the meandering years of immatUrity | 47seabirds may visit several colonies. In the latter part of the breeding
season, namely late August and early September, Clara Péron and David
Grémillet attached satellite transmitters to both immature (aged 4– 6)
and breeding adult Scopoli’s Shearwaters at a colony at the southern
end of Corsica.^5 In the next month adults concentrated their foraging in
waters just west of Corsica and Sardinia, while immatures often headed
east towards mainland Italy and there passed within 5 km of other shear-
water colonies. Such ‘prospecting’ visits mostly happened by night, pre-
sumably when this nocturnal bird would gain the most useful informa-
tion about the merits of the colony as a possible future home.
Let us ruminate for a moment, and set aside the possible advantages
to the young bird of scouting for other colonies at which it might even-
tually settle. If younger and older birds are feeding in different areas
and possibly catching different prey, that could be for one or both of
two reasons. Here is the first. Given that the adult birds are likely to
need to visit the colony more often, perhaps to feed the chick, then the
advantage of feeding close to the colony may be greater for them than
for the younger birds. The latter then benefit from feeding elsewhere
in a less crowded sea area. That would be analogous to those occasions
when I have abandoned a crowded payment till close to the entrance of
a department store, and sought a less crowded till on another floor. The
walk to the other floor was a trivial price to pay for quicker service.
This rationale for separation between younger and older birds is con-
ceptually distinct from the second. If younger birds are less efficient at
feeding, then they may benefit from keeping their distance from the
older birds, regardless of where the two groups feed. And we have al-
ready posited that the delayed start to breeding of seabirds may be asso-
ciated with a prolonged improvement in feedings skills.
A nice example of birds of different ages feeding in different areas,
coupled with evidence that the young are less efficient at foraging, also
comes from the Irish Sea. Annette Fayet and a team from the OxNav
group – the notably straightforward name for scientists at Oxford Uni-
versity studying animal navigation – focussed on Manx Shearwaters. They
breed on Skomer Island, within sight of the Grassholm gannets.^6 No
nooses were needed to catch these birds since immatures can be plucked
from the ground at night, when they visit the colony. Adults too are