Effects of weather and tides on feeding and flock positions of wintering redheads in the Chandeleur Sound,Louisiana

We studied the effects of weather and tides on percent feeding and flock positions of wintering redheads (Aythya americana Eyton) in the Chandeleur Sound, Louisiana, USA. Flock scans (n = 750) were made on 55 flocks from November through March of 1988–1989. The percent of the flock that was feeding was negatively correlated with time of day, temperature, water level, and distance of the flock from shore, and was positively correlated with wind velocity, flock size, fetch, and wave height; birds also fed more in early winter and during northerly winds. Flocks were closer to land earlier in the winter on cloudy, rainy, and windy days when waves were high, and those flocks were smaller than flocks farther from shore. Conditions associated with reduced fetch by flocks included later time of day, smaller waves, warmer air temperatures, northerly wind shifts, stronger winds, increasing cloud cover, and rain. Redheads minimized energy expenditure by foraging during low tides and in shallow water closer to shore; they increased feeding and reduced fetch during times of high thermoregulatory demands.     

Why on the snow? Winter emergence strategies of snow‐active Chironomidae (Diptera) in Poland

A long‐term study of adult non‐biting midges (Chironomidae) active in winter on the snow in mountain areas and lowlands in Poland yielded 35 species. The lowland and mountain communities differed significantly in their specific composition. The mountain assemblage was found to be more diverse and abundant, with a substantial contribution from the subfamily Diamesinae, whereas Orthocladiinae predominated in the lowlands. Orthocladius wetterensis Brundin was the most characteristic and superdominant species in the winter‐active chironomid communities in both areas. Only a few specimens and species of snow‐active chironomids were recorded in late autumn and early winter. The abundance of chironomids peaked in late February in the mountain and lowland areas with an additional peak in the mountain areas in early April. However, this second peak of activity consisted mainly of Orthocladiinae, as Diamesinae emerged earliest in the season. Most snow‐active species emerged in mid‐ and late winter, but their seasonal patterns differed between the 2 regions as a result of the different species composition and the duration of snow cover in these regions. Spearman's rank correlation coefficient tests yielded positive results between each season and the number of chironomid individuals recorded in the mountain area. A positive correlation between air temperature, rising to +3.5 °C, and the number of specimens recorded on the snow in the mountain community was statistically significant. The winter emergence and mate‐searching strategies of chironomids are discussed in the light of global warming, and a brief compilation of most important published data on the phenomena studied is provided.     

Clutch and egg size of Tree Swallows along an elevational gradient

How avian reproductive behavior changes at high elevations, and whether changes are the result of adaptation or constraint remains unclear. We compared clutch and egg sizes in two populations of Tree Swallows (Tachycineta bicolor), one at an elevation of ~2500 m a.s.l. in Wyoming's Bighorn Mountains and the other at ~1350 m at the base of these mountains. Females at the high‐elevation site began laying 10 d later, on average, than females at the lower site. Females at the high site laid an average of 0.4 fewer eggs than those at the low site, a significant difference. Eggs were also slightly (2.3%), but significantly, smaller at the high site. Smaller clutches and eggs at the high site may have resulted in part from greater energetic constraints on females. Females at this site faced colder, windier weather during egg formation which would have increased thermoregulatory costs while simultaneously reducing the abundance of prey, i.e., flying insects. Laying a relatively small clutch at the high‐elevation site may also be adaptive, however. Having a smaller brood could help ensure there is an adequate supply of food for each offspring during bouts of inclement weather that are more severe at higher elevations. Also, if the delay in breeding inherent at high elevations reduces the survival prospects of the young, then producing fewer young could enhance a female's chances of breeding again, perhaps at a different location.     

上海地区三带喙库蚊春季首次出现、季节分布及其与气象条件的关系

根据1982～1992年和2001～2002年上海奉贤地区每年3月～6月灯诱捕蚊的现场调查数据,采取相关对比分析、统计分析、天气图分析法,探讨三带喙库蚊春季首次出现、季节分布及其与气象条件的关系。结果表明,三带喙库蚊季节分布按蚊虫密度变化划分为首次出现期、季节增多期和混合发生期三个时期。三带喙库蚊春季首次出现的温度条件是：首现日当天和前1天的日平均气温均≥11.0℃,其2天的日平均气温累加值≥25.5℃,或首现日当天、前2天和后1天任意连续3天的日平均气温均≥11.0℃,其3天的日平均气温累加值≥34.0℃,结果三带喙库蚊春季首现日和首现日温度日期的差异在1～2天内(91.7%)。三带喙库蚊季节增多期其逐候蚊虫密度（Y₁）与平均气温（X₁）呈显著的正相关,用一元回归方程表示为：Y₁=-9.3534+0.7217X₁;至候平均气温≥18℃（平均始日为5月3日）进入三带喙库蚊混合发生期。总体上三带喙库蚊蚊虫密度季节分布与平均气温、“S”系风向变化存在密切关系。首次出现期至季节增多期三带喙库蚊突增日与锋面天气活动存在着较大的关联,候平均气温≥18℃是三带喙库蚊大量发生和进入峰期重要的温度指标。上述结果提示上海地区三带喙库蚊春季和初夏随气流北迁降落的可能性相当大。     

Roles of environmental variables and land usage as drivers of dung beetle assemblage structure in mopane woodland

Colophospermum mopane woodland covers large areas of dry lowland savanna in southeastern Africa. Dominant land usage is conservation (45%) with the remainder mostly modified by farming. Dung beetle responses to environment (dung type, habitat, weather) and land usage (conservation, farming, mining) were examined at Phalaborwa (23.9431°S 31.1411°E) in the Phalaborwa‐Timbavati Mopaneveld, South Africa. Partitioning of gamma species richness and diversity showed lower alpha values in mine areas than in farm and conserved areas. However, between‐land usage differences in species richness, alpha diversity, abundance and biomass, showed lower significance than those between dung type and different weather. At two sampling scales, three multivariate techniques variously separated assemblages according to land usage, dung type and weather. Analysis of 21 mean samples separated clusters according to dung type (Canonical Correspondence Analysis, CCA) or mine assemblages, conserved plus farm assemblages on pig plus elephant, or cattle dung (NMDS, Factor Analysis) with shared variance of >80% and unique variance of 16–18% per cluster. In analysis of 188 samples (CCA), each overlapping dung type cluster was offset in ordinal space with congruent patterns of separation according to land usage and weather (drier days distant from moister days; conserved plus farm areas distant from early succession mine areas, which were distant from disturbed and later succession mine areas). Mining, dung types, and moist conditions were the strongest contributors to between‐assemblage differences. Compared with conserved areas, dung beetle diversity is appreciably altered by mining but only slightly altered by intensive game farming or livestock ranching with subsistence agriculture.     

Cross-scale environmental influences on migratory stopover behaviour

Migratory species may be especially sensitive to climate change because their lifecycles are affected by dynamic ecological processes operating at global spatial scales. Insight into environmental effects upon en route decisions by migrants can therefore be a critical first step toward assessing their vulnerability to future climatic shifts. We extracted behaviour-related parameters from a recent formulation of multistate mark–recapture models, and used them to evaluate the importance of variation in local weather and broad-scale climate to decisions made by autumn passerine migrants at a coastal stopover site in Atlantic Canada. We found dramatic interannual fluctuations in the proportion of migrants that were transient (departing within a day of arrival), with annual average values ranging from 24% to 96% over the years 1996–2007. However, the relationships of stopover behaviour (transience and departure probability) to local weather (wind and precipitation) and to regional climatic fluctuations were similar across three distinct species groups and for birds of different fuel-loads, indicating the potential for both immediate (day-to-day) and long-term environmental influences (spanning several seasons). This cross-scale approach contributes valuable information toward the conservation of migrants in the face of a changing climate by (i) quantifying environmental influences on stopover behaviour in broad temporal and geographic contexts, and (ii) demonstrating largely parallel interannual variation in stopover site-use among birds with contrasting migratory timing and strategies.     

The Influence of Climate, Soils, Weather, and Land Use on Primary Production and Biomass Seasonality in the US Great Plains

Identifying the conditions and mechanisms that control ecosystem processes, such as net primary production, is a central goal of ecosystem ecology. Ideas have ranged from single limiting-resource theories to colimitation by nutrients and climate, to simulation models with edaphic, climatic, and competitive controls. Although some investigators have begun to consider the influence of land-use practices, especially cropping, few studies have quantified the impact of cropping at large scales relative to other known controls over ecosystem processes. We used a 9-year record of productivity, biomass seasonality, climate, weather, soil conditions, and cropping in the US Great Plains to quantify the controls over spatial and temporal patterns of net primary production and to estimate sensitivity to specific driving variables. We considered climate, soil conditions, and long-term average cropping as controls over spatial patterns, while weather and interannual cropping variations were used as controls over temporal variability. We found that variation in primary production is primarily spatial, whereas variation in seasonality is more evenly split between spatial and temporal components. Our statistical (multiple linear regression) models explained more of the variation in the amount of primary production than in its seasonality, and more of the spatial than the temporal patterns. Our results indicate that although climate is the most important variable for explaining spatial patterns, cropping explains a substantial amount of the residual variability. Soil texture and depth contributed very little to our models of spatial variability. Weather and cropping deviation both made modest contributions to the models of temporal variability. These results suggest that the controls over seasonality and temporal variation are not well understood. Our sensitivity analysis indicates that production is more sensitive to climate than to weather and that it is very sensitive to cropping intensity. In addition to identifying potential gaps in out knowledge, these results provide insight into the probable long- and short-term ecosystem response to changes in climate, weather, and cropping.