Lantana horror in the Ferncliffe forests

2008-11-26 00:00

“Somebody is killing birds in the Ferncliffe forests.” That was the first thought of Pietermaritzburg ornithologist Barry Taylor when he found birds with their claws gummed together. “That means they can’t perch and they can’t feed, so presumably they die.”

Taylor, a world authority on crakes, rails, cuckoo-shrikes and Old World flycatchers, has been ringing birds in the Ferncliffe forests for 10 years. “I’m trying to get an idea of bird populations and how they change. Lots of insect and fruit-eating birds come here in winter to feed.”

It was these birds that were being affected by the mysterious gum. “In one session where I ringed 87 birds, 79 of them had gum on their feet. It’s clearly quite a serious problem.”

Taylor first noticed the phenomenon four years ago. “I originally thought it was birdlime and that people were catching birds to eat them,” he says. But after investigation he realised there was no human agent involved and therefore the culprit must be something occurring in nature. “I thought it must be some exotic plant. I excluded Lantana, gum and wattle as they are all over the place and this gum secretion was not something recorded with them.”

Unable to identify an exotic culprit Taylor turned his attentions to indigenous plants. He drew another blank. “It was a total puzzle,” he says. “Then I recalled what Sherlock Holmes said: ‘When you have eliminated all which is impossible, then whatever remains, however improbable, must be the truth.’

“I went back and looked at Lantana and there it was: a sticky white secretion on the young stems where the flowers grow. It occurs from April to October in the dry deason, but mostly from May to August when it’s really dry and colder.

“You get it on your fingers, it turns black, goes hard and you then have to peel it off. With the birds it builds up as a deposit on the feet and then turns rock hard. Soon they can’t perch, they can’t feed and presumably they die.”

Species most affected are those that feed on insects, fruit and nectar: “sunbirds, white-eyes, bulbuls, warblers, prinias, mousebirds, and sometimes flycatchers”.

Lantana is a species from Central and South America that was introduced into this country for ornamental use and hedging. According to the new book Invasive Alien Plants in KwaZulu-Natal published by the Wildlife and Environment Society of South Africa, Lantana “forms dense impenetrable thickets, competing [with] and replacing indigenous plants, increasing erosion and seriously interfering with farming and forestry activities. It’s poisonous and can be toxic to cattle.”

Lantana is classified as a Category One invasive alien which means it may not be grown and must be eradicated. It is found throughout the Ferncliffe forests.

Although the culprit had been identified, that wasn’t the end of the story. “The Lantana in Ferncliffe is doing something that nobody knew about before,” says Taylor. “In countries where it’s an alien, Lantana has many varieties and these have not been fully investigated.”

Lantana can produce up to 58 chemicals to discourage various insects from eating it. This includes the sticky white secretion. “But here Lantana has no insect pests to stimulate its production, so why it [exudes the gum] is a mystery,” says Taylor.

“Only in Ferncliffe has it been shown to exhibit this behaviour, and also in Blackridge, where I live, which is at the same altitude. And, if anyone has a look, it’s probably found in Hilton too.”

Why Ferncliffe? “This Lantana variety is possibly unique to Ferncliffe because it’s a mist-belt forest, very damp with high rainfall and Lantana usually grows in dry areas. Maybe all that moisture stimulates its production.”

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