Avian Diversity in Agricultural Landscape: Records from Burdwan,West Bengal,India

Avianspecies assemblages are potential indicators of integrity and stability of ecosystem structure and functions. Characteristic avian fauna in landscapes enable predictions about the environmental state and possible deviations in the ecosystem functions. Documentation of avian species assemblages in different landscapes are therefore being emphasized from environmental monitoring perspective. As a primary effort, the present commentary depicts the avian species assemblage of agricultural landscapes, using Burdwan, West Bengal, India, as a study area. Employing line-transect method of continuous survey and opportunistic encounter, a total of 144 bird species under 51 families and 19 orders were recorded from the study area. The avian species richness was highest for the order Passeriformes followed by Charadriidae and rest 17 orders. Resident, local migrant and migrant species constituted 61.15, 31.65 and 7.20 % of the bird community, respectively. Most of the bird species (51.85 %) were associated consistently with the agricultural fields as their habitat followed by aquatic systems (29.20 %) and human habitat (18.98 %). The study records the presence of three species under IUCN Near Threatened category and many species exhibiting sparse population based on the encounter rate and number of individuals in the habitat. The observed richness of bird species in the study area calls for further studies on habitat preference, census and breeding biology to highlight species specific roles in ecosystem functions and sustenance of ecosystem services.     

Using soundscape recordings to estimate bird species abundance, richness, and composition

ABSTRACT Point counts are the most frequently used technique for sampling bird populations and communities, but have well‐known limitations such as inter‐ and intraobserver errors and limited availability of expert field observers. The use of acoustic recordings to survey birds offers solutions to these limitations. We designed a Soundscape Recording System (SRS) that combines a four‐channel, discrete microphone system with a quadraphonic playback system for surveying bird communities. We compared the effectiveness of SRS and point counts for estimating species abundance, richness, and composition of riparian breeding birds in California by comparing data collected simultaneously using both methods. We used the temporal‐removal method to estimate individual bird detection probabilities and species abundances using the program MARK. Akaike's Information Criterion provided strong evidence that detection probabilities differed between the two survey methods and among the 10 most common species. The probability of detecting birds was higher when listening to SRS recordings in the laboratory than during the field survey. Additionally, SRS data demonstrated a better fit to the temporal‐removal model assumptions and yielded more reliable estimates of detection probability and abundance than point‐count data. Our results demonstrate how the perceptual constraints of observers can affect temporal detection patterns during point counts and thus influence abundance estimates derived from time‐of‐detection approaches. We used a closed‐population capture–recapture approach to calculate jackknife estimates of species richness and average species detection probabilities for SRS and point counts using the program CAPTURE. SRS and point counts had similar species richness and detection probabilities. However, the methods differed in the composition of species detected based on Jaccard's similarity index. Most individuals (83%) detected during point counts vocalized at least once during the survey period and were available for detection using a purely acoustic technique, such as SRS. SRS provides an effective method for surveying bird communities, particularly when most species are detected by sound. SRS can eliminate or minimize observer biases, produce permanent records of surveys, and resolve problems associated with the limited availability of expert field observers.     

Synergistic effects of habitat configuration and land-use intensity shape the structure of bird assemblages in human-modified landscapes across three major neotropical biomes

Maximizing biodiversity persistence in heterogeneous human-modified landscapes is hindered by the complex interactions between habitat quality and configuration of native and non-native habitats. Here we examined these complex interactions considering avian diversity across 26 sampling sites, each of which comprised of three sampling points located across a gradient of disturbance: core native habitat fragment, fragment edge, and non-native adjacent matrix. The 78 sampling points were further nested within three neotropical biomes—Amazonia, Cerrado and Pantanal—in central-western Brazil. Matrix type consisted of cattle pastures in the Amazon and teak plantations in the Pantanal and Cerrado. We considered the interactive effects of (1) disturbance-context: fragment core, edge and adjacent matrix, (2) matrix type: tree plantation or cattle pastures, both subject to varying land-use intensity, and (3) native habitat configuration (fragment size, shape and isolation) on bird species richness, abundance and composition. Based on point-count surveys, we recorded 210 bird species. Bird species richness and abundance declined across the disturbance gradient, while genus composition only differed within the adjacent matrix, particularly cattle-pastures. The effect of native habitat area was positive but only detected at fragment edges. Overall bird diversity increased at sites characterized by higher availability of either relict trees within pasture landscapes or old-growth trees within teak plantation landscapes. The core of native fragments played a primary role in ensuring the persistence of bird diversity, regardless of fragment size. In contrast to pastures, tree plantations likely harbour a higher proportion of forest-dependent species while bird diversity can be further enhanced by reduced management intensity in both matrix types. Strategies to maximize avian persistence should not only include retaining native habitats, but also maximizing the size of core native habitats. Likewise, more structurally complex matrix types should be encouraged while maintaining low levels of land-use intensity.

     

Assessing the effects of selective logging on birds in Neotropical piedmont and cloud montane forests

In tropical and subtropical forests there is limited information about how to integrate sustainable timber management with the conservation of biodiversity. We examined the effect of selective logging on the bird community to help develop management guidelines to assure the conservation of biodiversity in forests managed for timber production. The study design consisted of control and harvested plots in piedmont and cloud forests of the subtropical montane forests of the Andes in northwestern Argentina. We conducted bird point-count surveys combined with distance estimation. Breeding season bird community composition was more similar between control and logged forest in both the cloud forest and piedmont, than between the two elevations, probably because Neotropical bird communities change dramatically along elevational gradients. Within each elevation zone, community composition changed significantly between harvested and control forests. Both between and within each elevation zone no significant differences in bird density were detected. Similarly, when we analyzed bird density according to diet guilds no general pattern could be extracted. However, we found a significantly greater density of cavity nesters and lower of non-cavity nesters in control plots, probably because most trees that can develop suitable cavities were extracted in logged plots and these plots had a greater structural diversity enabling more nesting resources. Grouping species according to their nesting habitat requirements has rarely been used in the neotropics and other tropical and subtropical forests, but focusing management attention on cavity nesters might address the most sensitive portion of the avian community as well as other species dependent on trees likely to hold cavities.     

Effects of intensive rice production practices on avian biodiversity in Southeast Asian managed wetlands

Rice fields are common throughout the agricultural landscape of Southeast Asia and sustain various bird species. These birds can provide ecosystem services, such as pest control, that improve agricultural yields whilst minimising the use of agrochemicals. This study quantified avian biodiversity in rice production landscapes during three farming stages in Peninsular Malaysia. In Malaysia, rice fields can be an important habitat for migrating birds due to Malaysia’s position on the East-Asian–Australasian Flyway. We determined bird abundance, species richness, and composition in rice field landscapes and compared these during different stages of rice growing. Wetland and terrestrial birds were counted in rice fields using the point-count method. Sixty sampling points were randomly established in three locations, from which 3447 individual birds of 46 species and 26 families were recorded. There was a significant difference in total bird abundance and species richness between the three different stages of rice growing. The growing stage supported greater bird abundance and species richness compared to the pre-harvest and post-harvest stages. Rice-growing provides temporary habitats to different bird species in this managed aquatic landscape. This implies the presence of abundant food, such as small fish and amphibians. The evidence from this study suggests that biodiversity-friendly agricultural practices should be implemented to improve habitat quality for birds in rice production landscapes.     

Estimating Abundances of Interacting Species Using Morphological Traits,Foraging Guilds,and Habitat

We developed a statistical model to estimate the abundances of potentially interacting species encountered while conducting point-count surveys at a set of ecologically relevant locations – as in a metacommunity of species. In the model we assume that abundances of species with similar traits (e.g., body size) are potentially correlated and that these correlations, when present, may exist among all species or only among functionally related species (such as members of the same foraging guild). We also assume that species-specific abundances vary among locations owing to systematic and stochastic sources of heterogeneity. For example, if abundances differ among locations due to differences in habitat, then measures of habitat may be included in the model as covariates. Naturally, the quantitative effects of these covariates are assumed to differ among species. Our model also accounts for the effects of detectability on the observed counts of each species. This aspect of the model is especially important for rare or uncommon species that may be difficult to detect in community-level surveys. Estimating the detectability of each species requires sampling locations to be surveyed repeatedly using different observers or different visits of a single observer. As an illustration, we fitted models to species-specific counts of birds obtained while sampling an avian community during the breeding season. In the analysis we examined whether species abundances appeared to be correlated due to similarities in morphological measures (body mass, beak length, tarsus length, wing length, tail length) and whether these correlations existed among all species or only among species of the same foraging guild. We also used the model to estimate the effects of forested area on species abundances and the effects of sound power output (as measured by body size) on species detection probabilities.     

On the efficiency of using song playback during call count surveys of Red-legged partridges (<Emphasis Type="BoldItalic">Alectoris rufa</Emphasis>)

Successful management practices for declining bird species depend often on long-term surveys acquired by point counts. Despite high standardization of field protocols, uncertain detection probability remains an important source of variability and bias in point-count data. This effect is of main importance in low-responsive species as the Red-legged partridge (Alectoris rufa), but it can be counterbalanced, increasing detection probability. In this 2-year study, we sampled using traditional point-count methods, followed by playback sessions for each repetition. We measured detection probability and the efficiency of playback for detectability in the context of a feasibility study on long-term point-count surveys for a harvested game bird, the Red-legged partridge. The results for both study years show a distinct increase in detection probability (23% and 45%, respectively) when using playback vs. the traditional point-count method. We also tested our results for heterogeneity, trap dependence, and time dependence, and no effect was detected. Thus, we suggest that the future design of long-term surveys on Red-legged partridges should consider abundance indices using playback sessions.     

Effects of habitat fragmentation and black-tailed prairie dogs on urban avian diversity

Urbanization and habitat fragmentation have the potential to influence bird communities. In addition, these phenomena, as well as ongoing lethal control measures, have also greatly reduced the range of the black-tailed prairie dog (Cynomys ludovicianus) since the beginning of the 20th century. Although prairie dogs are highly interactive species that can influence avian communities, few studies have investigated whether these interactions persist in urban settings. Our goal was to investigate the relative impacts of habitat fragmentation and prairie dogs on bird communities within an urban matrix. We performed bird surveys on 20 habitat fragments (10 colonized by prairie dogs, 10 uncolonized by prairie dogs) distributed throughout the Denver metropolitan area, and calculated Shannon–Weiner diversity and richness of all birds and native species, as well as total counts of grassland birds and raptors. Diversity, richness, and counts of many species increased with increasing fragment connectivity, and decreased on fragments isolated for longer periods of time. Avian diversity and richness did not differ between fragments with and without prairie dogs, suggesting that this element of the ecological role of prairie dogs is not fully retained in urban habitat. Future studies of the role of prairie dogs as keystone species in urban systems should include other taxa as well as consider the influence of the urban matrix surrounding prairie dog habitat. Our results emphasize that conservation of urban avian diversity should focus on landscape connectivity as well as local habitat features.     

样线法和网捕法在机场鸟情调查中的应用比较

鸟击事件主要发生在机场范围内,对机场周边生境的鸟类组成进行调查,是制定鸟击防范对策的重要前提。国内多数机场已经开展了相关的鸟类组成调查,但是选用的调查方法却存在较大差异。以样线法和网捕法两种常用的调查方法对沈阳桃仙国际机场周边的迁徙期鸟类进行了研究,旨在比较两种调查方法在机场鸟类群落组成调查中的效果及调查的鸟类群落组成差异。结果表明：两种方法均适合机场鸟类调研,共记录到鸟类97种,网捕法记录的鸟类种数（83种vs.57种）高于样线法,网捕法单独记录的鸟类种数（40种vs.14种）也高于样线法。尽管两种方法每期（半个月）调查的物种数和目的数量无明显差别,但随调查强度（如调查次数）增加,网捕法累计记录到的鸟类种类明显高于样线法,且较晚达到渐近线。另外,两种方法调查记录的鸟类群落组成也具有显著的差别,如网捕法记录到较多鹌鹑和鸮形目等夜间迁徙或活动鸟类,而样线法可记录到鹭科和雁鸭类水鸟等。这说明两种调研方法在鸟类调查中有较好的互补性。因此,本研究认为机场鸟情调研时应该根据鸟情特点,选择合适的鸟类调研方法,综合采用多种调研方法可更有利于获得科学的鸟情信息。     

Effects of ambient noise on detectability and localization of avian songs and tones by observers in grasslands

Probability of detection and accuracy of distance estimates in aural avian surveys may be affected by the presence of anthropogenic noise, and this may lead to inaccurate evaluations of the effects of noisy infrastructure on wildlife. We used arrays of speakers broadcasting recordings of grassland bird songs and pure tones to assess the probability of detection, and localization accuracy, by observers at sites with and without noisy oil and gas infrastructure in south‐central Alberta from 2012 to 2014. Probability of detection varied with species and with speaker distance from transect line, but there were few effects of noisy infrastructure. Accuracy of distance estimates for songs and tones decreased as distance to observer increased, and distance estimation error was higher for tones at sites with infrastructure noise. Our results suggest that quiet to moderately loud anthropogenic noise may not mask detection of bird songs; however, errors in distance estimates during aural surveys may lead to inaccurate estimates of avian densities calculated using distance sampling. We recommend caution when applying distance sampling if most birds are unseen, and where ambient noise varies among treatments.     

Do acoustic indices correlate with bird diversity? Insights from two biodiverse regions in Yunnan Province,south China

Human activities are affecting biodiversity to a greater extent than ever. Consequently, tools that can efficiently monitor changes in communities are becoming increasingly important. In the case of birds and other vocalizing animals, it has been suggested that passive acoustic methods can be used for this purpose. Multiple acoustic indices have been developed recently, to be used as proxies for species diversity. Preliminary results have been promising. Yet, before the indices can be applied widely, it is necessary to understand better how well they reflect the communities to be monitored, and how they perform under diverse environmental conditions. Here, we tested seven of the available indices, on sound recordings made in two biodiverse regions in Yunnan Province, south China. We assessed each index’s performance by measuring its correlation to bird species richness and diversity, estimated using point-count surveys. Each survey was conducted by an expert observer, at the same time each recording was made, and for the same duration. We also tested whether the performance of the indices was affected by levels of environmental dissimilarity between the sites sampled. We found that although no index showed a very strong correlation with species richness or diversity, three indices (the acoustic entropy, acoustic diversity and acoustic evenness indices) performed consistently better that the other four, showing moderate correlations. The levels of environmental dissimilarity among the sites did not seem to affect the performance of any of the indices tested, suggesting consistency − an important property for the indices to have. We conclude that although the acoustic indices have the potential to be used for passive acoustic monitoring, perhaps they need to be refined further before they can be applied widely. Meanwhile, they should be tested in more environments to reveal fully their potential and limitations.     

Relationships between bird species and tree species assemblages in forested habitats of eastern North America

Aim We examined the relative influence of geographical location, habitat structure (physiognomy), and dominant plant species composition (floristics) on avian habitat relationships over a large spatial extent. Although it has been predicted that avian distributions are more likely to covary with physiognomy than with floristics at coarse scales, we sought to determine, more specifically, whether there remained a significant association between gradients in assemblages of bird species and dominant plant species within a general biome type, after statistically controlling for structural variation and geographical location of sampling sites. Location Our sample consisted of a subset of North American Breeding Bird Census survey sites that covered most of the range of eastern forests, from Florida to Nova Scotia, and west to Minnesota and North Dakota (up to c. 2500 km between sites). Methods We restricted our analyses to the single year (1981) that provided the largest sample of sites (47) for which vegetation data were available within ± 2 years of the avian surveys. We examined the relationship between avian community composition and tree species composition over this series of forested plots. Data were divided into four sets: (1) bird species abundances, (2) tree species abundances, (3) physiognomic or structural variables and (4) geographical location (latitude and longitude). We performed separate detrended correspondence analysis ordinations of birds and trees, before and after statistically partialling out covariation associated with structural variables and geographical location. To gauge the relationship between the two sets of species we correlated site scores resulting from separate ordinations. We also compared continental‐scale patterns of variation in bird and tree assemblages to understand possible mechanisms controlling species distribution at that scale. Results Both bird and tree communities yielded strong gradients, with first‐axis eigenvalues from 0.75 to 0.97. All gradients were relatively long (> 4.0), implying complete turnover in species composition. However, geographical location accounted for < 10% of the total variation associated with any ordination. Prior to partialling out covariation resulting from location and physiognomy, bird species ordinations were strongly correlated with tree species ordinations. The strength of association was reduced after partialling, but one bird and one tree axis remained significantly correlated. There was a significant species–area effect for birds, but not for trees. Main conclusions There was a significant relationship between bird species assemblages and tree species assemblages in the eastern forests of North America. Even after partialling out covariation associated with spatial location and forest physiognomy, there remained a significant correlation between major axes from bird and tree ordinations, consistent with the hypothesis that floristic variation is likely to be important in organizing assemblages of birds within a general biome type, albeit over a much larger spatial extent than originally predicted. Forest tree species ordinations differed from bird species ordinations in several ways: trees had a higher rate of turnover along underlying environmental gradients; trees appeared more patchily distributed than birds at this scale; and tree species were more spaced out along the underlying ecological gradients, with less overlap. By understanding the relationship between bird assemblages and forest floristics, we might better understand how avian communities are likely to change if tree species distributions are altered as a result of climatic changes.     

Relationships of bird community structure and species distributions to two environmental gradients in the northern boreal forest

Few studies have explicitly examined avian community structure in the North American northern boreal forest Herein we report upon the results of bird surveys in mature stands of boreal forest in the Great Clay Belt Ontario. Canada We related trends in avian community structure and individual bird species abundance to two environmental gradients described in a landbase classification scheme called the Forest Ecosystem Classification a moisture and a nutrient-richness gradient Variation in environmental characteristics is limited in the Ontario Clay Belt and this was reflected in short environmental gradient lengths However major trends in avian community structure were strongly associated with the nutrient-richness gradient axis summarized by this scheme Analyses of avian community composition indicated a continuum from moist coniferous habitats to drier aspen-dominated mixed woodlands with several bird species occurring in varying abundances across the width of both gradients 48 of the 58 species examined showed statistically significant associations with at least one of the two multivariate gradient axes A smaller proportion of short-distance migrant species were associated with these gradients than were species in either the neotropical migrant or resident categories We used a multivariate variable (habitat breadth) to compare degree of habitat specialization across different migratory groups A large proportion of neotropical migrants showed a high degree of habitat specialization m mature Clay Belt forests, and neotropical species with small habitat breadths were more commonly associated with habitats dominated by broad-leaved deciduous tree species than either short-distance or permanent resident species We discuss our findings in relation to the post-glacial history of the Clay Belt region     

Unsupervised classification to improve the quality of a bird song recording dataset

Open audio databases such as Xeno-Canto are widely used to build datasets to explore bird song repertoire or to train models for automatic bird sound classification by deep learning algorithms. However, such databases suffer from the fact that bird sounds are weakly labelled: a species name is attributed to each audio recording without timestamps that provide the temporal localization of the bird song of interest. Manual annotations can solve this issue, but they are time consuming, expert-dependent, and cannot run on large datasets. Another solution consists in using a labelling function that automatically segments audio recordings before assigning a label to each segmented audio sample. Although labelling functions were introduced to expedite strong label assignment, their classification performance remains mostly unknown. To address this issue and reduce label noise (wrong label assignment) in large bird song datasets, we introduce a data-centric novel labelling function composed of three successive steps: 1) time-frequency sound unit segmentation, 2) feature computation for each sound unit, and 3) classification of each sound unit as bird song or noise with either an unsupervised DBSCAN algorithm or the supervised BirdNET neural network. The labelling function was optimized, validated, and tested on the songs of 44 West-Palearctic common bird species. We first showed that the segmentation of bird songs alone aggregated from 10% to 83% of label noise depending on the species. We also demonstrated that our labelling function was able to significantly reduce the initial label noise present in the dataset by up to a factor of three. Finally, we discuss different opportunities to design suitable labelling functions to build high-quality animal vocalizations with minimum expert annotation effort.     

太白山北坡夏秋季鸟类物种多样性

2006年5月～7月(夏季),9月～10月(秋季)在秦岭主峰太白山的北坡根据海拔和典型植被划分生境类型,在6种生境中选择典型样区划定样线并采用样线法对鸟类进行调查,根据鸟类的绝对数量和估算面积计算鸟类的绝对密度,并根据密度等级划分各生境类型中优势物种和常见物种。共观察到鸟类144种,其中留鸟102种,夏候鸟41种,冬候鸟1种。不同的海拔和不同生境类型中的鸟类物种丰富度和多度有较大差异,而且同一生境中鸟类多样性的季节性变化也很明显。无论是夏季还是秋季,低海拔农田带生境中鸟类的总密度最高,而高山灌丛草甸生境中的鸟类总密度最低。优势物种和常见物种在不同的生境类型组成也不相同,而且在不同季节也有变化。夏秋季的鸟类食性组成在农田带有显著差异,而其它生境类型中的鸟类食性夏秋季无明显差异,但是秋季植食性鸟类在各个生境类型中都有增多的趋势。物种丰富度和海拔梯度的关系显示在中海拔地区的鸟类丰富度最高。总体上,和20世纪80年代相比,太白山北坡的鸟类已经发生了明显的变化。     

浙江古田山自然保护区鸟类群落生态研究

对古田山地区鸟类进行的调查表明:该地区鸟类群落的主要鸟类共计48种,其中优势种有14种,占29.17％。根据鸟类生境的分布系数分析。中性分布型有(25—100％)28种,占58.33％。不同生境内鸟类群落的种类数目和群体密度存在差异,结构复杂的生境,其鸟类群落由三个分布群组成,如农田村落、农田河滩、混交林和阔叶林;结构简单的生境,如竹林、针叶林和迹地灌丛,其鸟类群落由二个分布群所组成。各种鸟类分布群在鸟类群落内的比例随栖息地结构的变化而改变。由于栖息地结构的变化同样也导致鸟类群落其他参数的变化,如Shannon-Wiener多样性指数、Simpson优势度、种间相遇机率PIE等。     

Does the presence of an observer affect a bird's occurrence rate or singing rate during a point count?

The approach or presence of an observer may affect the behavior of nearby birds, rendering them either more or less detectable than when no observer is present due to a change in singing rates. To test whether there are systematic detection biases associated with the presence of an observer during point count bird surveys, we compared the occurrence and singing rates of birds during a 10-min period immediately preceding the time when an observer arrived to conduct a count and during the formal count itself by extracting song information from autonomous sound recorders. We obtained recordings of 36 species of birds detected at ≥5 locations in one of three vegetation types, including burned conifer forest, green conifer/riparian streamside forest, and riparian bottomland/marshland. We found that species richness and both the probability of occurrence and singing rate for any of the species recorded were unaffected by the presence of an observer. In addition, the probability of occurrence did not differ significantly among four 2.5-min recording sessions during 10-min counts when an observer was present. Thus, the presence of an observer did not appear to introduce any detectable systematic bias that would make bird lists or unadjusted occurrence rates inaccurate on that basis alone. In addition, rates of bird occurrence across 2.5-min temporal subsets of a 10-min count did not vary in a systematic way that would violate the assumption of equal occupancy across adjacent time periods as sometimes used to build detection histories in occupancy modeling.     

Cedar Infestation Impacts Avian Communities along the Niobrara River Valley,Nebraska

Habitat modification has the potential to cause changes in structure and composition of bird communities. Our goal was to determine the response of Songbird community composition to eastern red cedar (Juniperus virginiana) removal in The Nature Conservancy's Niobrara Valley Preserve, Nebraska. We used point counts to survey birds in the riparian matrix of grassland and forest habitats. More than 60 species were recorded on surveys during 2004–2005. We also use the program PRESENCE to determine the response of five species to various habitat components, including cedar density: House Wren (Troglodytes aedon), Spotted Towhee (Pipilo maculates), Ovenbird (Seiurus aurocapillus), Red‐eyed Vireo (Vireo olivaceus), and Indigo Bunting (Passerina cyanea). Species richness estimates were highest in open and mixed habitat patches. Local populations of Ovenbirds and Red‐eyed Vireos responded positively to cedar density, whereas House Wren numbers declined as cedar density increased. Cedar abundance explained the most variation in bird community similarity between survey points; species richness increased as cedar density decreased. Habitat structure and composition drove variation in community composition and population abundance at fine, local scales within the Preserve. Fine‐scale management to remove cedar from local areas should increase diversity of avian species by maintaining a matrix of habitat types. Cedar removal at any scale will affect the composition of bird communities, and we encourage a structured approach to management decisions.     

Observer aging and long‐term avian survey data quality

Long‐term wildlife monitoring involves collecting time series data, often using the same observers over multiple years. Aging‐related changes to these observers may be an important, under‐recognized source of error that can bias management decisions. In this study, we used data from two large, independent bird surveys, the Atlas of the Breeding Birds of Ontario (“OBBA”) and the North American Breeding Bird Survey (“BBS”), to test for age‐related observer effects in long‐term time series of avian presence and abundance. We then considered the effect of such aging phenomena on current population trend estimates. We found significantly fewer detections among older versus younger observers for 13 of 43 OBBA species, and declines in detection as an observer ages for 4 of 6 vocalization groups comprising 59 of 64 BBS species. Consistent with hearing loss influencing this pattern, we also found evidence for increasingly severe detection declines with increasing call frequency among nine high‐pitched bird species (OBBA); however, there were also detection declines at other frequencies, suggesting important additional effects of aging, independent of hearing loss. We lastly found subtle, significant relationships between some species' published population trend estimates and (1) their corresponding vocalization frequency (n ≥ 22 species) and (2) their estimated declines in detectability among older observers (n = 9 high‐frequency, monotone species), suggesting that observer aging can negatively bias long‐term monitoring data for some species in part through hearing loss effects. We recommend that survey designers and modelers account for observer age where possible.     

雅安市区林地鸟类多样性及生态位分析

2009年12月至2010年12月,经过一个年周期的调察与统计,共记录雅安市区林地鸟类79种,隶属于8目32科。通过多样性指数与均匀度指数的测算发现,春秋两季大于夏冬两季,农田类型明显低于次生林、人工林及其他生境。在所有鸟类中,灰喉鸦雀(Paradoxornis alphonsianus)、白头鹎(Pycnonotussinensis)、红头长尾山雀(Aegithalos concinnus)、白颊噪鹛(Garrulax sannio)在不同季节均具有较高的优势度,发冠卷尾(Dicrurus hottentottus)、松鸦(Garrulus glandarius)、大山雀(Parus major)、绿背山雀(P.monticolus)具有最高的生态位宽度值。自20世纪60年代,雅安市区鸟类物种组成及栖息地随城市化进程均发生了较大变化。