supports underneath the platform, and therefore does not make any contribution to the guano.
Hu Berry noted a few other bird species that had been recorded on Bird Island. The three southern African gull species are regular: Kelp Gull Larus dominicanus, Hartlaub's Gull L. hartlaubii and Greyheaded Gull L. cirrocephalus, but have not been recorded breeding on the platform. Greater Flamingos Phoenicopterus ruber sometimes roost on the platform in flocks of up to 150 birds. Among the waders, the African Black Oystercatcher Haematopus moquini and Turnstone Arenaria interpres occur regularly, with occasional visits from other wader species.