The Greenland White-fronted Goose Anser albifrons flavirostris

1980s. They are now protected from hunting in
Britain and Ireland (since 1982) and the season
has been shortened to 16 August-30 April in
Greenland (from 1985). Immediately following
the implementation of protective legislation,
numbers at the two most important wintering
sites (Islay in the Inner Hebrides, SW Scotland
and Wexford Slobs, SE Ireland) increased, suggesting
that hunting was at least partially additive
to overall natural losses. Observations of individually
marked birds have shown that the
population tends to be site loyal: only 14% of birds
seen in consecutive winters changed site and 7%
per annum showed permanent emigration (MS7,
MS9, M. Frederickson unpublished data). Since
hunting took place at both sites up to the time of
protection, these cases offer an opportunity to
explore the effects of changes in hunting legislation
on the numbers using these sites. At Wexford,
hunting was permitted again in the winters
of 1985/86 and 1989/90. In this chapter, an attempt
is made to determine the role hunting
played in limiting numbers of Greenland Whitefronted
Geese at Wexford, using census data and
reviewing various different approaches to the
estimation of annual survival in this population.
8.2Were annual adult rates of return to
Wexford related to the size of the
annual kill?
Counts of Greenland White-fronted Geese have
been carried out at Islay and Wexford since at least
the winter of 1967/68. Since 1982, carefully coordinated
monthly counts have been carried out
following a standard procedure at both sites (see
Easterbee et al. 1990, Fox et al. 1994, MS14 for
details). In years prior to this, up to 40 counts were
carried out on Wexford Slobs in each winter, and
at least two complete counts of Islay were undertaken
annually. Large samples of birds have been
aged in each autumn since 1968/69 to determine
the proportions of first-winter birds present during
early autumn or winter. It is important to
understand whether the magnitude of the annual
hunting kill was responsible for changes in the
probability that a bird would return to either site
in the following year.
Based on the annual maximum count from each
winter (N) and proportion of juveniles in the
population J for each winter t, an assessment of
apparent annual adult return rate R t for Wexford
and Islay was determined as follows:
66
R t = (N t – J t N t )/N t-1
(1)
This measure includes the net balance of immigration/emigration
of individuals to each site as
well as true survival between years. Furthermore,
the measure suffers from sequential bias, in that
an overestimation of apparent survival in year t
is compensated for by an underestimation in year
t+1. However, as far as the numbers of geese returning
to the site is concerned, this measure has
some utility in determining the way in which local
abundance at a site varies over time. It seems
likely that changes in annual immigration/emigration
rates are relatively small, and probably
relatively constant, so that annual adult rate of
return to a wintering resort represents a proxy
measure of annual adult survival. Is it possible to
detect a change in annual adult return rate that
can be related to the number of birds killed in
any one year? Although not evidence of directly
additive mortality, such change would support
the argument that hunting at a known level has
an impact upon the probability of a bird returning
to a wintering site in a subsequent year.
At Wexford Slobs, the hunt was always limited
in time and space, and the size of the bag determined
for each year. Estimates of the numbers
shot in Wexford Harbour were less precise, so
annual totals killed there were estimated based
on observations and discussions with wildfowlers
in each season and these totals added to those
killed at the Slobs. When the moratorium on
shooting was lifted in 1985 and 1989, the bag was
strictly limited and the numbers shot were recorded.
In 1981/82-1983/84, a detailed study was
undertaken to assess the level of mortality on the
Wexford Slobs. Systematic (but not comprehensive)
searches were carried out using a trained
retriever dog on the Slobs and along the shores
of Wexford harbour to find the bodies of unretrieved
dead and dying geese. In 1981/82, when
hunting took place, 28 geese were found in this
way (in addition to the 142 reported shot), compared
to none in following years with protection
from shooting (D.W. Norriss in litt.). For this reason,
in all years when hunting occurred, an additional
20% was added to the known bag to allow
for geese mortally wounded or not retrieved
(based on general experience from many years
and specific investigations during 1981/82). In
this way, an annual kill was defined (K t ) for each
year with hunting at Wexford. The number of
birds killed K t was then expressed as a proportion
of the maximum numbers recorded N t to give