The Greenland White-fronted Goose Anser albifrons flavirostris
The Greenland White-fronted Goose Anser albifrons flavirostris
The Greenland White-fronted Goose Anser albifrons flavirostris
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Body mass (g)<br />
Body mass (g)<br />
4000<br />
3500<br />
3000<br />
2500<br />
Males<br />
2000<br />
04-15-99 04-20-99 04-25-99 04-30-99 05-05-99 05-10-99<br />
Date of capture<br />
4000<br />
3500<br />
3000<br />
2500<br />
Females<br />
2000<br />
04-15-99 04-20-99 04-25-99 04-30-99 05-05-99 05-10-99<br />
Date of capture<br />
Figure 4.1. Changes in body mass of staging adult male<br />
and female <strong>Greenland</strong> <strong>White</strong>-<strong>fronted</strong> Geese caught at<br />
Hvanneyri, west Iceland in spring 1999. Fitted regression<br />
lines are best fit least squares linear regression<br />
models. 2<br />
20th April 1999 (MS19), the average body masses<br />
of arriving birds were 2.75 kg (adult males) and<br />
2.51 kg (adult females). Assuming that the birds<br />
arriving at Hvanneyri were a representative sample<br />
of those departing Wexford, this meant that<br />
in 1999, geese arriving in Iceland had used 327 g<br />
and 277 g of fat respectively, assuming all the difference<br />
to be fat. This is slightly less than predicted<br />
by the Pennycuick calculation, but more than by<br />
the energetic flight range methods. However,<br />
these calculations are based on average values,<br />
and may not represent the true situation during<br />
the 1999 spring migration episode. <strong>The</strong>se estimates<br />
suggest that the geese had not depleted all<br />
the reserves accumulated over the mid-winter<br />
minimum body mass in Ireland (see chapter 3).<br />
Using the same regression models, and a mean<br />
departure date of 5th May 1999 (MS19), geese<br />
accumulated an average of 369 g (15% in adult<br />
females) and 451 g (a 16% increase in body mass<br />
in adult males) during their 15-day stay in Iceland.<br />
<strong>The</strong>se data are based upon observed lengths<br />
of stay of collared birds at Hvanneyri, which were<br />
slightly shorter than the average for the satellite<br />
tagged individuals. Nevertheless, the accumulation<br />
of 24.6 and 30 g body weight per day for females<br />
and males respectively is impressive during<br />
this short stopover. <strong>The</strong>ir estimated mean<br />
departure masses were thus 3.21 and 2.88 kg (for<br />
adult males and females) when departing for west<br />
<strong>Greenland</strong> from Hvanneyri, 129 and 96 g respectively<br />
heavier than the departure mass from Ireland.<br />
An alternative approach is to establish a calibration<br />
factor for field scores of abdominal profiles,<br />
based on the body mass of known individuals of<br />
known abdominal profile scores. <strong>The</strong>re was a<br />
good correlation between the API score and body<br />
mass amongst the geese caught at Hvanneyri (Figure<br />
4.2). Since large numbers of geese were scored<br />
every day at Hvanneyri (although not specifically<br />
assigned to sex class), this enables the generation<br />
of mean body mass values for geese staging at<br />
the farm using the relationships shown in Figure<br />
4.2 and assuming a sex ratio of parity. <strong>The</strong> results<br />
of this are shown in Figure 4.3. Mass accumulation<br />
does not appear linear (as suggested by catch<br />
data alone), suggesting that the catch data may<br />
actually slightly underestimate mass accumulation<br />
by the end of the staging period. Because the<br />
caught birds were cannon-netted over bait, it<br />
could be that the capture technique selected for<br />
birds in poor condition attracted to rich sources<br />
of food.<br />
Despite the many assumptions made in these simple<br />
calculations, it does appear that geese arrived<br />
in Iceland with a residue of the body stores accumulated<br />
on the winter grounds and then very<br />
rapidly increased body mass there. If it is assumed<br />
that the geese at Wexford are typical of those else-<br />
Body mass<br />
Body mass<br />
4000<br />
3500<br />
3000<br />
2500<br />
Adult Males<br />
2000<br />
0 1 2<br />
Abdominal profile score<br />
3 4<br />
4000<br />
3500<br />
3000<br />
2500<br />
Adult Females<br />
2000<br />
0 1 2<br />
Abdominal profile score<br />
3 4<br />
Figure 4.2. Relationship between abdominal profile<br />
score and body mass of captured adult male and female<br />
<strong>Greenland</strong> <strong>White</strong>-<strong>fronted</strong> Geese at Hvanneyri,<br />
spring 1999. 3<br />
37