Declines of ground-nesting birds in two areas of upland farmland in the south Pennines of England

CapsuleWe present evidence of large declines in numbers of breeding waders and passerines in some upland areas since the 1970s.

Aims Changes in numbers of ground-nesting birds are documented for two areas of the Pennines and are qualitatively related to recent land-use history.

Methods Territory mapping was used to estimate bird numbers on two areas (76 and 99 ha) in the Pennines for which more than 10 consecutive years of data were available from the BTO's Common Birds Census archives.

Results At both sites there were large declines in Lapwing Vanellus vanellus, Snipe Gallinago gallinago, Skylark Alauda arvensis, Twite Carduelis flavirostris and Reed Bunting Emberiza schoeniclus. The two sites differed in the timing of the declines but for Twite the trends were almost identical. By the late 1990s, numbers of most ground-nesting birds were far lower than in the 1970s. There was relatively little change in numbers of species breeding at either site.

Conclusions Progressive changes in land-use, involving loss of rough grassland and a switch from dairy to sheep farming, may have contributed to the declines at one of the sites. However, there was no obvious change in land-use or habitat loss at the other site where population declines began 5 to 10 years earlier. Such declines have probably occurred widely in moorland-edge areas during the last 30 years and multiple factors may be responsible.     

Associations between distance to forest and spatial and temporal variation in abundance of key peatland breeding bird species

Capsule Negative forest edge effects were detected for Willow Ptarmigan (Red Grouse) Lagopus lagopus and Dunlin Calidris alpina.

Aims To investigate the effects of distance to forest on the abundance and changes in abundance of four key peatland breeding bird species, and to measure changes in predatory bird numbers, in the peatlands of northern Scotland.

Methods Bird surveys were carried out in 2000 at 34 plots, covering 197 km² of peatland, and 80 forestry point‐count sites, first surveyed in 1988. Habitat data were also collected in 2000. We used multi‐model inference to investigate the associations between forest distance and other habitat variables, and the abundance, and changes in abundance, of four bird species of economic or conservation importance: Red Grouse, European Golden Plover Pluvialis apricaria, Dunlin and Common Greenshank Tringa nebularia.

Results There was strong evidence that distance to forest was negatively associated with Dunlin abundance and changes in Red Grouse abundance, but only weak evidence for negative associations with Golden Plover abundance and changes in Dunlin abundance. There was no evidence of a forest distance effect on Greenshank. Among predatory birds, there were no significant increases either on peatland plots or in new forestry plantations.

Conclusions This study provides evidence that, for a given habitat quality, Dunlin densities are lower, and Red Grouse declines more likely, near to forest edges, but weak evidence only that Dunlin declines are more likely, and Golden Plover abundance lower, near to forests. These results suggest that for at least two key peatland breeding birds, forest removal is likely to benefit birds breeding on adjacent unafforested peatland.     

Seed food preferences of granivorous farmland passerines

Capsule Large buntings prefer cereal grains whilst sparrows also take oily seeds.

Aims To determine seed food preferences of Tree Sparrow Passer montanus and Corn Bunting Emberiza calandra.

Methods Forty seed choice experiments were conducted at two sites over two winters. In each experiment, two seed types were provided and the number of visits made by birds to each type was recorded over a set period. At one site, Tree Sparrows were colour-ringed, allowing choices made by individual birds to be recorded. Data were also collected for House Sparrow Passer domesticus, Yellowhammer Emberiza citrinella and Reed Bunting E. schoeniclus.

Results All five species fed intensively on cereal grain, and wheat and oats were consistently preferred to barley. Sparrows and Reed Buntings also took maize, which was avoided by Corn Bunting and Yellowhammer. Tree Sparrow exhibited a broad diet, selecting cereal grain and oily seeds including sunflower and oilseed rape, but rye-grass seed was almost completely avoided.

Conclusion Cereal grain should be a key component of over-winter provision of seed for farmland passerines, especially when targeted at Corn Bunting and Yellowhammer. Oily seeds such as brassicas and sunflower will benefit species with more generalist diets, including Tree Sparrows.     

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.     

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.     

Agricultural land-use and the spatial distribution of granivorous lowland farmland birds

Current agricultural practices are believed to have contributed to the declines of many farmland bird species, especially seed‐eaters, throughout Europe. We investigated associations between the spatial distribution of fourteen granivorous farmland bird species and agricultural land‐use in Britain, using breeding bird atlas data and national agricultural statistics. Analyses were spatially referenced by 10x10 km square and variation due to broad‐scale geography and spatial auto‐correlation was controlled for. Generalized linear modelling analyses were used to select models describing variation in distribution explained by the available land‐use variables. The results show that relationships between distribution and agriculture tend to be species‐specific, but that some general effects can be identified. Features of intensive arable farming including large areas of sugar beet, wheat and oilseed rape tended to be associated with low frequencies of occurrence for 9–11 species, while large areas of younger (re‐seeded) grassland and high sheep stocking densities were associated with low frequencies in pastoral farmland for up to 12 species. One key feature of lower intensity farming, the presence of larger areas of fallow land, was positively related to frequency index for up to 11 species. The proportion of barley sown in spring and agricultural diversity were each associated with a range of complex relationships with frequency index across species, probably reflecting combinations of positive influences and artefacts of scale and geography. A variable describing the heterogeneity of farmland (the extent to which it is a mix of arable and pastoral land‐use) was negatively related to frequency index for eight species, but other results suggested that farming which is mixed at a smaller spatial scale is widely beneficial. The results reveal relationships between agriculture and the occurrence of granivorous farmland bird species which suggest both hypotheses for the causes of population change and directions for management action. However, data on several key features of agricultural practice (such as pesticide use) were unavailable, so their effects could not be tested, and the effects of the variables included could not be separated from those of other factors which are subject to complex geographical variation. Experimental comparisons of the effects of land‐use at the farm scale are needed to investigate such confounded influences on farmland bird occurrence.     

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.     

Assessing the implications of the loss of set‐aside for farmland birds

Between 1988 and 2007, set‐aside, a European Commission production control measure, took an average of 10% of arable farmland in the EU out of production each year. In 2007, the set‐aside rate was set to 0% and the scheme was later abandoned altogether. By assessing associations of farmland birds with set‐aside and quantifying the extent of set‐aside loss, this study aims to assess the implications of set‐aside loss for farmland bird conservation. During the lifespan of set‐aside, a large number of studies assessed the biodiversity value of set‐aside and other agricultural crops and habitats. Where possible we considered measurable benefits of set‐aside. However, some studies did not specify the type of set‐aside and in some cases set‐aside fields were grouped with cereal stubble fields. In these cases, we took the pragmatic approach of assessing the value of generic stubble fields as a conservative minimum estimate of the value of set‐aside fields. A re‐analysis of data from 30 intensive studies demonstrates that farmland bird densities tended to be higher on set‐aside than on either cereal or oilseed rape crops. Without mitigation, these are the two crops likely to replace most set‐aside fields. We estimate that 26–52% of the farmland populations of key granivorous passerines were present on stubble fields, giving an indication of the proportion of birds likely to be present on set‐aside fields within this broader category. An extensive survey of lowland farmland during winters 1999/2000, 2000/2001 and 2002/2003, repeated in February 2008, showed a doubling of the number of 1‐km squares with no stubble and a halving of the number of squares with more than 10 ha of stubble. After set‐aside abandonment, 72% of squares had no stubble in the important late winter period, confirming that many of the former stubble fields were retained as set‐aside. A simple correlative model suggests that this could cause a small increase in the rate of decline of Skylark Alauda arvensis and Yellowhammer Emberiza citrinella populations, assuming causal links between stubble area and demography. However, even if this assumption cannot be supported, these results clearly indicate that a significant proportion of some farmland bird populations will need to find alternative breeding and foraging habitats.     

Problems of censusing Reed Buntings,Sedge Warblers and Reed Warblers

The daytime dispersal of Starlings from an urban winter communal roost was monitored by colour marking 1424 birds according to age and sex. Reports received from members of the public suggested that dispersal was homogeneous with respect to age and sex composition at all distances from the roost. There was evidence that dispersal was geographically heterogeneous with respect to sex composition, and this observation is discussed in relation to correlated variation in agricultural practices.     

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.     

Densities and population estimates of breeding Skylarks Alauda arvensis in Britain in 1997

We present the results of a national survey of breeding Skylarks Alauda arvensis in Britain in 1997 carried out by the British Trust for Ornithology (BTO). Numbers of Skylarks and land-use types were recorded by volunteers in 608 1-km squares, selected using random stratification based on the Institute of Terrestrial Ecology's (ITE) Landscape Classification to avoid over- or under-sampling particular habitat types. The results suggest a maximum national population of around 1000 000 pairs. This agrees extremely well with the national population estimate of around 1046 000 pairs derived from the Breeding Bird Survey (BBS) of the BTO/Joint Nature Conservation Committee/Royal Society for the Protection of Birds, and provides further evidence for the robustness of the BBS as a national monitoring scheme for common and widespread species. The figure is approximately half that of the most recent published estimate of 2000 000 in 1988–91. However, the scale of this discrepancy is likely to reflect a bias in Atlas field methodology and site selection since there has been a real decline of approximately 9% since 1990. Arable squares supported the highest densities of Skylarks; 4.6–6.0 pairs per km², and 46–49% of the British breeding population was associated with arable areas. Marginal upland and upland areas supported lower densities but still accounted for approximately 34% of the estimated national breeding population. Differences in density at broad habitat scales were reflected in geographical differences across Britain, with southern and eastern arable regions supporting much higher densities than western and northern ones. At a finer scale, Skylarks occurred at highest densities on, and showed highest habitat preferences for, set-aside and various types of ungrazed grassland. Winter cereal, improved grassland and set-aside held the highest proportion of the Skylark population on farmland in England and Wales; grazed pasture, winter cereals and spring cereals held the highest proportion in Scotland.     

Comparative population dynamics of Common Sandpipers Actitis hypoleucos: living at the edge

Capsule Common Sandpiper populations at the edge of their range do not recruit so well.

Aims To compare the survival rates, breeding success and recruitment of a population near the edge of its range (Peak District) with one more centrally placed (Borders).

Methods Populations were censused weekly; adults and chicks were ringed, and apparent survival of adults determined by resighting colour-ringed birds. Breeding success was assessed from ringing chicks and the guarding behaviour of their parents over 3–4 weeks post-hatching.

Results Survival rates of adults and their breeding success were similar in the two sites. Recruits were rarely ringed chicks returning to near their natal site; they were usually newly recruited adults. In both, natal dispersal took returning chicks away from their natal site, by 3–6 km, but far more potential recruits returned to the Borders (51% compared with 4%). The population in the Borders was more variable, but recovered better from declines.

Conclusions There is no obvious difference in survival or reproductive rates that would explain the different recent fates of the two study populations. Differential survival over winter in West Africa (the presumed wintering grounds) is unlikely to explain the recent decline of the Peak District population, because conditions there should have affected the Borders population too. The Peak District population is exposed at the edge of the species' range, and it seems to be poorer breeding success across its general range that has caused the poorer recruitment there, and hence the decline.     

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.     

Agricultural intensification and the timing of breeding of Corn Buntings Miliaria calandra

Capsule In an intensively managed agricultural landscape, few females attempted a second brood.

Aims To investigate the effect of modern farming practices on the number of Corn Bunting breeding attempts.

Methods We compared the timing of breeding by Corn Buntings on the South Downs, West Sussex, with the habitat composition within 150 m of their nests.

Results Breeding was earlier in areas containing winter-sown wheat and set-aside than in areas containing spring-sown barley. Nests were earlier when cereal crops near the nest were more developed. The presence of unripe grain was a better predictor of the timing of breeding than the height of the crop. Double-brooding was extremely rare and few females re-laid after nest failures. Daily failure probabilities of clutches increased during the season, largely as a result of harvesting operations.

Conclusions Changes in the timing of cereal harvesting and the availability of uncultivated nesting habitat may have reduced the incidence of double-brooding in some intensive arable landscapes. Food availability may also limit the onset of breeding, further reducing the possibility of double-brooding.     

Evidence for declines in populations of grassland-associated birds in marginal upland areas of Britain

Capsule We report large declines among summer populations between 1968–80 and 2000.

Aim To assess changes in the status of breeding populations of birds in pastoral uplands.

Methods Volunteer observers revisited 13 areas of marginal upland in Britain where Common Birds Census data were collected during 1968–80. This allowed the status of 35 bird species to be examined over about 20 years and to make a comparison between grassland-based and woodland-based species.

Results For 12 species the decline in abundance was significant, particularly among passerines, such as Skylark Alauda arvensis, Wheatear Oenanthe oenanthe, Whinchat Saxicola rubetra, Yellow Wagtail Motacilla flava and Yellowhammer Emberiza citrinella, each of which declined by over 80%. Redshank Tringa totanus, Yellow Wagtail, Dipper Cinclus cinclus, Whinchat, Wheatear, Ring Ouzel Turdus torquatus and Yellowhammer were found on less than half the number of plots on which they were originally recorded. Most declining species were associated with grassland for nesting and foraging, compared to those species that increased (Wood Pigeon Columba palumbus, Pied Wagtail Motacilla alba, Carrion Crow Corvus corone, Jackdaw C. monedula and Goldfinch Carduelis carduelis) that were less specialized in their habitat requirements. Woodland or woodland edge species showed no significant change in status, suggesting that population declines among grassland species were not due to lower observer effort between recording periods.

Conclusion Long-term changes to grassland ecosystems in marginal upland areas of Britain may have influenced the status of bird populations.     

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.     

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.     

Changes in Danish farmland habitats and their populations of breeding birds

Habitat changes and the breeding bird populations were studied at Kraghede, N Jutland the years 1970–1980. Generally, agricultural practice was intensified leading to an increase in the area used permanently for growing barley, and the abandonment of grasslands and meadows. Animal husbandry decreased, until it was restricted to a small number of farms.
These habitat changes were the largest ones to occur in the Danish landscape for some 150–200 yr and had a significant influence on the breeding birds. Species confined to the meadows, such as the lapwing Vanellus vanellus , meadow pipit Anthus pratensis and others, decreased by 50–80% or even more. Species associated with the grassland when feeding, like the swallow Hirundo rustica , starling Sturnns vulgaris and magpie Pica pica , all had lower population levels at the end of the 1970's compared to those at the beginning of the decade.     

Integrated population monitoring of breeding birds in Britain and Ireland

Effective wildlife monitoring schemes identify changes in population variables that require conservation action. This must be based on an understanding of normal patterns of population variability. Monitoring schemes ideally provide data on the stages of the life cycle at which changes are taking place and indications of the probable causes of change.
The Integrated Population Monitoring Programme of the British Trust for Ornithology aims to fulfil these requirements for British birds. It encompasses existing BTO projects that measure population size, productivity and survival rates, principally the Common Birds Census, Waterways Bird Survey, Nest Record Scheme, Constant Effort (mist-netting) Sites Scheme and the Ringing Scheme. Integrated analyses of long-term BTO data are being used to study the population dynamics of individual species. Relationships established through such analyses will be used to construct models that will predict population performance, and against which observed performance can be compared.
A simple application of Integrated Population Monitoring is presented using data for the Song Thrush ( Turdus philomelos ), a species which has been declining throughout most of Britain since the mid 1970s. No reduction in reproductive performance was detected and the decline appears to have been brought about through reduced survival rates. Factors responsible for much of this decline were identified from a multiple regression model involving winter weather conditions.