Whither the water birds?

2014-08-30 00:00

DURBAN Bay has seen a dramatic decline in water bird species over the past few decades.

According to an article in the latest edition of the Durban Natural Science Museum’s popular magazine Thola, water bird counts done in the Durban Bay over the past 14 years show that overall numbers have “decreased frighteningly compared with historic times” and this decrease continues.

Once a month since July 1999, staff of the Durban Natural Science Museum and volunteers from Birdlife Port Natal travel the perimeter of the harbour in a naval Namacurra-class harbour patrol vessel, counting the water bird population.

“We choose the first spring tide of the month,” said David Allan, the museum’s curator of birds and author of the article. “If there is a problem with that, we take the option of using the second in the month.”

The team start off from Salisbury Island at 8.30 am and then trace the bay perimeter, returning to the starting point around 11.30 am. The count began when concerns were raised when the helicopter service transferring harbour pilots to ships off Durban was introduced in 1999. “It was thought it might disturb the water birds.”

The effect was minimal but the counts continued. There had been counts done in the sixties, seventies and eighties, which recorded the disappearance of black heron, the greater flamingo and yellow-billed stork.

“We began comparing our data set with those. But seven years of counting started showing the decrease in bird numbers in modern times.”

Earlier there had been a massive loss of habitat when the harbour was developed. The mangroves were removed, which meant an end to the heronries, while the sandbanks were dug out and filled in to provide deep-water facilities for ships.

This destroyed the habitat of wading species like Kittlitz plover, white-fronted and greater plovers. Their numbers gradually declined and disappeared during the counts. “We were seeing the tail end of a process,” said Allan.

Since the major harbour developments of the last century, there has not been much habitat change. “Over the past 15 years, it’s been fairly static,” said Allan. “But curlew sandpiper, ruddy turnstone and grey plover continue to decline.”

Some species that have held their own numbers-wise are pink-backed pelican, white-breasted cormorant, common greenshank and common tern.

The decline in numbers is evidence of the global decline in these species. All these birds are migrants and have experienced local habitat loss in other regions, which has led to reductions in their global populations. But the decline in migrant birds has seen resident birds go for the gap and this has led to a “meteoric rise” in numbers of Egyptian goose, woolly-necked stork and blacksmith lapwing in the harbour.

“A small number of generalists have replaced the original specialists,” said Allan.

From another perspective, the fish-eating birds such as cormorants, terns and kingfishers have survived better than those such as the waders who feed on invertebrates along the tideline.

“Creating deep water was good for fish and the cormorants have been especially benefited because they can swim down happily to depths of 16 metres.”

Conservation talk

EUGENE Moll, professor at the University of Western Cape in the Department of Bio­diversity and Conservation Biology, is giving a talk “Forest Ecology and Conservation of Forests and the Savannah grassland of KZN over the next 20 to 40 years” at the Pavilion Room, Simbithi Country Club, on September 4 at 6 pm. The cost is a voluntary R20 donation at the door. Inquiries: 032 946 5402/3/4.

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