The Greenland White-fronted Goose Anser albifrons flavirostris

stores, the rate of acquisition (and hence condition
state by a given time) will be affected by a
range of factors acting on the individual. For instance,
on the wintering grounds, the level to
which an individual can maintain suitable food
intake rates in relation to maintenance expenditure
is affected by primary external factors (such
as food quality or abundance). This is then modified
by secondary factors (such as rates of disruption
to feeding patterns through human disturbance
or intra-specific interference). If we assume
that the foraging ability of an individual is
related to its ability to accumulate stores in anticipation
of energetic expenditure, in the short
term we can use measures of feeding efficiency
and/or rates of change in individual condition
to contrast the relative costs and benefits of differing
foraging situations. Such a comparative
approach based on detailed observations of
marked individuals offers the opportunity to contrast,
for instance, the ability of individuals of
different status to accumulate stores in the presence/absence
of disturbance (Madsen 1995). It
becomes possible to compare rates of change in
body condition based on feeding on different
habitat types, or examine differences in birds of
different social rank. Viewed over longer time
scales, the short term ability to maximise efficiency
in store accumulation ensures not only the
survival of the individual but ultimately the recruitment
and lifetime reproductive output of the
individual. Based on the accumulated life histories
of individuals, we can contrast differences in
lifetime reproductive output as a fitness measure
of the different strategies used by individuals
throughout their lives.
On-going studies have already demonstrated the
ability to detect differences in energy accumulation
rates between Greenland White-fronted
Geese using different grass swards during spring
staging at the same site in Iceland (Nyegaard et
al. 2001). From observations of collared individuals,
it is known that different individuals exploit
different sward types, many showing consistent
patterns between years (chapter 4). This (not unexpectedly)
appears to influence the rate of
change in abdominal profile scores of individual
geese exploiting different sward types (MS18 and
unpublished data). The accumulation of more
individual life histories with details of habitat use,
patterns of store acquisition and condition on
departure from Iceland will enable the assessment
of the fitness consequences from such foraging
behaviour in the fullness of time. These linkages
82
between different elements in the life cycle are
essential if we are to obtain a deeper understanding
of how individuals perform in terms of survival
and reproduction measures with regard to
the environment they exploit.
There are thus 3 measures available to assess individual
performance: the balance of food intake
rate versus use over short periods, the rate of accumulation
of stores for completion of demanding
episodes in the life cycle and ultimately the
survival and reproductive output of the individual.
It is possible to combine specific detailed
investigation of these elements with the longer
term historical resighting data, which provide
records of how an individual has performed
throughout its life. For geese ringed as goslings
in their first winter, these records include which
areas and habitats they exploited at different times
of the year, when they separated from parents,
how often a bird has changed wintering site, how
often it returned to wintering areas with young
and how long it lived. What is interesting is to
see how individual decision-making can affect
feeding efficiency, condition and, ultimately, fitness.
Although Greenland White-fronted Geese
are highly site loyal, birds do change wintering
sites (MS9). In chapter 4, we saw how individual
birds tend to specialise on a particular grass sward
during staging in Iceland in spring, but some birds
do show the ability to change from less nutritious
swards to more profitable ones (Figure 4.9).
Hence, individual decision-making enables modifications
to feeding efficiency, condition and fitness,
and it is the consequences of these decisions
which offer insight into how individuals behave
and how this contributes to overall population
behaviour (Figure 9.5). Combinations of historical
data and new investigations enable use of
these measures to assess factors affecting individual
breeding success and survival and an attempt
is made to set out the major research objectives
in Appendix 2.
The priorities for the immediate future are to continue
to monitor the patterns in numbers and distribution
which is only possible on the wintering
areas (see Appendix 2 for details). The individual
marking programme at Wexford must continue
if we are to be in a position to interpret the changes
in numbers based upon the count information.
This programme should be extended to more individual
marking and monitoring at other sites
to construct the basis for comparative studies discussed
in greater depth below. The basic ration-