Summary1 Herbivores may initiate small changes to plant-soil systems that trigger positive feedbacks leading to rapid catastrophic shifts in vegetative states, including irreversible changes in soil properties. In the coastal marshes of Hudson and James bays, foraging by increasing numbers of lesser snow geese ( Chen caerulescens caerulescens A.O.U.) has led to loss of vegetation, and exposure and partial erosion of sediment. 2 Multi-temporal analysis of LANDSAT data has been carried out to detect vegetation change from 1973 to 1999 or later at nine sites in the coastal marshes of these bays where staging and/or breeding geese are present annually. 3 Images were co-registered, and for each image NDVI (Normalized Differential Vegetation Index) channels were generated. For each location, pairwise normalized differences were calculated between these NDVI images for each successive period defined by the imagery acquisition dates. The resulting secondary NDVI difference images expressed changes in NDVI values for each time interval and yielded three well-defined classes: water, vegetation decline and no detectable change in vegetation. 4 At the nine widely separated study sites, the intertidal saltmarsh (an ecological sere) has been lost (to a total of 35 000 ha) and an alternative stable state (exposed sediment) established. Similar changes have occurred elsewhere along the 2000-km coastline where the geese breed or stage. 5 Re-vegetation of these coastal marshes will take decades because of near-irreversible changes in soil properties that require erosion and re-deposition of unconsolidated sediment before large-scale plant colonization can occur, and because large numbers of geese continue to forage annually producing this dramatic top-down effect.

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Quantifying the costs and benefits of migration distance is critical to understanding the evolution of long-distance migration. In migratory birds, life history theory predicts that the potential survival costs of migrating longer distances should be balanced by benefits to lifetime reproductive success, yet quantification of these reproductive benefits in a controlled manner along a large geographical gradient is challenging. We measured a controlled effect of predation risk along a 3350-kilometer south-north gradient in the Arctic and found that nest predation risk declined more than twofold along the latitudinal gradient. These results provide evidence that birds migrating farther north may acquire reproductive benefits in the form of lower nest predation risk.

The Mid-Continent Population of the lesser snow goose, which breeds in the eastern and central Canadian Arctic and sub-Arctic, and winters in the southern United States and northern Mexico has increased 5-7% annually from the late 1960s to the mid-1990s, largely because of increased survival in response to an agricultural food subsidy. The rise in numbers complements the increased use of nitrogen fertilizers and a corresponding rise in yields of rice, corn, and wheat along the flyways and on the wintering grounds. In sub-Arctic migration areas and at Arctic breeding colonies, foraging by high numbers of birds has led to loss of coastal vegetation, adverse changes in soil properties and the establishment of an alternative stable state of exposed sediment, which can be detected with LANDSAT imagery. At a local scale, gosling growth, size and survival decreased in affected areas and other taxa have been adversely affected. The food subsidy on wintering and migration areas appears insufficient to meet reproductive demands as foraging in spring continues to occur on southern Hudson Bay staging and nesting areas. The recent introduction of liberal hunting regulations may reduce population size in the near term, but the revegetation of these coastal ecosystems will take decades to achieve. The present pattern of vegetation loss in these Arctic coastal systems is likely to continue in the forseeable future.

The energy and nutrient content of most agricultural crops are as good as or superior to natural foods for wild geese and they tend to be available in agricultural landscapes in far greater abundance. Artificial grasslands (fertilised native swards and intensively managed reseeds) offer far superior quality forage and higher intake rates than seminatural or natural grasslands. The availability of such abundant artificial food explains the abandonment of traditional habitats for farmland by geese over the last 50–100 years and favours no reduction in current levels of exploitation of agriculture. Continental scale spatial and temporal shifts among geese undergoing spring fattening confirm their flexibility to respond rapidly to broadscale changes in agriculture. These dramatic changes support the hypothesis that use of agricultural landscapes has contributed to elevated reproductive success and that European and North American farmland currently provides unrestricted winter carrying capacity for goose populations formerly limited by wetlands habitats prior to the agrarian revolution of the last century.

Agriculture has provided a nutritional subsidy to the Anatidae (swans, geese, ducks), which has affected their trophic relationships and the Arctic wetlands where they breed. The Mid-Continent Population of lesser snow geese, which breeds in the Canadian Arctic and which traditionally wintered in the coastal marshes of the Gulf States, now feeds in agricultural landscapes. The geometric growth of this population since 1970 is coincident with increased application of nitrogen to farmland and high crop yields. Widespread availability of agricultural foods allows the birds to meet much of their energy demand for migration and reproduction. Their migration conforms to a stepping stone model linked to land use, but feeding also takes place upon arrival on the Arctic breeding grounds. High bird numbers have dramatically affected coastal marshes of the Canadian Arctic. Foraging has produced alternative stable states characterized by sward destruction and near irreversible changes in soil properties of exposed sediments. Locally, this loss of resilience has adversely affected different groups of organisms, resulting in an apparent trophic cascade. A spring hunt was introduced in 1999 in an attempt to check population growth. The current annual cull is now thought to be higher than the replacement rate. Much of the decline of the Mid-Continent Population is probably linked to shooting, but the harassment of birds that fail to acquire sufficient food for reproduction may contribute. The agricultural food subsidy has led to a mismatch between this avian herbivore and its environment — a consequence of migratory connectivity that links wintering and breeding grounds. Key words: agricultural crops, lesser snow geese, migratory connectivity, Arctic coastal marshes, grubbing, hypersalinity, the spring hunt.

Sea ice is declining over much of the Arctic. In Hudson Bay the ice melts completely each summer, and advances in break-up have resulted in longer ice-free seasons. Consequently, earlier break-up is implicated in declines in body condition, survival, and abundance of polar bears (Ursus maritimus Phipps, 1774) in the Western Hudson Bay (WH) subpopulation. We hypothesised that similar patterns would be evident in the neighbouring Southern Hudson Bay (SH) subpopulation. We examined trends 1980–2012 in break-up and freeze-up dates within the entire SH management unit and within smaller coastal break-up and freeze-up zones. We examined trends in body condition for 900 bears captured during 1984–1986, 2000–2005, and 2007–2009 and hypothesised that body condition would be correlated with duration of sea ice. The ice-free season in SH increased by about 30 days from 1980 to 2012. Body condition declined in all age and sex classes, but the decline was less for cubs than for other social classes. If trends towards a longer ice-free season continue in the future, further declines in body condition and survival rates are likely, and ultimately declines in abundance will occur in the SH subpopulation.

The salt marshes at La Pérouse Bay, Manitoba, are described. Unconsolidated, water-saturated sediment is colonized by Hippuris tetraphylla, Puccinellia phryganodes, and Carex subspathacea. These sediments undergo frost heave, and on elevated mounds, Elymus arenarius var. mollis and Salix brachycarpa become established. This last species is the dominant one of the low willow tundra, which is the characteristic vegetation of the coastal strip. Where drainage is impeded in the upper marsh, relatively high salinities occur and species such as Salicornia europaea agg. and Triglochin maritima are present.A population of 10 000 to 20 000 lesser snow geese (Anser caerulescens) feed, in summer, on Puccinellia phryganodes, Carex subspathacea, Potentilla egedii, and Elymus arenarius var. mollis. The birds strip the shallow turf of Puccinellia in low lying areas between clumps of willow. This terracing of the surface creates depressions which become filled with water and ice. The role of geese in producing these ponds in the upper levels of salt marshes in the Arctic does not appear to have been reported previously. The ponds are subsequently colonized by Carex aquatilis and Triglochin maritima. The salt marsh gives way to an extensive fresh water marsh dominated by species of Salix, Eriophorum angustifolium, Calamagrostis neglecta, and Dupontia fisheri. The results are compared with data from other salt marshes in Hudson Bay and in the Arctic.