where seabirds find food | 159was undertaken in June/July, when immatures are visiting the colony
fairly frequently and are arguably as obliged to return there as are the
breeding adults. Nonetheless, compared to the adults that were visiting
the productive Irish Sea Front (see above p. 152), the immatures visited
less productive waters and gained less weight for each day they were
away from Skomer at sea. Consequently Fayet argued that the inferior
competitors, immatures, were excluded from the prime areas visited by
adults. Reasonable as that explanation is, it raises all sorts of questions
about the mechanisms of exclusion. It seems improbable that immatures
could not find the Irish Sea Front area by following tens of thousands of
adult Manx Shearwaters streaming back and forth from Skomer. The
question remains hanging: How does the presence of one group of birds,
the adults, in the area lead to it being (more or less) shunned by another
group, the immatures? Pictures of a wedding celebration come to mind,
the adults and small children joyous, the teenagers unable to make eye
contact on the margins.
Although the roles of male and female seabirds during laying and
chick- rearing are generally similar, this is less true during pre- laying,
and modern tracking has provided clear evidence that males and fe-
males, especially among the petrels, may use different sea areas at this
time (Chapter 5). Another possible driver of segregation between dif-
ferent groups of birds is breeding failure. As soon as a bird’s breeding
attempt fails, and the call of the breeding colony becomes less urgent, it
might pay the failed bird to forage further from the colony. Such a strat-
egy would have the merit of taking the bird beyond the colony’s zone of
local food depletion, Ashmole’s halo.
Helen Wade studied Great Skuas,^20 fairly or unfairly viewed as the
bully boys of the Scottish Northern Isles. Once caught with remotely-
controlled nooses, the skuas were fitted with solar- powered GPS track-
ers at two colonies in Orkney and Shetland. This enabled Wade to com-
pare the at- sea tracks of birds still actively breeding and those whose
breeding attempts had failed. The picture was satisfyingly clear; failed
breeders travelled further and ranged more widely from the colony than
active breeders.
These examples of different groups of birds, within a species, using
different areas in the breeding season lead to the huge question of why