The Greenland White-fronted Goose Anser albifrons flavirostris

Recommendations

Info

eas (see Raveling 1978, Ganter & Cooke 1996) based on their own internal condition and the prevailing environmental conditions. This would involve assessment by the females of their ability to meet the nutritional demands of laying differing numbers of eggs and incubating the clutch given available stores and the supplement possible from exogenous food sources. Evidence is accumulating to suggest that exogenous sources supply much, or perhaps all of the fat needed for egg formation (Choinière & Gauthier 1995, Ganter & Cooke 1996, Meijer & Drent 1999). Hence, access to adequate food resources prior to first egg date may have a considerable impact on the ability of a bird to reproduce successfully. We know little about female condition and its potential to affect reproductive success (before, during and after nesting), so the accumulation of knowledge relating to this parameter remains a priority. In particular, following body mass changes in particular individuals during the period from first arrival in west Greenland through to the end of incubation would be highly desirable. Tracking changes in body mass by capture and the use of balances under nests offers the opportunity to assess and contrast the potential of different individuals to successfully invest stores and reserves in reproductive attempts. Similarly, it is of great interest to understand more about how brood females recoup stores and reserves exploited during the laying and incubation period, a process about which we know nothing at present. Clearly behavioural adaptations (i.e. mechanisms resolving the conflict between self-maintenance and investment in brood protection) and dietary selection are both potentially involved, but could differ between individuals. Despite the recent expansion in total population size, the absolute numbers of successfully breeding pairs returning with young to the two major wintering sites combined have been more or less constant, suggesting some density-dependent mechanism is operating on the breeding grounds which restricts recruitment. Amongst known age marked individuals at Wexford, the probability of recruitment has declined over time and the mean age of first breeding has increased from c.3 prior to 1988 to c.5 years of age in subsequent years. Although difficult to measure in an objective way, the extent of breeding habitat available through- 56 out the summer range does not appear limiting. Nevertheless, the extent of habitat available in spring for pre-nesting feeding as well as later in the summer, are likely to vary with weather conditions, especially in the north. The Wexford geese breed mainly in the north of the breeding range, and the recent declines in fecundity of birds wintering at that site seem likely to be the result of conditions these birds encounter on their prebreeding and nesting areas. Their migration to west Greenland differs little in distance or route from the Scottish wintering element of the population that breed further south. They could experience less access to energy-rich foods (such as barley and potatoes) in western than in southern Iceland, which could enable greater energy stores to be accumulated by predominantly Scottish birds staging in these Iceland lowlands (MS4, MS19). However, if it is exogenous energy derived on the breeding areas that represents a major determinant of clutch size or quality, early arrival to staging areas in southern Iceland (MS19) would give these birds an advantage over geese breeding further north. The latter would not only compete with local breeders in the staging areas of central west Greenland but also then migrate northwards within Greenland with a high probability of encountering severe weather conditions on arrival at ultimate nesting grounds. As goose densities have increased in recent years, it may be that all potentially breeding White-fronted Geese are encountering more competition for limited resources in spring, but the birds still needing to continue north face increased competition from non-breeders. As there is no further habitat to the north of the current range into which to expand, it might therefore be expected that geese breeding in the north of the range show greater density-dependent effects on the summering areas than those nesting further south. There is some evidence that this is the case; on Islay, the production of young per potentially breeding female has not declined significantly, the decline in successful breeding being compensated for to some extent by increases in mean brood size in very recent years. Increased mean brood size implies (i) adequate stores to lay large clutches, (ii) to incubate these successfully and (iii) to raise goslings to fledging. If the breeding range of the Islay-wintering birds has not changed, it is unlikely that their increased brood sizes have been brought about by change in habitat. Since their breeding area (mainly 66-69ºN) is the area with greatest density of colonising breeding Canada
Geese, it might be expected that inter-specific interactions in this area would reduce reproductive output. It may have been the case in the 1970s (prior to the period of population expansion by restriction of winter hunting) the northern breeders had an advantage over southern breeders. Staging further south on the summer grounds gave the opportunity to accumulate nutrient and energy stores remote from breeding areas, but still time arrival to nesting areas to optimise food availability there. This seems to be reflected in greater productivity amongst Wexford compared to Islay birds at that time (Figures 6.2 and 6.4). Subsequently, conditions of greater population size have increased local feeding densities in spring and substantially increased moult migrant nonbreeder numbers using northern areas to regrow flight feathers. These changes in local density at key stages of the life cycle could potentially have turned the strategic advantage into an increasing disadvantage, especially at a time when a series of late springs has constrained the overall availability of early season food. It seems likely that breeding habitat has not changed in extent, but that the quantity (and pos- sibly the quality) of the resources available to females arriving in west Greenland have increased. Global climate models suggest there will be a short term and moderate warming of the central west Greenland coastal strip, whilst summer temperatures further north will be expected to fall. While increases in total population size may reduce overall access to finite food resources through competition, best quality individuals able to defend rich spring feeding areas could rapidly gain condition to invest in a clutch to be laid locally. Birds breeding further north face increased feeding competition, and poorer summer conditions later in the season on their own pre-nesting and breeding areas further north. Consequently, Wexford-wintering geese may be undergoing the very declines in fecundity predicted on the basis of climate change by Zöckler & Lysenko (2000), whilst Islay-wintering birds enjoy the positive benefits of this change. It would be interesting to analyse the historical meteorological archive to determine whether the difference in fecundity of these two elements of the population can be related to weather patterns in the north and south of the range. If not, there seem grounds for assessing in more detail the alternative explanations for these differences in breeding success in different elements of the population. 57
Page 1 and 2:
National Environmental Research Ins
Page 3 and 4:
National Environmental Research Ins
Page 5 and 6:
Contents Summary ..................
Page 7 and 8: Summary The Greenland White-fronted
Page 9 and 10: Greenland White-fronted Geese are u
Page 11 and 12: Dansk resumé Den grønlandske blis
Page 13 and 14: 1 Introduction 1.1 Why Greenland Wh
Page 15 and 16: The Greenland White-fronted Goose i
Page 17 and 18: more direct measures of 'body condi
Page 19 and 20: 2Limits to population size in recen
Page 21 and 22: Despite the morphological similarit
Page 23 and 24: Scotland, the wettest peat soils we
Page 25 and 26: of this goose population. At the sa
Page 27 and 28: Spring count 16000 12000 8000 4000
Page 29 and 30: 3 Accumulation of body stores and t
Page 31 and 32: Body mass (g) 3500 3000 2500 adult
Page 33 and 34: h -1 and none showed any sign of re
Page 35 and 36: labelled water), the precise extent
Page 37 and 38: 4 Spring staging in Iceland and the
Page 39 and 40: Body mass (g) Body mass (g) 4000 35
Page 41 and 42: Goose droppings/m 2 6 5 4 3 2 1 0 P
Page 43 and 44: er 3KJ was a behaviourally dominant
Page 45 and 46: 5 Pre-nesting feeding 5.1 Introduct
Page 47 and 48: imagery and searches in helicopters
Page 49 and 50: 6 Reproduction 6.1 Breeding distrib
Page 51 and 52: predicted that at the end of this p
Page 53 and 54: Percentage of juveniles Figure 6.1.
Page 55 and 56: Mean age of first breeding 8 7 6 5
Page 57: periods in each winter as the exten
Page 61 and 62: 7 Moult of flight feathers 7.1 Intr
Page 63 and 64: mass at different stages of regrowt
Page 65 and 66: of available fresh green growth of
Page 67 and 68: 8 Survival 8.1 Introduction Almost
Page 69 and 70: the hunting mortality rate K t for
Page 71 and 72: during the period when the populati
Page 73 and 74: lands. This process was certainly u
Page 75 and 76: 9 Synthesis 9.1 Anticipatory acquis
Page 77 and 78: Mass based on API scores 3600 3200
Page 79 and 80: social system has traditionally reg
Page 81 and 82: ers (J. Madsen unpubl. data). In th
Page 83 and 84: limitation which operates during an
Page 85 and 86: NUTRIENT & ENERGY ACCUMULATION RATE
Page 87 and 88: eeding geographical locations respe
Page 89 and 90: 10 Acknowledgements A thesis is sup
Page 91 and 92: mark and to Ebbe Bøgebjerg for the
Page 93 and 94: L. Kramer, J.N. Kristiansen, T. Lai
Page 95 and 96: Marked Individuals in the Study of
Page 97 and 98: mussels, Mytilus edulis. Journal of
Page 99 and 100: Nichols, J.D. (1991) Extensive moni
Page 101 and 102: Thompson, S.C. & Raveling, D.G. (19
Page 103 and 104: 12Appended manuscripts 1: Fox, A.D.
Page 105: National Environmental Research Ins
show all

The Greenland White-fronted Goose Anser albifrons flavirostris

Create successful ePaper yourself

Delete template?

Save as template?