Interspecific comparison of the fecal microbiota structure in three Arctic migratory bird species

The gut microbiota of birds is known to be characterized for different species, although it may change with feeding items. In this study, we compared the gut microbiota of birds with different feeding behaviors in the same habitat. We collected fecal samples from three Arctic species, snow buntings Plectrophenax nivalis, sanderlings Calidris alba, and pink‐footed geese Anser brachyrhynchus that are phylogenetically quite distant in different families to evaluate effects of diet on gut microbiota. Also, we characterized the prevalence of fecal bacteria using the Illumina MiSeq platform to sequence bacterial 16S rRNA genes. Our NMDS results showed that fecal bacteria of snow buntings and sanderlings were significantly distant from those of pink‐footed geese. Although all three birds were occupied by three bacterial phyla, Proteobacteria, Firmicutes, and Bacteroidetes, dominant taxa still varied among the species. Our bacterial sequences showed that snow buntings and sanderlings were dominated by Firmicutes and Bacteroidetes, while pink‐footed geese were dominated by Proteobacteria. In addition, the bacterial diversity in snow buntings and sanderlings was significantly higher than that in pink‐footed geese. Our results suggest that insectivorous feeding diet of snow buntings and sanderlings could be responsible for the similar bacterial communities between the two species despite the distant phylogenetic relationship. The distinctive bacterial community in pink‐footed geese was discussed to be related with their herbivorous diet.     

Distribution and Habitat Use of Ross's and Lesser Snow Geese During Late Brood Rearing

ABSTRACT We assessed spatial distribution and habitat use by Ross's and lesser snow geese (Chen rossii and C. caerulescens caerulescens) during late brood rearing to begin understanding goose-habitat interactions and monitoring key habitats around a rapidly growing nesting colony located at Karrak Lake, Nunavut, Canada. We conducted aerial surveys to count geese and georeference locations, then used Landsat Thematic Mapper satellite imagery to identify habitats associated with each flock. We observed 435 and 407 flocks and 36,287 and 32,745 birds in 1994 and 1995, respectively. Birds were somewhat uniformly distributed over the 5,000-km² study area, with larger aggregations occurring closer to the coast, about 70 km from the colony. We assessed habitat use using Bonferroni intervals at both the flock and individual scales. At the flock level, birds avoided lichen-heath, used other terrestrial habitats as available, and selected freshwater. At the individual level, geese selected lowland habitats: wet sedge meadow, hummock graminoid tundra, and freshwater, which accounted for about 70% of the birds observed, and avoided upland habitats. Selection of lowland habitats is likely due to greater availability of food and easier predator avoidance compared to drier upland areas. Because most geese in our study used freshwater habitats, our results demonstrate that assessment of carrying capacity, at least in the central Arctic, must be expanded beyond the coastal salt marshes traditionally considered by researchers and managers as primary brood-rearing habitat for mid-continent light geese.     

Using habitat selection theories to predict the spatiotemporal distribution of migratory birds during stopover – a case study of pink‐footed geese Anser brachyrhynchus

Understanding how animals select for habitat and foraging resources therein is a crucial component of basic and applied ecology. The selection process is typically influenced by a variety of environmental conditions including the spatial and temporal variation in the quantity and quality of food resources, predation or disturbance risks, and inter‐ and intraspecific competition. Indeed, some of the most commonly employed ecological theories used to describe how animals choose foraging sites are: nutrient intake maximisation, density‐dependent habitat selection, central‐place foraging, and predation risk effects. Even though these theories are not mutually exclusive, rarely are multiple theoretical models considered concomitantly to assess which theory, or combination thereof, best predicts observed changes in habitat selection over space and time. Here, we tested which of the above theories best‐predicted habitat selection of Svalbard‐breeding pink‐footed geese at their main spring migration stopover site in mid‐Norway by computing a series of resource selection functions (RSFs) and their predictive ability (k‐fold cross validation scores). At this stopover site geese fuel intensively as a preparation for breeding and further migration. We found that the predation risk model and a combination of the density‐dependent and central‐place foraging models best‐predicted habitat selection during stopover as geese selected for larger fields where predation risk is typically lower and selection for foraging sites changed as a function of both distance to the roost site (i.e. central‐place) and changes in local density. In contrast to many other studies, the nutritional value of the available food resources did not appear to be a major limiting factor as geese used different food resources proportional to their availability. Our study shows that in an agricultural landscape where nutritional value of food resources is homogeneously high and resource availability changes rapidly; foraging behaviour of geese is largely a tradeoff between fast refuelling and disturbance/predator avoidance.     

Breeding dispersal in a heterogeneous landscape: the influence of habitat and nesting success in greater snow geese

Despite numerous studies on breeding dispersal, it is still unclear how habitat heterogeneity and previous nesting success interact to determine nest-site fidelity at various spatial scales. In this context, we investigated factors affecting breeding dispersal in greater snow geese (Anser caerulescens atlanticus), an Arctic breeding species nesting in two contrasting habitats (wetlands and mesic tundra) with variable pattern of snowmelt at the time of settlement in spring. From 1994 to 2005, we monitored the nesting success and breeding dispersal of individually marked females. We found that snow geese showed a moderate amount of nest-site fidelity and considerable individual variability in dispersal distance over consecutive nesting attempts. This variability can be partly accounted for by the annual timing of snowmelt. Despite this environmental constraint, habitat differences at the colony level consistently affected nesting success and settlement patterns. Females nesting in wetlands had higher nesting success than those nesting in mesic tundra. Moreover, geese responded adaptively to spatial heterogeneity by showing fidelity to their nesting habitat, independently of snowmelt pattern. From year to year, geese were more likely to move from mesic to high-quality wetland habitat, regardless of previous nesting success and without cost on their subsequent nesting performance. The unpredictability of snowmelt and the low cost of changing site apparently favour breeding-site dispersal although habitat quality promotes fidelity at the scale of habitat patches.     

Do foraging methods in winter affect morphology during growth in juvenile snow geese?

Physical exertion during growth can affect ultimate size and density of skeletal structures. Such changes from different exercise regimes may explain morphological differences between groups, such as those exhibited by lesser snow geese (Chen caerulescens caerulescens; hereafter snow geese) foraging in southwest Louisiana. In rice‐prairie habitats (hereafter rice‐prairies), snow geese bite off or graze aboveground vegetation, whereas they dig or grub for subterranean plant parts in adjacent coastal marshes. Grubbing involves considerably more muscular exertion than does grazing. Thus, we hypothesized that rates of bone formation and growth would be lower for juveniles wintering in rice‐prairies than those in coastal marshes, resulting in smaller bill and skull features at adulthood. First, we tested this exertion hypothesis by measuring bills, skulls, and associated musculature from arrival to departure (November–February) in both habitats in southwest Louisiana, using both banded birds and collected specimens. Second, we used the morphological data to test an alternative hypothesis, which states that smaller bill dimensions in rice‐prairies evolved because of hybridization with Ross's geese (C. rossii). Under the exertion hypothesis, we predicted that bill and skull bones of juveniles would grow at different rates between habitats. However, we found that bill and skull bones of juveniles grew similarly between habitats, thus failing to support the exertion hypothesis. Morphometrics were more likely to differ by sex or change with sampling date than to differ by habitat. We predicted that significant, consistent skewness toward smaller birds could indicate hybridization with Ross's geese, but no skewness was observed in our morphological data, which fails to support the hybridization hypothesis. Further research is needed to clarify whether snow geese wintering in Louisiana represent a single polymorphic population that segregates into individually preferred habitats, which we believe at present to be more likely as an explanation than two ecologically and spatially distinct morphotypes.     

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

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.     

Resource partitioning in sympatric arctic-breeding geese: summer habitat use, spatial and dietary overlap of Barnacle and Pink-footed Geese in Svalbard

The spatial, habitat and dietary overlap of two breeding goose species was studied in Sassendalen, Svalbard, in summer 2003 based on abundance within 500 × 500‐m grid squares and faecal diet analyses during pre‐breeding, nesting and post‐hatching periods. More than half of all Pink‐footed Geese Anser brachyrhynchus occurred in the absence of Barnacle Geese Branta leucopsis during nesting and post‐hatching periods compared to c. 20% when concentrated by pre‐breeding snow cover. In contrast, only 5% of Barnacle Geese were observed in the absence of Pink‐footed Geese pre‐breeding, 15% during nesting, and 35% post‐hatching. Among six defined habitat types, Barnacle Geese resorted more to ‘upland’ habitats during pre‐breeding and nesting and to lowland lakes post‐hatching when compared to Pink‐footed Geese. Although Pink‐footed Geese showed less change in seasonal habitat preference, many shifted to the river valley bottom post‐hatching, giving access to open water (predator avoidance) and lush green vegetation (foraging for goslings). The smallest extent of distributional overlap between the two species occurred post‐hatching, but each species was also highly restricted by snow cover during pre‐nesting. The greatest extent of overlap in distribution and diet occurred during incubation, when large dietary variation between different breeding valleys reflected local food availability around nests (probably a result of nest‐site preference rather than food selection per se). Whether this means that increased interactions within and between the two goose species with future increases in local density are most likely to be manifest at this stage of the summer is impossible to determine without knowledge of available food resources and manipulative experiments. More detailed investigations of the effects of foraging by both species on plant structure, quality and community composition are necessary to predict likely outcomes of future changes in population densities of both species.     

Predicting Habitat Utilization and Extent of Ecosystem Disturbance by an Increasing Herbivore Population

Herbivory can lead to shifts in ecosystem state or changes in ecosystem functioning, and recovery from herbivory is particularly slow in disturbance-sensitive ecosystems such as arctic tundra. Herbivore impacts on ecosystems are variable in space and time due to population fluctuations and selective utilization of habitats; thus there is a need to accurately predict herbivore impacts at the landscape scale. The habitat utilization and extent of disturbance caused by increasing populations of pink-footed geese (Anser brachyrhynchus) foraging in the high arctic tundra of Svalbard were assessed using a predictive model of the population’s habitat use. Pink-footed geese arrive in Svalbard in early spring when they forage for belowground plant parts; this foraging (called grubbing) can cause vegetation loss and soil disturbance. Surveys of the extent and intensity of grubbing were carried out to develop predictive models that were subsequently tested against data collected during the following year from different areas. Both habitat type at a particular point and the amount of preferred fen habitat in the surrounding area were powerful predictors of grubbing likelihood and the developed model correctly classified over 69% of validation observations with an AUC of 0.75. Pink-footed geese showed a strong preference for wetter habitats within low-lying landscapes. Extrapolation of the predictive model across the archipelago showed that a maximum potential area of 2300 km² (3.8% of the archipelago) could be disturbed by grubbing. Thus, increasing populations of geese may cause large-scale vegetation loss and soil disturbance in arctic ecosystems.     

Gray-brown Mouse Lemurs (<Emphasis Type="Italic">Microcebus griseorufus</Emphasis>) as an Example of Distributional Constraints through Increasing Desertification

Climate change will impose new constraints on the distribution of species through desertification. Small-scale endemists common in biodiversity hotspots such as Madagascar are especially threatened. Among them are the gray-brown mouse lemurs (Microcebus griseorufus), which occupy the driest habitats in Madagascar of all Microcebus spp. We studied impacts of aridity on this species to identify critical factors for distributional limits. Accordingly, we compared populations of 2 adjacent habitats that differ in their humidity levels. We found that the more humid habitat provided more high-quality food and maintained a higher population density of Microcebus griseorufus, with individuals in better condition compared to the drier habitat. At the end of the wet, but not in the dry season, Microcebus griseorufus adjusted its home range size to local food plant density, which indicates that individuals optimize food intake in the wet season to prepare for the dry season. We found a negative exponential relationship between food plant density and home range size, which suggests an upper limit for the size of home ranges. According to this relationship, individuals from the drier habitat could not compensate for reduced food availability by enlarging their home range beyond this threshold. Thus, in case of declining food availability during the wet season due to a generally drier climate, individuals will not be able to extend their home ranges to include more food resources, and hence to accumulate enough fat reserves for the dry season. In consequence, they will have to migrate toward more mesic refugia. Migration, however, requires habitat connectivity, which is scarce in Madagascar’s largely anthropogenic and heavily fragmented landscape. Our data suggest that upper limits in home range sizes can limit a species’ ability to adapt to increasing aridity.     

Effects of agricultural change on abundance, fitness components and distribution of two arctic-nesting goose populations

Intensification of agriculture since the 1950s has enhanced the availability, competitive ability, crude protein content, digestibility and extended growing seasons of forage grasses. Spilled cereal grain also provides a rich food source in autumn and in winter. Long‐distance migratory herbivorous geese have rapidly exploited these feeding opportunities and most species have shown expansions in range and population size in the last 50 years. Results of long‐term studies are presented from two Arctic‐breeding populations, the Svalbard pink‐footed goose and the Greenland white‐fronted goose (GWFG). GWFGs have shown major habitat shifts since the 1950s from winter use of plant storage organs in natural wetlands to feeding on intensively managed farmland. Declines in local density on, and abandonment of, unmodified traditional wintering habitat and increased reproductive success among those birds wintering on farmland suggest that density‐dependent processes were not the cause of the shift in this winter‐site‐faithful population. Based on enhanced nutrient and energy intake rates, we argue that observed shifts in both species from traditionally used natural habitats to intensively managed farmland on spring staging and wintering areas have not necessarily been the result of habitat destruction. Increased food intake rates and potential demographic benefits resulting from shifts to highly profitable foraging opportunities on increasingly intensively managed farmland, more likely explain increases in goose numbers in these populations. The geographically exploratory behaviour of subdominant individuals enables the discovery and exploitation of new winter feeding opportunities and hence range expansion. Recent destruction of traditional habitats and declines in farming at northern latitudes present fresh challenges to the well being of both populations. More urgently, Canada geese colonizing breeding and moulting habitats of white‐fronted geese in Greenland are further affecting their reproductive output.     

Elk winter foraging at fine scale in Yellowstone National Park

The link between landscape properties and foraging decisions by herbivores remains unclear, but such knowledge is central to the understanding of plant–herbivore dynamics. Our goal was to determine whether fine-scale foraging paths of free-ranging elk (Cervus canadensis) respond to spatial structure of habitats in Yellowstone National Park. During winter 2002 we gathered elk-foraging information by following snow tracks in open habitats located on hillsides and flat terrain. The 21 snow paths surveyed were comprised on average of 15 discrete snow craters connected to each other by relatively straight-line movements. Our analyses revealed two levels of selection: elk chose where to dig, and how much search effort to allocate at digging sites based on habitat characteristics. On hillsides, elk preferentially dug in areas of greater biomass of grasses and forbs, and simply walked through poorer sites without digging. Individuals also searched more intensively, creating larger craters, where food biomass was higher. On flat terrain, crater size decreased with snow depth and increased with snow density. Correlated random walk models usually were adequate to characterize elk movement on flat terrain, but not on hillsides. First, as the number of movements between local foraging areas increased, elk displacements on hillsides became shorter than expected from random patterns. This trend on hillsides was strongly influenced by interindividual variation in movement behavior. Second, elk tended to forage perpendicularly to aspect, resulting in horizontal displacements. Our study demonstrates that free-ranging elk adjust their foraging to fine-scale habitat structure.     

The Origin of Winter Visitors to the British Isles 7. Fieldfare (Turdus pilaris)

Capsule Large‐scale intensification of agricultural management during the past 50 years has resulted in a reduction of invertebrate abundance and higher and denser ground vegetation. Food availability for insectivorous birds foraging on the ground has been negatively affected, but the interactions between birds and their food availability are complex and often species‐specific. Populations of Wrynecks Jynx torquilla are declining all over Europe, possibly because of reduced accessibility to their main prey, ground‐dwelling ants, due to higher and denser ground vegetation. However, it is not clear which ground vegetation structures are tolerated by foraging Wrynecks and which habitats are preferred.

Aims To identify the optimal ground vegetation structure and the main habitat types in which Wrynecks search for food.

Method We radiotracked seven Wrynecks in high‐intensity farmland in Switzerland to study foraging habitat use during the reproduction season. Several habitat variables were mapped at each foraging location and compared with locations selected randomly within individual home ranges.

Results Wrynecks preferentially foraged at places with ≥50% bare ground. Vegetation height was not important. Older fruit tree plantations and fallow land were the preferred foraging habitats.

Conclusion Conservation measures should concentrate on preserving semi‐open agricultural landscape matrices with loose ground vegetation cover to provide suitable foraging conditions. This can be achieved even in intensively managed farmland as illustrated in this study.     

Spring feeding by pink-footed geese reduces carbon stocks and sink strength in tundra ecosystems

Tundra ecosystems are widely recognized as precious areas and globally important carbon (C) sinks, yet our understanding of potential threats to these habitats and their large soil C store is limited. Land‐use changes and conservation measures in temperate regions have led to a dramatic expansion of arctic‐breeding geese, making them important herbivores of high‐latitude systems. In field experiments conducted in high‐Arctic Spitsbergen, Svalbard, we demonstrate that a brief period of early season belowground foraging by pink‐footed geese is sufficient to strongly reduce C sink strength and soil C stocks of arctic tundra. Mechanisms are suggested whereby vegetation disruption due to repeated use of grubbed areas opens the soil organic layer to erosion and will thus lead to progressive C loss. Our study shows, for the first time, that increases in goose abundance through land‐use change and conservation measures in temperate climes can dramatically affect the C balance of arctic tundra.     

Foraging behaviour and fuel accumulation of capital breeders during spring migration as derived from a combination of satellite‐ and ground‐based observations

The migration strategy of many capital breeders is to garner body stores along the flyway at distinct stopover sites. The rate at which they can fuel is likely to be strongly influenced by a range of factors, such as physiology, food availability, time available for foraging and perceived predation. We analysed the foraging behaviour and fuel accumulation of pink‐footed geese, an Arctic capital breeder, at their mid‐flyway spring stopover site and evaluated to what extent their behaviour and fuelling were related to physiological and external factors and how it differed from other stopovers along the flyway. We found that fuel accumulation rates of geese at the mid‐flyway site were limited by habitat availability rather than by digestive constraints. However, as the time available for foraging increased over the stopover season, geese were able to keep constant fuelling rate. Putting this in perspective, geese increased their daily net energy intake along the flyway corresponding to the increase in time available for foraging. The net energy intake per hour of foraging remained the same. Geese showed differences in their reaction to predators/disturbance between the sites, taking higher risks particularly at the final stopover site. Hence, perceived predation along the flyway may force birds to postpone the final fuel accumulation to the last stopover along the flyway. Flexibility in behaviour appears to be an important trait to ensure fitness in this capital breeder. Our findings are based on a new, improved method for estimating fuel accumulation of animals foraging in heterogeneous landscapes based on data obtained from satellite telemetry and habitat specific intake rates.     

Habitat and introduced predators influence the occupancy of small threatened macropods in subtropical Australia

Australia has had the highest rate of mammal extinctions in the past two centuries when compared to other continents. Frequently cited threats include habitat loss and fragmentation, changed fire regimes and the impact of introduced predators, namely the red fox (Vulpes vulpes) and the feral cat (Felis catus). Recent studies suggest that Australia's top predator, the dingo (Canis dingo), may have a suppressive effect on fox populations but not on cat populations. The landscape of fear hypothesis proposes that habitat used by prey species comprises high to low risk patches for foraging as determined by the presence and ubiquity of predators within the ecosystem. This results in a landscape of risky versus safe areas for prey species. We investigated the influence of habitat and its interaction with predatory mammals on the occupancy of medium‐sized mammals with a focus on threatened macropodid marsupials (the long‐nosed potoroo [Potorous tridactylous] and red‐legged pademelon [Thylogale stigmatica]). We assumed that differential use of habitats would reflect trade‐offs between food and safety. We predicted that medium‐sized mammals would prefer habitats for foraging that reduce the risk of predation but that predators would have a positive relationship with medium‐sized mammals. We variously used data from 298 camera trap sites across nine conservation reserves in subtropical Australia. Both dingoes and feral cats were broadly distributed, whilst the red fox was rare. Long‐nosed potoroos had a strong positive association with dense ground cover, consistent with using habitat complexity to escape predation. Red‐legged pademelons showed a preference for open ground cover, consistent with a reliance on rapid bounding to escape predation. Dingoes preferred areas of open ground cover whereas feral cats showed no specific habitat preference. Dingoes were positively associated with long‐nosed potoroos whilst feral cats were positively associated with red‐legged pademelons. Our study highlights the importance of habitat structure to these threatened mammals and also the need for more detailed study of their interactions with their predators.     

Nitrogen Depletion and Redistribution by Free‐Ranging Cattle in the Restoration Process of Mosaic Landscapes: The Role of Foraging Strategy and Habitat Proportion

In a mosaic landscape in N‐Belgium (W‐Europe), consisting of forest, grassland, and wooded pasture on former agricultural land, we assessed nitrogen redistribution by free‐ranging cattle (±0.2 animal units ha^?1 yr^?1). We examined if the spatial redistribution of nitrogen among habitats by cattle could restore nutrient‐poor conditions in preferred foraging habitats, and conversely whether such translocation could lead to extreme eutrophication in preferred resting habitats. We used nitrogen content of different diet classes, habitat use, foraging and defecation behavior, weight gain, and nitrogen losses in the actual situation to explore four different habitat proportion scenarios and two different foraging strategies to calculate a net nitrogen balance per habitat. An atmospheric deposition of 30 kg N ha^?1 yr^?1 with varying interception factors according to the habitat types was included in an integrated nitrogen balance. All scenarios showed a net nitrogen transport from grassland and wooded pasture to forest habitat. We found that nitrogen redistribution strongly depends on habitat proportion. Nitrogen losses from preferred grassland habitat can be high, given its proportion is small. Depletion is only to be expected at excretion‐free areas and probably is of minor importance to trigger the establishment of woody species. In general, nitrogen transported by cattle was much lower than input by atmospheric deposition, but grazing can compensate for high N inputs in excretion‐free areas and maintain grassland types that support critical loads of 20–25 kg N ha^?1 yr^?1. In none of the scenarios, N transport by cattle resulted in the exceeding of critical nitrogen loads to vulnerable forest ground vegetation.     

Identifying key habitats for the conservation of Bonelli's Eagle Aquila fasciata using radiotracking

Identifying the priority habitats of endangered species is crucial to implementing effective conservation actions. We characterize the key habitats used by Bonelli's Eagle Aquila fasciata, an umbrella and flagship species that is endangered in Mediterranean countries. We radiotracked 17 breeding individuals (10 males and seven females) in Catalonia (NE Iberian Peninsula) and used compositional analysis to determine the key habitats in home‐ranges of both sexes. The main habitats identified within the home‐range area were scrubland, coniferous forests, cropland, sclerophyllous forests, rock outcrops and urban areas, with little difference in habitat use between the sexes. Bonelli's Eagles preferred rocky habitats as breeding areas and scrubland as foraging areas, as these hold the highest abundance of their main prey, Rabbits Oryctolagus cuniculus and Red‐legged Partridges Alectoris rufa. Habitat selection varied seasonally in foraging areas: scrubland was the most preferred habitat type during the breeding season, whereas rocky areas were preferred during the non‐breeding season (although scrubland was also highly selected). Urban areas were avoided both as breeding and as foraging areas. Home‐range size was inversely correlated with the proportion of scrubland, suggesting that this is a key habitat for Bonelli's Eagle. To conserve this species effectively, policies that ensure the preservation of the cliffs used as breeding sites, as well as suitable management of the scrubland used for foraging, should be implemented in the areas inhabited by this species. The promotion of traditional land uses and management techniques that will enhance open areas in Mediterranean landscapes should in the future play an essential role in the conservation of Bonelli's Eagle in Mediterranean habitats.     

锡林河河漫滩草甸群落的结构与生产力及其排序

 锡林河河漫滩主要草甸群落的植物组成、群落构成规律、地上植物量、群落间生态关系的研究表明：1)踏头草甸以中间型荸荠(Eleocharis intersita)、无脉苔草(Carex enervis)、巨序剪股颖(Agrostis gigantea)和湿中生杂类草共同建群,其地上植物量为445.64gDM·m-2,是该区草原群落的2—4倍;密花凤毛菊(Saussurea acuminata)杂类草草甸的地上植物量为3584.50gFM·m-2(鲜重);马蔺(Iris lactea)杂类草草甸的地上现存量为1444.02gFM·m-2(鲜重)。2)与该区草原群落相比,草甸群落或没有单种建群植物,或单种建群植物的作用不很突出。说明了草甸优越的生境可满足多种植物共同充分生长。3)河漫滩不同草甸群落的排序表明：在积水生境中沼泽植被的外围、较为湿润的地段上分布着以莎草科植物为主的莎草(苔草)草甸;中度湿润的地段分布着以禾本科植物为主的禾草草甸;而相对较干的地段分布着以双子叶植物为主的杂类草草甸。     

Changes in abundance and spatial distribution of geese molting near Teshekpuk Lake,Alaska: interspecific competition or ecological change?

Goose populations molting in the Teshekpuk Lake Special Area of the National Petroleum Reserve—Alaska have changed in size and distribution over the past 30 years. Black brant (Branta bernicla nigricans) are relatively stable in numbers but are shifting from large, inland lakes to salt marshes. Concurrently, populations of greater white-fronted geese (Anser albifrons frontalis) have increased seven fold. Populations of Canada geese (Branta canadensis and/or B. hutchinsii) are stable with little indication of distributional shifts. The lesser snow goose (Anser caerulescens caerulescens) population is proportionally small, but increasing rapidly. Coastline erosion of the Beaufort Sea has altered tundra habitats by allowing saltwater intrusion, which has resulted in shifts in composition of forage plant species. We propose two alternative hypotheses for the observed shift in black brant distribution. Ecological change may have altered optimal foraging habitats for molting birds, or alternatively, interspecific competition between black brant and greater white-fronted geese may be excluding black brant from preferred habitats. Regardless of the causative mechanism, the observed shifts in species distributions are an important consideration for future resource planning.     

Predator behaviour and predation risk in the heterogeneous Arctic environment

1. Habitat heterogeneity and predator behaviour can strongly affect predator-prey interactions but these factors are rarely considered simultaneously, especially when systems encompass multiple predators and prey. 2. In the Arctic, greater snow geese Anser caerulescens atlanticus L. nest in two structurally different habitats: wetlands that form intricate networks of water channels, and mesic tundra where such obstacles are absent. In this heterogeneous environment, goose eggs are exposed to two types of predators: the arctic fox Vulpes lagopus L. and a diversity of avian predators. We hypothesized that, contrary to birds, the hunting ability of foxes would be impaired by the structurally complex wetland habitat, resulting in a lower predation risk for goose eggs. 3. In addition, lemmings, the main prey of foxes, show strong population cycles. We thus further examined how their fluctuations influenced the interaction between habitat heterogeneity and fox predation on goose eggs. 4. An experimental approach with artificial nests suggested that foxes were faster than avian predators to find unattended goose nests in mesic tundra whereas the reverse was true in wetlands. Foxes spent 3.5 times more time between consecutive attacks on real goose nests in wetlands than in mesic tundra. Their attacks on goose nests were also half as successful in wetlands than in mesic tundra whereas no difference was found for avian predators. 5. Nesting success in wetlands (65%) was higher than in mesic tundra (56%) but the difference between habitats increased during lemming crashes (15%) compared to other phases of the cycle (5%). Nests located at the edge of wetland patches were also less successful than central ones, suggesting a gradient in accessibility of goose nests in wetlands for foxes. 6. Our study shows that the structural complexity of wetlands decreases predation risk from foxes but not avian predators in arctic-nesting birds. Our results also demonstrate that cyclic lemming populations indirectly alter the spatial distribution of productive nests due to a complex interaction between habitat structure, prey-switching and foraging success of foxes.