140 | Chapter 7
colony show consistency of departure direction. Compared to females,
males are fonder of the north- east choice, making shorter trips (in dis-
tance and duration) and shallower dives in waters where there is tidal
mixing and prey is to be found at modest depths.^12 Probably because
they are heavier, the females tend to make deeper dives than males in
waters further offshore where the water column is stratified and prey
fish swim deeper. Thus the consistently different behaviour of males and
females helps distribute the birds across the North Sea, and reduces the
degree of mutual interference, to the benefit of both sexes.
‘Practice makes perfect’ is a familiar aphorism. It is plausible that
simply by consistently using a sea area, a seabird gains familiarity and
hence an advantage. It may know where to find food just as we can com-
plete shopping more quickly in a familiar supermarket where we know
which shelves carry such favourite items as peanut butter, ground coffee
and sardines. And if that sounds far- fetched, we shall sketch evidence in
the next chapter that feeding seabirds target such more or less perma-
nent marine features as ocean fronts, the supermarket shelves of the sea.
Despite these several plausible benefits of consistency, demonstrat-
ing its value to the perpetrators – the birds themselves – remains ex-
traordinarily difficult. There is an important logical reason why this
should be so. For example, Atlantic Puffins from the Isle of May colony,
off eastern Scotland, can be fitted with a geolocator device which, when
retrieved, reveals whether its wearer has spent the winter in the North
Sea or ventured into the North Atlantic Ocean.^13 This is very likely a
consistent choice, just as is the wintering area of Skomer Puffins. But –
and here’s the rub – the only puffins that yield information are those
that return to the Isle of May where their devices can be downloaded.
There is zero information on the wintering areas and consistency (or
otherwise) of those puffins that die at sea. Overcoming this problem
will be tough technically. The researcher needs to be confident that the
yet- to- be developed device is correctly reporting the whereabouts of its
wearer at the time of its demise far far out to sea, and that the (lack of)
signals do not represent battery failure or accidental detachment of the
device.
If the link between consistency and bird’s chances of survival is elu-
sive, there are at least hints that consistent birds breed more successfully.