Bokmakierie

km of this, it was 11h00 and we resolved to
turn back at 11h30. At 11h15 we spotted another
little bird on the fence top, white outer
tail, streaked breast, upside-down bill. It flew
nearer to us and perched so that Laurence
could see the “teardrop”; Sclater’s lark at
last! We watched its mate arrive and the two
began to feed on a bit of stony plain. I went to
look for a nest but no luck. Still, 6 out of 7 on
our last day!
The missing species, Black-eared Sparrow-lark,
is the easiest of all to identify so it
will keep for another day. We had done the
difficult ones, including 4 lark species so we
were well pleased with our trip and arrived
back in Johannesburg on Tuesday afternoon,
tired but content
Common Swifts Fly
For 10 Months Without A Break
A new study has confirmed that Common
Swifts can spend up to 10 months in the air
without landing.
The research, published in Current Biology,
involved attaching tiny geolocators to swifts
in southern Sweden. The tiny logging devices,
weighing just a matter of grams, are part
of a revolution in miniature electronics that
are enabling scientists to track smaller and
smaller birds.
The loggers include an accelerometer, to record
movement, and a light sensor. Given the
duration of the day and night and the time
of year, scientists can determine the north/
south position. Noting when the sun is at the
midday position gives an east/west location.
In 2014 and 2015, the team recaptured 19
swifts carrying these data loggers and found
that, as expected, the birds were spending
their winters in West Africa.
Dr Anders Hedenström, a biologist at the
University of Lund, and his team reported
that three of the 19 birds never rested. Some
did rest occasionally at night for brief periods,
but the data loggers showed that all the birds
stayed in the air for over 99 per cent of the
time when they weren’t nesting.
The data confirms what has long been predicted
— that the birds stayed aloft when not
nesting. It also endorses the use of geolocators
as an invaluable tool for monitoring birds’
movements — to put it into context, around
50,000 Common Swifts have been ringed in
Sweden over the past century, but only one
ringed individual had ever been recovered
south of the Sahara.
The recordings also showed that long ascents
by swifts, observed during the summer,
happen throughout the year. During these
ascents, often at twilight, the birds climb up
to almost three kilometres in altitude.
Dr Hedenström speculated that the birds
may ascend to such heights to sleep safely.
How birds cope with the need to sleep
remains a mystery. A recent study showed
that frigatebirds can sleep on the wing, albeit
for much shorter periods than they do when
on land. Currently the recording devices that
observe brain activity weigh too much to fit to
swifts, but this may well change in the future.
40 | Bokmakierie December 2016 No 247