Tens of thousands of swallows have died in Limpopo province a week before they were due to migrate to Europe, said BirdLife SA on Wednesday.

Executive director Gerhard Verdoorn said the vast climate changes during March, from the extremely hot to the bitterly cold, played a major role in the death of the swallows.

About three weeks ago, cold air from Angola passed over Namibia and Botswana and entered the South African Lowveld. Temperatures plummeted from 21° to 9°.

"Because of this, the birds could not feed properly as it was too wet and too rainy for them to get the food. They became hypothermic (low body temperatures) and hypoglycaemic (low blood-sugar levels)," said Verdoorn.

Farmers and people in the area became alarmed as they thought the birds were being poisoned.

"The tens of thousands of birds were falling down everywhere and just dying," he said.

The birds were supposed to migrate on March 23, the day of the equinox, but disaster struck around March 17 when temperatures dropped rapidly.

"The bulk of birds that did manage to survive started their migration on March 28," said Verdoorn.

No short-term solutions

The mass death of birds started in about 2000 in the Bushveld and Free State.

"Over the past couple of years it has become a more-frequent occurrence and it is not only the swallows that are being affected but several other species of birds."

Verdoorn said there were no short-term solutions to the problem as no one could change the weather.

"The weather changes occurring are vast. February was regarded as being the wet month and March the drier one, but now the situation has changed.

"A long-term solution to the problem would be to reduce our greenhouse gas emissions, by using less energy, burning less petrol thereby reducing carbon-dioxide emissions which can have changes on climate change," said Verdoorn.