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31.
Håkan Karlsson Johan Bäckman Cecilia Nilsson Thomas Alerstam 《Behavioral ecology and sociobiology》2010,64(12):2021-2031
Using tracking radars, we investigated the variability of flight directions of long-distance nocturnal passerine migrants
across seasons (spring versus autumn migration) and sites at the southern (56° N) and northern (68° N) ends of the Scandinavian
Peninsula (Lund versus Abisko). Whilst most migrants at Lund are on passage to and from breeding sites in Fennoscandia, the
majority of the migrants at Abisko are close to their breeding sites, and migration at Abisko thus to a large degree reflects
initial departure from breeding sites (autumn) or final approach to breeding destinations (spring). The radar data were used
to test predictions about differences in orientation and wind drift effects between adult and juvenile birds (a large proportion
of autumn migrants consists of juvenile birds on their first journey), between situations far away from or near the goals
and between different phases of migration (initial departure, en route passage, final approach to goal). The concentrations
(both total and within-night concentrations) of flight directions differed significantly between seasons as well as sites,
with the highest concentration at Lund in spring (mean vector length of track directions, r = 0.79) and lowest at Abisko during spring (r = 0.35). Partial wind drift and partial compensation were recorded at Lund, with a similar effect size in spring and autumn,
whilst possible wind drift effects at Abisko were obscured by the large directional scatter at this site. The results from
Lund support the prediction that the high proportion of juveniles in autumn contributes to increase the directional scatter
during this season, whilst there was no support for predictions of differential wind drift effects between seasons and situations
with different goal distances. The most striking and surprising result was the exceedingly large scatter of flight directions
at Abisko, particularly in spring. We suggest that such an exaggerated scatter may be associated with final approach orientation,
where migrants reach their specific goals from all various directions by final navigation within a more wide-ranging goal
region. The larger scatter of autumn flight directions at Abisko compared to Lund may be due to exploratory flights in variable
directions being more common at initial departure from breeding sites than later during migratory passage. These surprising
results highlight the importance of studying and analysing orientation during final approach to (and initial departure from)
migratory goals for understanding the orientation systems of migratory birds. 相似文献
32.
In many species, the ability to evade predators is known to be periodically impaired by increased weight loads due to feeding
and reproduction. Not only may extra weight reduce escape speed, but feeding and mating can also make the prey more noticeable
to visually hunting predators. A number of butterfly species mate for hours, and if a mating couple is disturbed, one of the
butterflies is responsible for flying, whereas its partner remains still. This study investigated the ability of male Pieris napi butterflies to fly while mating, with the prediction that mate carrying impairs flight ability compared to single flying
males and that males with relatively high flight muscle ratios (FMR; male thorax mass/male + female body mass) will have better
flight performance in copula. Our results clearly show that whereas single males always take off at steep angles and fly upwards,
couples invariably have a negative take-off angle and rarely gain height. Moreover, landing height of the couples is positively
associated with higher FMR. Hence, male flight ability when in copula is positively associated with a high relative thorax
mass. Butterfly pairs may thus be at greater risk of predation as a consequence of their impaired flight ability, especially
couples with critically low FMRs (<16%). 相似文献
33.
Zagaria Cecilia Schulp Catharina J. E. Kizos Thanasis Verburg Peter H. 《Regional Environmental Change》2018,18(5):1467-1479
Regional Environmental Change - Multi-stakeholder perceptions of landscape changes are increasingly recognized as essential inputs to discussions on future landscape developments, particularly when... 相似文献
34.
Avian escape strategy is highly dependent on the ability to fly, and the success rate of raptor attacks is reduced if the
prey gets fully airborne. Therefore, when escaping from predator attacks, the initial take-off is crucial and a rapid take-off,
high velocity, and high angle of ascent maximize the chance of survival. However, due to the laws of gravity, birds face a
trade-off between maximizing its linear acceleration and maximizing its rate of climb when taking off. The optimal policy
between velocity and angle of ascent when a bird escapes from an attacking predator might depend on the detailed nature of
the predator’s attack, the proximity to cover, and the presence of conspecifics. Many small birds rely on a quick dash to
protective cover. In this study, we examine how the availability of protective cover affects take-off strategy in birds. Male
great tits (Parus major) were subjected to a surprise attack by a model predator either in the presence or absence of protective cover. When attacked
by the predator, great tits took off and perched in the cover when it was available. Birds subjected to the predator attack
in the absence of cover took off in 10° higher angle of ascent and flew faster in the start of the take-off, compared to birds
that took off in the presence of cover. Thus, this study for the first time shows that a bird do trade off speed with angle
of ascent in an adaptive way, depending on the presence of protective cover. 相似文献
35.
Cecilia Weistrand Koidu Norén Anita Nilsson 《Environmental science and pollution research international》1997,4(1):2-9
Concentrations of polychlorinated biphenyls (PCB), polychlorinated naphthalenes (PCN), polychlorinated dibenzo-p-dioxins (PCDD), polychlorinated dibenzofurans (PCDF), hexachlorobenzene and methylsulphonyl metabolites of PCB were determined in blood plasma from potentially exposed workers and controls. Three of the potentially exposed subjects had worked with cable incineration and two were electricians. Extraction of the organochlorine compounds and lipids were performed using the lipophilic gel Lipidex. Different adsorbents and gel permeation chromatography were applied for further purification of the samples and separation of analytes. Determinations of the chlorinated compounds were made by using gas chromatography with electron-capture detection and gas chromatography-mass spectrometry. Only small differences in the concentrations of organochlorine compounds were found in the plasma from the three subject groups. Thus, specific exposure of the workers could not be confirmed. 相似文献
36.
The complexity of development activities, in which the interactions between various forces often mean that outcomes are unpredictable and unanticipated, highlights the importance of objective and comprehensive evaluations. In the specific case of the evaluation of towns east and south of Colombo water supply projects, the findings have major implications for the implementation of the Millennium Development Goals, if the water-related objectives are to be fulfilled. The study found that 30% of the households of these towns that are receiving clean, piped water are not using it for drinking. Instead, they are continuing to drink contaminated well water. Whereas it is considered that the main beneficiaries of water supply projects have been women and people who are sick, elderly, or disabled, the general perception is that the health conditions of the families have not improved with the provision of clean water (in fact, many claim that their health conditions have deteriorated). In spite of the higher cost of the supplied water, people are willing to pay for it as long as the supply is reliable. 相似文献
37.
The paper presents an overview of the present situation of the Mexico City Metropolitan Area (MCMA). The analysis indicates an urgent need to radically improve the current water supply and wastewater management practices, to become sustainable. The MCMA is one of the most rapidly growing urban centers of the world, with a population of about 21 million people, a very high rate of immigration and numerous illegal settlements. In order to meet the increasing water demand, successive governments have focused almost exclusively on supply management and engineering solutions, which have resulted in investments of hundreds of millions of USD and the construction of major infrastructure projects for interbasin water transfer. Environmental, economic and social policies associated with water management are mostly inadequate and insufficient, which is resulting in increasing deterioration in the environment, health and socioeconomic conditions of a population living in one of the largest urban agglomerations of the world. Surprisingly, however, no long-term strategies on demand-management, reuse, conservation, and improved water-management practices have been developed so far. 相似文献
38.
本文分析了瑞典地区1961~2000年极端日降水量的空间尺度、区域变化和与之相关的天气类型.根据30km滞后距离计算的统计相关图估计年平均降水量、日降水量的99%分位值和平均年最大日雨量变化的空间尺度分别为100km、60~100km和40~70km.采用最大相似因子分析方法确定了82个站点极端降水量的区域相关.并发现有11个因子可以提供给最佳因子解决方案.极端事件发生时的天气类型是根据以逐日海平面气压为基础的客观系统划分的,并经过主观(包括锋面)修正.总体来看,极端降水事件的发生,63%在气旋类天气,32%在锋面类天气,3%在定向类天气,2%在反气旋类天气.然而,极端事件各种天气类型的发生频次不同地区之间有所不同. 相似文献
39.
Michelle Ramos-Robles Wesley Dáttilo Cecilia Díaz-Castelazo Ellen Andresen 《Die Naturwissenschaften》2018,105(3-4):29
Interactions between fleshy fruited plants and frugivores are crucial for the structuring and functioning of biotic communities, particularly in tropical forests where both groups are diverse and play different roles in network organization. However, it remains poorly understood how different groups of frugivore species and fruit traits contribute to network structure. We recorded interactions among 28 plant species and three groups of frugivores (birds, bats, and non-flying mammals) in a seasonal forest in Mexico to determine which species contribute more to network structure and evaluate the importance of each species. We also determined whether fruit abundance, water content, morphology traits, and fruiting phenology are related to network parameters: the number of interactions, species contribution to nestedness, and species strength. We found that plants did not depend on a single group of frugivores, but rather on one species of each group: the bird Pitangus sulphuratus, the bat Sturnira parvidens, and the non-flying mammal Procyon lotor. The abundance, size, and water content of the fruits were significantly related to the contribution to nestedness, number of interactions, and species strength index of plant species. Tree species and birds contributed mainly to the nested structure of the network. We show that the structure of plant-frugivore networks in this seasonal forest is non-random and that fruit traits (i.e., abundance, phenology, size, and water content) are important factors shaping plant-frugivore networks. Identification of the key species and their traits that maintain the complex structure of species interactions is therefore fundamental for the integral conservation of tropical forests. 相似文献
40.
Valente Tommaso Ventura Daniele Matiddi Marco Sbrana Alice Silvestri Cecilia Piermarini Raffaella Jacomini Carlo Costantini Maria Letizia 《Environmental science and pollution research international》2023,30(1):298-309
Environmental Science and Pollution Research - Microplastic pollution is one of the greatest environmental concerns for contemporary times and the future. In the last years, the number of... 相似文献