106 | Chapter 5
species targeting the same prey as boobies, the total number of seabirds
on Ascension, around 25,000, was 50 times greater than on St Helena,
around 500. Whether during incubation or chick- rearing, the GPS- tagged
Ascension boobies undertook journeys that were around twice as long
in distance and duration as those of the St Helena birds. However, the
‘idler’ St Helenan boobies had the higher breeding success, likely be-
cause there was more food close by the smaller colony.
If the birds are influencing food supply in the vicinity of their colony,
it would make sense if colonies were spaced out across the available is-
lands, headlands, and cliffs. And more than 30 years ago, even before
the invention of GPS, Bob Furness and Tim Birkhead, respectively hail-
ing from the Universities of Glasgow and Sheffield, reported as much.^29
They found that, for four British seabird species, larger colonies were
surrounded by larger zones more or less bereft of other colonies of the
species than were smaller colonies.
While this implies a tendency for the birds from each colony to forage
in a colony- specific zone, no- one anticipated the extraordinary results
that emerged when Ewan Wakefield of Leeds University co- ordinated
tracking of 184 chick- rearing Northern Gannets from 12 colonies dotted
around Great Britain, Ireland and northern France.^30 The birds’ forag-
ing tracks fanned out from the colonies. So far, so expected. But the lack
of overlap of the tracks of the birds from neighbouring colonies was
startling. It was almost as if the birds had encountered a mid- ocean
‘Trespassers will be prosecuted’ sign, and obediently turned around.
(See Map 6.) Most striking was the pattern off the west of Ireland. There
are situated two colonies, Little Skellig (29,700 pairs) and, about 30 km
to the south, Bull Rock (3,700 pairs). Little Skellig birds head over-
whelmingly north-west, away from neighbouring Bull Rock (and the
Irish mainland), while the Bull Rock birds head south.
Just how this segregation of birds between colonies arises remains
mysterious. Ewan Wakefield speculates “We wondered whether birds, at
least partly, learn the best feeding areas by following other gannets leav-
ing their own colony. If this happened over several gannet generations,
a tradition of avoiding the areas exploited by the neighbours, the gan-
nets from other colonies, could build up.” The idea gains credence from
Wakefield’s observation that immature gannets follow adults departing