Survival and dispersal in a new Barnacle Goose population 81
©Wildfowl & Wetlands Trust
Wildfowl
(2013) 63: 72–89
model there was no difference in survival
between birds ringed as juvenile compared
with birds ringed as adult, and survival did
not differ between the sexes, but survival did
vary between years (Table 2). Although only
three years of re-sightings data are available
to date, survival does seem to be in the same
order of magnitude as for geese from the
Delta area (Fig. 1, Table 3), and decreased
from 90% in 2009 to < 70% in 2011.
Effects of hunting
In the Delta area, survival rates have
declined since the first year of ringing in
2004, and in Fryslân survival similarly
decreased between 2009 and 2012. This
decrease may be associated with increasing
hunting pressure on Barnacle Geese during
the summer months, to prevent damage to
agricultural crops. Prior to 2006, Barnacle
Geese were legally protected from hunting
in the Netherlands throughout the year.
Summer hunting of Barnacle Geese has
been permitted in the province of Zuid-
Holland since 2006, however, and annual
bag numbers have risen from 679 in 2006
to 5,852 in 2011 in the Delta area
(Faunabeheereenhed (FBE) Zuid-Holland,
unpubl. data; Table 4). In Fryslân, Barnacle
Geese have been shot legally during summer
since 2010, but bag numbers are still modest
(Table 4). The number of ringed birds
reported as shot has also increased over the
past six years, but is low compared with the
total bag numbers (Table 4); it is difficult to
relate bag numbers to survival because the
accuracy of the numbers reported has not
been determined. Estimates of the numbers
of geese breeding in the two areas are based
on a single annual count in July, and the July
count is in the middle of the hunting period
so includes an unknown part of the annual
hunting bag. Nevertheless, these figures do
give some hint about the potential impact of
hunting on the number of geese breeding in
the Netherlands. When the annual bag
numbers are simply divided by the annual
July count, this yields a figure that should at
least be indicative of the proportion of the
breeding geese removed by hunting in
recent years. It is also possible to estimate
hunting mortality from the number of
ringed birds reported shot, with the number
reported shot, divided by the reporting rate
(derived from the survival analyses) and
divided again by the number of birds ‘at
risk’ (calculated as the expected number of
colour-marked birds alive during each
summer using the annual survival figures)
yielding an estimated value for hunting
mortality. However, this is far from precise
as the reporting rate does not differentiate
between shot birds and birds that died from
other causes, and the reporting rate is also
unreliable because of the relatively low
numbers of ring recoveries. Results of both
calculations are given in Table 4. The
calculated annual figures for hunting
mortality were then considered in relation to
the annual survival estimates from the
survival analyses (Fig. 2).
Dispersal
Natal dispersal of Barnacle Geese hatched
in the Netherlands was considerable. Of
those males for which a breeding location
was known or could be inferred from the
data, 56% bred within 10–100 km from their
original site of ringing and 38% bred > 100
km from their site of ringing (Fig. 3).
