Yellow-billed kites. Supplied image.
Yellow-billed kites. Supplied image.

’Speedsters of the bird kingdom’ face extinction as their food sources are under threat

By Shaun Smillie Time of article published May 29, 2021

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There is an ornithological mystery that is puzzling scientists.

Yellow billed kites are not known as the speedsters of the bird kingdom. Rather, they seem to spend their days lazily gliding the thermals on the hunt for something to eat.

But not all is what it seems.

Not so long ago, one yellow billed kite was discovered to have travelled to Rwanda from South Africa in quick time.

“So it went from just outside Pietermaritzburg to Hoedspruit (Limpopo) in a day. And then the next day, from there to the top of Zimbabwe into that corner with Mozambique. And then straight up to Rwanda. So, huge distances,” explains Professor Colleen Downs, of the School of Life Sciences, at the University of KwaZulu-Natal.

Now the question is: did the bird get some assistance from some high altitude jet stream in its intra African migration? Or was this bird’s journey unusual when compared to others of its species?

Until quite recently, ornithologists were unable to peek into the long haul flights of birds. Migration pathways had to be pieced together from sightings and the odd bird found that had been previously ringed.

Now, increasingly small tracking devices are telling the tale of where birds go, and how they get there.

The yellow billed kite that Downs and her team were tracking had a tracker that carries a sim card and uses cellular technology.

As part of their continuing study, they have fitted tracking devices to eight other yellow billed kites and will publish their results, soon.

Trackers are now being placed on even smaller birds. Just over a week ago, researchers from the University of Lund, Sweden, revealed in the Journal, iScience, a study they had conducted on Common Swifts.

These small birds with their long swept back wings are known to spend as much as ten months of the year in continuous flight. They even sleep while flying.

They migrate to sub Saharan Africa in the summer, and have also been spotted gliding over Joburg.

Swifts were also suspected to be able to travel long distances quickly. But what the scientists discovered was astonishing. These birds were clocked travelling an average of 570 kilometres a day. The maximum distance recorded in the study was more than 830 kilometres a day over nine days.

“We have discovered that Common Swifts breeding in the most northern part of the European breeding range perform the fastest migrations of swifts recorded so far, reaching above the predictions,” says Susanne Åkesson of Lund University. “The Swifts seem to achieve these high speeds over substantial distances -- on average about 8,000 kilometres one way -- in spring by using a mixed migration strategy, with fuelling at stopover and a fly-and-forage strategy, meaning they feed and fuel a bit each day.”

Åkesson and her colleagues used tracking technology that geolocates using light to track the birds.

As these birds return to their breeding sites each year, they were able to recover many of the trackers.

The study suggests that swifts might forecast the weather, so that, the winds will assist their flights.

“They seem to time their departures for migration, such that, the winds will be favourable for the coming flight period ahead. This means they do not react directly to local winds, but to what they expect to find along the route ahead during the next few days,” she says, explaining that the birds might do this by gauging the air pressure associated with weather patterns.

As trackers even reduce further in size, Downs believes that they will be able to delve into the secret lives of even smaller birds.

“Are these little brown guys that come from Siberia to Africa, like some of the Reed Warblers. So we've got ringing data, people have ringed them in Siberia. And then we caught them here in Pietermaritzburg. When they come in the summer, so I think, those distances, and given their size, they will be really spectacular. That is once we get some kind of transmitter that's small enough to fit them,” says Downs.

The benefit is that information gleaned from these tracking devices could help in conserving some of these bird species.

The researchers studying the Common Swift have expressed concern that the bird’s reliance on insects may put them at risk, due to pesticide use by humans. And climate change could have an influence on weather and wind patterns, that might impact their migration routes.

But the trackers of the future will not only reveal the lives of the bird kingdom’s migratory species.

Bird ringing has also thrown up a couple of other little mysteries. One involves a Cape white-eye, a bird that at first glance appears to hop from one garden to the next.

“We ringed a white-eye in Pietermaritzburg and they found it at Ladysmith (a distance of 170km). So, some of the small things we don't even realise are moving about,” says Downs.

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