The Greenland White-fronted Goose Anser albifrons flavirostris

7.4 Limits to suitable moulting habitat
and potential inter-specific
competition in the future
Since the mid-1980s, Greenland White-fronted
Geese have faced a major change at their moulting
sites. Canada Geese Branta canadensis interior
have become established as a common breeding
bird in areas of west Greenland previously only
exploited by Greenland White-fronted Geese
(MS13). Resightings and recoveries from ringed
birds have shown that these geese winter in the
eastern United States, from Massachusetts and
Connecticut south to Delaware and probably
originated from the Ungava Bay population of
Canada Geese that breed in northern Quebec
(MS22). The Canada Geese arrive in late May and
commence nesting in habitats close to open water,
so that there appears little competition in time
and space for breeding habitat between this species
and the Whitefront. However, during the
moult, White-fronted and Canada Geese use the
same habitats and areas to regrow flight feathers.
At this time, both species are largely confined to
areas within 50 m of open water. During this
phase in the life cycle, increased nutrient demands
and enhanced predation risk means there is an
increased potential for direct competitive effects.
In sympatric situations, the diet of White-fronted
Geese showed high niche overlap with the colonising
species and included higher levels of poor
quality bryophytes than at moult sites from which
Canadas were absent (Jarrett 1999, Kristiansen &
Jarrett in Kristiansen 2001). Faecal analysis suggested
that Canada Geese had a broad dietary
range which changed little between sympatric
and allopatric sites; in contrast, allopatric
Whitefronts showed very narrow niche breadth
scores based on faecal content, suggesting this
species is a specialist grazer (Kristiansen 1997,
Jarrett 1999, Kristiansen & Jarrett in Kristiansen
2001). It would therefore appear that Whitefronts
coexisting with Canadas switched to a more generalised
diet, perhaps in response to competition
from Canada Geese for favoured food items. The
two species appeared to segregate where they
occurred together. In 45 agonistic interactions
between the species, Canada Geese won on every
occasion, even when outnumbered. As a consequence,
Whitefronts would stop feeding and
adopt alert postures when Canada Geese approached
to within 3 metres (Jarrett 1999). In a
study area in Isunngua, numbers of both Whitefronted
and Canada Geese increased from 1988,
but in the mid 1990s, Greenland Whitefronts be-
62
gan to decline, and have disappeared as moulting
birds from many lakes favoured in this area
where Canada now predominate. The results
from extensive studies are about to be published
(Kristiansen & Jarrett in Kristiansen 2001). However,
the implication from this study of a small
area was that Whitefronts forced to moult with
Canada Geese may be subject to exploitative competition
as favoured plants are eaten out and interference
competition when the dominant species
physically prevent them from accessing potential
feeding areas. Data from the 1999 aerial
survey suggest that although both species showed
highest densities in the same Kangerlussuaq region,
at a local scale the two species were less
likely to occur together than would be expected
by chance (MS23). Whether this is a consequence
of 'avoidance' competition or active exclusion remains
conjecture.
7.5 Conclusions and discussion
The few studies of moulting Greenland Whitefronted
Geese suggest that these birds show no
anticipatory accumulation of fat stores in preparation
for moult. Rather, they shed and regrow
flight feathers at their lowest level of annual body
mass (equivalent to mid-winter minimum body
mass). Since most studied northern and arctic
geese show similar patterns, it is inferred that
Greenland Whitefronts can derive all the necessary
energy and protein required to complete the
moult from exogenous sources. This suggests that
under studied circumstances, moult habitat was
not then limiting.
On the other hand, the confinement of moulting
birds to the proximity of open water from which
they can escape terrestrial predators inevitably
constrains the amount of exploitable habitat available
to flightless geese. This has been found to
equate to a potential feeding zone of at most 150
m from water in other species (e.g. Madsen &
Mortensen 1987, Kahlert et al. 1996) and possibly
less than 50 m in Greenland Whitefronts (Kristiansen
& Jarrett in Kristiansen 2001). This particular
spatial limitation on foraging at this stage of the
annual cycle suggests that this is a potential limitation
on habitat availability on the summering
areas.
In July, the moulting geese are confined to parts
of the landscape adjacent to water bodies to which
they can escape to evade predators. The amount