wind and waves | 117Chaucer suggested for small birds in the Prologue to the Canterbury
Tales? Over 600 years after Chaucer wrote, an astounding answer has
emerged for adult Great Frigatebirds – and presumably the answer would
be similar for juveniles.
Niels Rattenborg from Germany’s Max Planck Institute for Orni-
thology was able to make electroencephalogram (EEG) recordings of
Great Frigatebirds breeding in the Galápagos and flying over the ocean
for up to 10 days. The recordings indicated periods of sleep, just as human
sleep can be detected by EEG monitoring. At sea, the birds slept in short
bursts totalling about 42 minutes in each 24- hour period, mostly at
night. This represented major sleep loss compared to the daily total of
just over 12 hours achieved when ashore.
More remarkably still, the team was able to obtain independent data
from both the left and right hemispheres of the birds’ brains. While
about half the onshore sleep involved just one hemisphere, this propor-
tion increased to three- quarters at sea. The frigatebirds could then keep
one eye open, literally and metaphorically, for hazards. But the fact that
one- quarter of at- sea sleeping involved both hemispheres simultaneously
established that flight control could be maintained, even when both
halves of the brain were asleep. Perhaps wisely the frigatebirds tended
to be a little higher above the sea when asleep (160 m) than when awake
(135 m).^8
The tactics used by travelling penguins as they negotiate waves, and
by flying seabirds as they wrest energy from air moving above sea, do not
bring the story to an end. These tactics are employed at relatively small
spatial scales. Let us extend the story up the spatial scale.
***
Particularly among those birds that roll from side to side as they main-
tain an intimate relationship with the wind – one might almost say kiss
the wind on their journeys – the journeys are by no means straight.
Albatrosses employing dynamic soaring are zig zagging at the scale of
100 metres or thereabouts, and this pattern has been picked up by GPS
tracking.^9 Similarly with shearwaters, and a predictable outcome is that
the speed with which the birds travel between two fixed points is lower