The Greenland White-fronted Goose Anser albifrons flavirostris

with rank. This suggests that dominant pairs were
better at securing the best nest sites, as well as
protecting eggs and broods from predation (Warren
1994).
The establishment of such dominance hierarchies
clearly offers a mechanism that results in asymmetric
patterns of individual nutrient acquisition
in a situation where resources are limiting. Young,
inexperienced birds (or those of poor quality)
have low social status relative to older (or better
quality) individuals. They therefore lack both access
to nutrients and the skills necessary to maximise
food intake rates, and suffer reduced fitness
as a result. Indeed, recent evidence suggests
that low reproductive success in early years is due
to the inexperience of paired females in food and
feeding area selection. This specifically hinders
their ability to build up reserves in preparation for
nesting (Black & Owen 1995). In that study of Barnacle
Geese, declines in reproductive success in
later years were attributed to the male, and thought
to be linked to declining fighting ability, which
determines access to optimal feeding sites for the
female and acquisition and defence of best nest
sites (Black & Owen 1995). Hence, within a pair,
the ability of both individuals to maintain social
and nutrient status (of different nature) has an
impact upon their reproductive success at different
times throughout the duration of the pair bond.
In its recent evolutionary history, the Greenland
White-fronted Goose was a specialist feeder. It
exploited the highly nutrient rich overwintering
organs of a very narrow range of species associated
with a rare and localised biotope (Sphagnumfilled
depressions) in a geographically restricted
habitat type (oceanic pattern mire systems restricted
to the western fringe of Europe, chapter
2). The use of such a resource also necessitates an
appreciation of the periodic recovery patterns of
such a finite food source over more than one
growth season. This might favour a process of
cultural learning to effectively exploit patchy
feeding resources in time (e.g. sequential exploitation
cycles of Phleum over a few days and of
Eriophorum angustifolium over at least 2 years) and
space. Seen in this historical context, a long-lived
herbivorous goose species with such a highly
specific diet would be subject to severe limitations
on resource availability. This is especially the case
on the 'survival' habitat where the fitness consequences
of food availability are potentially likely
to affect mortality as well as reproductive output.
Selection seems highly likely to favour indi-
76
viduals that can maintain extended family links.
These enable the youngest (and potentially the
most socially inferior) birds to retain high social
rank by continued association with their parents,
siblings and other kin (i.e. groups with the highest
social status). In this way, youngest birds can
elevate their functional social rank and, by association
with near kin in large groups, can gain
access to (and defend) best feeding patches. At
the same time they gain experience and competence
in feeding skills, knowledge of migration
routes and staging areas and even observe and/
or assist in breeding attempts by their parents on
the nesting areas (MS11, MS12). Other group
members benefit from the association through
shared vigilance and food finding, and the parents
benefit by shared vigilance in pre-nesting
feeding and in nest defence on the breeding areas.
In a relatively long-lived bird, the gain in social
status and learned experience during the
younger years might offset the loss of breeding
potential in this period, which represents an investment
in future breeding potential when departure
from the family unit finally takes place.
Given that reproductive success first increases
and then declines in later years within all studied
goose populations (see above), this long association
with kin ultimately bears a cost in forgone
reproductive output. Ultimately, the balance
of the conflict between the cost of remaining with
kin versus lost reproductive output should tip
towards investment in the individual’s own reproduction
rather than that of kin. Only in the
case of poor quality individuals is it likely that
the benefit of helping in the reproductive success
of related birds outweighs that of pairing and
leaving the family to invest in its own reproductive
future. Hence, at some point, a young bird
must pair up, leave the family group and effectively
lose social rank and fall to the level of a
'flock of two' in the population as whole. This
mechanism, whereby potentially the most fit, fecund
animals must temporarily lose social status
by sacrificing their links with the dominant
groups in an attempt to breed, is apparently unusual
amongst geese. Family break-up occurs most
frequently during the first or second winters
amongst studied goose species. Nevertheless, in
a resource-limited system, this offers a densitydependent
regulatory mechanism for recruitment
of Greenland White-fronted Geese into the breeding
population.
It is not possible to know whether the prevailing