Overwinter Survival Rates Research Articles

Scope and adaptive value of modulating aggression over breeding stages in a competitive female bird

Abstract In seasonally breeding animals, the costs and benefits of territorial aggression should vary over time; however, little work thus far has directly examined the scope and adaptive value of individual-level plasticity in aggression across breeding stages. We explore these issues using the tree swallow (Tachycineta bicolor), a single-brooded bird species in which females compete for limited nesting sites. We measured aggressiveness in nearly 100 females within 3 different stages: (1) shortly after territory-establishment, (2) during incubation, and (3) while caring for young chicks. Based on the timing, direction, and magnitude of behavioral changes between stages, we used k-means clustering to categorize each female’s behavior into a “plasticity type.” We then tested whether plasticity type and stage-specific aggression varied with key performance metrics. About 40% of females decreased aggressiveness across consecutive breeding stages to some degree, consistent with population-level patterns. 33% of females exhibited comparatively little plasticity, with moderate to low levels of aggression in all stages. Finally, 27% of females displayed steep decreases and then increases in aggression between stages; females exhibiting this pattern had significantly lower body mass while parenting, they tended to hatch fewer eggs, and they had the lowest observed overwinter survival rates. Other patterns of among-stage changes in aggressiveness were not associated with performance. These results reveal substantial among-individual variation in behavioral plasticity, which may reflect diverse solutions to trade-offs between current reproduction and future survival.

Boldness suppresses hoarding behavior in food hoarding season and reduces over-wintering survival in a social rodent.

The "pace-of-life" syndrome (POLS) framework can encompass multiple personality axes that drive important functional behaviors (e.g., foraging behavior) and that co-vary with multiple life history traits. Food hoarding is an adaptive behavior important for an animal's ability to adapt to seasonal fluctuations in food availability. However, the empirical evidence for the relationships between animal personality and hoarding behavior remains unclear, including its fitness consequences in the POLS framework. In this study, the Mongolian gerbil (Meriones unguiculatus), a social rodent, was used as a model system to investigate how boldness or shyness is associated with food hoarding strategies during the food hoarding season and their impact on over-winter survival and reproduction at both individual and group levels. The results of this study showed that, compared with shy gerbils, bold gerbils had a lower effort foraging strategy during the food hoarding season and exhibited lower over-winter survival rates. However, bold-shy personality differences had no effect on over-winter reproduction. These findings suggest that the personality is a crucial factor influencing the foraging strategy during the food hoarding season in Mongolian gerbils. Personality may be related to energy states or the reaction to environmental changes (e.g., predation risk and food availability) in bold or shy social animals. These results reflect animal life history trade-offs between current versus future reproduction and reproduction versus self-maintenance, thereby helping Mongolian gerbils in adapting to seasonal fluctuations in their habitat.

Data mining hive inspections: more frequently inspected honey bee colonies have higher over-winter survival rates

Honey bee colonies frequently suffer from high over-winter losses attributed to various factors, including management, poor nutrition, pests, pathogens, and parasites. Most beekeepers have only limited control over these factors. This study looks at the role of the number and timing of hive inspections in relation to over-winter losses, which beekeepers can largely control. The impact of hive inspections on over-winter survival is usually difficult to measure in traditional studies due to confounding factors, including geography, sample size, and variability in practices. This study mines data collected, anonymized and shared from an apiary management software system and includes data from 4,072 hives managed by 717 beekeepers across the continental United States (U.S.) over a five-year period from (2013–2018), consisting of 60,920 inspections to identify the relationship between hive inspections and over-winter survival. Hives are grouped into nine climate zones deemed similar by the National Oceanic and Atmospheric Association (NOAA), and inspections were grouped by season for analysis. Results suggest that more frequent hive inspections are associated with higher over-winter survival rates across most U.S. regions. Unexpectedly, this also includes having relatively more inspections during the winter months in every region. Also, surprisingly only one of the nine climatic regions had significantly different average over-winter survival rates despite the significant geographic and climate difference across the continental U.S. This finding suggests that other factors like management actions may be more important to over-winter survival rates than climate. Finally, this inspection analysis shows that the number of inspections performed by beekeepers is a relevant factor in predicting over-winter hive mortality.

Characteristics of Carbon, Nitrogen and Phosphorus Stoichiometry and Nutrient Reabsorption in Alfalfa Leaves with Different Fall-Dormancy Levels in Northern Xinjiang, China

Alfalfa productivity and cold resistance in different regions are influenced by the fall-dormancy level of alfalfa. However, it is unclear whether the stoichiometric characteristics and nutrient resorption efficiency in alfalfa leaves also vary with the fall-dormancy level. In order to further understand the differences in nutrient absorption and requirements of different fall-dormant alfalfa, we conducted field trials on 30 different fall-dormancy alfalfa cultivars for 2 consecutive years in 2020 and 2021. We investigated the concentrations of carbon, nitrogen, and phosphorus in mature and senescent alfalfa leaves; nutrient stoichiometry ratios; and the coupling relationship between nutrient reabsorption efficiency and dry matter yield. The differences in nutrient reabsorption, fall dormancy, and dry matter yield of different fall-dormant alfalfa, and the correlation between indicators were utilized to further analyze the regulatory mechanisms of nutrient reabsorption in different fall-dormancy alfalfa varieties. The results demonstrated that the nitrogen reabsorption efficiency (NRE) and phosphorus reabsorption efficiency (PRE) of leaves increased first and then decreased with the increase in fall dormancy, whereas the carbon reabsorption efficiency (CRE) showed the reverse tendency. Different fall-dormancy alfalfa varieties significantly affected the dry matter yield and nutrient absorption in the first cut, while the last cut had the lowest variable coefficient and impact. There was a significant decrease in the over-winter survival rate of alfalfa as the fall-dormancy level increased, whereas the over-summer survival rate was less affected by the fall-dormancy level. As the growth year increased, there was a significant decrease in the over-winter survival rate. Among mature leaves, the NRE and PRE showed a significant positive correlation with the C concentration, while they showed a significant negative association with the N and P concentrations. In the same cut, the dry matter yield decreased with the increase in CRE but increased with the increases in NRE and PRE, while there was no significant trend in dry matter yield and nutrient resorption efficiency (NuRE) between different cuts. Taken together, the alfalfa survival rate and dry matter yield were relatively better in the moderate fall-dormancy (fall-dormancy level, FD = 4, 5) types and fall-dormancy (FD = 3) type, with a corresponding increase in the reabsorption requirements for nitrogen and phosphorus.

Integration of transcriptome and proteome analysis reveals the mechanism of freezing tolerance in winter rapeseed

Winter rapeseed seedlings are susceptible to low temperature during overwintering in Northwest China, leading to reduced crops production. Freezing stress is one of the main environmental stresses in Northwest China from late autumn to early spring, an eventful period for overwinter survival rate of winter rapeseed. However, the molecular mechanism of freezing tolerance formation is still very backward in winter rapeseed. In this study, using a pair of freezing-sensitive and freezing-resistant cultivars NQF24 and NTS57, the exhaustive effects of freezing stress on freezing tolerance formation were evaluated by analyzing leaf at the levels of transcriptome, proteome, physiology and ultrastructure. There were 8497 and 7358 differentially expressed genes (DEGs) and 418 and 573 differentially abundant proteins (DAPs) identified in the leaf of NQF24 and NTS57 under freezing stress, respectively. Function enrichment analysis showed that most of the enriched DEGs and DAPs were associated with plant hormones signal transduction, fatty acid metabolism, ribosome, plant-pathogen interaction and secondary metabolites biosynthesis. Freezing tolerance is formed by enhanced signals transduction, increased the biosynthesis of protein and secondary metabolites, enhanced reactive oxygen species (ROS) scavenging, more osmolytes, lower lipid peroxidation, and stronger cell stability. These results can be taken as selection indicators in freezing tolerance breeding program in rapeseed.

Overwinter behavior, movement, and survival in a recently reintroduced, endangered amphibian, Rana muscosa

Basic natural history information is critical for species conservation but is often deficient for endangered species, which can be rare and difficult to study. This is particularly true for behavior and natural history during the winter in temperate regions, when site access can be challenging. For translocation programs in temperate regions, however, winter may be a critical time to assess movement, survival, and threats to persistence in order to understand the causes of translocation failures. Using radiotelemetry, we monitored movement from fall through spring in reintroduced, ex situ bred individuals (N = 21) of the endangered mountain yellow-legged frog (Rana muscosa) to characterize behavior during brumation (overwinter dormancy), overwinter infection prevalence of the fungal pathogen Batrachochytrium dendrobatidis (Bd), and survival. We found that movement rates were variable but low in comparison to other sites. Frogs moved more in the fall when temperatures were warmer in comparison to the winter and spring. However, some frogs still moved (very small distances) even when water temperatures were below 2 °C and snow covered the ground. Frogs were difficult to detect visually, but were almost always in water, including during brumation, when they usually appeared to be in underwater rock caves and crevices in pool habitat. Frogs appeared to be spatially clustered in 3–5 groups throughout the study period and those within a group were often located <1 m from one another. Overwinter survival rates were low: over 70% of animals were confirmed dead, and all were suspected dead by mid-May. While sample size was limited, Bd prevalence and infection intensity increased during the winter and spring, which may have contributed to mortality rates. This study sheds light on a poorly understood life history phase for an endangered amphibian and will inform future management activities to protect this species.

Contribution of late-litter juveniles to the population dynamics of snowshoe hares.

Determining the factors driving cyclic dynamics in species has been a primary focus of ecology. For snowshoe hares (Lepus americanus), explanations of their 10-year population cycles most commonly feature direct predation during the peak and decline, in combination with their curtailment in reproduction. Hares are thought to stop producing third and fourth litters during the cyclic decline and do not recover reproductive output for several years. The demographic effects of these reproductive changes depend on the consistency of this pattern across cycles, and the relative contribution to population change of late-litter versus early litter juveniles. We used monitoring data on snowshoe hares in Yukon, Canada, to examine the contribution of late-litter juveniles to the demography of their cycles, by assigning litter group for individuals caught in autumn based on body size and capture date. We found that fourth-litter juveniles occur consistently during the increase phase of each cycle, but are rare and have low over-winter survival (0.05) suggesting that population increase is unlikely to be caused by their occurrence. The proportion of third-litter juveniles captured in the autumn remains relatively constant across cycle phases, while over-winter survival rates varies particularly for earlier-litter juveniles (0.14-0.39). Juvenile survival from all litters is higher during the population increase and peak, relative to the low and decline. Overall, these results suggest that the transition from low phase to population growth may stem in large part from changes in juvenile survival as opposed to increased reproductive output through the presence of a 4th litter.

Delayed Sowing Dates Affected Alfalfa Overwintering Survival Rates by Reducing Soil Temperature Stress

This study explored the effect of sowing time on alfalfa overwintering and its mechanisms. Gongnong No. 1 alfalfa was sown on July 1, July 16, August 1 and August 15, 2017, and was not cut at the end of autumn. The soil temperature changes in the 10 and 20 cm soil layers were monitored during the overwintering period, and bare land was monitored as a control. The growth characteristics of alfalfa were observed at the end of autumn, and the overwintering survival rate was measured at the end of April 2018. Research shows that as the sowing delay increased, the alfalfa hay yield, plant height, root collar diameter and overwintering survival rate decreased gradually. The minimum temperature of the 10 and 20 cm soil layers decreased as the sowing delay increased, and the diurnal temperature difference increased. Compared with that of alfalfa sown on August 15, the aboveground biomass of alfalfa sown on July 1 increased the average minimum temperature difference in the 10 and 20 cm soil layers by 3.12°C and 2.99°C, respectively, and reduce the average diurnal temperature difference by 3.33°C and 2.15°C. These results indicated that delaying alfalfa sowing reduces the cover on the field, which results in substantial differences in the minimum temperature and the diurnal temperature difference between the 10 and 20 cm soil layers. Our research has suggested that the minimum temperatures of the 10 and 20 cm soil layers and the increase in the diurnal temperature difference are important reasons for low overwintering survival rates in alfalfa. Therefore, sowing should occur in early July, and mowing should not be performed at the end of autumn in northern China.

Living Near the Edge: Variability in Abundance and Life Cycle of the Blue Crab Callinectes sapidus (Rathbun, 1896) in Eastern Long Island Sound

Long Island Sound (LIS) is near the northern limit for the range of year-round populations of the blue crab Callinectes sapidus (Rathbun, 1896). This study sampled blue crabs for 7 y with a trawl in LIS and with traps in the estuarine portion of three rivers in eastern Connecticut. Year-to-year abundance of blue crabs was highly variable. A strong correlation was found between the abundance in the summer and the water temperatures in the prior winter, suggesting that these large interannual fluctuations are caused by varying overwinter survival rates. Winter mortality due to low water temperatures may be the controlling factor in determining the northern range limit for resident populations of blue crabs and for their abundance in northern waters, such as LIS. Long-term trawl surveys in LIS show a shift in abundance from cold-temperate to warm-temperate species, which correlates with rising water temperatures. Longer term studies are required to determine whether the blue crab population in LIS is increasing as a result of global warming. Previous studies have not investigated the blue crab life cycle north of New Jersey, including LIS. This study found that all stages of their life cycle occur in LIS. Male and immature female blue crabs were found primarily in the upper, less saline sections of LIS subestuaries. Mature and egg-bearing females occurred primarily in the deeper, higher salinity waters of LIS. These results are consistent with the blue crab life cycle as described in locations south of LIS, such as Chesapeake Bay.

Studies on the cold tolerance of ratoon \u2018Chaling\u2019 common wild rice

BackgroundRice is the staple food of many people around the world. However, most rice varieties, especially widely grown indica varieties and hybrids, are sensitive to cold stress. In order to provide a basis for the utilization of a common wild rice (CWR, Oryza rufipogon Griff.) named ‘Chaling’ CWR in cold-tolerant rice breeding and deepen the understanding of rice cold tolerance, the cold tolerance of ratoon ‘Chaling’ CWR was studied under the stress of the natural low temperature in winter in Changsha, Hunan province, China, especially under the stress of abnormal natural low temperature in Changsha in 2008, taking other ratoon CWR accessions and ratoon cultivated rice phenotypes as control.ResultsThe results showed that ratoon ‘Chaling’ CWR can safely overwinter under the natural conditions in Changsha (28° 22′ N), Hunan province, China, which is a further and colder northern place than its habitat, even if it suffers a long-term low temperature stress with ice and snow. In 2008, an extremely cold winter appeared in Changsha, i.e., the average daily mean temperature of 22 consecutive days from January 13 to February 3 was − 1.0 °C, and the extreme low temperature was − 4.7 °C. After subjected to this long-term cold stress, the overwinter survival rate of ratoon ‘Chaling’ CWR was 100%, equals to that of ratoon ‘Dongxiang’ CWR which is northernmost distribution in the word among wild rice populations, higher than those of ratoon ‘Fusui’ CWR, ratoon ‘Jiangyong’ CWR, and ratoon ‘Liujiang’ CWR (63.55–83.5%) as well as those of ratoon ‘Hainan’ CWR, ratoon ‘Hepu’ CWR, and all the ratoon cultivated rice phenotypes including 3 japonica ones, 3 javanica ones, and 5 indica ones (0.0%).ConclusionsThe results indicate that ratoon ‘Chaling’ CWR possesses strong cold tolerance and certain freezing tolerance.

Sympatric Atlantic puffins and razorbills show contrasting responses to adverse marine conditions during winter foraging within the North Sea

BackgroundNatural environments are dynamic systems with conditions varying across years. Higher trophic level consumers may respond to changes in the distribution and quality of available prey by moving to locate new resources or by switching diets. In order to persist, sympatric species with similar ecological niches may show contrasting foraging responses to changes in environmental conditions. However, in marine environments this assertion remains largely untested for highly mobile predators outside the breeding season because of the challenges of quantifying foraging location and trophic position under contrasting conditions.MethodDifferences in overwinter survival rates of two populations of North Sea seabirds (Atlantic puffins (Fratercula arctica) and razorbills (Alca torda)) indicated that environmental conditions differed between 2007/08 (low survival and thus poor conditions) and 2014/15 (higher survival, favourable conditions). We used a combination of bird-borne data loggers and stable isotope analyses to test 1) whether these sympatric species showed consistent responses with respect to foraging location and trophic position to these contrasting winter conditions during periods when body and cheek feathers were being grown (moult) and 2) whether any observed changes in moult locations and diet could be related to the abundance and distribution of potential prey species of differing energetic quality.ResultsPuffins and razorbills showed divergent foraging responses to contrasting winter conditions. Puffins foraging in the North Sea used broadly similar foraging locations during moult in both winters. However, puffin diet significantly differed, with a lower average trophic position in the winter characterised by lower survival rates. By contrast, razorbills’ trophic position increased in the poor survival winter and the population foraged in more distant southerly waters of the North Sea.ConclusionsPopulations of North Sea puffins and razorbills showed contrasting foraging responses when environmental conditions, as indicated by overwinter survival differed. Conservation of mobile predators, many of which are in sharp decline, may benefit from dynamic spatial based management approaches focusing on behavioural changes in response to changing environmental conditions, particularly during life history stages associated with increased mortality.

Effects of Eutrophication and Different Water Levels on Overwintering of Eichhornia crassipes at the Northern Margin of Its Distribution in China.

When exotic species are introduced into new areas, establishment is a vital step in their invasion process. Therefore, overwintering strategies determine whether an exotic species from low latitudes can successfully invade middle- and high-latitude areas. In this study, we investigated the effects of nutrient and water drawdown on overwintering in an exotic aquatic plant from the tropical zone, Eichhornia crassipes, at the northern margin of its distribution in China. The population density, size of individuals, and the size and nitrogen concentration of overwintering organs (stem base) of E. crassipes that grew in high-nutrition water were greater than those that grew in low-nutrient water before winter. The overwinter survival rate of E. crassipes was significantly affected by the water level and nutrient. The thick and dense floating mat of E. crassipes can increase the temperature of water bodies; therefore, the overwinter survival rate of E. crassipes was higher in constant-water-level and high-nutrient treatment. In contrast, due to the loss of heat preservation provided by the floating mats and the low nitrogen concentration in the stem base, all individuals of E. crassipes died in constant-water-level and low-nutrient treatment. In the water-drawdown treatments, the stem base of E. crassipes was directly exposed to low-temperature air; therefore, the overwinter survival rate of E. crassipes was lower. Our results reveal that eutrophication can not only improve the competitiveness of E. crassipes but can also improve the survival rate of overwintering plants in temperate regions. Our study also suggests that removing nutrients from the water and regulating the water level can limit the invasion of E. crassipes in temperate and subtropical regions.

How extreme is extreme? Demographic approaches inform the occurrence and ecological relevance of extreme events

AbstractProjected increases in the variability of both temperature and precipitation will result in the greater likelihood and magnitude of extreme weather (e.g., cold snaps, droughts, heat waves) with potential implications for animal populations. Despite the ecological consequences of extreme weather, there are several challenges in identifying extreme events and measuring their influence on key demographic processes in free‐living animals. First, there is often a mismatch between the spatial and/or temporal resolution of biological and climate data that could hinder our ability to draw accurate inferences about how species and populations respond to extreme events. Second, there are multiple approaches for identifying an extreme event ranging from statistical definitions (e.g., standardized deviates) to species‐specific biological thresholds. Lastly, the impacts of extreme weather on species can vary as a function of differences in exposure and intrinsic sensitivity to climate variability. In the Northern Hemisphere, rapid warming has contributed to a “wobblier” jet stream that promotes the higher likelihood of cold Arctic air moving southward and leading to more extreme winter conditions. Due to these conditions, the Upper Midwest experienced two of the coldest winters in the past 35 yr during 2014 and 2015. We combined radiofrequency identification technologies with fine‐scale weather data and standard capture–mark–recapture analyses to estimate weekly and overwinter survival rates of a common winter passerine, the Black‐capped Chickadee (Poecile atricapillus), in a near continuous fashion. Using both statistical and biological definitions of weather extremes, we found that declining ambient temperatures reduced survival (despite the presence of favorable microclimates), and that biologically defined thresholds of extreme weather were better at explaining variation in survival than statistical ones. Moreover, habitat fragmentation interacted with temperature to modify the exposure of birds to extreme weather with survival consequences, but sensitivity, as measured by body condition, did not appear to play a significant role. These results provide a novel contribution to the understanding of how extreme weather may interact with local‐ and landscape features to influence the demography of species and populations, and suggest potential opportunities for climate‐change adaptation in human‐dominated landscapes.

Impacts of Sand Burial and Wind Erosion on Regeneration and Growth of a Desert Clonal Shrub.

Sand burial and wind erosion caused by sand movement are common phenomena in desert environments, but the effects on clonal shrub have rarely been investigated. Here, we assessed how sand movements affect the population regeneration capacity of juvenile clonal fragments of the shrub Calligonum mongolicum growing in mobile desert sand dunes. We investigated the population status and natural regeneration capacity in three types of mobile dunes (heavy wind erosion, heavy sand burial and moderate sand burial). Clonal propagation of C. mongolicum was markedly different across sites. Moderate sand burial sites had the largest ramet density and bud number per unit length of rhizome, and the overwinter survival rate was significantly higher at sand burial sites than at wind erosion sites, suggesting that C. mongolicum may have well adapted to the moderate sand burial environment. We further examined the effects of clonal integration on clonal regeneration of this species. Physiological, biochemical and morphological characteristics of parent and daughter ramets growing in heterogeneous sandy habitats (sand burial or wind erosion) were measured. The results showed that being connected or severed from the maternal plant critically determined survival of daughter ramets on wind eroded rhizomes. When eroded rhizomes remained connected, the mother ramets had the highest chlorophyll a, b and a + b contents. However, both the mother plant and the daughter ramets undergoing erosion had higher proline and soluble protein levels than sand buried ramets. Meanwhile, the daughter ramets undergoing sand burial had higher photosynthetic rates (Pn), chlorophyll fluorescence parameters (Fm and Fo), and phenotypic traits of assimilating shoots, i.e., node number, length and volume than wind-eroded ramets. However, significant differences with mother plants, whether connected or severed, were very limited. It was concluded that moderate sand burial environments promoted clonal reproduction and growth of C. mongolicum. Additionally, physiological integration with mother raments in favorable conditions can alleviate stress on daughter ramets exposed to wind erosion. This physiological effect may do not occur for sand buried daughter ramets. These survival strategies and phenotypic responses should be carefully considered in shrub and sand dune management in sand fixation plantations of C. mongolicum.

Increased overwinter mortalities of white-tailed deer (Odocoileus virginianus) fawns during a drought year

Mortality rates of white-tailed deer (Odocoileus virginianus (Zimmermann, 1780)) fawns have been quantified throughout North America. Few studies, however, have assessed cause-specific mortality of fawns after the first 3 months of life or during a severe weather event. During 2010–2014, we captured and radio-tracked 93 fawns in southern and central Illinois and recorded 18 mortality events. In order of importance, survival rates were affected by days since capture, year of drought, age at capture, week after capture (1 or 0 indicator), and region. Estimated overwinter (fall through spring) survival rate (±SE) of fawns in both regions during 2010–2014 was 0.83 ± 0.04. However, estimated overwinter survival rates were depressed during 2012–2013, following the severe drought of 2012 (0.63 ± 0.11 or 0.66 ± 0.11 depending on the model). Main causes of mortality were capture-related and predation, though some dead deer also showed signs of hemorrhagic disease. We suspect that the extreme drought of 2012 created favorable conditions for fall–spring mortality of fawns, due to elevated disease transmission and lower forage quality and quantity for deer. In addition, drought may have contributed to predation by reducing abundance of alternative prey. Our results suggest that severe weather conditions during summer can substantially impact overwinter fawn survival.

Larval exposure to field-realistic concentrations of clothianidin has no effect on development rate, over-winter survival or adult metabolic rate in a solitary bee, Osmia bicornis.

There is widespread concern regarding the effects of agro-chemical exposure on bee health, of which neonicotinoids, systemic insecticides detected in the pollen and nectar of both crops and wildflowers, have been the most strongly debated. The majority of studies examining the effect of neonicotinoids on bees have focussed on social species, namely honey bees and bumble bees. However, most bee species are solitary, their life histories differing considerably from these social species, and thus it is possible that their susceptibility to pesticides may be quite different. Studies that have included solitary bees have produced mixed results regarding the impact of neonicotinoid exposure on survival and reproductive success. While the majority of studies have focused on the effects of adult exposure, bees are also likely to be exposed as larvae via the consumption of contaminated pollen. Here we examined the effect of exposure of Osmia bicornis larvae to a range of field-realistic concentrations (0–10 ppb) of the neonicotinoid clothianidin, observing no effect on larval development time, overwintering survival or adult weight. Flow-through respirometry was used to test for latent effects of larval exposure on adult physiological function. We observed differences between male and female bees in the propensity to engage in discontinuous gas exchange; however, no effect of larval clothianidin exposure was observed. Our results suggest that previously reported adverse effects of neonicotinoids on O. bicornis are most likely mediated by impacts on adults.

Stress responses of juvenile brown trout under winter conditions in a laboratory stream

Winter can be a challenging period for fish in northern temperate rivers and streams, particularly in those that are channelized, structurally simple or regulated by, for instance, hydropower. In these systems, dynamic sub-surface ice formation commonly occurs and stable periods with ice cover may be short. Under these adverse conditions, access to shelters has been shown to be an important factor that influences overwinter survival, and exclusion from shelters by anchor ice may cause stress. Here, stress responses of juvenile brown trout under simulated winter conditions in an artificial stream were studied. Trout were subjected to three treatments in which the trout (1) were excluded from an instream wood shelter, simulating the effects of anchor ice, (2) had access to the shelter or (3) had surface ice cover in addition to the shelter. There was a positive correlation between ventilation frequency and plasma cortisol concentration. Trout without access to shelter had 30% higher ventilation frequency than trout with instream shelter and surface ice, but no differences in cortisol concentration or stress colour were found between the treatments. River regulation that reduces surface ice and increases anchor ice formation may lead to increased stress and consequently reduce overwinter survival rates.

Switchgrass (Panicum virgatum L.) from North Dakota—a New Bioenergy Crop for the Nemoral Zone of Europe

ABSTRACTParallel to the growing interest in switchgrass (Panicum virgatum L.) in southern countries of Europe, there is enhanced interest in knowing about its potential adaptability in the European regions with cool and moderate climates. The objective of this work was to characterize important agricultural parameters of switchgrass originated from North Dakota in order to identify the most valuable accessions for further research, propagation, and breeding in the Nemoral zone of Europe. The selection aimed at evaluating overwintering and productivity of switchgrass, with the ultimate objective of biomass quality improvement. Field trials were carried out in the central lowland of Lithuania during 2012–2014 on 33 germplasm accessions of switchgrass originating from North Dakota. Allthe tested accessions exhibited almost similar overwinter survival rate, i.e., 93.7–96.7%. Significant differences were observed in mean dry matter yields of all the tested accessions harvested once or twice per season (P < 0.05). The higher yielding accessions during both study years were differentiated. The yield potential of these accessions depended on a number of morphological traits, including internode thickness, plant height, panicle length, and leaf and stem weight per tiller (P < 0.05). Ash and mineral composition was associated with the genotype and the year of biomass harvest (P < 0.05). The switchgrass genotypes originating from North Dakota appeared to be adaptable to the European environment with cool and moderate climate and short growing season. The best-performing accessions can serve as a valuable genetic source for future breeding programmes.

Factors limiting early life stage survival and growth during endangered Wyoming toad reintroductions

Understanding the limiting factors of recovery is essential for guiding sound management of endangered species. The Wyoming toad (Anaxyrus baxteri) is a critically endangered amphibian whose cause of decline and inability to reestablish breeding populations despite early life stage reintroductions remains unknown; habitat degradation and the pathogen Batrachochytrium dendrobatidis (Bd) are 2 potential contributing factors. In 2013, we experimentally tested the effects of habitat factors under food-supplemented and predator-protected conditions (i.e., mesh field enclosures) on time to metamorphosis, the proportion of tadpoles that metamorphosed, tadpole and toadlet size, the proportion of toadlets remaining in enclosures at release (approx. 1 month post-metamorphosis), and Bd prevalence in early life stages of Wyoming toads at Mortenson Lake National Wildlife Refuge. In 2014, we tested the effects of small-scale application of vegetation height management on toadlet size, the proportion of toadlets that remained, and Bd prevalence until 1 month post-metamorphosis. In 2013, median time to metamorphosis (25.5 days) was shorter in warmer water temperatures and proportion of tadpoles that metamorphosed was 0.70. In 2013, toadlet size was positively related to forb cover up to 35% and although overall treatment effect was not significant, mid-vegetation height treatments (10–30 cm) had fewer small toadlets at release than short (0–10 cm) and tall (>30 cm) vegetation heights. In 2014, vegetation height treatment (11.49–31.6 cm) had marginal support for estimating larger size at release. Batrachochytrium dendrobatidis was not detected in water samples or on post-metamorphic toadlets. Our results suggest that in mesh field enclosures, time to metamorphosis is shorter in warm water. In addition, vegetation heights of 10–30 cm and up to 35% forb cover within terrestrial mesh enclosures could increase Wyoming toad post-metamorphic size, which could increase overwinter survival rates. Using mesh field enclosures for soft-release may improve the effectiveness of early life stage reintroduction efforts, but predator attraction and density-dependent growth need to be considered. Habitat management can also influence growth and survival of early life stages of amphibians and may benefit reintroduction efforts for other species. © 2015 The Wildlife Society.

High within‐winter and annual survival rates in a declining Afro‐Palaearctic migratory bird suggest that wintering conditions do not limit populations

For migratory birds, it is necessary to estimate annual and overwinter survival rates, identify factors that influence survival, and assess whether survival varies with age and sex if we are to understand population dynamics and thus inform conservation. This study is one of the first to document overwinter and annual survival from the wintering grounds of a declining Afro‐Palaearctic migrant bird, the WhinchatSaxicola rubetra. We monitored a population of marked individuals for which dispersal was low and detectability was high, allowing accurate estimates of survival. Annual survival was at least 52% and did not differ significantly across demographic groups or with habitat characteristics or residency time in the previous winter. Overwinter survival was very high and monthly survival at least 98% at some sites. Although winter residency varied spatially and with age, lower residency did not correlate with reduced annual survival, suggesting occupancy of multiple wintering sites rather than higher winter mortality of individuals with shorter residency. Our results suggest that mortality occurs primarily outside the wintering period, probably during migration, and that wintering conditions have minimal influence on survival. The similarity between survival rates for all age and sex classes when measured on the wintering grounds implies that any difference in survival with age or sex occurs only during the first migration or during the post‐fledging stage, and that selection of wintering habitat, or territory quality, makes little difference to survival in Whinchats. Our findings suggest that the wintering grounds do not limit populations as much as the migratory and breeding stages, with implications for the conservation of declining Afro‐Palaearctic migrants more widely.