stick or twist? | 133from spatial consistency; for example a chosen area may be character-
ised by warmer water than used by most other members of the species.
Birdwatchers will be familiar with lines of Northern Gannets head-
ing in a chevron formation to who- knows- where. In fact, individual
gannets leaving the breeding colony in search of food tend to depart
towards the feeding grounds in a flight that is straight and consistent.
At least that is true for the gannets setting forth from Bass Rock in the
outer Firth of Forth, Scotland. They have two preferred directions, one
north- east to an area north- east of Aberdeen, and another south- east to
seas off north- east England. All nine birds satellite- tracked by Keith
Hamer, then of Durham University, showed a decided preference for
one or other direction, and indeed four ‘south- east’ birds shunned the
north- east alternative altogether, at least when carrying a tag.^1 Only
when gannets are in the general area where food is likely do they adopt
a more tortuous searching flight path, so- called area- restricted search.
Doubtless they are keeping a lookout for other fishing gannets, a sure-
fire signal of food.
The consistent departure direction admits of two explanations. The
first is that gannets do indeed have personally preferred foraging direc-
tions. An alternative is that gannets return to an area where they have
found food quickly, only switching to another area if the search has
been forlorn. If birds were mostly following such a ‘Win/Stay: Lose/
Shift’ strategy, the colony observation would be of most birds consis-
tently heading out in their individually chosen direction – but some-
times switching. And switching would be more likely the longer the
observation period. Ewan Wakefield returned to the Bass Rock around
a decade after Keith Hamer’s study. Following gannets over two weeks,
time enough for seven trips, Wakefield reported no decay in consistency
over time.^2 The gannets were also consistent from one year to the next.
They really did seem reluctant to change their spots and did not employ
the ‘Win/Stay: Lose/Shift’ strategy.
Not only do certain gannets prefer certain directions, there are gan-
nets with distinct feeding preferences. More precisely, there are some
that routinely scavenge behind fishing boats, and others that virtually
shun this type of feeding. The gannets in question were studied by Sa-
mantha Patrick at the Welsh colony of Grassholm,^3 a small lump of an