滇西南稻区白背飞虱种群特征及其关键影响因子

为明确滇西南沧源县稻区白背飞虱Sogatella furcifera的种群发生特征及其影响因子,于2010-2019年通过灯诱监测和田间调查的方法,分析沧源县白背飞虱的越冬种群、灯诱种群及田间种群发生特征,并对白背飞虱种群数量的影响因素进行相关性分析.结果表明:(1)白背飞虱以成、若虫在再生稻、落粒稻上越冬,越冬虫量最...     

基于标记-重捕模型开展野生动物红外相机种群监测的方法及案例

红外相机技术的广泛应用推动了动物种群生态学研究方法的发展和革新, 特别是基于标记-重捕模型框架通过非损伤取样方式对物种数量和密度等种群参数的可靠估计, 为保护濒危物种和评估保护成效提供了有力的科学依据。对于身体上具有独特天然标记的动物(如多数猫科动物), 可依据红外相机拍摄身体上的独特斑点或条纹鉴别个体, 再运用标记-重捕模型, 估计动物种群数量、密度等参数。本文概述了标记-重捕模型的基本原理、特点以及国内外的应用, 特别是近年来发展出的空间标记-重捕模型。总结了从相机布设到数据分析的具体流程、操作原则, 并以青城山家猫为实例, 展示了应用红外相机数据通过空间标记-重捕模型估计种群密度和数量的基本步骤。最后展望了该模型在种群动态、景观廊道设计、资源选择等方面的应用和发展趋势。     

云南师宗白背飞虱前期迁入种群的虫源地分布与降落机制

通过对1990—2012年云南省师宗县4—5月出现的白背飞虱灯诱高峰日进行轨迹模拟以及降虫高峰日的风场分析,得到以下结果:4月下旬,师宗上空盛行西风,白背飞虱虫源主要来自缅甸东北部,部分来自越南北部和金三角地区;5月份,西南风为盛行风向,其中上中旬的虫源地主要分布在越南西北部、老挝北部和滇西南,缅甸东北部可提供部分虫源;下旬则主要分布在滇西南,部分虫源来自越南西北部、老挝北部和缅甸东北部。对降虫高峰期的大气环流背景、峰日风温场、降雨等气象因子的分析结果表明,降水、风切变和气流垂直扰动是造成白背飞虱集中降落的主要因子。     

Variation in the abundance of Red-breasted Mergansers Mergus serrator on a Scottish river in relation to season, year, river hydrography, salmon density and spring culling

Red-breasted Mergansers Mergus serrator were counted in the river North Esk, Scotland, and on the sea nearby, 1987–1990. Pairs arrived at the river estuary from early winter, but the main influx to freshwater took place in late April and in May, when breeding pairs dispersed far upriver. Females began incubation from late May. Most young hatched in July and fledged by late September. Males left the river in June and congregated at an offshore moulting site, their numbers peaking in August, and dispersed rapidly in September.
Breeding density and total duckling production decreased with increasing distance upstream, decreasing river width and increasing gradient and elevation. The total number of breeding pairs and their distribution on the river were similar from year to year, despite variable numbers killed, suggesting a stable breeding population near the upper limit the habitat would support in those years. It also suggested that killing mergansers in April was an ineffective way to reduce the population. The spatial variation in merganser breeding density was not correlated with the density of their main spring food, parr of salmon Salmo salar , but could have been related to its availability.
The production of well-grown ducklings varied annually and was inversely correlated with river flow during the main period of hatch. It is argued that Red-breasted Mergansers breed late in the year because the hatching of ducklings in July coincides with an abundance of their food, large aquatic invertebrates and tiny juvenile fish.     

Population dynamics of Bemisia argentifolii (Homoptera: Aleyrodidae) on spring collard and relationship to yield in the lower Rio Grande Valley of Texas

Seasonal population dynamics of the silverleaf whitefly, Bemisia argentifolii Bellows & Perring [formerly known as the sweetpotato whitefly, B. tabaci (Gennadius) Biotype "B"], was investigated on collard (Brassica oleracea L. variety acephala) during spring 1998 and 1999 in the Lower Rio Grande Valley of Texas. Yield loss caused by whitefly was determined by using insecticides to suppress whitefly populations to a low level. Although B. argentifolii populations of adults and immatures fluctuated greatly from April to June during the two seasons, the relative values were similar. Adult whiteflies first appeared on the plants in early April, increased rapidly within the month, peaked in May, and declined at the end of the season in early or mid-June. Whitefly eggs appeared on plants soon after adults were found, but high numbers of eggs were observed on foliage until late May 1998 and mid- and late May 1999. Nymphs and pupae increased slowly before June 1998 and increased early in May 1999. Whitefly population levels appeared to be positively associated with the availability and the growth of host plants until plant maturation, afterward being negatively related with plant quality in the late season. Temperature, rainfall, and natural enemies were not key factors in regulating population dynamics during the two seasons. Collard plants with heavy infestations of whiteflies were unmarketable because of the damage caused by honeydew and sooty mold on the foliage. Application of a combination of fenpropathrin (Danitol) and acephate (Orthene) not only significantly reduced the whitefly infestation levels but also reduced plant foliar damage, resulting in marketable foliage with six to seven times greater yield and higher quality compared with the untreated plants.     

The influence of planting date,transgenic Bt maize and hybrid relative maturity on European corn borer Ostrinia nubilalis (Lepidoptera: Crambidae) ovipositional patterns

A three year study was carried out at Hoytville and at Wooster, Ohio, USA from 2006 to 2008 to investigate the influence of planting date, transgenic maize and hybrid maturity on Ostrinia nubilalis (Hubner) population dynamics and oviposition patterns. Maize plants were planted in late April or early May, mid‐May and early June during each year. The moth flight pattern showed bivoltine generations during the three years. The first moth flight peaked in June, with the populations declining during July. The second moth flight peaked in August and declined towards the end of September or early October. Egg mass density did not differ significantly between transgenic and non‐transgenic maize of different maturities. Significant differences were observed, however, among planting dates, sampling dates, and sampling date × planting date interactions. Generally higher numbers of egg masses from second generation moths were deposited on late planted maize than middle and early plantings.     

基于红外相机数据评估华南地区豹猫的种群密度和活动节律

可靠的种群密度数据对野生动物的保护和管理十分重要。豹猫(Prionailurus bengalensis)是中国分布最广且常见的猫科动物, 但野生种群密度估算的研究并不多。本研究于2020年6月至2021年5月在香港新界嘉道理农场暨植物园开展红外相机调查, 利用空间标记-重捕法估算当地豹猫的种群密度并用核密度估计方法分析其活动节律。本次调查以网格方式布置红外相机, 在约1.5 km²的研究范围之内设置了19个相机位点, 每个位点安装2台相机以获取豹猫身体两侧花纹来进行个体识别。连续12个月调查共捕获113次有效的豹猫拍摄事件, 当中仅61次事件的照片足够清晰以进行个体识别。基于种群封闭的要求, 我们以2个月为单位将12个月的数据分为6个采样期去分析豹猫种群密度, 结果显示仅两个采样期的估算值最为准确, 分别为0.64 ± 0.31 (0.26-1.55)只/km²和0.87 ± 0.48 (0.31-2.40)只/km², 是已知全球豹猫密度最高的地点之一。结果还发现, 雨季研究地点的豹猫并无明显的日活动节律, 在旱季则偏夜行-晨昏行性多一些, 但也有一定的日间活动; 雨季和旱季的日活动节律无显著差异。本研究是首次以个体识别配以空间标记-重捕模型对中国大陆地区豹猫种群密度调查的研究; 我们也提出一些关于红外相机架设方法的建议, 以提高照片个体识别的准确度并增加重捕次数, 最后提高密度估算的准确度。本研究也进一步证明豹猫适应性极强, 在活动节律上表现出极高的可塑性, 在严格保护下可以恢复健康的种群。     

Seasonal prevalence and susceptibility to agrochemicals of Tyrophagus similis (Acari: Acaridae) in spinach buds and agricultural soil under greenhouse conditions

Seasonal prevalence of Tyrophagus similis was investigated from 1997 to 1998 in two spinach greenhouses in central Japan. Susceptibility of T. similis to agrochemicals was also tested in the laboratory. Tyrophagus similis density in the soil was low during the high temperature period from May to August. The density rapidly increased in late autumn and remained at a high level during the cool season from December to February. The number further increased in April and then rapidly decreased in May. The high temperatures in the greenhouses from spring to early autumn are considered the main causes of population decrease. Mites on spinach buds increased the number after those on and in the soil increased. Mites attacked spinach buds mostly in late autumn and early spring. Dichlorvos did not reduce the number of mites in either greenhouse even though it was highly toxic under laboratory condition. This discrepancy suggests that the mites in both the soil and spinach buds had little direct contact with the chemicals. These data suggest that once crop damage by mites is detected, it is usually too late to use chemicals, and that mites that live in the buds are protected from agrochemicals. This revised version was published online in July 2006 with corrections to the Cover Date.     

Seasonal prevalence and susceptibility to agrochemicals of Tyrophagus similis (Acari: Acaridae) in spinach buds and agricultural soil under greenhouse conditions

Seasonal prevalence of Tyrophagus similis was investigated from 1997 to 1998 in two spinach greenhouses in central Japan. Susceptibility of T. similis to agrochemicals was also tested in the laboratory. Tyrophagus similis density in the soil was low during the high temperature period from May to August. The density rapidly increased in late autumn and remained at a high level during the cool season from December to February. The number further increased in April and then rapidly decreased in May. The high temperatures in the greenhouses from spring to early autumn are considered the main causes of population decrease. Mites on spinach buds increased the number after those on and in the soil increased. Mites attacked spinach buds mostly in late autumn and early spring. Dichlorvos did not reduce the number of mites in either greenhouse even though it was highly toxic under laboratory condition. This discrepancy suggests that the mites in both the soil and spinach buds had little direct contact with the chemicals. These data suggest that once crop damage by mites is detected, it is usually too late to use chemicals, and that mites that live in the buds are protected from agrochemicals.     

Spatial and temporal patterns of abundance of the potato leafhopper among red maples

A study was conducted in the 2001 growing season to examine the relative abundance, dispersion and distribution of the potato leafhopper (Empoasca fabae) among trees of 24 red maple (Acer rubrum) clonal selections. Yellow sticky traps hung from the trees were used to estimate the relative number of aerial potato leafhoppers among trees, starting on 1 May 2001 and stopping on 4 September 2001. More insects were collected from the east side of the plot than from the other sides in May, but no differences were significant late in the season. Few leafhoppers were collected during May, but the number of leafhoppers collected on traps rapidly increased and peaked during June. Afterwards, populations decreased and just a few individuals were trapped late in the season. Overall, significantly more leafhoppers were caught on traps hanging from trees of clone 56026 and 55410 than on trees of the other clones. Dispersion of the potato leafhopper changed from being aggregated in May, to being random in August, and also differed among the different clones. Populations tended to aggregate with increases in population numbers. Positive significant autocorrelations were detected at short distances in May, suggesting an aggregated spatial pattern early in the season. Yet, different autocorrelation patterns were detected within each block later in the season. Our results indicate that management practices could be developed to minimise pesticide use by targeting smaller areas with the highest populations at the right time of the season.     

A Comparison of Grizzly Bear Demographic Parameters Estimated from Non-Spatial and Spatial Open Population Capture-Recapture Models

Capture-recapture studies are frequently used to monitor the status and trends of wildlife populations. Detection histories from individual animals are used to estimate probability of detection and abundance or density. The accuracy of abundance and density estimates depends on the ability to model factors affecting detection probability. Non-spatial capture-recapture models have recently evolved into spatial capture-recapture models that directly include the effect of distances between an animal’s home range centre and trap locations on detection probability. Most studies comparing non-spatial and spatial capture-recapture biases focussed on single year models and no studies have compared the accuracy of demographic parameter estimates from open population models. We applied open population non-spatial and spatial capture-recapture models to three years of grizzly bear DNA-based data from Banff National Park and simulated data sets. The two models produced similar estimates of grizzly bear apparent survival, per capita recruitment, and population growth rates but the spatial capture-recapture models had better fit. Simulations showed that spatial capture-recapture models produced more accurate parameter estimates with better credible interval coverage than non-spatial capture-recapture models. Non-spatial capture-recapture models produced negatively biased estimates of apparent survival and positively biased estimates of per capita recruitment. The spatial capture-recapture grizzly bear population growth rates and 95% highest posterior density averaged across the three years were 0.925 (0.786–1.071) for females, 0.844 (0.703–0.975) for males, and 0.882 (0.779–0.981) for females and males combined. The non-spatial capture-recapture population growth rates were 0.894 (0.758–1.024) for females, 0.825 (0.700–0.948) for males, and 0.863 (0.771–0.957) for both sexes. The combination of low densities, low reproductive rates, and predominantly negative population growth rates suggest that Banff National Park’s population of grizzly bears requires continued conservation-oriented management actions.     

标记重捕法对模式产地霸王岭睑虎种群资源调查

霸王岭睑虎Goniurosaurus bawanglingensis是海南岛特有种,自2002年被命名以来,因种群数量小、分布区窄、栖息地破碎化等因素被《中国生物多样性红色名录》列为易危(VU)等级,种群资源现状尚不清楚。2018年7—8月,根据霸王岭睑虎种群分布,在模式产地霸王岭国家级自然保护区内选择了2个样区,首次采用植入电子标签的标记重捕法对种群密度、性比、窝卵数、成幼比等开展调查,并比较了雌雄个体的形态特征。结果显示:样区A种群密度为846只/hm^2,性比1.6∶1,成幼比7∶1;样区B种群密度为591只/hm 2,性比1.2∶1,成幼比10∶1。窝卵数为1~3枚,87%的窝卵数为2枚。身体量度特征(除吻长外)在两性间差异无统计学意义。研究结果进一步补充了霸王岭睑虎的基础生态学资料,可为资源状况评估和保护提供依据。此外,本研究证实了植入电子标签是对睑虎属Goniurosaurus物种野外标记研究的一种简单、有效的方法,可对动物进行长期标记。     

Some population dynamics of the Bank vole, Clethrionomys glareolus and the Wood mouse, Apodemus sylvaticus in mixed woodland

The population dynamics of Clethrionomys glareolus Schr.and Apodemus sylvaticus (L.) in mixed woodland in County Durham, were studied from March 1963 to January 1965. Two areas of 0.9 ha (2.25 acres) each were trapped monthly and information was obtained on population size, reproduction, survival and growth from marked animals.
Clethrionomys populations increased from June to an autumn peak; then declined, at first rapidly, but then more slowly in winter, before reaching a spring trough. The breeding season of Clethrionomys was from May to December; juveniles were caught from mid-June to December. Survival was in general poor during the breeding season but good at other times. Survival of young born early in the summer was particularly good on one of the areas and some individuals lived long enough to breed in two successive years. On both areas young born early in the year matured rapidly and bred in the year of their birth. Young born in late summer and early autumn ceased growing at a weight of about 14.5 g, remained immature, and formed the bulk of the overwintering population. Growth was completed at the time of sexual maturation the following spring.
Trapping failed to provide adequate samples of juvenile Apodemus in summer to account for subsequent recruitment. The possibility that a substantial proportion of the adult population of this species was also either trap shy or had emigrated temporarily is discussed. Breeding occurred from April until the following January, but the numbers trapped remained very low throughout the early months of the breeding season. Large scale recruitment of young fecund animals into the trap-revealed population occurred during the autumn. Apodemus males continued to grow rapidly during the winter.     

A computer simulation of the epidemiology of the rice dwarf virus

An epidemiological system model was developed to evaluate the role of factors which were responsible for the prevalence of rice dwarf virus (RDV) transmitted by the green rice leafhopper, Nephotettix cincticeps. Simulation tests were conducted by varying values of the following three parameters: the vector density, the coefficient of the efficiency of feeding acquisition of RDV of the vector, and that of efficiency of RDV transmission by the vector. The effect of each parameter was assessed in terms of changes in percentages of infected insects and of infected rice hills. Both the percentages of infected insects and of infected rice hills increased rapidly with increasing vector density within a range of low vector density. The former increased linearly when the acquisitive coefficient was increased. But the percentage of infected rice hills was affected to a lesser extent. The percentage of infected insects and that of infected rice hills increased exponentially with increasing values of the transmission coefficient. The results obtained from the simulation tests were discussed in relation to the ecological factors which caused the recent prevalence of RDV.     

Factors affecting detection probability of burrowing owls in southwest agroecosystem environments

Estimating range-wide population trends of western burrowing owls (Athene cunicularia) requires standardized survey protocols that correct for detection bias in environments that support large owl populations. High concentrations of owls exist in irrigated agroecosystems within the southwest United States, yet little is known about the factors that affect detection bias during owl surveys in these systems. I used closed-population capture-recapture models to evaluate 4 factors that could affect the probability of a surveyor detecting an owl activity center (i.e., nest burrow) during visual surveys where owls are the focal object and analyzed the relationship (linear or curvilinear) between specific factors and detection probability. I recorded 1,199 detections of owls from 132 capture-recapture surveys within 12 sites of the Imperial Valley agroecosystem in California, USA between 16 April and 20 May 2006. I also conducted 96 time budget surveys throughout the day and used mixed linear models to evaluate the effect of each factor on probability of an owl activity center being available for detection (i.e., ≥1 owls above ground) during surveys. Model selection results indicated that detection probability was influenced by ambient air temperature interacting with wind speed. Detection probability followed a curvilinear relationship that resembled bell-shaped curve along a temperature gradient, with the maximum detection probability shifting as a function of wind speed. At low temperatures, detection probability declined with increased wind speed, but this relationship was reversed at high temperatures, producing a 3-dimensional pattern in detection probability characterized by a saddle-shaped hyperbolic paraboloid response surface. The probability of an activity center being available for detection declined curvilinearly with increased temperature and explained 51% of the variation in detection probability. Given the broad range of detection probabilities, correcting visual survey counts for detection bias is necessary for comparing population estimates among regions and through time. Survey designs intended to estimate abundance of owls in southwest agroecosystems should incorporate methods to estimate and correct for variation in detection probability that include measurements of ambient temperature and wind speed for use as covariates. © 2011 The Wildlife Society.     

Life-cycle variation inPanonychus akitanus Ehara (Acarina:Tetranychidae)

The life history ofPanonychus akitanus Ehara was studied in two Hokkaido populations on dwarf bamboos. The Sapporo population overwintered both as egg and female adult onSasa senanensis, and the Tomakomai population overwintered as egg onSasa apoiensis. Mites of the Sapporo population produced four or five generations from late April to late November or early December. The eggs that had overwintered began to hatch in mid-May, and this hatching period overlapped with that of eggs laid in late April by females that had overwintered. Therefore, mites with different overwintering stages would interbreed. Most eggs that had overwintered in the Tomakomai population hatched in mid-May, and about four generations were produced before early December, when only eggs were found. The density of mites per leaf of the Sapporo population reached a maximum in early May on old leaves and in late June on new leaves, and thereafter gradually decreased. The Tomakomai population initially decreased in density after hatching in the spring, but rapidly dispersed to new leaves, reached a peak in early September, and then gradually decreased. The maximal density was about 10 times higher and the distribution was less clumped (lower values of the aggregation index,m/m) than that of the Sapporo population. This was probably because the Sapporo mites could utilize only the underside of sporadically distributed leaves which were curled by spiders, whereas the Tomakomai mites inhabited any part of the leaf undersurface of the hairy host plant. Predators observed were phytoseiid mites and larvae of gall midges. The predatory effect on the Sapporo population was not clear. In the Tomakomai population, the number of gall midges correlated with the number of spider mites better than that of phytoseiid mites.     

转cry1Ab/vip3H+epsps基因粳稻对非靶标害虫稻叶蝉田间种群的影响

转基因作物可能带来的风险之一是对非靶标生物尤其是非靶标植食者产生潜在的影响。本研究采用吸虫器取样法, 通过在浙江长兴2地点3年的试验评价了新型抗虫/耐除草剂转cry1Ab/vip3H+epsps基因粳稻（G6H1）及其亲本对照（秀水110, XS110）对稻叶蝉田间种群动态的影响。结果表明： 叶蝉类主要有黑尾叶蝉Nephotettix cincticeps (Uhler)、 二点叶蝉Cicadula fascifrons (Stål)和电光叶蝉Deltocephalus dorsalis Motschulsky组成, 其中黑尾叶蝉是优势种。虽然3种叶蝉的种群密度随着地点和年份的不同有所不同, 但是转基因水稻对3种叶蝉种群密度的年度变化均没有显著性影响。少数年份, 黑尾叶蝉成虫、 若虫及其两者总密度的时间动态在转基因水稻和对照田之间存在差异, 大多数年份, 趋势一致且无显著差异 （P>0.05）。另外, 二点叶蝉和电光叶蝉种群的时间动态在转基因水稻和对照田之间也相似。综合评价认为, 本供试转基因水稻品系G6H1对稻田稻叶蝉种群无明显的负面影响。     

Review of capture-recapture methods applicable to noninvasive genetic sampling

The use of noninvasive genetic sampling to identify individual animals for capture-recapture studies has become widespread in the past decade. Strong emphasis has been placed on the field protocols and genetic analyses with fruitful results. Little attention has been paid to the capture-recapture application for this specific type of data beyond stating the effects of assumption violations. Here, we review the broad class of capture-recapture methods that are available for use with DNA-based capture-recapture data, noting the array of biologically interesting parameters such as survival, emigration rates, state transition rates and the finite rate of population change that can be estimated from such data. We highlight recent developments in capture-recapture theory specifically designed for noninvasive genetic sampling data.     

大中型兽类种群数量估算的研究进展

大中型兽类种群数量的估算是动物生态学中重要的基本问题, 受到研究者、管理者和公众的共同关注。国际上从20世纪中期开始研究该问题, 已出现了多种研究方法和相应案例, 且还在快速发展, 但世界各地仍有很多物种的种群数量尚未知晓。在我国, 从20世纪80年代开始调查大中型兽类种群数量, 取得了重要进展, 也还有很多物种的种群数量尚不清楚。因此, 有必要归纳国际上种群数量估算的研究进展, 同时, 总结国内研究的现状、优势和趋势, 供研究者参考。本文首先选择估算大中型兽类种群数量的原理、数据来源和模型这3个要素归纳出简明的研究框架, 将现有的多种方法置于其中予以阐述。在该框架下, 根据估算原理分为4大类方法, 为距离取样法、标志重捕法、基于遇见率法和遥感影像直接计数法。针对每一大类方法, 论述其基本原理模型和模型假设, 说明能实现该原理的相应数据来源(视觉观测、红外相机拍摄、DNA微卫星识别、卫星定位跟踪、声音监测或遥感影像)的特点及如何实现该原理, 评价其适用性及优缺点, 并选择其中具有可比性的方法予以比较评价。其次, 参照该研究框架, 总结我国的研究现状, 分析未来发展的优势和趋势: 我国的红外相机数据积累充分, 可以发展以此为数据源的距离取样法、标志重捕法和基于遇见率法; 发展以粪便样品为数据来源的距离取样法和粪便DNA标志重捕法; 相比地面调查数据, 获取高分辨率遥感影像数据更容易, 尽量以此估算符合适用条件的大中型兽类的种群数量。最后, 本文提出了适用于我国大中型兽类种群数量的估算方法的选择流程, 供研究者参考。     

Monitoring populations of Western Sandpipers and Pacific Dunlins during northward migration on the Fraser River Delta,British Columbia, 1991–2013

The Fraser River Delta in British Columbia, Canada, is a globally significant stopover site for shorebirds, but the population status and trends of many species that use the site remain uncertain. We describe an ongoing program to monitor population trends of the two most abundant species, Western Sandpipers (Calidris mauri) and Dunlins (Calidris alpina), during northward migration. Counts of these species were conducted at a mudflat where large flocks assembled at mid‐tide from 15 April to 15 May, 1991–2013, and we estimated species‐specific counts as the product of daily total flock counts and species proportions obtained during supplementary sampling. The median peak count of both species combined was 177,000 birds, and occurred between 24 April and 3 May. Ratios (proportions) of the two species followed a predictable pattern during the migration period, with a low proportion of Western Sandpipers (3%–20%) in flocks before 20 April, followed by a rapid increase to 80%–100% between 25 April and 10 May and a variable decrease to 30%–80% by 15 May. Mean counts of Western Sandpipers showed no significant trend over the study period. Mean counts of Dunlins showed a non‐linear trend, decreasing until 2001 and then increasing to 2013. Bias and random error in field counts were quantified by comparing field counts to counts made from photographs taken during surveys, and analysis revealed that field counts had a downward, but predictable, bias, accounting for >90% of birds present, with a stochastic error rate of 28.0%. Uncertainty in total population estimates was high after accounting for the effect of length of stay and sampling error. Population estimates suggested that 600,000 Western Sandpipers and 200,000 Dunlins typically passed through the site during northward migration. Our estimates indicate the usefulness of daily counts at major stopover sites during northward migration as an effective tool for monitoring shorebird populations, and underscore the need for conserving such sites.