Gitte Høj Jensen

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

Abstract 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.

Hunting migratory geese: is there an optimal practice?

Since the mid-20th century, many European and North American goose populations have increased dramatically in numbers, causing conflict with agricultural interests in their staging and wintering areas. In some cases, to mitigate such impacts of rapid population increases, population control has been attempted by increasing harvest rate. In this study, we investigated how autumn-staging pink-footed geese Anser brachyrhynchus responded to hunting, with a view to determine hunting practice that would lead to an increase in the hunting bag. There was a significant increase in the distance between the hunting site and the goose flocks, on comparing goose distribution on the day before the hunt up to one day after the hunt. The effect was significant when at least 10 shots were fired per site but not when 1–10 shots were fired. The timing of shooting in relation to migratory phenology did not affect the time taken by the geese to return to the hunting site, but after a hunt in the early part of the staging season, the number of geese in the study area increased more rapidly than towards the end of the season. The maximum number of geese shot per hunting event was obtained when hunting events were separated by three days. Our results indicate that hunters can increase local harvest by temporal and spatial optimisation of practices. These results may be used as a tool in wider-scale regional and international processes to regulate the population size of pink-footed geese by shooting, depending on the willingness of landowners, hunters and managers to coordinate hunting practices.

Environmental factors affecting numbers of pink-footed geese Anser brachyrhynchus utilising an autumn stopover site

For huntable waterbird species, the autumn migration strategy may be important for their fitness, as their behaviour and environmental factors may influence their exposure to hunting mortality. Hunting activity may also reduce the access to food resources which may be limited in the wintering areas, thereby affecting winter survival. In this study we assessed the possible influence of food resources, weather conditions, inter-specific competition and hunting intensity (as a measure of possible disturbance) on abundance and distribution of pink-footed geese Anser brachyrhynchus at their main autumn stopover site in Norway. The results show that food resources in term of spilt cereal grain were abundant, even by the time the geese had moved on. Snow cover did not limit the food availability during the main migratory period. Inter-specific competition with greylag geese Anser anser reduced food supplies locally and appeared to be increasing. Goose hunting intensity varied among sites and our data indicate a negative relationship between hunting intensity and the rate at which geese consumed the food resources. Collectively, our results suggest that the majority of pink-footed geese leave the stopover area earlier than they would otherwise, when hunting intensities are high. In the case of pink-footed geese, population consequences of disturbance is not a concern at present; however, an international species management plan calls for 1) keeping disturbance low in areas where geese do not cause conflicts with agriculture to prevent them being pushed to areas with problems, and 2) increased harvest to reduce and stabilise the population size. Both objectives can be met by reducing hunting disturbance in mid-Norway and it is recommended that a better local organisation of hunting is implemented.

The dilemma of where to nest: influence of spring snow cover, food proximity and predator abundance on reproductive success of an arctic-breeding migratory herbivore is dependent on nesting habitat choice

Abstract Pink-footed geese Anser brachyrhynchus nest in two contrasting but commonly found habitats: steep cliffs and open tundra slopes. In Svalbard, we compared nest densities and nesting success in these two environments over ten breeding seasons to assess the impact of spring snow cover, food availability to nesting adults and arctic fox Vulpes lagopus (main terrestrial predator) abundance. In years with extensive spring snow cover, fewer geese at both colonies attempted to breed, possibly because snow cover limited pre-nesting feeding opportunities, leaving adults in poor breeding condition. Nesting success at the steep cliff colony was lower with extensive spring snow cover; such conditions force birds to commit to repeated and prolonged recess periods at far distant feeding areas, leaving nests open to predation. By contrast, nesting success at the open tundra slope was not affected by spring snow cover; even if birds were apparently in poor condition they could feed immediately adjacent to their nests and defend them from predators. Foxes were the main nest predator in the open tundra slopes but avian predators likely had a larger impact at the steep cliffs colony. Thus, the relative inaccessibility of the cliffs habitat may bring protection from foxes but also deprives geese from readily accessing feeding areas, with the best prospects for successful nesting in low spring snow cover years. Our findings indicate that spring snow cover, predator abundance and food proximity did not uniformly influence nesting success of this herbivore, and their effects were dependent on nesting habitat choice.

Landscape selection by migratory geese: Implications for hunting organisation

Over the last decades, many wild goose populations have increased significantly and are now causing conflicts with socioeconomic and biological interests. To mitigate impacts of rapid population increases, population control by increasing harvest has been attempted. In this study we seek to guide the design of a regional autumn goose hunting organisation in agricultural landscapes by identifying areas suitable for hunting, which have high probability of occurrence of pink-footed geese Anser brachyrhynchus and/or a short return time by geese to fields subject to hunting. To identify areas suitable for hunting in Nord-Trøndelag County, mid-Norway, we used species distributions models (SDMs), a broadly accepted tool in conservation planning for spatial refuge organisation. The prediction was that the highest probability of goose occurrence exists for large fields, away from small roads and near water bodies serving as safe roosting sites. Additionally, return time was predicted to be shortest for large fields near roosting sites and away from big roads. A combined map of goose occurrence and return time showed similar prediction for high goose occurrence and short return time; hence areas most suitable for hunting are large fields, close to roost sites and away from roads. If hunters and landowners are willing to coordinate goose hunting at a landscape level, they can use the prediction maps as guidance, with the likely benefit that they collectively can shoot more geese. Such local and regional organisation can become a powerful tool in the harvest management of geese.