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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

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