Birds and mangroves

Posted on 14 June by Carl Vernon in Ecology

Birds and mangroves

Three species of mangroves have been planted at the Nahoon River estuary here at East London. Some of the trees are now over 40 years old and besides their growth in size, they have increased in numbers such that there are now at least 2000. The tidal flats of the estuary has changed from mudflats to a woodland. In the 1970s one could see up to twelve species of waders on the mudflats and the only place in the district to find the terek sandpiper. Now waders are scarce and the commonest of them is the blacksmith plover a relative newcomer which colonised the district in the 1980s.


In the 1970s and 1980s, the plain-back pipit was the only bird that nested on the tidal flats. In the bush fringing the tidal flats there was a good variety of bird species and a good place to hear, but seldom see elusive species like buff-spotted flufftail and knysna warbler. With the growth of the mangroves the situation has changed and bush birds have started utilising the mangroves. This in contrast to my experience of mangroves in the Transkei at the Ntafufu and Mngazana estuaries near Port St. Johns. I never found any bush bird species breeding in the mangroves there, although at Ntafufu I saw, and photographed a mangrove kingfisher in a mangrove tree.


So far, here at Nahoon, ten species of birds have been found nesting in the mangroves. These include olive thrush, puffback shrike, cape batis, yellow-eye canary, cape white-eye, black-eyed bulbul, red-eyed dove, paradise flycatcher, and black sunbird. These birds live in the bush on the periphery of the tidal flats and commute to the mangroves across the grassland that separates the bush from the mangroves. A probable reason for the birds choosing to nest in the mangroves may be to evade the predators that eat eggs and chicks. One wonders how long it will be before the monkeys, leguaans, snakes and genet find out about this and start moving into the mangroves.


This year, on several occasions at Nahoon estuary, when the tide is out, small flocks of crowned guineafowl have been seen amongst the mangroves. They appear to be foraging, but so far, they have not been seen to eat anything. Amongst the managroves, there is an apparent dearth of suitable vegetable food for them and one wonders what they are searching for. Could it be that they are taking fiddler crabs ? These crabs are associated with mangroves. They are a recent addition to the fauna of the Nahoon tidal flats, and now common. Further observations may elucidate the question.


Change is constantly taking place and the bird species come and go. In July 2005, a spotted thrush appeared in my garden. It was the first record of such a species since a specimen was collected here in 1960. Just last week there was a secretary bird striding over the mown verge of Coad Road in Beacon Bay. Species move in to take advantage of opportunities created by changing environmental conditions and go when those opportunities are exhausted. In the past 36 years there have many changes in the East London avifauna. The colonisation of the city by the palm swift, grey-headed bush shrike and pied crow are notable examples. 


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