The Greenland White-fronted Goose Anser albifrons flavirostris

Mass based on API scores
3600
3200
2800
2400
2000
1600
1200
early Jan
late Jan
early Feb
Wexford
late Feb
early Mar
late Mar
during recesses from the nest by the female, these
bouts are rare and of short duration (see chapter
6). It would therefore seem that, based on observations
of the 'median' female and the calculations
presented here, meeting the energetic and
nutritional costs of laying a clutch and completing
successful incubation is not possible. On this
basis, most females in any given year are unlikely
to attain nutrient and energy thresholds necessary
to reproduce. That said, observations from
several years indicate considerable individual
variation in abdominal profiles between individuals.
Indeed, some birds show considerably faster
rates of accumulation of body mass than do others.
It seems likely, therefore, that only those relatively
few individuals able to accumulate stores
at rates well above the mean throughout the prelude
to breeding will therefore have the potential
to attempt to breed. On this basis, it would appear
that a large proportion of geese could potentially
arrive in west Greenland having failed
to reach threshold condition for successful reproduction.
The crucial questions, therefore, concern the
mechanisms that are likely to affect the ability of
the individual to acquire the necessary nutrients
early Apr
late Apr
Iceland
early May
Greenland
late May
clutch of 3
clutch of 6
incubation with 3 eggs
incubation with 6 eggs
Figure 9.2. Estimated fortnightly median body mass
of adult male ( or ) and adult female ( or ) based
on field observations of abdominal profiles and their
observed changes through the first half of the year.
Graph contrasts the slow accumulation of stores at
Wexford (solid symbols, solid line) with the rapid accumulation
in Iceland (open symbols solid line) and
in Greenland (solid symbols dotted line). Costs of laying
3 and 6 egg clutches have been subtracted from
the late May median values, and costs of incubation
from these values (based on fat and protein costs from
Table 9.1). Note that this approach underestimates
body mass at all stages because of the effects of using
fortnightly means, hence the differences in some measures
compared to direct mass determinations used
earlier.
early June
late June
for survival and reproduction at each critical
stage. Assuming that the environment is not unlimited
in its ability to supply nutrients, a critical
factor is likely to be the local density of geese.
This factor affects the ability of an individual to
achieve threshold nutrient requirements. What
factors enable some individuals to survive and
breed whilst others cannot? There is abundant
evidence that amongst relatively long lived avian
species such as geese, breeding performance increases
with age (e.g. Owen 1984, Forslund &
Larsson 1992, Cooke et al. 1995). More older birds
attempt to breed than among young age classes
and a greater proportion of older birds breed more
successfully. For example, Raveling (1981) found
although geese 4+ years of age comprised 26% of
the potential breeding population, they produced
more than 50% of young in Giant Canada Geese
Branta canadensis maxima. Specifically, older birds
lay earlier, larger and heavier clutches than young
birds, which ultimately result in more offspring
fledged.
However, reproductive performance in geese generally
increases only for the first 5-6 years of life
(Rockwell et al. 1983, 1993, Forslund & Larsson
1992). This is not consistent with the hypothesis
of reproductive restraint in younger years (Curio
1983), which would predict increasing reproductive
effort throughout life. It would therefore appear
that in many goose populations, young individuals
are constrained from performing well,
perhaps through the lack of social status that permits
access to best feeding opportunities.
Dominance hierarchies have long been recognised
in goose flocks (Boyd 1953, Hanson 1953, Raveling
1970) and rank has been shown to increase with
age (Lamprecht 1986, Black & Owen 1995). However,
amongst birds of the same age class, dominance
explained much of the variation in reproductive
performance, suggesting this was the
overriding factor (Lamprecht 1986, Warren 1994).
Most evidently, dominance determines individual
feeding opportunity through securing and defence
of best feeding opportunities (e.g. Teunissen
et al. 1985, Prop & Loonen 1988, Prop & Deerenberg
1991, Black et al. 1992). This in turn has consequences
for food intake rates, since peck rates
and feeding rates have been found to correlate
positively with dominance (e.g. Warren 1994).
Social status also affects whether a goose pair is
able to obtain and hold a nesting territory. In situations
where predation limits output, hatching
success and fledging rate were also correlated
75