The Greenland White-fronted Goose Anser albifrons flavirostris

Mean age of first breeding
8
7
6
5
4
3
2
1
0
1982 1984 1986 1988 1990 1992 1994 1996
Cohort year
Figure 6.7. Mean age of first successful breeding (+ SE,
determined by the return of an individual to the wintering
grounds with at least one gosling) of goslings
captured and marked in their first winter at Wexford
since ringing commenced in 1983. Note that there are
still several surviving birds from cohorts hatched since
1992 that have yet to breed and could yet recruit in
future years, although these would only raise the mean
age of first breeding for these latter cohorts.
of survivors of cohorts from 1988 onwards (Figure
6.7) will increase mean age at first breeding
and make very little proportional difference to the
proportions breeding shown in Figure 6.6.
Mean brood size amongst flavirostris has always
been relatively high compared to other Whitefronted
Goose races, varying between 2.4 and 4.2
at both Wexford (mean 3.4 ± 0.07 SE) and Islay
(mean 3.1 ± 0.07 SE) during the years 1968-1999.
Mean brood size at Wexford was highly significantly
correlated with proportion of young in
winter, but there was no such relationship on Islay.
There was a tendency for larger broods with
increasing age of first breeding (MS8). This suggests
that there could be some reproductive benefit
to the individual from prolonged association
with parents (in terms of production of young at
their first breeding attempt). There has been a
sudden increase in brood size amongst birds wintering
on Islay in very recent seasons, despite no
change in the observer or methods used to sample
this parameter there (Figure 6.8). This has resulted
in the mean brood size on Islay exceeding
that at Wexford (generally always the converse
until the mid-1990s, Figure 6.8). While in the 1970s
and 1980s the productivity of the Wexford birds
was nearly always greater than that of Islay wintering
birds, in recent years this difference has
reduced, and Islay productivity has in several
recent years exceeded that at Wexford. Evidence
for any density-dependent relationship for productivity
was weak amongst the Scottish wintering
flocks (Pettifor et al. 1999) and non-existent
Mean brood size
5
4
3
2
1960 1970 1980
Census year
1990 2000
Wexford
Islay
Wexford
Islay
Figure 6.8. Mean annual brood size of Greenland
White-fronted Geese returning to the two major wintering
areas of Wexford and Islay. The vertical arrow
indicates the point at which the population was protected
from hunting on the wintering grounds (i.e. at
both sites). The decline in brood size at Wexford since
1983 is statistically significant, as is the significant increase
on Islay 9 .
amongst the Wexford wintering element of the
population.
6.6 What does limit reproduction in this
population?
We may be very encouraged that recent years
have seen a huge increase in the basic descriptive
knowledge relating to the breeding biology
and ecology of Greenland White-fronted Geese.
However, from a conservation point of view, all
the descriptive information is useless if we are
unable to identify and understand the processes
involved. Direct comparisons with other Whitefronted
Goose races show that proportionally
fewer flavirostris of potential breeding age return
to the wintering areas with young. Yet when they
do breed, they return with more juvenile geese
per family than those of other races (see comparisons
in Table 6.1). The implication is that the reproductive
potential of the population is locked
up in a small number of highly successful breeding
pairs. The question therefore remains: why
do so few females of breeding age return with
young? And why is this number presently declining?
Is it because of delayed pairing (and prolonged
parent offspring associations) compared
to other races (MS8, MS11)? Do offspring simply
associate with parents and siblings because they
can contribute to the reproductive output of kin
and accumulate reproductive knowledge during
a period when they have little prospect of breeding
successfully? Or do they pair no later than
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