100 | Chapter 5
relatively infrequent visits, fed further from the nest than adults with
large chicks. I found that they did.^18 This might have twin merits: it
would reduce the risk of attracting predators to nests with small chicks,
and leave food close to the nest to be used when the older offspring were
at their most demanding. The second advantage only comes to pass if the
wheatears successfully defend their territory against other wheatears –
as they generally do. It seems far less likely to work for a seabird where,
as far as is known, no individual has its own defended and exclusive
feeding area.*
This leaves several possibilities for a seabird. The pedestrian possibil-
ity, the null hypothesis in science- speak, is that the parent’s foraging
range alters little with chick age. Alternatively the foraging range could
expand for one of several reasons. During the brood phase, the parent
might remain close at hand. Later, when the chick can be left for longer
periods and gulp down larger meals at one time, the parent might for-
age further afield. This trend would be reinforced if food were depleted
near the colony. Finally, a parent might collect food for its chick(s) quite
near the colony, minimizing the transport costs, but go further afield to
feed itself where competition from its fellows is probably lower. This
strategy, effectively leaving chick food close to the colony, bears com-
parison with the wheatear idea.
Satellite tracking has shown albatrosses to remain close to the colony
during the brood- guard phase. For instance, the Black- browed Alba-
trosses of South Georgia mostly feed north of the colony during incu-
bation, the females somewhat further away (1,700 km) than the males
(1,000 km). For both sexes, these ranges contract to a mere 300 km
during the brood- guard stage, before expanding again once the chick
can be left unattended between feeds.^19 Other albatrosses, such as the
Wandering Albatross, show a similar pattern; birds are particularly con-
centrated near the colony during the brood- guard stage. To protect the
birds from tragic interactions with fishing vessels, there is a strong case
for closing the waters around the colony to fishing during this key pe-
riod, as has been done around South Georgia.
- (^) See page 106 for evidence that adjacent colonies have distinct feeding areas, albeit ones that
are probably not defended in the way that nest sites or territories are.