126 | Chapter 6
non- breeding areas, might encounter this energy- sapping obstacle when
heading south in the autumn. However the equatorial westerlies blow
most reliably from June until the beginning of November, just before
the mid- November passage of Cory’s Shearwaters through the region.^20
Of course it might be a coincidence that the birds’ passage through the
area occurs just as the winds abate. Or it might not!
***
In the previous sections, I have attempted an overview of how many
aspects of seabirds’ lives are adapted to make efficient use of the winds
that are such a feature of their marine domain. But the weather is vari-
able. That is a statement of the obvious. The equally obvious corollary is
that, at least sometimes, the weather can disrupt the birds’ lives. The
disruption can run the full gamut, from a storm, which is a troublesome
but temporary disruption to provisioning the young, to a full- blown
life- threatening hurricane. Now then is the moment to describe how
modern studies have revealed how horrid weather has inconvenienced
seabirds, or worse. This is particularly relevant in current times when
climate change models predict more variable weather, and a greater
likelihood of stormy weather, for many parts of the world.
At the inconvenient end of the range of impacts is the effect of wind
on European Shags feeding off Scotland’s east coast. Because the shags
come ashore at night, the time spent foraging each day, as evidenced by
daily number of hours with wet feet, could be determined when the
immersion loggers on their feet were retrieved one or two years after
first deployment. What Sue Lewis of Edinburgh University discovered
was intriguing.^21 Daily foraging time was lower when the wind was in the
west than in the east, the latter associated with a long fetch across the
North Sea and hence rougher seas. However daily foraging time dropped
as wind speed increased. Putting it anthropomorphically, it perhaps
became a waste of time for the shags to search for food in seas stirred
up by stronger winds. But the decline in foraging with wind speed was
more pronounced in the larger males than the smaller females.* Just why
- (^) Males are about 18% heavier than females.