Large-scale habitat use of some declining British birds

1. Large-scale habitat use of eight species of breeding birds was considered using data collected across Britain. The species were skylark Alauda arvensis (L.), dunnock Prunella modularis (L.), blackbird Turdus merula (L.), song thrush Turdus philomelos (L.), starling Sturnus vulgaris (L.), linnet Carduelis cannabina (L.), bullfinch Pyrrhula pyrrhula (L.) and reed bunting Emberiza schoeniclus (L.). All are linked by roughly synchronous population declines over the last 25 years in southern Britain (and mostly in farmland landscapes). Discussion is limited to the conservation status of these species.
2. Breeding densities were estimated for broad habitat types and these were used to estimate population sizes within habitat types. Confidence limits on the estimates were derived using a bootstrap procedure.
3. For most species considered, farmland holds a high proportion of their population (in excess of 50% for four species), reflecting the predominance of this land use across Britain. This suggests that sympathetic changes in farming practices are likely to provide the best mechanism for improving the status of these species.
4. Substantial proportions of particular species occur outside farmland, but different species occur in different habitats. A considerable proportion of skylarks occur on upland moor, bullfinches in wooded habitats, and reed buntings in riparian habitats. Conservation of this group of species thus requires appropriate management of the wider countryside, including their main habitats.
5. Habitats associated with human habitation hold > 20% of the British populations of blackbird, song thrush and starling, and considerable numbers of other species. The management of parks, gardens and other 'green space' may have an important impact on their populations and should not be neglected by conservationists.     

Line transect sampling from a curving path

Cutting straight line transects through dense forest is time consuming and expensive when large areas need to be surveyed for rare or highly clustered species. We argue that existing paths or game trails may be suitable as transects for line transect sampling even though they will not, in general, run straight. Formulas and software currently used to estimate local density using perpendicular distance data can be used with closest approach distances measured from curving transects. Suitable paths or trails are those for which the minimum radius of curvature is rarely less than the width of the shoulder in the detection probability function. The use of existing paths carries the risk of bias resulting from unrepresentative sampling of available habitats, and this must be weighed against the increase in coverage available.     

Assessing the Relative Efficiency of Termite Sampling Methods along a Rainfall Gradient in African Savannas

Although termites are ecosystem engineers in tropical and sub‐tropical environments, the study of termite ecology is often constrained by sampling difficulties and a lack of established sampling protocols, particularly for savannas. The efficiency and relevance of different methods along climatic gradients, even within a single biome, is largely unknown. Here, we compare the relative contribution of two commonly used sampling methods, cellulose baits and active searching transects, in quantifying savanna termite diversity along a rainfall gradient in South Africa; sampling was conducted during the wet season across four markedly different savanna types. We also assessed the usefulness of different forms of baiting techniques. The relative efficiency of sampling method varied with annual rainfall. In arid savannas, baiting was as effective as active searching transects at sampling termite diversity and we recommend the use of baiting rather due to it being less labor intensive. In savannas of moderately low to intermediate rainfall, baiting and transects sampled different termite species and so both are deemed necessary for an accurate assessment of termite diversity. In contrast, in wetter savannas transects gave a better assessment of diversity, with cellulose baits not contributing much to diversity assessment. The efficiency of baiting techniques differed across the rainfall gradient, with baits needing to be left in the field for a longer period in more arid savannas. We conclude that habitat type, even within a single biome, will determine the sampling method or methods necessary to quantify termite diversity accurately.     

鸟类调查的样线法和样点法比较:以崇明东滩春季盐沼鸟类调查为例

为了探讨样线法和样点法对盐沼湿地鸟类调查的有效性及适用性, 我们于2008年3–5月采用固定距离样线法和固定半径样点法对崇明东滩盐沼鸟类进行了调查。5次调查共记录到鸟类24种, 其中样线法记录到19种, 样点法记录到21种, 两种调查方法平均每次记录到的鸟类种数没有显著差异, 表明两种方法对盐沼鸟类种类的发现能力相似。两种方法得到的鸟类密度之间有显著的相关性,说明两种方法在反映鸟类群落中每种鸟类的相对数量方面具有可比性。但除了仅在一种调查方法中记录到的种类, 样点法调查得到的每种鸟类密度和鸟类总密度均高于样线法的调查结果。因此, 在对鸟类种群或群落的时空特征进行比较时, 需要考虑所采用的调查方法对调查结果的影响。     

Review of Some Important Techniques in Wildlife Sampling and Sampling Errors

This paper reviews some of the important methods for estimating animal numbers or densities based on (i) direct counts of population units as used in quadrat, strip, line-transect and line-intercept sampling and (ii) indirect counts and indices, such as capture-mark recapture, change-in-ratio, catch-effort methods and indices based on track counts, call, roadside and pellet-group counts, etc.     

Estimating the Barents Sea polar bear subpopulation size

A large-scale survey was conducted in August 2004 to estimate the size of the Barents Sea polar bear subpopulation. We combined helicopter line transect distance sampling (DS) surveys in most of the survey area with total counts in small areas not suitable for DS. Due to weather constraints we failed to survey some of the areas originally planned to be covered by DS. For those, abundance was estimated using a ratio estimator, in which the auxiliary variable was the number of satellite telemetry fixes (in previous years). We estimated that the Barents Sea subpopulation had approximately 2,650 (95% CI approximately 1,900–3,600) bears. Given current intense interest in polar bear management due to the potentially disastrous effects of climate change, it is surprising that many subpopulation sizes are still unknown. We show here that line transect sampling is a promising method for addressing the need for abundance estimates.     

Spatial sampling to detect slug abundance in an arable field

Overuse of molluscicides by farmers in arable systems can lead to environmental and product contamination. Here we assess a simple and inexpensive surface trapping method for monitoring populations of slugs (Deroceras reticulatum and Arion intermedius). This method was biased against small slugs, and against A. intermedius, when compared to direct soil sampling. Regression was used to model the relationship between the results of surface trapping and soil sampling methods. Spatial Analysis by Distance IndicEs (SADIE) algorithms were used to describe the spatial relationships between the two sets of samples. Using both traditional statistical methods and spatial statistics, the spatial information collected from surface traps was sufficient to identify patches and gaps in slug numbers and possibly to allow the spot application of slug control, and thus provide land managers who experience slug damage with a way of reducing molluscicides use, whilst maintaining slug control. Further improvements and applications of the model are discussed.     

Point Transect Sampling Along Linear Features

Summary Distance sampling is a widely used methodology for assessing animal abundance. A key requirement of distance sampling is that samplers (lines or points) are placed according to a randomized design, which ensures that samplers are positioned independently of animals. Often samplers are placed along linear features such as roads, so that bias is expected if animals are not uniformly distributed with respect to distance from the linear feature. We present an approach for analyzing distance data from a survey when the samplers are points placed along a linear feature. Based on results from a simulation study and from a survey of Irish hares in Northern Ireland conducted from roads, we conclude that large bias may result if the position of samplers is not randomized, and analysis methods fail to account for nonuniformity.     

Efficient single-survey estimation of carnivore density using fecal DNA and spatial capture-recapture: a bobcat case study

Population density estimates are necessary to inform management and conservation, yet are difficult to obtain for cryptic species such as carnivores, and often require intensive sampling. We implemented a single-survey, closed session, scat sampling protocol to estimate bobcat density using fecal DNA and spatial capture-recapture at two sites over five sessions in Virginia, USA. We employed a Poisson encounter model to allow for multiple detections on scat transect segments over a single collection interval, and compared single session and multistrata (closed, multi-site, multisession) spatial capture-recapture (SCR) approaches to estimate density for each site and session. We found improved precision for most estimates using the multistrata SCR approach, sharing data on baseline detection and individual movement across sites and sessions. We suggest the summer session estimates are representative of the resident population, that differences in density between summer and winter are representative of potential net recruitment, and that differences between consecutive summer sessions are representative of the net recruitment realized for the population (dependent on survival and emigration). Finally, we assessed factors affecting precision in single session model estimates and provide recommendations to improve detection and reduce credible intervals that may be applicable across the bobcat range and to other carnivore species. The single survey transect methodology provides flexibility in monitoring carnivore populations specifically, or as part of concurrent monitoring for multiple carnivore species. This methodology has potential to dramatically increase the effectiveness of conservation and management dollars, improving our ability to monitor carnivore populations and assess conservation needs and actions.     

Impacts of grazing and burning on spider assemblages in dry eucalypt forests of north‐eastern New South Wales,Australia

Abstract In the dry eucalypt forests of north‐eastern New South Wales, Australia, cattle grazing occurs at low intensities and is accompanied by frequent low‐intensity burning. This study investigated the combined effects of this management practice on the ground‐dwelling and arboreal (low vegetation) spider assemblages. Spiders were sampled at 49 sites representing a range of grazing intensities, using pitfall trapping, litter extraction and sweep sampling. A total of 237 spider morphospecies from 37 families were collected using this composite sampling strategy. The abundance, richness, composition and structure of spider assemblages in grazed and ungrazed forest sites were compared and related to a range of environmental variables. Spider assemblages responded to a range of environmental factors at the landscape, habitat and microhabitat scales. Forest type, spatial relationships and habitat variability at the site scale were more important in determining spider assemblages than localized low‐intensity grazing and burning. However, it is possible that a threshold intensity of grazing may exist, above which spiders respond to grazing and burning. Although low‐intensity grazing and burning may not affect spider assemblages below a threshold stocking rate, that stocking rate has yet to be established.     

Techniques for assessing the abundance of Brown Hares Lepus europaeus

Over the last few decades, there have been significant declines in Brown Hare Lepus europaeus numbers throughout Europe, leading to concern for their status in many countries. In Britain, there were no quantified data on the extent of this decline, on current population levels, or any baseline against which to monitor future population changes. The need for a quantified national hare survey led to this evaluation of the techniques available to assess hare numbers. Published information on counting hares is reviewed, and various techniques compared by applying them to a number of sites in southern England. Three basic approaches are available: counts of inactive hares, counts of active hares and indirect methods. Counts of inactive hares include total clearance, wide belt and line transect counts. Total clearance counts give an absolute figure, but are labour intensive and can only be applied to restricted areas. Wide-belt assessments are difficult to apply in certain habitats and even in open areas tend to produce a substantial over-estimate. Line transect counts are easy to undertake and are not labour intensive but should only be applied to large areas, or data from several small areas combined. Counts based on active hares are more problematical, because it is difficult to determine what proportion of the population is inactive at any one time. Spotlight counts based on variable circular plots are the most accurate but difficult to apply widely, and twilight counts are very subjective in their interpretation, especially when surveying small areas or areas with a large proportion of concealing habitats. Of the indirect methods, dung pellet counts can be valuable in specific areas but are difficult to apply across a range of habitats. We concluded that, of the various techniques considered, line transect counts have the greatest potential for a national survey, but need to be stratified so that enough transects are undertaken within each habitat stratum to obtain a reliable mean population estimate for each stratum.     

Relative efficiency of pitfall trapping and hand-collecting from plots for sampling of millipedes

Millipedes were sampled by hand-collecting from plots and by pitfall trapping at three forest sites in central Tasmania. Seven days of pitfall trapping each month over one year was less efficient than four weeks of hand-collecting in autumn, yielding fewer species and fewer specimens per working day in the field. Hand-collecting is likely to provide more accurate data on species diversity and relative abundance for a range of litter invertebrates.     

An odometre for underwater transects

A simple device for the measurement of length (or area) along an underwater transect is described. This instrument is pushed or pulled by SCUBA divers along lake or river bottoms and the rotation of a paddle wheel is recorded on a digital counter. The device eliminates the need for straight line and smooth bottom transects, and allows for greater versatility than that provided by the more usual rope line transect.     

Evaluation of a sweep net electrofishing method for the collection of small fish and shrimp in lotic freshwater environments

A major limitation of methods for collecting small fish and shrimp is that no single method is equally effective for all species or all life history stages. We compared the efficacy of the sweep net electrofishing (SNE) method with two other commonly used sampling methods for the collection of small fish and shrimp, the standard sweep net (SW) and the point abundance electrofishing (PAE) method developed by Copp & Penaz (1988). The effectiveness of the three methods was compared under three different current speeds in an Australian lowland river. The SNE method collected an order of magnitude more shrimp and a greater size range than the other two methods, irrespective of the current speed. The SNE method captured a similar number of fish to the SW method, but significantly more individuals than the PAE method. However, the two electrofishing methods caught a greater size range of both fish and shrimp than did the SW method. The effectiveness of the SNE method appears to be due to its ability to immediately capture shocked individuals, thereby lessening the likelihood of escape. Whilst the SNE method is not quantitative, its high level of effectiveness is likely to be particularly useful in systems with low densities of fish and shrimp.     

Prevalence and effects of Argemone Mexicana (Papaveraceae) on biodiversity in Ethiopia

The prevalence and potentials of Argemone mexicana on biodiversity was assessed at Farta, Gondar and Bahir Dar zuria districts. The study areas were stratified into 100 m by 5 m as roadside, fallow land and farmland transect belts. Its effects as poultry feed component were studied on three poultry breeds. Body weights, abnormalities in appetite, egg production and health were recorded. The results indicated that the mean prevalence of Argemone per transect belt in roadside land (17.41 ± 5.9) was higher than that of fallow land (3.35 ± 0.8) and farmland (2.65 ± 0.8) at Farta district. The number and distribution of native plant species under the shed of A. mexicana in roadside, fallow land and farmland per transect belts were 1.15 ± 1.6, 2.25 ± 1.8 and 1.15 ± 0.5, respectively. The number and distribution of Argemone plants in the roadside land per transect increased by 163.4%, 158.5% and 151.9% from 2006 to 2010 in above respective districts. The mean losses in appetite, body weight and egg production were higher in exotic and cross bred than in indigenous chicken ecotypes. Therefore, A. mexicana had negative impacts on biodiversity, native plant species and when used as animal feed components.