The effects of habitat and spatial features of wetland fragments on the abundance of two rallid species with different degrees of habitat specialization

The management of wild gamebirds for shooting involves a combination of habitat management (woodland, field boundaries and game crops), winter feeding and control of potential nest predators, any of which could benefit other birds, including nationally declining species associated with farmland habitats. Changes in numbers of passerines were monitored over six years in relation to game management on farmland in Leicestershire. Nest success was monitored over four years and, for some species, was inversely related to abundance of breeding corvids. Abundance of breeding passerines increased during the period of game management. Species whose breeding populations have declined nationally (coincident with agricultural intensification) showed the greatest increases in abundance relative both to other species, and to the same nationally declining species in nearby farmland. The precise mechanism by which the game management package contributes to increased breeding numbers is not understood and is likely to differ between species. However, these results show that further integration of wild game management into farming systems could have conservation benefits for nationally declining farmland birds.     

Observer variation in estimates of Meadow Pipit Anthus pratensis and Skylark Alauda arvensis abundance on moorland

Capsule Counts least susceptible to observer effects were those within 25 m of a transect and the total number along a transect, with observer effects greater for distance sampling.     

Laying dates and clutch size of open-nesting passerines in the Czech Republic: a comparison of systematically and incidentally collected data

Data are presented on laying date and clutch size (n) of Blackcap Sylvia atricapilla (1434), Song Thrush Turdus philomelos (298), Garden Warbler S. borin (260), Yellowhammer Emberiza citrinella (254), Blackbird T. merula (231), Chaffinch Fringilla coelebs (206), Chiffchaff Phylloscopus collybita (202), Icterine Warbler Hippolais icterina (95) and Dunnock Prunella modularis (89), recorded during an intensive study (since 1993) in woodland habitats of Eastern Bohemia, Czech Republic (49 °54 ′N, 16 °02 ′E). Results are compared with two other data sets (a local study and national nest record scheme) collected by Czech volunteer ornithologists during 1945–85 and with other published data from central Europe. There is no evidence that the laying dates and clutch size of the nine species changed at the regional scale over the past decades, and mean values generally match their known geographical variability. Significant species differences were found among the three Czech data sets in both laying dates and clutch size. Most of the differences could be explained as an artefact of seasonally biased sampling of nests, which in turn influenced mean clutch size. Even a systematic study with a standard searching effort on fixed plots provided biased data for some species.     

Factors affecting songbird communities using new short rotation coppice habitats in spring

The aim of this study was to describe the songbird communities occupying willow and poplar short rotation coppice (SRC) crops during the breeding season, and to identify the features of existing plantations that affect their abundance. Songbird point-counts were undertaken at 66 different plots of SRC at 29 sites throughout Britain and Ireland during spring 1993. Measures of vegetation and coppice management in each plot were also taken. The songbird species using the SRC survey plots were similar to those reported from traditional coppice habitats. Willow SRC contained more resident and migrant songbird species than poplar SRC. Warbler species and buntings in particular were rarely recorded from poplar plots. Finches, tits and thrushes were recorded equally from both willow and poplar. More migrant species were recorded from year 2 willow coppice (i.e. in its third growth season since winter cutting) than in either year 1 or year 3. Most resident species selected older willow or poplar coppice growth up to year 3 or 4, the oldest age classes in the sample. These 4-year trends for migrant and resident songbirds are similar to those observed in traditional coppice woodland over a 10- or 12-year rotation. Skylark and Meadow Pipit were recorded from recently cut SRC plots (year 0). In a regression analysis, the number of songbird species and individuals, particularly migrants, were found to be positively related to the increased structural density or complexity of the coppice vegetation.     

Seasonal and between-sex differences in the diet of Black Grouse Tetrao tetrix

Capsule Dietary differences between sexes and seasons reflected diversity in plant availability and habitat preferences.

Aims To analyse Black Grouse diet through the identification of plant and invertebrate material found in the crop.

Methods Crops were dissected and the content categorized into plant species and components (i.e. leaf, stem, flower, fruit and seed). Multivariate analysis was used to test for seasonal, sex- or location-related differences in the diet.

Results Plant fragments accounted for 98% of the diet and included 53 plant species or taxa. Invertebrates made up the remaining 2%. Diet varied significantly between seasons and sexes. Both sexes ate more ericaceous shrubs in autumn and winter, with females eating more than males. The plant parts eaten varied seasonally. In summer, fruits, flowers and seeds were favoured over leaves, which dominated in winter.

Conclusions With few trees, birds were reliant upon Heather in autumn and winter.     

Diversity and abundance of birds in relation to forest fragmentation,habitat quality and heterogeneity

This study investigated the importance of habitat quality and habitat heterogeneity for the abundance and diversity of breeding birds in continuous forest and in forest fragments surrounded by farmland in central Sweden. Positive correlations were found between species number and area, volume of Aspen Populus tremula and habitat heterogeneity. Spatial segregation of habitats at a relatively fine-grained scale is suggested to allow for the co-occurrence of more species. The abundance of at least 18 of the species in this study was influenced by fragmentation, and nine of these species preferred fragments to forest sites. The total density of birds was higher in fragments than in forest sites, probably because several fragment species forage in farmland surrounding the sites and a few also forage at edges. Nine species were more common in forest sites than in fragments, but only one species was restricted to continuous forest. However, several fragments were relatively close to forests (150 m) and forest was common in larger scale contexts. The abundance of most species (25 of 33 species) in this study was correlated with habitat quality variables (i.e. variables measuring the size, volume and diversity of ‘tree species’). Among these habitat variables the most important was the occurrence of deciduous trees which seemed to be important for 14 species. The second most important habitat factor seemed to be the diameter of trees, which was positively correlated with the abundance of eight species of which five are hole-nesters. Among coniferous trees, six species were positively correlated with the volume of Norway Spruce Picea abies, whereas no species seemed to be correlated with the volume of Pine Pinus sylvestris.     

Agricultural habitat-type and the breeding performance of granivorous farmland birds in Britain

Conservation concern about granivorous birds has led to the implication of changing agricultural practices as causes of widespread population decline. We investigate relationships between breeding performance and the agricultural environment for ten granivorous farmland bird species (Stock Dove Columba oenas, Skylark Alauda arvensis, Tree Sparrow Passer montanus, Chaffinch Fringilla coelebs, Greenfinch Carduelis chloris, Linnet C. cannabina, Bullfinch Pyrrhula pyrrhula, Reed Bunting Emberiza schoeniclus, Yellowhammer E. citrinella and Corn Bunting Miliaria calandra). We analyse long-term, extensive data from the British Trust for Ornithology's Nest Record Scheme on breeding performance per breeding attempt with respect to farmland type (arable, grazing or mixed) and time (pre- and post-1975–76). The influence of habitat is investigated at two different scales: within the nesting territory and at the landscape level. Relationships between farmland type and (temporal changes in) breeding performance tended to be species-specific, but a few patterns were each common to some species. Improvements in breeding performance occurred across all three farmland types for four declining species. Grazing farmland seems to have deteriorated as breeding habitat for Linnet and arable/mixed farmland for Reed Bunting. Mixed farming at the territory scale supported better breeding performance for four species, three of which (Bullfinch, Yellowhammer and Corn Bunting) have declined concurrently with mixed farming. Pastoral landscapes supported better breeding performance for up to seven species, six of which have undergone large declines. Arable landscapes supported better breeding only for the stable or increasing Chaffinch and Greenfinch. Different relationships between farming regime and breeding performance were found at the two scales considered.     

The role of fruit diet within a temperate breeding bird community in southern Spain

In southern temperate regions many fleshy-fruited plant species ripen their fruits during the breeding or early post-breeding season and these are consumed by resident birds. I studied the frugivore community of the summer-fruiting tree Frangula alnus ssp. baetica in southern Spain and the significance of fruit in the diet of adult and recently fledged birds. Twelve species consumed F. alnus fruits. Almost 97% of the foraging visits were carried out by the four most abundant species, Robin Erithacus rubecula, Blackcap Sylvia atricapilla, Blackbird Turdus merula and Blue Tit Parus caeruleus. During the ripening season Robins and Blackcaps concentrated at fruit-rich sites. Entire families of Blackcap and Blackbird regularly entered fruiting trees together. In contrast, adult Robins always foraged solitarily, and accounted for only 4% of the tree visits, while 96% were realized by recently fledged birds of the first brood. In all species, young birds foraged as efficiently as adults. F. alnus fruits are not part of the regular nestling diet, but they are a significant part of the diet for recently fledged Robins during their postnatal dispersal. Conversely, these are the most important and effective seed dispersers while adult Robins scarcely take part in the dispersal of F. alnus seeds.     

The movements of the Kittiwake

Capsule During winter songbirds were far more abundant in game cover crops than conventional agricultural habitats.

Aims To quantify game crop use during winter by farmland songbirds when compared with conventional farmland at a regional scale.

Methods Songbirds were counted on 20 farms in eastern Scotland. The number of songbirds using game crops was compared with a sample of nearby conventional crops – with particular emphasis on set-aside and cereal stubbles.

Results Game crops supported up to 100 times as many birds per hectare, of significantly more species, than the other two habitat categories. Many of these species were those currently causing concern because of their declining populations.

Conclusion Game crops could provide opportunities for increasing food resources to songbirds whose populations may be limited by food availability and possibly arrest population declines. At present, the only measures likely to facilitate this are the government's various agri-environment schemes.     

The phenology of spring bird migration to north Norway

Capsule There was no evidence of a long-term trend in arrival dates of spring migrants over the last 20 years in north Norway.

Aims To investigate the effect of climate on the timing of spring arrival of many species at their northern limit of breeding distribution and to seek evidence of any long-term trend.

Methods Observations of spring arrivals of 71 species into Troms, north Norway (69–70°N) between 1970 and 2000 by members of the local branch of the Norwegian Ornithological Society were analysed and related to available weather parameters.

Results The first migrants arrive in mid-March when air temperatures are still below 0°C and c. 1 m of snow is on the ground, with the main influx in late April and throughout May. By then much of the snow has melted and temperatures are c. 5°C. There was no evidence of a long-term trend in the median dates of arrival across 31 species in Troms between 1980 and 2000. However among 14 species for which detailed data exist in a limited area around Tromsø, the Golden Plover Pluvialis apricaria showed a significant trend towards an earlier arrival and the Willow Warbler Phylloscopus trochilus showed the opposite. Spring migration tended to be advanced during warm springs, and seven of the above subsets of 14 species showed significant negative correlations between their arrival dates and temperature. One showed a positive correlation.

Conclusion The data collected to date are a good baseline for future studies of the effects of climate change on migration phenology.     

Winter use of wild bird cover crops by passerines on farmland in northeast England

Capsule Declining farmland species were more abundant in these crops which can be matched to the birds' requirements.

Aims To assess the use of seed-bearing crop by a range of bird species in winter.

Methods The study was carried out over three winters at a site in County Durham (England). Eleven bird species were represented, five of which are nationally targeted for conservation action.

Results Bird abundance was significantly higher where wild bird cover crops were present. Kale Brassica napus and Quinoa Chenopodium quinoa were the most used crop species, although cereals and linseed were also used.

Conclusion Simple crop mixtures can be designed to meet the needs of farmland bird communities. Our results suggest that seed production may be limited within government agri-environment schemes by restrictions on fertilizer use. The agronomy of seed-bearing crops for birds requires further investigation.     

Spatial and temporal variation in breeding parameters of two south-temperate populations of House Wrens

Studies of variation in breeding parameters are often based on temporal analyses of a single population. However, to differentiate between the effects of regional and local factors, neighboring populations with limited interpopulational dispersal need to be compared. We studied two nearby (< 5 km apart) populations of House Wrens (Troglodytes aedon bonariae) at two ranches (Los Zorzales, 10 years; La Esperanza, 13 years) in south-temperate Argentina to assess the possible effects of regional and local factors on breeding phenology. For each breeding season, we recorded laying dates, clutch sizes, and length of the breeding season, and estimated the reproductive synchrony of first and second breeding attempts. We examined how these breeding parameters were affected by weather, population density, and rates of nest failure. With favorable temperatures during the pre-reproductive period (September–October), wrens in both populations initiated first breeding attempts earlier. However, ordinal laying dates were also affected by local factors, with wrens at Los Zorzales initiating breeding attempts earlier than those at La Esperanza. We found a spatial correlation in clutch sizes between populations for the 2007–2012 breeding seasons, but clutch sizes of first and second nesting attempts showed low variability. Reproductive synchrony of first nesting attempts varied among years, suggesting an effect of regional factors. However, we detected no synchronization between populations and were unable to identify environmental variables that explained the temporal variation. Ordinal laying dates of second clutches were strongly correlated with the ordinal laying dates of first clutches. We also found that the length of breeding seasons was longer when daily nest mortality rates were lower. Although environmental factors seemed to affect the decision of when to start breeding, pairs with successful first nesting attempts were more likely to initiate second nests, thus affecting the length of the breeding season. The spatial variation and temporal variation of the breeding parameters of House Wrens in our study provide evidence of marked plasticity in their breeding decisions and allowed us to identify local and regional environmental factors related to this variation.     

Small-scale spatial variation in the interactions between Prunus mahaleb and fruit-eating birds

We studied fleshy fruit consumption by birds on individualPrunus mahaleb trees in four plots in northwestern Spain.We found large variation among trees in the relative contribution of differentbird species to fruit removal. This variation, which occurred on a scale ofmeters, was correlated with the distance from the tree to nests ofPhoenicurus ochruros, a major fruit consumer, and with thekind of microhabitat surrounding each tree. In the four plots studied, treeslocated farther away from P. ochruros nests receivedrelatively fewer visits by this species, and relatively more byTurdusmerula and Sylvia atricapilla. These three mainconsumer species differed in the kinds of microhabitats (rocks, loose stones,bare or grassy soil, and woody vegetation) where they flew after visitingP. mahaleb, and thus they probably created differentpatterns of seedfall. This study adds to the evidence that environmentalfactorsextrinsic to plants, and acting at different spatial scales, greatly influencethe identity of the fruit consumers visiting individual trees. This influenceundermines the chances that fruit traits become evolutionary modified so as toattract those consumers providing the best seed dispersalservicesto the plants.     

次生林不同类型森林边缘的鸟类物种丰富度及个体多度比较

边缘效应对动物的分布及行为会产生一定的影响,在鸟类生态学研究中已证实某些鸟类在森林内部和森林边缘区域存在着物种丰富度和个体多度的差异。于1999至2001年的春夏季,在吉林省左家自然保护区对阔叶林/农田边缘、阔叶林/灌丛边缘及阔叶林/针叶林边缘3种不同类型边缘地带的鸟类物种丰富度及个体多度进行了比较研究。结果表明,不同年间鸟类物种丰富度无显著变化,但个体多度存在着一定的波动。不同类型森林边缘的鸟类物种丰富度存在着一定的差异,阔叶林/灌丛边缘的鸟类物种丰富度最高,而阔叶林/针叶林边缘的鸟类物种丰富度最低。鸟类个体多度的总体趋势在3种不同类型的边缘差异不显著,但存在种间差异,灰椋鸟、灰头啄木鸟和喜鹊在阔叶林/农田边缘的个体多度最高,斑啄木鸟、黄胸、三道眉草和日本树莺在阔叶林/灌丛边缘的个体多度最高,而沼泽山雀、冕柳莺和山在阔叶林/针叶林边缘的个体多度最高。     

Seasonal clutch size variation of multi-brooded bird species: comparisons between breeding season and latitudes

Single- and multi-brooded species of birds differ in their seasonal patterns of clutch size. Single-brooded species start with a maximum clutch size that declines continuously as the season progresses, whereas the clutch sizes of multi-brooded species usually increase to a mid-season maximum peak and then decrease progressively until the end of the breeding season. Previous studies have shown that multi-brooded migrant species present seasonal patterns that are similar to single-brooded species at high latitudes but similar to multi-brooded non-migratory species at lower latitudes. We studied the Greenfinch Carduelis chloris and Goldfinch C. carduelis populations in eastern Spain (Sagunto, Valencia) between 1975 and 2002 to compare seasonal variations in clutch sizes between years with early and late starts to the breeding season. The period over which clutch sizes increase was longer when the breeding season started earlier. The Goldfinch population showed no pattern of initial increase in clutch size when there was a late start to the breeding season: a late start shortens the season giving them less time to breed, and may also coincide with maximum food availability. Thus, the pattern of single-brooded species was observed. In the Greenfinch population, a trend toward the seasonal pattern of single-brooded species was also observed when the following indices were compared: clutch size increase, modal timing, initial slope and timing of maximum clutch size. We have also compared the seasonal patterns of clutch size of both species in eastern Spain with the patterns observed in Britain. Our results show that for both Goldfinches and Greenfinches, the non-migrant southern populations of Sagunto in eastern Spain do not tend towards a more multi-brooded seasonal pattern of clutch size than the migrant Goldfinches of Britain.     

Effects of human disturbance on spatial and temporal feeding patterns of Blackbird Turdus merula in urban parks in Madrid,Spain

We studied how human presence in three urban parks in Madrid (Spain) might affect Blackbird densities by changing feeding behaviour patterns. Our specific purposes were: (a) to ascertain the effect of park visitors on Blackbird feeding behaviour; (b) to analyse the influence of human disturbance on foraging success; and (c) to determine how humans affect Blackbird spatial and temporal patterns of habitat use. Pedestrians were the main source of flushing responses in all sampled parks, followed by Magpies Pica pica and dogs accompanying visitors. Blackbird responses to visitors entailed more time being vigilant and moving away from people and less time searching for food (decreasing food intake), a response that remained constant in the three parks. The number of pedestrians was positively correlated with Blackbird distance to pathways and negatively correlated with distance to protective cover. The number of active birds decreased with increase in the number of pedestrians during the day. Blackbird density was negatively related to the number of visitors per park. Our results confirmed that human disturbance negatively affects Blackbird feeding strategies in urban parks, ultimately modifying spatial and temporal patterns of habitat selection and abundance. Since such responses could also affect densities of other urban species by the same process, we propose some management measures to decrease the levels of disturbance as well as to enhance the recreational use of urban parks.     

Spatial and temporal variation in population trends in a long‐distance migratory bird

Aim Over the past three decades, evidence has been growing that many Afro‐Palaearctic migratory bird populations have suffered sustained and severe declines. As causes of these declines exist across both the breeding and non‐breeding season, identifying potential drivers of population change is complex. In order to explore the roles of changes in regional and local environmental conditions on population change, we examine spatial and temporal variation in population trajectories of one of Europe’s most abundant Afro‐Palaearctic summer migrants, the willow warbler, Phylloscopus trochilus. Location Britain and Ireland. Methods We use national survey data from Britain and Ireland (BBS: BTO/RSPB/JNCC Breeding Bird Survey and CBS: BWI/NPWS/Heritage Council Countryside Breeding Survey) from 1994 to 2006 to model the spatial and temporal variation in willow warbler population trends. Results Across Britain and Ireland, population trends follow a gradient from sharp declines in the south and east of England to shallow declines and/or slight increases in parts of north and west England, across Scotland and Ireland. Decreasing the spatial scale of analysis reveals variation in both the rate and spatial extent of population change within central England and the majority of Scotland. The rates of population change also vary temporally; declines in the south of England are shallower now than at the start of the time series, whereas populations further north in Britain have undergone periods of increase and decline. Main conclusion These patterns suggest that regional‐scale drivers, such as changing climatic conditions, and local‐scale processes, such as habitat change, are interacting to produce spatially variable population trends. We discuss the potential mechanisms underlying these interactions and the challenges in addressing such changes at scales relevant to migratory species.     

Exploring the effects of truncated,pooled and sexed data in distance sampling estimation of breeding bird abundance

Capsule Field methods used by the UK's Breeding Bird Survey (BBS) provide a practical approach to estimating breeding bird abundance and this paper discusses how they might be adapted to increase accuracy.

Aims Using Salisbury Plain as a case study, examine the use of distance sampling to produce estimates of breeding bird abundance.

Methods During 2005, 157 1 km squares were surveyed on Salisbury Plain using the UK’s BBS methods, with the exception that all birds were sexed whenever possible and allocated to one of five distance bands (0–10 m/10–25 m/25–100 m/100–250 m/ >250 m). Data were modelled to investigate the effects of truncated, pooled and sexed bird data in estimating breeding populations.

Results Pooling of the inner distance bands made little difference to estimates, while truncation over 100 m affected them by up to 25%, generally leading to an increase in density and the width of the confidence limits. The national BBS does not distinguish between bird sexes and therefore any density estimate produced relates to individuals. Our analysis suggests that halving the number of individuals (assuming an equal sex ratio) could lead to significant underestimation of population. This is particularly the case for species where there are differences in detectability between sexes or skewed sex ratios. In such cases, the density of males may represent a more accurate assessment of the population.

Conclusions Bird surveys incorporate distance sampling because it assesses changes in detection probability and this paper suggests how these methods might be adapted to increase accuracy. Changes include increasing both survey effort (e.g. number of visits or distance covered), the number of distance bands, and recording sexed bird data. Numbers of pairs or territories could then be estimated by either halving the density of individuals, or using the density of males, whichever is highest. These suggestions have not been tested against a known population and further work is desirable.