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1.
The “value of information” (VOI) is a generic term for the increase in value resulting from better information to guide management, or alternatively, the value foregone under uncertainty about the impacts of management (Yokota and Thompson, Medical Decision Making 2004; 24 : 287). The value of information can be characterized in terms of several metrics, including the expected value of perfect information and the expected value of partial information. We extend the technical framework for the value of information by further developing the relationship between value metrics for partial and perfect information and describing patterns of their performance. We use two different expressions for the expected value of partial information to highlight its relationship to the expected value of perfect information. We also develop the expected value of partial information for hierarchical uncertainties. We highlight patterns in the value of information for the Svalbard population of the pink‐footed goose (Anser brachyrhynchus), a population that is subject to uncertainty in both reproduction and survival functions. The framework for valuing information is seen as having widespread potential in resource decision making, and serves as a motivation for resource monitoring, assessment, and collaboration. 相似文献
2.
We investigated how population changes and fluctuations in the pink‐footed goose might have been affected by climatic and anthropogenic factors. First, genomic data confirmed the existence of two separate populations: western (Iceland) and eastern (Svalbard/Denmark). Second, demographic inference suggests that the species survived the last glacial period as a single ancestral population with a low population size (100–1,000 individuals) that split into the current populations at the end of the last glacial maximum with Iceland being the most plausible glacial refuge. While population changes during the last glaciation were clearly environmental, we hypothesize that more recent demographic changes are human‐related: (1) the inferred population increase in the Neolithic is due to deforestation to establish new lands for agriculture, increasing available habitat for pink‐footed geese, (2) the decline inferred during the Middle Ages is due to human persecution, and (3) improved protection explains the increasing demographic trends during the 20th century. Our results suggest both environmental (during glacial cycles) and anthropogenic effects (more recent) can be a threat to species survival. 相似文献
3.
Reinhard Prestele Peter Alexander Mark D. A. Rounsevell Almut Arneth Katherine Calvin Jonathan Doelman David A. Eitelberg Kerstin Engström Shinichiro Fujimori Tomoko Hasegawa Petr Havlik Florian Humpenöder Atul K. Jain Tamás Krisztin Page Kyle Prasanth Meiyappan Alexander Popp Ronald D. Sands Rüdiger Schaldach Jan Schüngel Elke Stehfest Andrzej Tabeau Hans Van Meijl Jasper Van Vliet Peter H. Verburg 《Global Change Biology》2016,22(12):3967-3983
Model‐based global projections of future land‐use and land‐cover (LULC) change are frequently used in environmental assessments to study the impact of LULC change on environmental services and to provide decision support for policy. These projections are characterized by a high uncertainty in terms of quantity and allocation of projected changes, which can severely impact the results of environmental assessments. In this study, we identify hotspots of uncertainty, based on 43 simulations from 11 global‐scale LULC change models representing a wide range of assumptions of future biophysical and socioeconomic conditions. We attribute components of uncertainty to input data, model structure, scenario storyline and a residual term, based on a regression analysis and analysis of variance. From this diverse set of models and scenarios, we find that the uncertainty varies, depending on the region and the LULC type under consideration. Hotspots of uncertainty appear mainly at the edges of globally important biomes (e.g., boreal and tropical forests). Our results indicate that an important source of uncertainty in forest and pasture areas originates from different input data applied in the models. Cropland, in contrast, is more consistent among the starting conditions, while variation in the projections gradually increases over time due to diverse scenario assumptions and different modeling approaches. Comparisons at the grid cell level indicate that disagreement is mainly related to LULC type definitions and the individual model allocation schemes. We conclude that improving the quality and consistency of observational data utilized in the modeling process and improving the allocation mechanisms of LULC change models remain important challenges. Current LULC representation in environmental assessments might miss the uncertainty arising from the diversity of LULC change modeling approaches, and many studies ignore the uncertainty in LULC projections in assessments of LULC change impacts on climate, water resources or biodiversity. 相似文献
4.
Phenotypic differentiation is often interpreted as a result of local adaptation of individuals to their environment. Here, we investigated the skull morphological differentiation in 11 populations of the white‐footed mouse (Peromyscus leucopus). These populations were sampled in an agricultural landscape in the Montérégie region (Québec, Canada), at the northern edge of the distribution of the white‐footed mouse. We found a strong pattern of phenotypic differentiation matching the genetic structure across these populations. Landscape fragmentation and the presence of geographic barriers, in particular north–south oriented rivers, contribute to this differentiation and modulate the pattern of rapid ongoing northward range expansion of the white‐footed mouse in response to climate warming. We conclude that while large rivers and postglacial recolonization routes have shaped the current pattern of distribution and differentiation of white‐footed mouse populations, further local differentiation is occurring, at the scale of the landscape. We posit that the northern expansion of the white‐footed mouse is achieved through successive independent founder events in a fragmented landscape at the northern range edge of the species. The phenotypic differentiation we observe is thus a result of a number of mechanisms operating at different spatial and temporal scales. 相似文献
5.
We model the carbon balance of European croplands between 1901 and 2000 in response to land use and management changes. The process‐based ORCHIDEE‐STICS model is applied here in a spatially explicit framework. We reconstructed land cover changes, together with an idealized history of agro‐technology. These management parameters include the treatment of straw and stubble residues, application of mineral fertilizers, improvement of cultivar species and tillage. The model is integrated for wheat and maize during the period 1901–2000 forced by climate each 1/2‐hour, and by atmospheric CO2, land cover change and agro‐technology each year. Several tests are performed to identify the most sensitive agro‐technological parameters that control the net biome productivity (NBP) in the 1990s, with NBP equaling for croplands the soil C balance. The current NBP is a small sink of 0.16 t C ha?1 yr?1. The value of NBP per unit area reflects past and current management, and to a minor extent the shrinking areas of arable land consecutive to abandonment during the 20th Century. The uncertainty associated with NBP is large, with a 1‐sigma error of 0.18 t C ha?1 yr?1 obtained from a qualitative, but comprehensive budget of various error terms. The NBP uncertainty is dominated by unknown historical agro‐technology changes (47%) and model structure (27%), with error in climate forcing playing a minor role. A major improvement to the framework would consist in using a larger number of representative crops. The uncertainty of historical land‐use change derived from three different reconstructions, has a surprisingly small effect on NBP (0.01 t C ha?1 yr?1) because cropland area remained stable during the past 20 years in all the tested land use forcing datasets. Regional cross‐validation of modeled NBP against soil C inventory measurements shows that our results are consistent with observations, within the uncertainties of both inventories and model. Our estimation of cropland NBP is however likely to be biased towards a sink, given that inventory data from different regions consistently indicate a small source whereas we model a small sink. 相似文献
6.
Lukas Egli Carsten Meyer Christoph Scherber Holger Kreft Teja Tscharntke 《Global Change Biology》2018,24(5):2212-2228
Closing yield gaps within existing croplands, and thereby avoiding further habitat conversions, is a prominently and controversially discussed strategy to meet the rising demand for agricultural products, while minimizing biodiversity impacts. The agricultural intensification associated with such a strategy poses additional threats to biodiversity within agricultural landscapes. The uneven spatial distribution of both yield gaps and biodiversity provides opportunities for reconciling agricultural intensification and biodiversity conservation through spatially optimized intensification. Here, we integrate distribution and habitat information for almost 20,000 vertebrate species with land‐cover and land‐use datasets. We estimate that projected agricultural intensification between 2000 and 2040 would reduce the global biodiversity value of agricultural lands by 11%, relative to 2000. Contrasting these projections with spatial land‐use optimization scenarios reveals that 88% of projected biodiversity loss could be avoided through globally coordinated land‐use planning, implying huge efficiency gains through international cooperation. However, global‐scale optimization also implies a highly uneven distribution of costs and benefits, resulting in distinct “winners and losers” in terms of national economic development, food security, food sovereignty or conservation. Given conflicting national interests and lacking effective governance mechanisms to guarantee equitable compensation of losers, multinational land‐use optimization seems politically unlikely. In turn, 61% of projected biodiversity loss could be avoided through nationally focused optimization, and 33% through optimization within just 10 countries. Targeted efforts to improve the capacity for integrated land‐use planning for sustainable intensification especially in these countries, including the strengthening of institutions that can arbitrate subnational land‐use conflicts, may offer an effective, yet politically feasible, avenue to better reconcile future trade‐offs between agriculture and conservation. The efficiency gains of optimization remained robust when assuming that yields could only be increased to 80% of their potential. Our results highlight the need to better integrate real‐world governance, political and economic challenges into sustainable development and global change mitigation research. 相似文献
7.
Tobias Kuemmerle Jed O. Kaplan Alexander V. Prishchepov Ilya Rylsky Oleh Chaskovskyy Vladimir S. Tikunov Daniel Müller 《Global Change Biology》2015,21(8):3049-3061
Forests often rebound from deforestation following industrialization and urbanization, but for many regions our understanding of where and when forest transitions happened, and how they affected carbon budgets remains poor. One such region is Eastern Europe, where political and socio‐economic conditions changed drastically over the last three centuries, but forest trends have not yet been analyzed in detail. We present a new assessment of historical forest change in the European part of the former Soviet Union and the legacies of these changes on contemporary carbon stocks. To reconstruct forest area, we homogenized statistics at the provincial level for ad 1700–2010 to identify forest transition years and forest trends. We contrast our reconstruction with the KK11 and HYDE 3.1 land change scenarios, and use all three datasets to drive the LPJ dynamic global vegetation model to calculate carbon stock dynamics. Our results revealed that forest transitions in Eastern Europe occurred predominantly in the early 20th century, substantially later than in Western Europe. We also found marked geographic variation in forest transitions, with some areas characterized by relatively stable or continuously declining forest area. Our data suggest extensive deforestation in European Russia already prior to ad 1700, and even greater deforestation in the 18th and 19th centuries than in the KK11 and HYDE scenarios. Based on our reconstruction, cumulative carbon emissions from deforestation were greater before 1700 (60 Pg C) than thereafter (29 Pg C). Summed over our entire study area, forest transitions led to a modest uptake in carbon over recent decades, with our dataset showing the smallest effect (<5.5 Pg C) and a more heterogeneous pattern of source and sink regions. This suggests substantial sequestration potential in regrowing forests of the region, a trend that may be amplified through ongoing land abandonment, climate change, and CO2 fertilization. 相似文献
8.
Although metal legbands have been an important scientific tool, their use for estimation of harvest and survival relies on samples of dead birds harvested by hunters using shotguns. We hypothesized that the force of steel pellets discharged from a shotgun, within the range of conditions normally experienced by goose hunters, was sufficient to reduce probability of band retention. We conducted 8 experimental trials to estimate retention per round fired at aluminum bands normally applied to arctic-nesting geese in relation to effects of 1) target range (20 m vs. 40 m), 2) steel pellet size (4.57 mm [BB] vs. 3.81 mm [number 2]), 3) cartridge size (76.2 mm [3 in.] vs. 69.9 mm [2.75 in.]), and 4) number of rounds fired (up to 25). There was nearly complete band retention (0.999/round) at 40 m regardless of shot size or shell size used. Retention per round fired at 20 m declined to between 0.984 and 0.987 for number 2 shot and between 0.968 and 0.974 for BB shot. Our conclusions apply to unworn bands, so we recommend further simulations to assess how retention may change with age of bands as they erode or corrode on free-ranging geese. Bias in estimates associated with loss of older bands from shotgun discharge could be adjusted if bias is estimated as done in this article. © 2011 The Wildlife Society. 相似文献
9.
Alberto G. O. P. Barretto Göran Berndes Gerd Sparovek Stefan Wirsenius 《Global Change Biology》2013,19(6):1804-1815
Does agricultural intensification reduce the area used for agricultural production in Brazil? Census and other data for time periods 1975–1996 and 1996–2006 were processed and analyzed using Geographic Information System and statistical tools to investigate whether and if so, how, changes in yield and stocking rate coincide with changes in cropland and pasture area. Complementary medium‐resolution data on total farmland area changes were used in a spatially explicit assessment of the land‐use transitions that occurred in Brazil during 1960–2006. The analyses show that in agriculturally consolidated areas (mainly southern and southeastern Brazil), land‐use intensification (both on cropland and pastures) coincided with either contraction of both cropland and pasture areas, or cropland expansion at the expense of pastures, both cases resulting in farmland stability or contraction. In contrast, in agricultural frontier areas (i.e., the deforestation zones in central and northern Brazil), land‐use intensification coincided with expansion of agricultural lands. These observations provide support for the thesis that (i) technological improvements create incentives for expansion in agricultural frontier areas; and (ii) farmers are likely to reduce their managed acreage only if land becomes a scarce resource. The spatially explicit examination of land‐use transitions since 1960 reveals an expansion and gradual movement of the agricultural frontier toward the interior (center‐western Cerrado) of Brazil. It also indicates a possible initiation of a reversed trend in line with the forest transition theory, i.e., agricultural contraction and recurring forests in marginally suitable areas in southeastern Brazil, mainly within the Atlantic Forest biome. The significant reduction in deforestation that has taken place in recent years, despite rising food commodity prices, indicates that policies put in place to curb conversion of native vegetation to agriculture land might be effective. This can improve the prospects for protecting native vegetation by investing in agricultural intensification. 相似文献
10.
Richard A. Houghton 《Global Change Biology》2013,19(9):2609-2612
This study proposes that carbon fluxes identified as being from land use and land‐cover change (LULCC) include only that component of a flux that can be attributed to LULCC, exclusive of the effects of environmental change (CO2, climate, N, etc.). This proposal seems too obvious to need saying, but published estimates of the LULCC flux are widely variable for reasons that have more to do with modeling environmental effects than with LULCC. 相似文献
11.
We developed a continental energetics‐based model of daily mallard (Anas platyrhynchos) movement during the non‐breeding period (September to May) to predict year‐specific migration and overwinter occurrence. The model approximates movements and stopovers as functions of metabolism and weather, in terms of temperature and frozen precipitation (i.e., snow). The model is a Markov process operating at the population level and is parameterized through a review of literature. We applied the model to 62 years of daily weather data for the non‐breeding period. The average proportion of available habitat decreased as weather severity increased, with mortality decreasing as the proportion of available habitat increased. The most commonly used locations during the course of the non‐breeding period were generally consistent across years, with the most inter‐annual variation present in the overwintering area. Our model revealed that the distribution of mallards on the landscape changed more dramatically when the variation in daily available habitat was greater. The main routes for avian migration in North America were predicted by our simulations: the Atlantic, Mississippi, Central, and Pacific flyways. Our model predicted an average of 77.4% survivorship for the non‐breeding period across all years (range = 76.4%–78.4%), with lowest survivorship during autumn (90.5 ± 1.4%), intermediate survivorship in winter (91.8 ± 0.7%), and greatest survivorship in spring (93.6 ± 1.1%). We provide the parameters necessary for exploration within and among other taxa to leverage the generalizability of this migration model to a broader expanse of bird species, and across a range of climate change and land use/land cover change scenarios. 相似文献
12.
SIDNEY G. TAYLOR 《Global Change Biology》2008,14(2):229-235
Thirty‐four years (1972–2005) of water temperature data and extensive biological observations at Auke Creek, Alaska indicate a general warming trend that affected the native pink salmon (Oncorhynchus gorbuscha) population. Serial environmental records at nearby Auke Bay, Alaska over 46 years show trends of increasing air and sea surface temperatures. Trends of increased total precipitation and earlier date of ice out on nearby Auke Lake also occurred, but not at significant rates. Average water temperatures during the incubation of pink salmon in Auke Creek increased at a rate of 0.03 °C yr?1 over the 34‐year period. For the 1972–2005 broods, midpoints of fry migrations from Auke Creek ranged between April 2 and May 7, and there was a trend of earlier migration of pink salmon fry at a rate of ? 0.5 days yr?1. The migration timing of adult salmon into Auke Creek also showed a trend toward earlier timing. The earlier adult migration combined with warmer incubation temperatures are related to earlier migration of pink salmon fry. If the observed warming trend continues, Auke Creek may become unsuitable habitat for pink salmon. Given the trend for salmon fry to migrate earlier, a larger portion of the population may become mismatched with optimum environmental conditions during their early marine life history. If salmon adults continue to migrate into the creek earlier when water temperatures are commonly high, it will result in increased prespawning mortality. 相似文献
13.
土地利用变化是自然演变与人类活动共同作用的结果,大量的人口流动一定程度上将影响土地利用方式,进而对区域生态环境质量产生影响作用。因此,研究人口流动对土地利用变化的影响及生态效应,能为合理调控区域人地关系,促进区域生态环境与经济的平衡发展提供理论支持。基于长时序高空间分辨率土地利用数据,以具有典型移民现象的四川省凉山州为研究区,针对移民驱动下的土地利用时空变化特征及其诱发的生态效应进行研究分析。结果表明：（1）2000—2020年间,受人口迁移影响,凉山州土地资源的利用结构和程度都发生了相应改变,以耕地、草地、林地及不透水面的面积变化最为显著。在人口迁入较多的西昌、冕宁和德昌等县市内,供人类生活、生存所需要的耕地和建筑用地的数量显著增加;相反,对于大量人口迁出的喜德、昭觉和美姑等地区,人类活动强度的降低为生态用地的恢复和重建提供了条件,生态用地面积不断上涨。（2）受土地利用类型、地形条件、人口分布等因素的影响,凉山州整体生态环境质量呈西高东低、北高南低的空间分布格局。2000—2020年,整体生态环境质量仅下降了0.36%,总体较为稳定。（3）生态环境质量改善区域集中于东部的越西、美姑及昭觉等县市,而生态环境质量降低的区域主要位于盐源、会里、西昌和德昌等县市。生态环境质量的改变与区域移民活动存在紧密联系,其中由移民迁入引发的耕地和不透水面对生态用地的挤占,对生态环境质量退化贡献比重达87.97%,而随着移民迁出为生态工程的实施提供条件,凉山州内生态用地面积共增加775.84 km2。 相似文献
14.
15.
Pete Smith Joanna I. House Mercedes Bustamante Jaroslava Sobocká Richard Harper Genxing Pan Paul C. West Joanna M. Clark Tapan Adhya Cornelia Rumpel Keith Paustian Peter Kuikman M. Francesca Cotrufo Jane A. Elliott Richard McDowell Robert I. Griffiths Susumu Asakawa Alberte Bondeau Atul K. Jain Jeroen Meersmans Thomas A. M. Pugh 《Global Change Biology》2016,22(3):1008-1028
Soils are subject to varying degrees of direct or indirect human disturbance, constituting a major global change driver. Factoring out natural from direct and indirect human influence is not always straightforward, but some human activities have clear impacts. These include land‐use change, land management and land degradation (erosion, compaction, sealing and salinization). The intensity of land use also exerts a great impact on soils, and soils are also subject to indirect impacts arising from human activity, such as acid deposition (sulphur and nitrogen) and heavy metal pollution. In this critical review, we report the state‐of‐the‐art understanding of these global change pressures on soils, identify knowledge gaps and research challenges and highlight actions and policies to minimize adverse environmental impacts arising from these global change drivers. Soils are central to considerations of what constitutes sustainable intensification. Therefore, ensuring that vulnerable and high environmental value soils are considered when protecting important habitats and ecosystems, will help to reduce the pressure on land from global change drivers. To ensure that soils are protected as part of wider environmental efforts, a global soil resilience programme should be considered, to monitor, recover or sustain soil fertility and function, and to enhance the ecosystem services provided by soils. Soils cannot, and should not, be considered in isolation of the ecosystems that they underpin and vice versa. The role of soils in supporting ecosystems and natural capital needs greater recognition. The lasting legacy of the International Year of Soils in 2015 should be to put soils at the centre of policy supporting environmental protection and sustainable development. 相似文献
16.
Forest restoration is expected to play a pivotal role in reducing extinctions driven by deforestation and climate change over the next century. However, spatial and temporal patterns of restoration (both passive and active) are likely to be highly variable depending on degree of land use change as well as levels of forest and soil degradation and residual vegetation. Uncertainties regarding the spatial and temporal reinstatement of forest on degraded land make it difficult to determine where future investment in active restoration should be targeted. We used satellite data to quantify change in the extent and foliage projection cover (FPC) of woody vegetation returning to land previously cleared of subtropical rainforest in eastern Australia. We show a modest recovery of woody vegetation but document high variability in this trend between local areas, expanding by over 5% in some situations but declining by up to 2% in others over the last decade (1999–2009 period). This was accompanied by minor change in average FPC (?0.2 to 4.2%). Overall, decadal expansion in woody vegetation was most apparent in local areas with intermediate levels of existing forest reestablishment and was most likely to occur on steep terrain near existing vegetation. These results provide a valuable first evaluation of where restoration is occurring and the likely time frame required to meet conservation objectives under a business as usual scenario. This knowledge enables returns from current investment to be quantified and can be used to better allocate funds for restoration in the future. 相似文献
17.
Wei Li Philippe Ciais Bertrand Guenet Shushi Peng Jinfeng Chang Vincent Chaplot Sergey Khudyaev Anna Peregon Shilong Piao Yilong Wang Chao Yue 《Global Change Biology》2018,24(10):4731-4746
The net flux of CO2 exchanged with the atmosphere following grassland‐related land‐use change (LUC) depends on the subsequent temporal dynamics of soil organic carbon (SOC). Yet, the magnitude and timing of these dynamics are still unclear. We compiled a global data set of 836 paired‐sites to quantify temporal SOC changes after grassland‐related LUC. In order to discriminate between SOC losses from the initial ecosystem and gains from the secondary one, the post‐LUC time series of SOC data was combined with satellite‐based net primary production observations as a proxy of carbon input to the soil. Globally, land conversion from either cropland or forest into grassland leads to SOC accumulation; the reverse shows net SOC loss. The SOC response curves vary between different regions. Conversion of cropland to managed grassland results in more SOC accumulation than natural grassland recovery from abandoned cropland. We did not consider the biophysical variables (e.g., climate conditions and soil properties) when fitting the SOC turnover rate into the observation data but analyzed the relationships between the fitted turnover rate and these variables. The SOC turnover rate is significantly correlated with temperature and precipitation (p < 0.05), but not with the clay fraction of soils (p > 0.05). Comparing our results with predictions from bookkeeping models, we found that bookkeeping models overestimate by 56% of the long‐term (100 years horizon) cumulative SOC emissions for grassland‐related LUC types in tropical and temperate regions since 2000. We also tested the spatial representativeness of our data set and calculated SOC response curves using the representative subset of sites in each region. Our study provides new insight into the impact grassland‐related LUC on the global carbon budget and sheds light on the potential of grassland conservation for climate mitigation. 相似文献
18.
土壤有机碳是陆地碳库的重要组成部分,也是当前全球碳循环和全球变化研究的热点。土地利用/覆被变化及土地管理变化通过影响土壤有机碳的储量和分布,进而影响温室气体排放和陆地生态系统的碳通量。研究土地利用变化影响下的土壤有机碳储量及其动态变化规律,有助于加深理解全球气候变化与土地利用变化之间的关系。在阅读国内外有关文献的基础上,分别从土地利用及其管理方式变化的角度,概括了土地利用变化对土壤有机碳的影响过程与机理;针对当前研究的两大类方法,即实验方法和模型方法,分类详细介绍了它们各自的特点以及存在的一些问题。在此基础上,提出今后土地利用变化对土壤有机碳影响研究的发展趋势。 相似文献
19.
John W. Mallord Christopher J. Orsman Japheth T. Roberts Kwame Boafo Roger Q. Skeen Danaë K. Sheehan Juliet A. Vickery 《Ibis》2018,160(4):805-815
Populations of long‐distance migrant birds are declining but it is unknown what role land cover change in non‐breeding areas may be playing in this process. Using compositional analysis, we assessed habitat selection by one such migrant, the Wood Warbler Phylloscopus sibilatrix, at a wintering site in the forest–savannah transition zone in Eastern Region, Ghana. There was a preference for forest, a habitat that is in marked decline at this site. Annual habitat mapping revealed that the area of forest declined by 26% between 2011/12 and 2013/14, mainly through clearance for conversion to arable land. Numbers of birds changed throughout the season, but despite the reduction in the preferred forest habitat, there was no change in the total number of birds recorded at the site over the study period. The number of birds recorded at a point was positively related to the proportion of cleared land, plantation and, to a lesser extent, dense forest within 100 m. Investigation of the fine‐scale habitat preferences of radiotagged Wood Warblers suggested that there was an optimum number of trees, around 66–143 per hectare, at which estimated probability of occupancy was 0.5, falling to a probability of 0.2 at 25 trees per hectare. We suggest that Wood Warblers may be buffered against the loss of forest habitat by their ability to utilize degraded habitats, such as well‐wooded farmland, that still retain a substantial number of trees. However, the continued loss of trees, from both forest and farmland is ultimately likely to have a negative impact on wintering Wood Warblers in the long‐term. 相似文献
20.
A recently developed radar‐based technique permitted empirical re‐evaluation of the established but poorly supported theory that migrating North American waterfowl (Anatidae) use landscape features such as rivers as leading lines. Ducks departing the Illinois River Valley in the autumn of each of 15 years travelled SSE with a mean track that was 68° different from the 220° course of the Illinois River (P ≤ 0.001). We conclude that leading lines were unimportant navigation aids for ducks leaving this major stopover site in autumn and suggest that rivers have less effect on the spatial course of duck migration than previously thought. Timing of departures was examined in a representative subset of 8 years and found to be consistent, with a mean start time of 44 min after civil sunset. 相似文献