The Greenland White-fronted Goose Anser albifrons flavirostris

er 3KJ was a behaviourally dominant individual
able to win agonistic encounters in order to retain
access to the Phleum fields, or whether the
rare forays of H4A into Phleum swards were simply
lack of experience or knowledge is impossible
to determine. Aggressive encounters between
geese were very rarely observed away from
sources of water, so it seems unlikely that overt
interference determines access to highest density
or highest quality food (MS26). Nevertheless,
there is no doubt that the use of different swards
in different fields has some effect on the rate of
accumulation of body stores for the next migration
episode onwards to west Greenland (MS18,
Nyegaard et al. 2001). Hence, it would appear that
this presents a potential mechanism by which
different individuals, staging on the same farm,
exploiting different fields, may depart from Iceland
having accumulated different levels of body
stores because of their access to different hayfields
during their period of spring staging.
We still know very little about the extent and
importance of feeding on natural wetlands in Iceland.
Certainly the rhizomes of Carex lyngbyei
have a very high metabolizable energy content
in spring (McKelvey 1985) and it is important in
the nutritional ecology of other northern waterfowl
(Grant et al. 1994). Significant numbers of
Greenland White-fronted Geese feed on Carex
meadows, especially in the middle part of the
staging period in the Borgarfjörður region where
such habitat is extensive. This suggests that this
habitat could be an important supplement to
grassland feeding, either for the population as a
whole, or perhaps for individual birds that specialise
on this food. The same is true for the
Eriophorum angustifolium-dominated wetlands,
where it is known that some birds exploit this
food in the absence of alternative grasslands (because
such hayfields do not exist in the vicinity).
At Hvanneyri at least, based on observations of
colour-marked individuals, it is known that geese
that specialise on hayfield feeding do take to Carex
lyngbyei meadows and E. angustifolium wetlands
at certain periods during spring staging. Whether
this is due to depletion of the grassland resource
or improvement in the quality and/or availability
of these natural foods is a subject of continuing
investigation.
4.6 Conclusions & discussion
Greenland White-fronted Geese arriving in Ice-
land after the 1999 spring migration from Ireland
were on average 277 g (females) and 327 g (males)
lighter than mean departure mass in Ireland. Assuming
these mean values represent the real costs
of flight over the distance involved, this is less
than predicted, based on the aerodynamic predictions.
Studies at one of the most heavily used
spring staging areas at Hvanneyri in western Iceland
show rapid accumulation of body stores
during the stopover period. Based on a caught
sample and the use of field scores of abdominal
profiles converted to mass, the geese increased
body mass by at least 30g and 25 g per day during
the mean 15-day staging period there. The
total increase in body mass at this time was
slightly less than that over the mid-December to
mid-April period on the winter grounds. As in
the case of the pre-migration period in Ireland, it
remains to be demonstrated precisely what this
increase in body mass equates to in terms of body
constituents. Although there was some evidence
that geese fed on adjacent wetlands, most of the
increase observed in this study was sustained on
the new green growth of cultivated grasslands.
The three most common grass species showed
differences in profitability because of leaf densities
and nutritional quality, which affected rates
of intake and hence accumulation of stores (Nyegaard
et al. 2001). Individual geese show different
patterns of exploitation of the three grass species.
Therefore, there is the potential for density
effects and social status to play a role in determining
differential rates of individual nutrient
acquisition on the staging areas, which could affect
fitness. Because much of this rapid rate of
body store accumulation is linked to green above
ground plant production, it is therefore likely to
be highly temperature dependent and likely to
vary considerably with season. There is a need to
assess whether there are differences in the rates
of body mass accumulation between the birds
feeding on traditional bog (mainly Eriophorum
angustifolium) and sedge-meadow (mainly Carex
lyngbyei) habitats and those studied on farmland.
Furthermore, given the unusually large field size
at Hvanneyri and the relative lack of disturbance,
it is important to contrast the relative energetic
costs and gains to a bird staging at this site versus
other farms elsewhere in the staging range
where disturbance rates are higher. This rapid rate
of body store accumulation clearly makes this
brief stop-over period more critical, in terms of
balancing costs and gains, than other periods of
the life cycle, and we need an adequate understanding
of what factors affect nutrient acquisi-
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