92 | Chapter 5
every right to expect their husbands and partners to play a full role in
tending the (monstrous) newborn.
So it is with seabird clutches. Once laid, the eggs must receive contin-
uous protection and warmth, and it normally falls to the male to take
the first significant turn of incubation duty shortly after laying. This
is simply because such a substantial proportion of the female’s body
reserves have been put into egg formation that she lacks the reserves
needed to sustain her over an incubation stint of any length. She must
head out to sea to replenish those reserves or, in a few species such as
some terns, rely on the male to bring food to her while she continues to
incubate.
With the male normally taking the first major stint on the egg, the
stage is set for the remainder of incubation. Male and female alternately
take turns to protect the eggs, while the partner is at sea feeding, be-
coming plumper, and building up the body reserves that will allow him
or her to take over egg duties several days or weeks hence.
But within this general pattern lies intriguing variation. In some spe-
cies, particularly those feeding close to shore and probably close to the
colony, the time each bird spends incubating before relief by the part-
ner is quite short. Herring Gulls rarely sit longer than five hours. The
journeys possible in that time cannot be extensive.
The larger auks, such as Razorbills and guillemots, change over about
once a day, but sometimes sit continuously for up to two days. They
evidently don’t have the time to fly very far from the colony and fit in
feeding. This is confirmed by the latest findings. When a team led by
Tony Gaston of Environment Canada attached GPS devices to Brün-
nich’s Guillemots incubating on Coats Island, at the entrance to Hud-
son Bay, they found the average maximum distance the birds flew from
the colony was 20 and 27 km in two different years, barely half an hour’s
flying. Birds from Digges Island, where the colony was ten times the size,
flew on average 96 km, about four times further than the Coats Island
birds, possibly because the greater concentration of hungry birds on
Digges had depleted food close to the colony and generated a halo.^8
Support for the halo idea also comes from a study of Razorbills, close
relatives of Brünnich’s Guillemots, lead by Akiko Shoji of the OxNav
group. Attaching a GPS logger and a time- depth- temperature recorder