Occupancy Patterns of Breeding American Black Ducks

Occupancy patterns can assist with the determination of habitat limitation during breeding or wintering periods and can help guide population and habitat management efforts. American black ducks (Anas rubripes; black ducks) are thought to be limited by habitat and food availability during the winter, but breeding sites may also limit the size or growth potential of the population. The Canadian Wildlife Service conducts an annual breeding waterfowl survey that we used to explore the hypothesis that black duck carrying capacity is limited by wetlands available for breeding in Québec, Canada. We applied single-visit, multi-species occupancy models to the 1990–2015 population survey data to determine if there was evidence the black duck population was limited by breeding habitat. Using a dynamic (multi-season) occupancy modeling approach, we estimated latent occupancy (occupancy accounting for imperfect detection) of black ducks and then used latent occupancy estimates to derive occupancy, colonization, and extirpation rates. We jointly modeled the occupancy dynamics of black ducks and other duck species in wetlands where both species were present. Throughout the duration of the survey, 44% of wetlands were never observed to be occupied by black ducks. Occupancy models showed wetland size was positively associated with occupancy at the first time step (initial occupancy) and colonization. All 2-species models indicated initial black duck occupancy, persistence (continued occupancy), and colonization were positively associated with the presence of a second species. Colonization rate over the 26-year period ranged from 7% to 27% across all models. Extirpation rates were similar and were constant through time within each model. Low occupancy rates, combined with approximately equal colonization and extirpation rates, suggest there are available wetlands for breeding black ducks in their core breeding area. If breeding habitats are not saturated, this suggests migration or wintering areas may be more limiting to black duck population abundance. © 2019 The Wildlife Society.     

Effects of seasonal migration on the latitudinal distribution of west Palaearctic bird species

This paper examines seasonal changes in the latitudinal distribution of birds (excluding seabirds) that breed in the western Palaearctic. Some resident species occupy ranges that span less than 5° of latitude year-round, while some migrant species range over more than 120° of latitude during the course of a year. Among migrant species of land and freshwater habitats, the latitudinal spans of breeding and wintering ranges are correlated. In general, species that breed over a narrow span of latitude also winter over a narrow span of latitude, and vice versa. Among both groups, for any given span of breeding range, species that winter partly in Eurasia and partly in Africa winter over a wider latitudinal span than those that winter entirely within Eurasia or entirely within Africa. Among coastal birds, there is no correlation between the latitudinal spans of breeding and winter areas; most shorebird species breed over a narrow span of (northern) latitude and winter over a wide span distributed linearly along coastlines. Several migration patterns can be distinguished, from complete overlap of breeding and wintering ranges in year-round residents, through partial separation of summer and winter ranges, to complete separation of summer and winter ranges in different geographical regions. In some such species, the gap between breeding and wintering ranges spans up to 55° of latitude (6000 km).     

Environmental and demographic determinants of avian influenza viruses in waterfowl across the contiguous United States

Outbreaks of avian influenza in North American poultry have been linked to wild waterfowl. A first step towards understanding where and when avian influenza viruses might emerge from North American waterfowl is to identify environmental and demographic determinants of infection in their populations. Laboratory studies indicate water temperature as one determinant of environmental viral persistence and we explored this hypothesis at the landscape scale. We also hypothesized that the interval apparent prevalence in ducks within a local watershed during the overwintering season would influence infection probabilities during the following breeding season within the same local watershed. Using avian influenza virus surveillance data collected from 19,965 wild waterfowl across the contiguous United States between October 2006 and September 2009 We fit Logistic regression models relating the infection status of individual birds sampled on their breeding grounds to demographic characteristics, temperature, and interval apparent prevalence during the preceding overwintering season at the local watershed scale. We found strong support for sex, age, and species differences in the probability an individual duck tested positive for avian influenza virus. In addition, we found that for every seven days the local minimum temperature fell below zero, the chance an individual would test positive for avian influenza virus increased by 5.9 percent. We also found a twelve percent increase in the chance an individual would test positive during the breeding season for every ten percent increase in the interval apparent prevalence during the prior overwintering season. These results suggest that viral deposition in water and sub-freezing temperatures during the overwintering season may act as determinants of individual level infection risk during the subsequent breeding season. Our findings have implications for future surveillance activities in waterfowl and domestic poultry populations. Further study is needed to identify how these drivers might interact with other host-specific infection determinants, such as species phylogeny, immunological status, and behavioral characteristics.     

The Effect of Sea Level Rise on Dabbling Duck Energetic Carrying Capacity

Waterfowl migrating and overwintering in the Atlantic Flyway depend on adequate availability of wetland plant communities to survive winter and fuel reproduction in the subsequent breeding season. Energetics models are the primary tool employed by conservation planners to estimate energetic carrying capacity based on energy supply and demand in different wetlands to assist with effective habitat conservation. Coastal impoundments have been used to provide a consistent, annual source of energy for migrating and wintering waterfowl. But few studies have attempted to comprehensively assess the relative value of managed coastal impoundments compared with unmanaged tidal salt marshes to wintering waterfowl in the Mid-Atlantic region with further consideration to the effect of sea level rise changing availability. We estimated biomass and energy of preferred foods for 5 dabbling duck species in 7 impoundments and 3 tidal salt marshes over winter by collecting soil core (n = 1,364), nekton (n = 426), and salt marsh snail (Melampus spp.; n = 87) samples in October, January, and April 2011–2013. Food-energy density was greater in freshwater impoundments for nearly all dabbling ducks (range = 183,344–562,089 kcal/ha), and typically greater in brackish impoundments (range = 169,665–357,160 kcal/ha) than most tidal salt marsh communities (range = 55,693–361,429 kcal/ha), whereas mudflat (range = 96,223–137,473 kcal/ha) and subtidal (range = 55,693–136,326 kcal/ha) communities typically contained the least energy. Extrapolating to the state level, we estimated 7.60 × 10⁹–1.14 × 10¹⁰ kcal available within a 16-km buffer from the Delaware Bayshore, depending on species. Combining estimates for daily energy expenditure and food energy, we estimated 2.86 × 10⁷–7.06 × 10⁷ duck energy days currently available to dabbling ducks over winter. We estimated that in the next century, dabbling duck carrying capacities are likely to decrease under all but the most conservative sea level rise scenarios because of the gradual replacement of land-cover types that provide high energy density (i.e., low marsh, high marsh communities) with those that provide low energy density (i.e., subtidal, mudflat communities). Coastal impoundments in Delaware, USA, will provide increasingly important habitat for wintering dabbling ducks in the coming decades provided they are properly maintained and retain their current energetic density because they will contain a growing proportion of the available duck energy days on the landscape. Our research will assist managers in meeting target population goals for dabbling ducks in Delaware and the Mid-Atlantic region by highlighting key differences in the function and value of various wetlands. © 2021 The Wildlife Society.     

Estimating partial observability and nonlinear climate effects on stochastic community dynamics of migratory waterfowl

1. Understanding the impact of environmental variability on migrating species requires the estimation of sequential abiotic effects in different geographic areas across the life cycle. For instance, waterfowl (ducks, geese and swans) usually breed widely dispersed throughout their breeding range and gather in large numbers in their wintering headquarters, but there is a lack of knowledge on the effects of the sequential environmental conditions experienced by migrating birds on the long-term community dynamics at their wintering sites. 2. Here, we analyse multidecadal time-series data of 10 waterfowl species wintering in the Guadalquivir Marshes (SW Spain), the single most important wintering site for waterfowl breeding in Europe. We use a multivariate state-space approach to estimate the effects of biotic interactions, local environmental forcing during winter and large-scale climate during breeding and migration on wintering multispecies abundance fluctuations, while accounting for partial observability (observation error and missing data) in both population and environmental data. 3. The joint effect of local weather and large-scale climate explained 31·6% of variance at the community level, while the variability explained by interspecific interactions was negligible (<5%). In general, abiotic conditions during winter prevailed over conditions experienced during breeding and migration. Across species, a pervasive and coherent nonlinear signal of environmental variability on population dynamics suggests weaker forcing at extreme values of abiotic variables. 4. Modelling missing observations through data augmentation increased the estimated magnitude of environmental forcing by an average 30·1% and reduced the impact of stochasticity by 39·3% when accounting for observation error. Interestingly however, the impact of environmental forcing on community dynamics was underestimated by an average 15·3% and environmental stochasticity overestimated by 14·1% when ignoring both observation error and data augmentation. 5. These results provide a salient example of sequential multiscale environmental forcing in a major migratory bird community, which suggests a demographic link between the breeding and wintering grounds operating through nonlinear environmental effects. Remarkably, this study highlights that modelling observation error in the environmental covariates of an ecological model can be proportionally more important than modelling this source of variance in the population data.     

芜湖市冬夏季鸟类多样性分析

2004年5月至2005年2月,对芜湖市4种典型生境（农田居民区、城市园林、河漫滩湿地和河流湿地）的冬夏季鸟类进行调查,并探讨4种生境冬夏两季鸟类多样性指数.共记录鸟类117种,隶属于15目31科.农田居民区、城市园林和河漫滩湿地夏季鸟的种类数、G-F指数高于冬季,河流湿地冬季鸟的种类数、Shannon-Wiener指数、Pielou指数均明显高于夏季.城市园林鸟的种类数、G-F指数最高,河漫滩湿地Shannon-Wiener指数、Pielou指数最高.夏季的农田居民区和冬季的城市园林鸟类密度最大,分别为31.1140和42.9160 ind·hm^-2,而河流湿地鸟的种类数、密度、Shannon-Wiener指数、G-F指数均最低.增加栖息地异质性、减少人为干扰可以提高鸟类多样性.     

Patterns of habitat and invertebrate diet overlap between tiger salamanders and ducks in prairie potholes

During the breeding season, migratory waterfowl are attracted to wetlands characterized by high macroinvertebrate availability. Many of these prairie potholes are fishless and this apparent void is filled, at least partially, by tiger salamanders. Based on gut contents from 98 tiger salamanders and published diet data from over 1500 ducks, we show that there is general overlap in diet between both larval and adult tiger salamanders and 10 duck species. Furthermore, when the ducks were split into foraging guilds and compared with tiger salamanders, prey type overlap was 1.7 times higher and prey size was 1.8 times higher with dabbling ducks than diving ducks. Field surveys show that tiger salamander density is more highly correlated with diving duck density across potholes than dabbling duck density. Tiger salamanders have higher diet overlap with dabbling ducks than diving ducks whereas tiger salamanders have higher spatial overlap with diving ducks than dabbling ducks suggesting that these consumers coarsely partition diet and habitat resources. It has been reported that tiger salamanders have specialized diets that are associated with foraging preferences for benthic habitats. This view is too narrow: in southwestern Manitoba, Canada, tiger salamanders are more general consumers with diets more like dabbling ducks that forage mostly in planktonic and littoral habitats. Our results suggest that dabbling and diving ducks are, to different extents, liable to the effects of indirect interactions, specifically competition for common prey, with tiger salamanders.     

Seasonal variation in the range areas of the diurnal rodent Octodon degus

Both breeding activity and abundance and quality of available food are expected to influence daily movements of animals. Animals are predicted to range over large areas to meet high energy demands associated with reproduction (females) or to increase mating success (males). However, animals should expand their range areas whenever food conditions deteriorate. To examine the extent to which breeding activity versus food availability influence space use, we compared the size and location of range areas (home ranges) of the degu (Octodon degus), a diurnal rodent from semiarid environments of north-central Chile, during the austral winter and summer seasons. Degus produce young during the austral spring (September-October) when high-quality food is readily available. In contrast, degus do not breed during the austral summer (January-March) when food is scarce and of low quality. We predicted that degus would range over smaller areas in winter if the availability of food has a greater influence on space than breeding activity. Individuals were radiotracked in winter and the following summer over a 3-year period. Surveys of herbaceous cover were conducted during winter and summer to determine seasonal changes in the abundance and quality of primary food. In summer degus expanded and moved the location of their range areas to locations with available food. Given that preferred food was less abundant in summer than winter, we suggest that degu range areas are strongly influenced by food conditions.     

The influence of floodplain habitat on the quantity and quality of riverine phytoplankton carbon produced during the flood season in San Francisco Estuary

Primary productivity, community respiration, chlorophyll a concentration, phytoplankton species composition, and environmental factors were compared in the Yolo Bypass floodplain and adjacent Sacramento River in order to determine if passage of Sacramento River through floodplain habitat enhanced the quantity and quality of phytoplankton carbon available to the aquatic food web and how primary productivity and phytoplankton species composition in these habitats were affected by environmental conditions during the flood season. Greater net primary productivity of Sacramento River water in the floodplain than the main river channel was associated with more frequent autotrophy and a higher P:R ratio, chlorophyll a concentration, and phytoplankton growth efficiency (α^B). Total irradiance and water temperature in the euphotic zone were positively correlated with net primary productivity in winter and early spring but negatively correlated with net primary productivity in the late spring and early summer in the floodplain. In contrast, net primary productivity was correlated with chlorophyll a concentration and streamflow in the Sacramento River. The flood pulse cycle was important for floodplain production because it facilitated the accumulation of chlorophyll a and wide diameter diatom and green algal cells during the drain phase. High chlorophyll a concentration and diatom and green algal biomass enabled the floodplain to export 14–37% of the combined floodplain plus river load of total, diatom and green algal biomass and wide diameter cells to the estuary downstream, even though it had only 3% of the river streamflow. The study suggested the quantity and quality of riverine phytoplankton biomass available to the aquatic food web could be enhanced by passing river water through a floodplain during the flood season.     

Landscape and habitat affect frequency of artificial duck nest predation by native species,but not by an alien predator

Annual Finnish breeding duck surveys over the last 30 years show declining abundance among several species and greater declines on eutrophic waters than oligotrophic lakes. It has been suggested that habitat-related differences in the rate of increase in predation pressure is a potential explanation for contrasting duck population trajectories between habitats. We assessed potential duck nest predation risk and predator presence in various duck breeding habitats in Finland and Denmark by monitoring 333 artificial duck nests with wildlife cameras during 2017–2019. Predation rates differed between landscapes and habitats: nest predation rate and predator diversity were lowest in forested and highest in agricultural landscapes. Forest nests further from water bodies survived better than nests around shorelines of permanent lakes. Of the 16 different predator species detected, the most common were Eurasian magpie (Picapica), hooded crow (Corvus corone) and raccoon dog (Nyctereutes procyonoides). While predation by specific native predator species was typically associated with particular habitats and landscapes, the alien raccoon dog appeared to be a true habitat generalist, ubiquitous and common across all habitats and landscapes. Based on these results, the higher duck nest predation pressure along shorelines, especially in agricultural landscape lakes, due to increased diversity and abundance within the predator community, may contribute to the declining population trends of ducks.     

Possible competitive interactions between overwintering tufted duck (Aythya fuligula (L.)) and fish populations of Lough Neagh,Northern Ireland: evidence from diet studies

The overwintering population of tufted duck (Aythya fuligula) on Lough Neagh, Northern Ireland, has varied over the last three decades, with numbers declining in the early 1980s but then increasing to former levels in the late 1980s. Population fluctuations of recently introduced roach (Rutilus rutilus) mirrored these trends. The present study explores the possibility that competition for benthic food resources is responsible for these changes by examining the diets of tufted duck, roach and other major fish species of the lake. Diet overlaps were generally high due to the common consumption of chironomid larvae. The diet of tufted duck overlapped most with that of roach because these two species were the only significant consumers of molluscs. This evidence provides further support for a tufted duck — roach competition hypothesis.     

Evolution of winter molting strategies in European and North American migratory passerines

Molt is critical for birds as it replaces damaged feathers and worn plumage, enhancing flight performance, thermoregulation, and communication. In passerines, molt generally occurs on the breeding grounds during the postbreeding period once a year. However, some species of migrant passerines that breed in the Nearctic and Western Palearctic regions have evolved different molting strategies that involve molting on the overwintering grounds. Some species forego molt on the breeding grounds and instead complete their prebasic molt on the overwintering grounds. Other species molt some or all feathers a second time (prealternate molt) during the overwintering period. Using phylogenetic analyses, we explored the potential drivers of the evolution of winter molts in Nearctic and Western Palearctic breeding passerines. Our results indicate an association between longer photoperiods and the presence of prebasic and prealternate molts on the overwintering grounds for both Nearctic and Western Palearctic species. We also found a relationship between prealternate molt and generalist and water habitats for Western Palearctic species. Finally, the complete prealternate molt in Western Palearctic passerines was linked to longer days on the overwintering grounds and longer migration distance. Longer days may favor the evolution of winter prebasic molt by increasing the time window when birds can absorb essential nutrients for molt. Alternatively, for birds undertaking a prealternate molt at the end of the overwintering period, longer days may increase exposure to feather‐degrading ultra‐violet radiation, necessitating the replacement of feathers. Our study underlines the importance of the overwintering grounds in the critical process of molt for many passerines that breed in the Nearctic and Western Palearctic regions.     

Interactions between the roach,Rutilus rutilus,and waterfowl populations of Lough Neagh,Northern Ireland

Synopsis Following the introduction of roach, Rutilus rutilus, to a large eutrophic lake in ca. 1973, a subsequent increase in the abundance of this cyprinid through the 1970s was accompanied by a decline in the numbers of one of the lake&s most abundant overwintering waterfowl, the tufted duck, Aythya fuligula, and an increase in overwintering piscivorous great crested grebes, Podiceps cristatus. We suggest that these contrasting trends are causally related and that competition for benthos and increased prey availability are the mechanisms responsible for the changes in the tufted duck and grebe populations respectively. In agreement with these hypotheses, a reduction in the roach population during the mid 1980s was accompanied by a recovery of tufted ducks and a decline of grebes.     

Transmission of influenza reflects seasonality of wild birds across the annual cycle

Influenza A Viruses (IAV) in nature must overcome shifting transmission barriers caused by the mobility of their primary host, migratory wild birds, that change throughout the annual cycle. Using a phylogenetic network of viral sequences from North American wild birds (2008–2011) we demonstrate a shift from intraspecific to interspecific transmission that along with reassortment, allows IAV to achieve viral flow across successive seasons from summer to winter. Our study supports amplification of IAV during summer breeding seeded by overwintering virus persisting locally and virus introduced from a wide range of latitudes. As birds migrate from breeding sites to lower latitudes, they become involved in transmission networks with greater connectivity to other bird species, with interspecies transmission of reassortant viruses peaking during the winter. We propose that switching transmission dynamics may be a critical strategy for pathogens that infect mobile hosts inhabiting regions with strong seasonality.     

FACTORS AFFECTING THE FOOD SUPPLY AND BREEDING SEASON OF RESIDENT BIRDS AND MOVEMENTS OF PALAEARCTIC MIGRANTS IN A TROPICAL AFRICAN SAVANNAH

The fact that Palaearctic migrants arrive in the northern tropical savannah of Africa during the dry season suggests potential competition for food with African species. Moreover, in the southern tropical savannah African species breed during the rainy seasons, when Palaearctic migrants are present. In the equatorial area of Serengeti, East Africa, an index of the food supply for insectivorous birds was obtained from 3 years of light-trap measurements and sweep net samples. Adults of Lepidoptera, Coleoptera, Orthoptera and Isoptera are sparse in the dry season but become locally abundant after the first rainstorms that mark its close. They are apparently blown by converging winds ahead of the inter-tropical front and settle to lay eggs where rain has fallen. These early storms therefore produce localized superabundances of food. In the ensuing rainy seasons insect abundance remains high. African insectivorous birds breed during the wet period, reaching a peak two months after the insect increase. It is suggested that this lag is due to the need to recover body condition, build up reserves for eggs, develop gonads and wait for vegetation and insect larvae to develop. In the samples available, breeding records of above-ground nesters peaked in the first rains, while ground-nesters peaked in the second (main) rains. Predators bred towards the end of the rains, when there is an abundance of fledglings and small mammals. Thus the food supply could act as the ultimate factor determining the timing of the breeding season in this area. Palaearctic migrants arrive in the Serengeti 4–10 weeks ahead of the main rain front. However, most species are only found where rain has fallen recently. When conditions dry up they move on to other wet areas. Thus they overlap with African species only where there is a superabundance of insects. When the rains become widespread Palaearctic migrants disperse into their usual habitats, and therefore appear not to compete for available resources with closely related species of African birds. The situation in West Africa, where residents and migrants overlap throughout the dry season, cannot be explained in the same terms.     

Salinity as a constraint affecting food and habitat choice of mussel-feeding diving ducks

Observations of freshwater drinking in Eiders feeding primarily on mussels led us to hypothesize that the highly saline sea water enclosed in mussels could cause salt-related dehydration problems in the ducks, since they consume entire mussels. The proportion of sea water increases with increasing mussel size. Smaller duck species are more sensitive to the higher salt content of larger mussels than are larger ducks; however, salt stress may be avoided by feeding in habitats with lower salinity, by feeding on less salty food items, by utilizing smaller mussels, by drinking fresh water, or by employing low energy foraging techniques. A possible evolutionary strategy for solving the salt problem might be to increase body mass, enabling ducks to utilize larger mussels without passing an upper salt consumption limit. At the same time, foraging on larger mussels is more economical. Although large size facilitates the utilization of brackish and marine environments, it may be selected against in ducks breeding in fresh water, where fish competition may reduce optimal food item size. In conclusion, salinity is an important habitat barrier in both breeding and overwintering diving ducks, but there are various ways of crossing this barrier. To understand better how ducks utilize their habitats, however, it is necessary to measure habitat salinity levels and the size of both ducks and their preferred and less-preferred food types.     

Community Structure of Wetland Birds During Spring Migration Through the Rainwater Basin

Abstract: Staging areas and migratory stopovers of wetland birds have the potential to function as geographic bottlenecks; entire populations within a flyway may be affected by the quality and quantity of available wetland habitat at stopover sites. Although approximately 90% of playa wetlands in the Rainwater Basin (RWB) region of south-central Nebraska, USA, have been destroyed, the area still provides essential stopover habitat for >10 million waterfowl each spring. We evaluated community patterns and species associations to assess importance of assembly rules in structuring wetland bird communities during migration and to better facilitate multispecies conservation and management strategies. We surveyed 36–40 playas twice weekly in the RWB and observed approximately 2.6 million individual migratory wetland birds representing 72 species during 3 spring migrations 2002–2004. We evaluated spatial and temporal species co-occurrence patterns of geese, dabbling ducks, diving ducks, and shorebirds using null model analysis. Goose species co-occurrence scores did not differ from random in any year of the study, suggesting that goose species frequently use the same habitats during migration. Co-occurrence patterns among dabbling ducks were not different than expected by chance in any year; however, when we evaluated co-occurrence at a weekly scale, dabbling ducks co-occurred less often than expected during weeks of peak migration (high abundance), indicating that dabbling duck species spatially segregated at high densities. Diving duck co-occurrence patterns did not differ from random in any year, suggesting that diving duck species used the same habitats during migration. Shorebird species co-occurred less often than expected in 2002 and 2004, and during weeks of high shorebird abundance, indicating that shorebird communities were distinctly structured during those times. Most association values among lesser snow geese (Chen caerulescens) and dabbling duck species were positive, indicating dabbling ducks did not avoid wetlands with snow geese, a concern for waterfowl managers. However, we frequently observed snow geese and dabbling ducks using different microhabitats within a wetland, which indicate species associations and co-occurrence patterns may have occurred at a finer spatial scale than we measured. This approach of co-occurrence analysis will allow wildlife managers charged with multispecies management at migration stopover sites to make informed conservation and management decisions based on community structure rather than historic single-species approaches.     

Seasonal Dependent Effects of Flooding on Plant Species Survival and Zonation: a Comparative Study of 10 Terrestrial Grassland Species

Past research has provided compelling evidence that variation in flooding duration is the predominant factor underlying plant species distribution along elevation gradients in river floodplains. The role of seasonal variation in flooding, however, is far from clear. We addressed this seasonal effect for 10 grassland species by testing the hypothesis that all species can survive longer when flooded in winter than when flooded in summer. We carried out an inundation experiment under simulated conditions of summer and winter flooding in the greenhouse. The results showed that all species survived longer under winter floods than under summer floods. However, responses upon flooding were species-specific. All summer flood-tolerant species had high tolerance for winter floods as well, but summer flood sensitive species survived either a little longer, or dramatically longer when flooded under simulated winter conditions. Next, we examined whether winter or summer survival best predicted the lower distribution limits of the species as measured in a natural flooding gradient after an extremely long winter flood. We found a strong significant relationship between the lower distribution limits of species in the field and their tolerance to summer floods, although we measured the lower limits 14 years after the latest major summer flood. In contrast, no such significant relationship existed with species tolerance to winter floods. Some relatively intolerant species occurred at much higher floodplain elevations as was expected from their tolerance to winter inundation in the experiments. This suggests that zonation patterns as created by occasional summer floods may be maintained for a long time, probably due to the limited ability of species to re-colonise lower positions in the floodplain.     

Winter fish community structures across floodplain backwaters in a drought year

We examined fish community structures in floodplain backwaters in the Kiso River, Central Japan, in an uncommon drought year. Nine floodplain backwaters with varying levels of flood inundation frequency were surveyed for winter fish communities, and measured for local environmental variables in summer and winter periods. The winter fish community was better represented, with less diverse and physiologically tolerant species in backwaters with a decreasing flood pulse frequency. The temporal frequency of hypoxic conditions (dissolved oxygen of <2 mg l^?1) and chlorophyll a in summer explained the heterogeneity of the fish community along the gradient of inundation frequency, while no variables measured in winter had an explanatory power. These results suggest that drought-induced, infrequent flood pulses in the autumn–winter period limited the dispersal opportunity of fishes, and thus maintained community structures selected by summer limiting factors until the survey took place in winter. Future comparisons of our data with those in non-drought years would provide important implications to the sustainable management of floodplains for wintering fishes against the increasing probability of future flow regime changes.     

Snow evens fragmentation effects and food determines overwintering success in ground-dwelling voles

Climate instability strongly affects overwintering conditions in organisms living in a strongly seasonal environment and consequently their survival and population dynamics. Food, predation and density effects are also strong during winter, but the effect of fragmentation of ground vegetation on ground-dwelling small mammals is unknown. Here, we report the results of a winter experiment on the effects of habitat fragmentation and food on experimental overwintering populations of bank voles Myodes glareolus. The study was conducted in large outdoor enclosures containing one large, two medium-sized or four small habitat patches or the total enclosure area covered with protective tall-grass habitat. During the stable snow cover of midwinter, only food affected the overwintering success, body condition, trappability and earlier onset of breeding in bank voles. However, after the snow thaw in spring, habitat fragmentation gained importance again, and breeding activities increased the movements of voles in the most fragmented habitat. The use of an open, risky matrix area increased along the habitat fragmentation. Our experiment showed that long-lasting stable snow cover protects overwintering individuals in otherwise exposed and risky ground habitats. We conclude that a stable winter climate and snow cover should even out habitat fragmentation effects on small mammals. However, along prolonged snow-free early winter and in an earlier spring thaw, this means loss of protection by snow cover both in terms of thermoregulation and predation. Thus, habitat cover is important for the survival of small ground-dwelling boreal mammals also during the non-breeding season.