The Greenland White-fronted Goose Anser albifrons flavirostris

in place from the late 1940s onwards in the United
Kingdom ensured the increase in goose numbers
to the present day. However, the numbers of several
populations stabilised in the 1970s and 1980s,
generally thought associated with density dependence
(e.g. Figure 1 in Pettifor et al. 2000).
Largely unseen from the perspective of the wintering
grounds, Pink-footed Geese nesting in Iceland
and Barnacle Geese in Svalbard expanded
to new colonies, and showed renewed periods of
increase that could not be predicted on the basis
of population-based models constructed using
demographic data from previous years.
It is often extremely difficult to determine the
strengths of density dependence in empirical
studies (e.g. Pollard et al. 1987). Historical population
data are likely to be collected over a very
narrow range of population sizes and environmental
conditions, unlikely to offer the basis for
robust predictions for the future (see discussion
in Pettifor et al. 2000). For this reason, it has been
argued that models predicting the response of a
population to environmental change need to be
based upon the aggregative total of individual
behaviours (Goss-Custard 1985, Goss-Custard &
Durell 1990). In this way, models can be developed
to predict effects of change in the environment
on a population based on the cumulative
sum of individual responses under novel circumstances.
Such models have been developed using
game theory to explore how individuals of
varying competitive ability can exploit a patchy
and variable food supply. The classic models have
been built based upon maximising individual fitness
in Oystercatcher populations, by Goss-Custard
and co-workers at individual site (Goss-Custard
et al. 1995a,b) and at population levels (Goss-
Custard et al. 1995c,d). Such models need to be
large scale and encompass the entire annual cycle,
as exemplified by the application of Pettifor
et al (2000) to other goose populations. The application
of such models to the Greenland Whitefronted
Goose would identify the key model parameters
required and could prove extremely
important to our understanding of future potential
change.
9.4 Conclusions
There is accumulating evidence to suggest that
during the latter half of the 19th Century, the
Greenland White-fronted Goose began a shift in
habitat use from very limited small-scale habitat
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types to emerging (and far less geographically
restricted) agricultural habitats. Nevertheless, the
population has continued to be geographically
restricted by virtue of its winter site fidelity, and
continues to probe for the underground storage
parts of plants (bulbils, stolons, rhizomes, etc.),
even in current agricultural landscapes, far more
than other western European goose populations.
Greenland White-fronted Geese appear behaviourally
constrained by inherent site fidelity and
a general conservatism with respect to the exploitation
of novel habitats. Only one small new wintering
flock is known to have become established
in the last 25 years (MS14). Although geese have
shown shifts from natural and semi-natural feeding
habitats to managed grasslands, these have
only occurred when these grasslands are created
in close proximity to existing feeding areas. While
there are abundant areas of such grasslands available
throughout Scotland and Ireland, currently
unexploited by Greenland White-fronted Geese,
there are no signs of colonisation of such suitable
habitat away from traditionally used roost sites.
Hence while the potential for extensive spread of
the population looks possible, the capacity of the
population to do so has been limited to in-filling
in close proximity to existing home ranges exploited
by the current wintering flocks.
Assuming that this site fidelity holds for other
periods of the life cycle, its potential breeding,
staging and wintering range is geographically
limited. This inevitably limits the potential carrying
capacity of the habitat globally and is likely,
at some stage, to lead to an eventual limitation
on total population size. Nevertheless, as we have
seen, different habitats have the potential to limit
population change in different ways, and to return
to the ideas of Alerstam and Högstedt, these
can be divided into 'breeding' and 'survival' habitats,
where such factors may operate. Hence, we
can conceive of winter, spring staging and prebreeding
habitats as comprising the 'breeding'
habitat in so far as any or all could potentially
limit reproductive output in the population as a
whole. Equally, we could conceive of 'survival'
habitat including the moulting areas in Greenland,
since the successful regrowth of flight feathers
is essential for flight, to enable movement between
all the geographical areas used by geese in
their completion of the annual cycle.
Hence, breeding and survival habitats and the life
cycle processes completed in these habitats are
not necessarily limited to breeding and non-