Conclusions and discussion

Ruttledge & Ogilvie (1979) suggested that the loss of peatland habitat might have concentrated Greenland White-fronted Geese into areas where they were easier to shoot. Not only would this have had an adverse effect on survival rates, but it would also have made them more sensitive to hunting disturbance. Human disturbance in gen-eral has since been shown to have a major influ-ence on the size and trends in numbers of several flocks (Norriss & Wilson 1988, 1993, MS14). In former times, the bogs and moorlands they ex-ploited would have provided food, daytime rest-ing areas and nighttime roosts all with very little disturbance. It would therefore seem likely that the extensive historical loss of such feeding sites for wintering flocks and increasing levels of dis-turbance, reduced their ability to acquire neces-sary stores to survive and reproduce at that time.

It does seem likely that habitat loss in such a site-faithful population made it more vulnerable to hunting and disturbance. Since hunting does ap-pear to have a direct depressing effect on overall survival rate, it seems more likely that increased susceptibility to hunting (prior to the 1980s) caused the declines and extinctions that occurred then. Nevertheless, reduction in breeding output through failure to accumulate sufficient body stores could also have resulted from the increased disturbance experienced at unfamiliar wintering sites. However, we shall never know precisely how changes in habitat availability affected the demography of the population and caused the changes in local wintering numbers at specific sites.

There is no doubt, however, that despite contin-ued loss of traditional peatland feeding areas during the latter part of the 20^th Century, the Greenland White-fronted Goose proved itself as able as other grey geese to exploit new and novel agricultural habitats. Flocks initially moved to rough pastures and flooded grassland, but latterly have also exploited intensively managed

grass-0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

1982 1984 1986 1988 1990 1992 1994 1996 1998

Estimated annual juvenile survival rate

Figure 8.4. Annual juvenile survival rate (± 95% CL) for Greenland White-fronted Geese caught at Wexford, 1983/84-1997/98 based on observations and recover-ies of neck-collared individuals using the MARK suite of programs (see text and Appendix 1 for details)¹². Open symbols indicate those seasons when the hunt-ing season was opened at Wexford for a limited shoot.

Note the unusually low survival rate of geese marked as goslings in 1988/89 that was not linked to hunting kill in that season.

0 0.1 0.2 0.3 0.4 0.5

1980 1985 1990 1995 2000

Probability of moving between sites

Wexford to Islay Islay to Wexford

Figure 8.5. Transition probabilities for Greenland White-fronted Geese moving between Wexford and Islay and vice versa for each year from 1983/84-1997/

98. There are no significant trends in the movement of individually marked birds over the period based on observations of neck-collared birds¹².

lands. This process was certainly underway when the geese began to exploit the newly created Sloblands in Wexford Harbour (probably at or around 1910, Ruttledge & Ogilvie 1979), despite the complete absence of boglands in the vicinity.

Despite their traditional habitat and high winter site fidelity, these geese have shown an ability to exploit new habitat opportunities. That said, only one flock of White-fronted Geese is known to have colonised and established an entirely new win-tering site since 1982. The process of exploiting grassland habitats, either those that are semi-natural or of low intensity agriculture, has con-tinued to the present day. Although many flocks still resort to peatland habitats to feed and sleep at night, there are few flocks remaining that ex-ploit bogs by day (MS14, MS24). Norriss & Wilson (1993) argued that this transition to more agri-cultural grassland was not forced upon the geese by habitat loss in very recent times, but that the geese responded to the creation of more profit-able feeding habitats without loss of traditional ones. This change has been occurring gradually since the 1950s, and therefore does not coincide with the dramatic increase in numbers that has occurred since protection from hunting. Hence, while it is possible to argue that increases in total numbers since the 1970s have been associated with increasing use made by the population of more intensively managed farmland, this cannot be anything more than a contributory factor ena-bling contemporary increase, rather than the spe-cific cause. This is further supported by the fact that the population range has effectively re-mained the same in the last 20 years, although several winter flocks have disappeared.

This ability to adapt to the exploitation of new habitats may be linked to the availability of such habitats in the neighbourhood of traditional flock ranges. In areas of Scotland where extensive ar-eas of intensively managed grassland are avail-able (e.g. Islay, Kintyre, Stranraer), Greenland White-fronted Geese have switched to these whilst retaining traditional roosts. This process has presumably run in parallel with improving grassland management practices since the early 1960s. In areas with little intensive grassland management and no tillage (e.g. many of the Hebridean islands such as Jura, Mull, Skye and Lewis) flocks remain small (see land use classifi-cation maps in Mackey et al. 1998). Equally, in areas with suitable extensive arable and managed grassland but no traditionally used roosts, the

species is totally absent (e.g. in Ayrshire and large areas of Dumfries). However, flocks with winter-ing areas with the greatest area of improved grass-land within traditionally used areas have tended to show increases in their number. This is in con-trast to those flocks where land use has changed little, or agricultural land has been abandoned.

In this way, there appears some fitness conse-quences to the availability of managed grassland which affects the rate of change in local winter-ing numbers, although it is far from clear if these relate to annual adult survival, reproduction or rates of immigration/emigration. Investigations of these parameters in relation to habitat and in-dividual quality remain a priority for future re-search.

In contrast, it would appear from the evidence presented here and in MS14 that, prior to protec-tion, the numbers of birds wintering at Wexford and Islay were limited prior to protection by the numbers shot. These two sites have held some 60% of the population since protection, hence this limitation was a significant one. There are no ac-curate collated hunting statistics for Islay. Since protection on the wintering grounds in 1982, the return rate of birds to Wexford and Islay has been more or less constant. At Wexford, incorporating the numbers killed into a simple model suggests that the return rate has not changed since the late 1960s. Hence the product of annual survival and emigration/immigration balance has remained constant at around 88.4% over 3 decades of large-scale land-use change. The relative stable num-bers during 1968-1982 seem to have been due to the balance between hunting off-take and changes in annual breeding success. Immediately after protection, numbers increased consistent with the same probability of annual return rate. In the ab-sence of the hunt, this resulted in the increased numbers. The increase has continued at rates regulated by the potential of reproduction to re-place lost individuals.

Since the start of the 1990s, the numbers winter-ing at Wexford have shown signs of decline due to falling fecundity (chapter 6) and to catastrophic losses of young and their parents in 1990, hence declines in reproduction appear now to be limit-ing the numbers at Wexford. Since the reduction in fecundity is mirrored amongst the wintering numbers on Islay and perhaps other wintering areas as well, this seems to be a general phenom-enon in the population as whole in recent years.

On Islay, the reduction in reproduction rate has

not yet been sufficient to halt the linear annual increase in numbers since protection.

The Greenland White-fronted Goose was a popu-lation that was declining due to habitat loss and hunting, but where protection from hunting has increased survival in proportion to the former size of the hunting bag, enabling the population to enter a phase of increase. Apparently confined to

traditional areas by behavioural site loyalty throughout its range, the population has shown signs of slowing its expansion in numbers in very recent years due to declining reproductive success.

9.1 Anticipatory acquisition of nutrients,