adUlt migrations | 67Now the twist. Maria Dias’ team tracked Cory’s Shearwaters from the
colony on the Salvage Islands, just north of the Canaries. Successive
winter journeys were documented for 14 birds, nine of which used the
same wintering area in successive winters, mostly the Benguela Current.
The other five switched between years, two birds South to North Atlan-
tic, two from the western to eastern South Atlantic and one from the
Benguela to Agulhas Currents.^18 Although the switching between years
meant birds might spend a winter 7000 km from where they passed the
previous winter, the team failed to identify any switching triggers. For
example, males were as liable to switch as females, and the birds switch-
ing (which were on average in their late teens) were of similar age to
those remaining faithful to a wintering area. I wonder whether the var-
ious areas may generally offer equally favourable conditions for Cory’s
Shearwaters, such that visiting one area rather than another has few
consequences. If that is right, the average bird might routinely migrate
to one area, but occasionally visit others to ensure it was not missing
a feeding bonanza. This idea assumes the birds are familiar with all the
wintering areas and Maria Dias describes the amazing journeys of one
bird that, in two successive winters while 4 and 5 years old and there-
fore still immature, visited all the wintering areas. To do so entailed
flying 108,000 km: “A truly epic feat of flying. I hope it paid off and the
bird could make good use of its knowledge of the various areas in later
life,” says Dias.
***
The world, or at least the 70 percent of our world that is sea, has been
the canvas as we have explored some of the breathtaking migratory jour-
neys undertaken by seabirds as they travel between their breeding
grounds and the sea areas used outside the breeding season. Still to be
answered are questions about the details of these journeys. At what speed
are migrations undertaken? Are the journeys non- stop or interrupted
by periods of rest and recuperation? Given that most seabirds remain
with the same breeding partner year after year, do they also manage to
remain together outside the breeding season? It is a pleasingly romantic
thought. If they do not, are there any differences in the sea areas utilised