When birds of a feather flock together
March 30 2015 at 05:30pm
By Tony Carnie
Most of us know that summer is coming to an end and winter will soon be upon us.
But what was the peculiar “telepathic” signal from nature that seems to have echoed through the bush of southern Africa last Thursday.
That’s the question bird watchers are asking after seeing thousands of tiny falcons beginning to flock together in preparation for a remarkable journey to the other side of the world.
Just after 7.20am on Thursday, Ian Macdonald of Kube Yini Private Game Reserve near Mkuze took careful note as a group of nine Amur Falcons took off from a power line and flew off towards the west. As they gained altitude they changed direction sharply to the north.
Later that same afternoon, hundreds of the species were noticed by Annette Gerber gathered on power lines along the eastern shores of Lake St Lucia. “There were so many of them that I stopped my car to watch. And then, whoosh… they suddenly took off as one – as if a switch had been flicked. The air was full of falcons flying northwards,” she said.
Gerber said a group of visitors from Cape Vidal stopped next to her and reported they had also seen a group of about 300 Amur falcons flying north.
What they were witnessing was the start of one of the longest migrations in the world by a raptor species – an amazing 15 000km journey from Africa to northern China and south-eastern Siberia.
David Allan, the curator of birds at the Durban Natural Science Museum, said there were quite a few bird species that gathered in large numbers, often quite vocally, before migration.
While the precise triggering mechanisms remained a mystery, Allan said there seemed to be a social element of group decision-making before migration.
“You don’t want to be the first to leave in case you get your timing wrong. So maybe they think it is better to ‘follow the herd’.”
Allan said one of the critical cues seemed to be the shorter hours of daylight as [southern hemisphere] winter approached, rather than a sudden change in temperature.
However, weather conditions were also likely to play a part as the birds would try to avoid flying into strong headwinds. After leaving South Africa, the falcons fly northwards along the east coast of Africa to Somalia. From there they turn sharply east to cross the ocean between Africa and India. On this stage they have to fly non-stop for two to three days without rest.
Allan said some researchers had suggested that their migration coincided with a similar migration by dragonflies – allowing the falcons to snatch a bit of “padkos” en route.
Allan said Belgian bird expert Marc Herrimans had studied red-backed shrikes in Botswana several years ago and noticed that more than 90% of these birds departed on one particular night, a remarkable observation as shrikes were not a social species.
While the journey from South Africa to China can take two to three weeks, with short feeding stops along the way, German bird researcher Prof Bernd Meyburg has also reported the case of a satellite-tagged Amur falcon female that flew non-stop from Somalia to Mongolia in five days.