The Greenland White-fronted Goose Anser albifrons flavirostris

Inferred body mass (g)
Figure 4.3. Comparison of change in daily median abdominal
profile scores of Greenland White-fronted
Geese recorded in the field and back converted to body
mass from the calibration curves shown in Figure 4.2,
compared with fitted regression models for change in
body mass obtained from catches (shown in Figure
4.1).
where in the wintering range and that all geese
accumulate mass at the same rate as those captured,
the geese departing Hvanneyri left with
516 g (adult males) and 503 g (adult females) more
body mass than the mid-winter minimum mass
level. Assuming this increase includes 60-90% fat,
departure fat stores would amount to 302-453 g
(females) and 310-464 g (males). Again, this certainly
underestimates the true extent of fat deposits,
since mid-winter mass is unlikely to represent
lean mass levels. Abdominal profile measures
suggest this may underestimate slightly the
true rate of increase amongst the geese at
Hvanneyri. Given that a substantial proportion
of this accumulation in Iceland was required to
restore fat depots and that the mid-winter minimum
mass included some fat reserves at that
time, this is a substantial and adequate source of
fat to fuel the crossing of the Denmark Strait and
ice cap to the summering areas beyond.
4.5 Habitat utilisation in Iceland in
spring
Greenland White-fronted Geese probably traditionally
used as their natural food source the
lower stem storage organs of Eriophorum angustifolium
and Carex lyngbyei that grew in abundance
in the lowland wetlands as their natural food
source (MS4, MS19, MS27). Although the area of
intact mire and undamaged wetland in southern
and western Iceland remains large, despite much
drainage in the 1970s and 1980s, it is clear that
most spring staging Greenland White-fronted
Geese now exploit agricultural grasslands. The
most favoured grasslands are short-cropped hay-
38
4000
3500
3000
2500
Adult male captures
Adult female captures
Based on abdominal profiles
2000
14-Apr 19-Apr 24-Apr 29-Apr 4-May
fields that offer the most open dense swards,
which exhibit rapid growth in spring. The geese
glean waste from the harvests of previous autumns
in the form of potatoes (especially in the Þykkvibær
area of Holt) and barley (especially in the
Hvolsvöllur area in Hvolhreppur) in the southern
lowlands, as these are released from the winter
snow prior to ploughing. Such crops are not cultivated
to any great extent in the west (MS24).
The results of detailed studies at Hvanneyri have
shown that spring staging geese differentiate between
different grassland sward types on the basis
of food quantity and quality (MS15, MS16,
MS24, MS25, MS26, Nyegaard 2001). The geese
feed on all three of the most abundant grass species
occurring in the sward, namely Phleum pratense,
Poa pratensis and Deschampsia caespitosa, but
each species is exploited in different ways and at
different times according to growth form. Alopecurus
pratensis also occurs, but is not especially
favoured by the geese.
The fields at Hvanneyri can be classified as being
dominated by one or other species of grass (where
one species constitutes more than 50% of the
sward) or are co-dominant (i.e. where 2 species
of grass differ by less than 20% in their coverage).
Combining cumulative goose counts from all classified
fields at Hvanneyri shows that Phleum supports
significantly greater densities of geese than
Poa, Deschampsia or Alopecurus dominated fields
(see Figure 4.4), although the last species was only
present in very mixed swards on 5 of the fields. A
Cumulative goose use per ha
800
700
600
500
400
300
200
100
0
Phleum Poa Poa/Des. Des. Alopec.
Sward category (dominant species in sward)
Figure 4.4. Cumulative goose use of fields of different
sward composition, expressed as total geese per hectare
(+ SE) during the spring staging period at Hvanneyri
in 1997. Swards were composed of dominant
Phleum pratense, Poa pratensis, Deschampsia caespitosa
and Alopecurus pratensis or co-dominant Poa/Deschampsia
as indicated.