The Greenland White-fronted Goose Anser albifrons flavirostris

3 Accumulation of body stores and the flight to Iceland
3.1 Introduction
Greenland White-fronted Geese return each year
to Greenland for the summer. The challenge to
each individual as daylength increases is to attain
a body condition that will enable it to undertake
spring migration, first to Iceland and thence
over the Greenland Ice Cap to the breeding range
on the west coast. To attain that body condition
will, at minimum, involve the necessary mechanical
adjustments to flight architecture and the accumulation
of sufficient energy stores to sustain
long distance migratory flight. How are these
stores of protein and fat, respectively, accumulated
through the winter and spring? When are
such stores accumulated and what factors may
affect the ability of an individual to reach the necessary
minimum levels to start the flight northwards
and to complete it safely? Most geese of
the genus Anser reach sexual maturity at the age
of 2 or 3 years (Owen 1980). Only a small proportion
of Greenland White-fronted Geese more than
two years of age breed successfully (see chapter
6). There may be different thresholds of stores accumulated
en route to the breeding grounds that
could affect the ability of an individual to reproduce
successfully. For instance, stores of fat could
be sufficient to provide a female with fuel for the
entire journey and to invest in clutch initiation,
but still fall short of the amount required to sustain
the female through incubation. Under such
circumstances, the relatively long-lived individual
survives to attempt to breed in a subsequent
year, despite failing to return with young
in this particular season. Inability to accumulate
fat stores sufficient to fly to Iceland in the first
stage of migration would have a direct impact on
the survival of the individual. The accumulation
of body stores in anticipation of events in the annual
cycle of the geese is therefore of considerable
importance for the fitness of an individual
and has consequences for the population, by having
a direct effect on survival and reproduction.
3.2Spring accumulation of body stores
on the wintering grounds
Geese show a predictable rheostasis in body mass
during the course of the winter. It is generally
assumed that geese maintain a level of body stores
that represents a trade-off between the likely need
to utilise such stores and the costs of maintenance.
Most studies of waterbirds have shown a pattern
of mass accumulation during autumn followed
by a decline in winter and an increase in spring
(e.g. Mallard Anas platyrhynchus Owen & Cook
1977, Dunlin Calidris alpina Pienkowski et al.
1979). However, relatively few studies have determined
the change in body mass of geese at any
one wintering area throughout the entire nonbreeding
period. In general terms, this represents
a cycle of rebuilding depleted stores (generally
of fat) exploited to fuel the often long flight from
autumn staging areas. These fresh stores are hypothesised
to be accumulated in anticipation of
severe weather during the middle part of the winter.
In mid-winter, limits to food intake, short foraging
daylength and low temperatures may combine
to necessitate the periodic use of such stores
to supplement exogenous sources of energy (e.g.
Ebbinge 1989, Owen et al. 1992, but see also
Therkildsen & Madsen 2000). In late winter, depletion
of these stores often results in lowest levels
of body mass as daylength increases, followed
by a period of rapid accumulation of body mass
in preparation for the spring migration towards
the ultimate breeding areas (Owen et al. 1992),
although such spring pre-migration fattening is
not typical of all arctic-nesting geese (see Flickinger
& Bolen 1979, Ankney 1982). Nevertheless, in
several studied species, female geese may increase
their body weight by 41-53% over winter
levels (see for example McLandress & Raveling
1981).
Not all late winter/spring mass accumulation represents
fat, since birds about to undertake a
major migration episode after an essentially sedentary
winter period are likely to have to reconstruct
their (i) digestive and (ii) flight architecture
(e.g. McLandress & Raveling 1981, Piersma
1990). These modifications enable more efficient
accumulation of reserves and through shifting of
internal protein reserves, the enlargement of
breast musculature to sustain prolonged periods
of flight (Piersma 1994). Whether mass changes
in winter affect breeding success in geese has yet
to be demonstrated, but there are clear links between
breeding success and body condition in late
spring (e.g. Ebbinge 1989, Black et al. 1991, Madsen
1995). Hence, the mass dynamics of Green-
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