Causes of the redistribution of Pink-footed Geese Anser brachyrhynchus in Britain

The numbers of Pink-footed Geese Anser brachyrhynchus wintering in Britain have been increasing exponentially since the 1950s. The numbers of geese at virtually all roost sites have increased, but the most dramatic increase has been in Norfolk, the southernmost region occupied in Britain. This redistribution was most likely caused either by the increase in the population forcing greater numbers of geese towards more southerly sites as the result of a buffer effect, by a decrease in the quality of sites elsewhere in the range or by an increase in the attractiveness of Norfolk. Co-ordinated counts of geese around Britain and historical data of changes in agricultural practice in Norfolk were used to examine these possibilities. No evidence was found for buffer effects, degradation of sites elsewhere or an increase in food availability in Norfolk. The major difference between Norfolk and other Pink-footed Goose sites is in the food type available in Norfolk, namely harvested Sugar Beet Beta vulgaris remains. This food is of high quality and the geese are not disturbed whilst feeding on it because of its limited commercial value. The pattern of redistribution of Pink-footed Geese may therefore be the result of cultural learning of the benefits of feeding on Sugar Beet.     

Pre-nesting feeding selectivity of Pink-footed Geese Anser brachyrhynchus in artificial grasslands

The pre-nesting feeding ecology of Pink-footed Geese Anser brachyrhynchus was studied in southern Iceland in April and May 1989–1992. Extensive surveys showed that prior to movement to their nesting areas in the interior, Pink-footed Geese fed mainly on intensively managed grasslands of the southern lowlands. Faecal analysis showed that geese feeding in hayfields foraged almost exclusively on the most commonly reseeded species, Timothy grass Phleum pratense , which made up the majority (41% by number of green shoots) of new growth in studied hayfields. Dropping counts, as an indicator of goose use, were highly significantly correlated in all years with density of growing Phleum shoots in individual field units. Geese showed a response in feeding patterns to changes in Phleum density as a result of reseeding patterns. Analysis of forage quality in 1991 showed that Phleum shoots had a higher protein content than all other grasses present in hayfields, with the exception of Deschampsia caespitosa. The latter species showed similar levels of protein, but its tussocky nature precluded effective grazing by the geese. Phleum was similar in fibre content to other common grasses. Based on removal of tagged plants, geese grazed predominantly on the youngest leaves of Phleum , which also had higher protein content and lower fibre than older leaves and attached dead leaves, which were rarely taken by geese. Geese grazed shorter length classes of youngest leaves, which showed higher protein content than longer, older terminal leaves. Recently created grassland habitat has increased the opportunities for female geese to supplement their reserves during the crucial prelude to clutch initiation by selecting the highest quality plant species and the most nutritious parts of that forage.     

Weights of Pink-footed Geese in autumn

The results of sample surveys, representing the major ecological divisions, indicate that Ireland holds more Peregrines than estimated previously. The species is recovering well from the earlier effects of pesticides.     

Snow-patch foraging by pink-footed geese Anser brachyrhynchus in south Iceland

The pre-nesting feeding behaviour of pink-footed geese was studied in hayfields in southern Iceland during the late spring of 1989. Persistent snow-patches protected underlying grass from the effects of severe night-time frost. Areas within 1 m of snow-patches had significantly greater amounts of green material than those further away; green material contained more than double the protein of brown, dead material, which predominated in open fields. Geese spent nearly 60 times more time feeding within 1 m of snow patches than expected by chance, and 20 times more time within 2–5 m. Their feeding rates here were faster and their step rate slower than further away. In this way, the geese selected the prime forage as soon as it became available.     

Colonization history of the high-arctic pink-footed goose Anser brachyrhynchus

Population structure and phylogeography of the pink-footed goose, Anser brachyrhynchus Baillon 1833, was studied using mtDNA control region sequences (221 bp) from 142 individuals. Present breeding areas of the species in Greenland, Iceland, and Svalbard were largely covered by ice during the late Pleistocene. In pairwise comparisons phiST estimates showed significant differentiation among eastern and western populations, whereas sampling localities within both areas were not differentiated. The mtDNA data indicate that the populations have separated recently (less than 10 000 years ago) and present breeding areas were colonized from one refugial population. The levels of haplotype and nucleotide diversity were approximately five times higher for the eastern population compared to the western population and suggest that the latter was colonized by a subset of eastern birds. Time to the most recent common ancestor of the species is 32 000-46 000 years, i.e. the present mtDNA variation of the pink-footed goose has accumulated during the last 0.1 My. Estimates of the long-term female effective population size (5400-7700 for the eastern population) imply that the refugial population of the pink-footed goose has been large. Tundra habitats were more extensive in cold periods of the late Pleistocene than today and may have sustained population sizes that allowed the accumulation of extant genetic polymorphism. It is not probable that the postulated small refugial areas in the high latitudes had a significant role in maintaining this diversity.     

Declining winter survival and fitness implications associated with latitudinal distribution in Norwegian Greylag Geese Anser anser

The Norwegian Greylag Goose Anser anser population has been increasing steadily over the past few decades, causing increasing nuisance in terms of agricultural crop damage. This, in combination with the importance of Greylags as a hunting target, has called for demographic estimates for the population to assist in management decisions. To this end, we analysed long-term mark–recapture data using Cormack–Jolly-Seber models embedded in program MARK to obtain survival estimates for the population. No sex-specific difference, or age effect on survival after juveniles had completed their first migration (3 months of age), was evident. Mean first-year survival was reported as 0.485 and annual survival of older birds as 0.700. On a monthly basis, survival in Greylags during summer and winter was very similar over the study period. A significant linear decline in winter survival from 0.909 to 0.807 was, however, apparent during the study period. Over the second half of the study (1994–2002), summer survival was about 3% lower than in the first half (1986–94) but no linear relationship was evident. We found a significant inverse relationship between Greylag survival during summer and latitudinal distribution in Norway. A similar relationship was evident between survival and annual bag numbers. The changes in adult survival observed in this study are likely to have had a substantial impact on the growth rate of the Norwegian Greylag population.     

Finding food in a highly seasonal landscape: where and how pink footed geese Anser brachyrhynchus forage during the Arctic spring

Food accessibility and availability in the highly seasonal Arctic landscape can be restricted by snow cover and frozen substrate, particularly in early spring. Therefore, to determine how a long distance migratory herbivore forages in such a landscape, pink‐footed geese Anser brachyrhynchus at an early spring feeding area in Svalbard were studied. Birds arrived in mid May when extensive snow cover restricted habitat availability. Geese fed in all habitats, but the highest densities occurred in wet tundra. However, prolonged snow lie restricted access to wet areas compared to dry and mesic habitats. Above ground biomass was very low in all habitats; yet sizeable amounts occurred below ground. In line with this, the majority of birds (86%) grubbed for below ground plant storage organs such as stem bases and rhizomes. Wet habitat contained greater quantities of edible and lower amounts of inedible below ground material (ratio 1:0.3) than dry (ratio 1:9) or mesic (ratio 1:4) areas. Although foraging in wet habitat prevented geese from encountering high proportions of inedible plant parts, forage species characteristic of this habitat, such as Dupontia grasses and the rush Eriophorum scheuchzeri, were more difficult to extract than food plants typical of drier habitats such as the forb Bistorta vivipara. Hence, we suggest that wet areas are preferred by pink‐footed geese, but the prolonged snow lie there made it necessary to use less preferred but much more abundant drier habitats, which experienced earlier snowmelt and indeed accommodated more than half of all goose foraging recordings.     

Olfaction and Feeding Behaviour in Juvenile Geese (Anser a. anser and Anser domesticus)

Juvenile geese start reacting to odours at the age of 11 to 20 h. In inexperienced goslings head-shaking is released by the odours of plants on which adult geese would not feed (e.g. lavender, violet etc.). Goslings aged 4 to 9 days show a quantitatively different reaction to different odours, such as sage, dwarf-pine, dill etc. Goslings quickly become habituated to odours, they will not react any more if an odorant is presented too often.     

Survival of Svalbard pink-footed geese Anser brachyrhynchus in relation to winter climate, density and land-use

1. Global change may strongly affect population dynamics, but mechanisms remain elusive. Several Arctic goose species have increased considerably during the last decades. Climate, and land-use changes outside the breeding area have been invoked as causes but have not been tested. We analysed the relationships between conditions on wintering and migration staging areas, and survival in Svalbard pink-footed geese Anser brachyrhynchus. Using mark-recapture data from 14 winters (1989-2002) we estimated survival rates and tested for time trends, and effects of climate, goose density and land-use. 2. Resighting rates differed for males and females, were higher for birds recorded during the previous winter and changed smoothly over time. Survival rates did not differ between sexes, varied over time with a nonsignificant negative trend, and were higher for the first interval after marking (0.88-0.97) than afterwards (0.74-0.93). Average survival estimates were 0.967 (SE 0.026) for the first and 0.861 (SE 0.023) for all later survival intervals. 3. We combined 16 winter and spring climate covariates into two principal components axes. F1 was related to warm/wet winters and an early spring on the Norwegian staging areas and F2 to dry/cold winters. We expected that F1 would be positively related to survival and F2 negatively. F1 explained 23% of survival variation (F1,10=3.24; one-sided P=0.051) when alone in a model and 28% (F1,9=4.50; one-sided P=0.031) in a model that assumed a trend for survival. In contrast, neither F2 nor density, land-use, or scaring practices on important Norwegian spring staging areas had discernible effects on survival. 4. Climate change may thus affect goose population dynamics, with warmer winters and earlier springs enhancing survival and fecundity. A possible mechanism is increased food availability on Danish wintering and Norwegian staging areas. As geese are among the main herbivores in Arctic ecosystems, climate change, by increasing goose populations, may have important indirect effects on Arctic vegetation. Our study also highlights the importance of events outside the breeding area for the population dynamics of migrant species.     

Snow conditions as an estimator of the breeding output in high-Arctic pink-footed geese Anser brachyrhynchus

The Svalbard-breeding population of pink-footed geese Anser brachyrhynchus has increased during the last decades and is giving rise to agricultural conflicts along their migration route, as well as causing grazing impacts on tundra vegetation. An adaptive flyway management plan has been implemented, which will be based on predictive population models including environmental variables expected to affect goose population development, such as weather conditions on the breeding grounds. A local study in Svalbard showed that snow cover prior to egg laying is a crucial factor for the reproductive output of pink-footed geese, and MODIS satellite images provided a useful estimator of snow cover. In this study, we up-scaled the analysis to the population level by examining various measures of snow conditions and compared them with the overall breeding success of the population as indexed by the proportion of juveniles in the autumn population. As explanatory variables, we explored MODIS images, satellite-based radar measures of onset of snow melt, winter NAO index, and the May temperature sum and May thaw days. To test for the presence of density dependence, we included the number of adults in the population. For 2000–2011, MODIS-derived snow cover (available since 2000) was the strongest indicator of breeding conditions. For 1981–2011, winter NAO and May thaw days had equal weight. Interestingly, there appears to have been a phase shift from density-dependent to density-independent reproduction, which is consistent with a hypothesis of released breeding potential due to the recent advancement of spring in Svalbard.     

Within-pair testosterone covariation and reproductive output in Greylag Geese Anser anser

In monogamous animals, reproductive success may vary considerably among pairs. To study this variation, we focussed on reproductive events and the circannual hormonal co-ordination within pairs during the reproductive cycle. Testosterone was chosen as covariable for both sexes because of its mediator function between behaviour and physiology. In a flock of free-living Greylag Geese Anser anser , individual faecal samples were collected weekly from 23 pairs over a complete annual cycle. From the faeces, equivalents of testosterone, oestrogen and other steroid hormones were analysed by enzyme immunoassay. In contrast to correlations between male and female testosterone, no correlations were found between oestrogen-oestrogen or oestrogen-testosterone. Therefore, only testosterone (T) is considered here. Sex-specific differences in T were in amplitude rather than in the annual timing of maxima and minima. However, the annual timing varied to some degree between individuals within sexes. Therefore, we examined the degree of annual testosterone correlation (TC) within pairs. Pairs that nested had significantly higher TC over the year than pairs that did not. The higher the within-pair TC, the larger the clutches and the heavier the eggs. Also, TC in the year investigated was positively and significantly correlated with the pairs' long-term reproductive output. No correlation was found between TC and the duration of the pair-bond, individual age, or age difference from pair partner. We suggest that TC is a measure of behavioural synchrony and, therefore, pair-bond quality. We consider whether within-pair TC results from mate choice.     

Circumpolar variation in morphological characteristics of Greater White-fronted Geese Anser albifrons

Capsule Greater White-fronted Geese show significant variation in body size from sampling locations throughout their circumpolar breeding range.

Aims To determine the degree of geographical variation in body size of Greater White-fronted Geese and identify factors contributing to any apparent patterns in variation.

Methods Structural measures of >3000 geese from 16 breeding areas throughout the Holarctic breeding range of the species were compared statistically.

Results Palearctic forms varied clinally, and increased in size from the smallest forms on the Kanin and Taimyr peninsulas in western Eurasia to the largest forms breeding in the Anadyr Lowlands of eastern Chukotka. Clinal variation was less apparent in the Nearctic, as both the smallest form in the Nearctic and the largest form overall (the Tule Goose) were from different breeding areas in Alaska. The Tule Goose was 25% larger than the smallest form. Birds from Greenland (A. a. flavirostris) were the second largest, although only slightly larger than geese from several North American populations. Body size was not correlated with breeding latitude but was positively correlated with temperature on the breeding grounds, breeding habitat, and migration distance. Body mass of Greater White-fronted Geese from all populations remained relatively constant during the period of wing moult. Morphological distinctness of eastern and western Palearctic forms concurs with earlier findings of complete range disjunction.

Conclusions Patterns of morphological variation in Greater White-fronted Geese across the Holarctic can be generally attributed to adaptation to variable breeding environments, migration requirements, and phylo-geographical histories.     

Staging site fidelity of Greenland White-fronted Geese Anser albifrons flavirostris in Iceland

Capsule Based upon resighting histories of marked individuals, a high level of site loyalty was found for Greenland White-fronted Geese staging in Icelandic stopover areas in spring and autumn.

Aims To determine levels of within- and between-season staging site fidelity, to assess whether offspring adopt the staging areas of their parents and to determine relationships between Icelandic staging areas and winter provenance of individuals.

Methods Sequential resighting histories and recoveries (2658 observations) of 415 different individually marked geese were analysed from the period 1986–99.

Results In spring, > 90% of goslings associated with parents and siblings and all goslings were subsequently seen <4 km from where they were first sighted with parents in spring. Ninety-six percent of all multiple within-spring resightings of 192 marked individuals were within 4 km of each other; three geese moved 88 km from the southern to the western staging areas. Four percent of the 45 marked geese seen in two consecutive springs and none of the 27 birds seen in consecutive autumns moved more than 4 km between years. By contrast, significantly more (12%) moved greater than 4 km in subsequent seasons between spring/autumn (n = 56) and autumn/spring (n = 49). All these individuals shifted to Hvanneyri Agricultural College in autumn, the only declared hunting-free area for Greenland White-fronted Geese. Based upon resighting histories and recoveries of shot birds, Scottish wintering birds were more likely to use southern staging areas, and Wexford (Ireland) wintering birds were generally more likely to be seen staging in the western lowlands in Iceland.

Conclusions Given the apparent cultural reinforcement of patterns of use of staging areas in Iceland, the high levels of site loyalty and the relatively limited exchange between southern and western staging areas, we argue for strategic refuge designation throughout both staging areas to protect the population.     

Mutual benefits of associations between breeding and non-breeding White-fronted Geese Anser albifrons

The relationships between yearlings and adult pairs of White-fronted Geese Anser albifrons were studied during pre-nesting, laying and early incubation in the central Canadian Arctic. Prior to nesting, females of lone pairs spent 75–81% of their time feeding, while males spent only 42–47% of time feeding and 46–50% alert. In pairs with one or more associated yearlings, both females and males fed significantly more and spent less time vigilant. Yearlings spent significantly less time (59%) feeding when alone compared with 71–76% when with pairs. Associations between yearlings and paired adults were most frequent before adult females began prospecting for nest sites. No prospecting pairs were associated with yearlings. After the egg-laying period, groups of geese, predominantly yearlings, made distraction flights over humans and terrestrial predators approaching nests, in contrast to the more cryptic behaviour of nesting pairs. The presence of groups of geese associated with some nest sites suggests that continuing parent-offspring relationships may involve assistance with nest defence.     

Assessing body condition and energy budget components by scoring abdominal profiles in free-ranging pink-footed geese Anser brachyrhynchus

An abdominal profile index (API) was developed for pink-footed geese Anser brachyrhynchus as a measure of body condition. On basis of carcass analysis of 56 adult geese with known API prior to collection, we found significant linear relationships between API against body mass, abdominal fat and total energy content. Hence, changes in API reflect net energy intake rates. As an example of the applicability of the calibration, we compared APIs of individually marked geese before and after long migration episodes and estimated the cost of flight at 8.9 kJ/km. In addition we estimated gain rates at three major staging sites along the spring flyway indicating an increase in fueling rates with latitude. Calibration of APIs and energy contents offers new opportunities for field studies of waterfowl energetics.     

An approach to the assessment of change in the numbers of Canada Geese Branta canadensis and Greylag Geese Anser anser in southern Britain

Capsule Population change in geese was assessed using an approach that requires a relatively small sampling effort.

Aims During the 1999 breeding season a survey was carried out to determine if the numbers of introduced Canada and re-established Greylag Geese in southern Britain had changed since 1988–91 and whether any change had occurred in areas with previously high or low Canada Goose densities.

Methods A randomized stratified sample of 246 tetrads from the 24 156 tetrads covered between 1988–91 in this area, as part of the New Atlas of Breeding Birds, were resurveyed. Eight habitat categories were used in the stratification and were based on 1-km-square summary data obtained from the CEH Land Cover Map of Great Britain (water cover and urbanization) and LANDCLASS stratification (upland/lowland). The five habitat categories with the highest densities of Canada Geese and the greatest variance in numbers were sampled.

Results Between 1989 and 1999, the number of Canada Geese on land with over 5% water cover and on lowland with some water cover increased by on average 156%, an average rate of increase of 9.9% per annum. Southern Britain probably now holds a minimum of 82 000 Canada Geese. Between 1989 and 1999, the number of Greylag Geese on land with over 5% water cover and on lowland with some water cover increased by on average 214%, an average rate of increase of 12% per annum. Southern Britain probably now holds a minimum of 30 000 Greylag Geese.

Conclusion Maximum densities of Canada Geese may have been reached in high-density habitats but their numbers are still increasing very rapidly. Greylag Geese are increasing even more rapidly.     

A demographic comparison of two Nordic populations of Greylag Geese Anser anser

Greylag Geese Anser anser have been neck-banded on an annual basis in Scania, southern Sweden since 1984 and in Norway since 1986 as part of a Nordic Greylag project. This has yielded a large database of resightings, which we used here to estimate and compare survival rates between the two populations by means of mark–recapture models. Estimated adult survival was sex-dependent in the Scanian population, probably a result of differential neck band retention rates in this population. Mean juvenile survival was about 12% higher in the Scanian population (0.603 vs. 0.485). Adult survival in the Norwegian population was 0.728 (males 0.733; females 0.725), and in males and females from the Scanian population was 0.711 (0.752 after accounting for higher neck band loss in males) and 0.771, respectively. Over the course of the study, juvenile survival in the Scanian population increased substantially, and adult survival was constant, whereas both these parameters declined in the Norwegian population. This study demonstrates that the two Nordic populations are demographically distinct and gives further support to the notion that they should be treated as separate management units. The decline of 10% in adult survival in the Norwegian population, the cause of which still remains uncertain, is likely to have had a major impact on the growth of this population.     

Lack of competition between barnacle geese Branta leucopsis and pink-footed geese Anser brachyrhynchus during the pre-breeding period in Svalbard

The feeding ecology of barnacle geese and pink-footed geese was studied in Sassendalen, Svalbard during the pre-nesting period (late May) to assess the potential for inter-specific competition. Barnacle geese fed almost exclusively (97%) by grazing above-ground plant material, mostly (79%) along snow edges in moss-mat habitats. Pink-footed geese fed mostly (93%) by excavating below-ground parts of plants, mostly (56%) away from snow and were more evenly distributed between habitat types. Barnacle goose faeces contained mostly (62%) moss, that of pink-footed geese mostly (48%) below-ground plant storage organs (especially Bistorta viviparum L.). Principal components analysis of dropping contents showed no overlap in species diet in allopatry or sympatry. There was little overlap in diet and feeding ecology of the two species at this pre-nesting feeding site. Hence, unless increased goose feeding densities affect future vegetation density and composition, under present circumstances, increasing numbers of either species is unlikely to affect foraging conditions for the other at this important stage in the annual cycle. However, such changes could have local density-dependent intra-specific effects.     

Adjustments to nitrogen metabolism during wing moult in Greylag Geese, Anser anser

1. This study examined the nitrogen balance of free-living flightless moulting Greylag Geese, Anser anser , in relation to food quality, nitrogen absorption, food retention time and nitrogen excretion rates.
2. Food intake rates during moult were the same as those before and after the flightless period, but total daily time spent foraging fell by 58% from 9·45 h to 3·96 h. Dropping production during moult was 43%, and mean dropping mass 42% of that before and after moult, suggesting a considerable increase in food passage time through the gut during moult. Nitrogen absorption increased from 25% prior to moult to 47% during moult.
3. At the same time, excreted dry mass uric acid in faecal material fell by 68%, such that the proportion of nitrogen absorbed and retained in the body as a proportion of the nitrogen ingested in food rose from 16% prior to moult to 42% during moult.
4. Based on these significant increases in nitrogen absorption and decreases in nitrogen excretion, geese were able to compensate for reduced food intake and derive sufficient nitrogen from their diet to re-grow flight feathers.     

Nest site preference by Greylag Geese Anser anser in reedbeds of different harvest age

Maintenance of reedbeds and their associated avifauna requires intervention management to modify natural succession by means of, for example, reed cutting. Nest site density of Greylag Geese Anser anser in relation to time since reedbeds were last harvested was studied at Vejlerne nature reserve, Denmark (57°00–07'N, 8°50'–9°10'E). Low nest densities were found in areas in the first four years after cutting followed by high densities in areas unharvested for five or six years. Subsequently, nest density remained high for four to seven years (depending on site) before declining to low levels again. Areas cut in the year of study and areas cut more than 16 years before contained virtually no nests. The increase in nest density with time since last harvest seemed to be related to an increase in vegetation cover (reed stem density). Areas harvested more than 16 years before probably became too dense for the geese, and newly harvested areas had too low a shoot density, hence their low nest density. However, more detailed studies are needed to establish causal relationships.