A review of invertebrates and seed-bearing plants as food for farmland birds in Europe

Dietary information was reviewed for 22 bird species typically found in farmland areas across Europe using 100 references from the UK and other European countries for which quantitative data were presented. The number of studies and degree of taxonomic resolution available varied considerably between the species and, for some, dietary information was only available prior to agricultural intensification and may be unrepresentative of current feeding habits. Consequently, some caution is required in interpreting the results because of the different methods of data collection between the studies and the biases in analytical techniques for prey detectability. Food availability was rarely quantified in the study areas, and diet may have reflected availability or preference. Plant families and invertebrate orders were ranked in their importance separately for adult diet in the breeding and nonbreeding seasons and for chicks. The most important plant families overall were Poaceae, Polygonaceae, Caryophyllaceae, Cruciferae, Compositae, Chenopodiaceae and Labiatae, although the last two were unimportant for chicks. A number of key species were also identified. Similarities in dietary preferences were observed among Fringillidae (finches) and members of the Columbidae (doves and pigeons). Fringillidae and Carduelis cannabina (linnet) were associated with plants that occur in seminatural habitats, while Emberiza citrinella (yellowhammer), Phasianidae (partridges) and Columbidae were shown to be more closely associated with plants of agricultural environments. The most important invertebrate orders overall were Coleoptera adults, Hemiptera adults, Arachnida, Lepidoptera larvae/pupae, Diptera adults, Lepidoptera adults, Diptera larvae/pupae and Hymenoptera adults. During the nonbreeding season, a smaller number of invertebrate taxa were important. For adults in the breeding season and for chicks, there were 10 families of invertebrate that were important for four or more bird species (Aphididae, Carabidae, Chrysomelidae, Curculionidae, Elateridae, Formicidae, Scarabeidae, Staphylinidae, Tenthredinidae and Tipulidae). In the nonbreeding season, Curculionidae and Lumbricidae were important in the diet of three species. A few species exhibited a narrow diet range, selecting invertebrates from only one or two families. Similarities in dietary composition were observed among closely related bird species, while that of chicks and adults sometimes differed.     

Songbirds using crops planted on farmland as cover for game birds

We counted songbirds in crops planted on shooting estates specifically for game management purposes on farmland in Britain and elsewhere in Europe. Winter game crops provide cover and feed areas for pheasants Phasianus colchicus and red-legged partridge Alectoris rufa, while summer game crops are designed to provide brood-rearing cover for these species. In central and southern England, 30 plots of winter game crops, either kale, quinoa or cereal up to 2 ha in area, and 30 adjacent arable-field plots, were surveyed for birds up to six times at monthly intervals during the winter 1997–1998. In the Scottish lowlands, six plots of summer game crops up to 4 ha in area, and adjacent arable fields were surveyed in summer 1999 or 2000. The winter game plots contained more than ten songbirds per hectare in most months, while the adjacent arable-field plots contained less than one. In all three winter game crop types, songbird numbers declined significantly in the second half of the winter while numbers in the arable fields did not. Of the 26 species recorded in the winter game crops, 10 have undergone rapid decline over the last 30 years. Considering these declining species alone, the winter game crops still contained more individuals than the adjacent arable fields throughout the winter. Densities in both the kale and quinoa were higher than in the cereal game crop. The six summer game crops sampled in mid-summer contained on average 2.9 songbirds per hectare, while the adjacent arable fields contained 0.4. Of the 14 species recorded in these summer game crops, eight have undergone rapid or moderate declines over the last 30 years. Although winter and summer game crops are planted in relatively small plots and hence concentrate birds, these plots are widely planted and our results suggest that they benefit birds on farmland.     

Using fledged brood counts of hedgerow birds to assess the effect of summer agri-environment scheme options

A key aim of many European agri-environment schemes (AES) is to improve biodiversity on farmland. In recent years, several countries have been looking at long term trends in the spring adult population size of a target group of farmland birds as an indicator of this. The overall trend in these indicators is however not upwards. While this might suggest we need to look at the design and deployment of habitat management options within schemes, there is an increasing view that we also need to refine and improve our indicators, or the way we monitor them.Relating spring adult bird population size to AES options is problematic not least because of the time lag between the deployment of those designed to enhance bird breeding success in summer, and the spring surveys the following year. At the other end of the scale detailed studies of breeding success in farmland birds have practical/cost restraints. We argue that to understand the impact on farmland birds of particular summer options within AESs we need to be able to estimate the breeding success of local bird populations quickly and cheaply. This would enable us to relate particular AES options to the breeding performance of the birds actually using them.Complementing a previous study of woodland birds, we assess the likelihood of encountering fledged broods of hedgerow nesting bird species during transect surveys without finding nests, and then apply a simple mark-recapture analysis technique to provide an index of breeding success for those species. Following spring adult assessments, counts of fledged broods were undertaken four times a week during April, May, June and July, in four 2.5 km hedgerow transects, at four sites in southern England in 2010. Mean daily detection probabilities of fledged broods of 16 common hedgerow birds were calculated from these counts using the software Presence. For 15 out of these 16 species these detection probabilities were sufficiently high for a programme of fledged brood surveys, involving just two or three visits per week from mid-May to mid-July, to provide a useful estimate of breeding success.The survey technique and associated analyses make certain assumptions when providing estimates of breeding success and these are discussed. Little is known about initial dispersal in passerine fledglings and a study in hedgerows may be useful here. However our pilot study suggests that the method could have application as a relatively easily derived productivity index for hedgerow birds, and hence an additional method available to study the impact of certain AES options on indicator species, or for research studies.     

Agri-environment scheme enhances breeding populations of some priority farmland birds in Northern Ireland

Capsule: The abundance of Tree sparrow Passer montanus, House Sparrow Passer domesticus and Yellowhammer Emberiza citrinella, three priority farmland birds, increased over a 5-year period in response to a targeted agri-environment scheme (AES).

Aims: To assess the effects of a targeted AES on the abundance of a suite of farmland bird species over a 5-year period.

Methods: We compare temporal changes in abundance of 12 farmland bird species of conservation concern on 33 AES and 22 control farms in County Down, Northern Ireland. Five of these species were designated targets for conservation action under the Countryside Management Scheme (CMS).

Results: CMS management was associated with more positive changes in abundance for three of the five target species and more negative changes for one target species (albeit caused mainly by a large reduction at a single farm). CMS management had little influence on the abundance of non-target species or on avian species richness. Farm-scale changes in abundance were generally unrelated to the extent of local CMS provision, the only exception involved House Sparrow and seed-rich winter habitats.

Conclusion: This study demonstrates that generic AES land management can improve the population status of target farmland birds on farms with AES management.     

Measuring the functional responses of farmland birds: an example for a declining seed-feeding bunting

1. Many farmland bird species have undergone significant declines. It is important to predict the effect of agricultural change on these birds and their response to conservation measures. This requirement could be met by mechanistic models that predict population size from the optimal foraging behaviour and fates of individuals within populations. A key component of these models is the functional response, the relationship between food and competitor density and feeding rate. 2. This paper describes a method for measuring functional responses of farmland birds, and applies this method to a declining farmland bird, the corn bunting Miliaria calandra L. We derive five alternative models to predict the functional responses of farmland birds and parameterize these for corn bunting. We also assess the minimum sample sizes required to predict accurately the functional response. 3. We show that the functional response of corn bunting can be predicted accurately from a few behavioural parameters (searching rate, handling time, vigilance time) that are straightforward to measure in the field. These parameters can be measured more quickly than the alternative of measuring the functional response directly. 4. While corn bunting violated some of the assumptions of Holling's disk equation (model 1 in our study), it still provided the most accurate fit to the observed feeding rates while remaining the most statistically simple model tested. Our other models may be more applicable to other species, or corn bunting feeding in other locations. 5. Although further tests are required, our study shows how functional responses can be predicted, simplifying the development of mechanistic models of farmland bird populations.     

Population changes of breeding waders on farmland in relation to agri-environment management

Capsule Population response of breeding waders to agri-environment management varied between management options and species; implementation has been on too small a scale to reverse national population declines.

Aims To test whether numbers of five breeding wader species have shown a more positive response between 1992 and 2005, at sites with appropriate agri-environment management, than at sites that have remained outside such schemes.

Methods Using data from 60 pairs of farmland study areas in Scotland first surveyed in 1992/93, before agri-environment scheme (AES) implementation, and again in 2005, after scheme implementation, we tested at both site and field scales whether changes in the abundance of five breeding wader species were associated with AES management options designed to benefit these species.

Results Changes in breeding wader abundance were more positive on sites in AES, especially for Northern Lapwings Vanellus vanellus and Common Redshanks Tringa totanus, even though management had not been targetted specially at breeding waders on those sites. However, AES management was associated only with modest population increase for Common Redshanks, and a reduction in the magnitude of decline for Northern Lapwings. At the field scale, there was evidence for Northern Lapwings, Common Redshanks and Common Snipe Gallinago gallinago that options which limited grazing and other agricultural activity were associated with more positive outcomes than those which also manipulated water levels.

Conclusions AES management for breeding waders slowed, and in some cases reversed, breeding wader decline at field and farm scales. These benefits were from options that limited grazing and agricultural operations during the breeding season, but not those that also aimed to raise water levels. A possible explanation is that when wetland options are applied to agriculturally marginal fields, grazing reduction or abandonment, and succession to rank vegetation cover then occur over the course of 5-year agreements, with detrimental effects for breeding waders. Verification arrangements need to be robust enough to guard against this. Levels of agri-environment provision in 2005 were too limited and too poorly targeted at remaining key areas for breeding waders to be able to halt or reverse national population declines.     

Use of field margins managed under an agri-environment scheme by foraging Barn Swallows Hirundo rustica

Capsule: Barn Swallows Hirundo rustica were more likely to forage along arable field margins that were enhanced with wildflowers or legumes than control grass margins.

Aims: To determine if foraging Barn Swallows displayed preferences for specific arable field boundary habitats (grass margins versus floristically enhanced margins) that were managed as part of an agri-environment scheme. We also aim to determine how Barn Swallow food abundance related to these habitats.

Methods: Two foraging activity surveys took place on all grass and floristically enhanced margins (n?=?56) present within the 600 m foraging range of seven Barn Swallow colonies during June and July 2016. Margin habitat use was measured by recording the presence/absence of foraging individuals during surveys, the total number of individuals and by calculating an index of foraging activity. Habitat information relating to adjacent boundary type, transect crop type and neighbouring crop type were also recorded.

Results: Foraging Barn Swallows were significantly more likely to be recorded when survey transects included a floristically enhanced margin, but there was no significant impact of floristically enhanced margins on the total number of individuals recorded or on the index of foraging activity. Foraging activity was higher along grass verges and hedgerows when compared to treelines and was positively related to length weighted Diptera abundance (a measure of food biomass).

Conclusion: Our results suggest that there may be a role for floristically enhanced margins in the conservation of Barn Swallows on arable farmland. More research, however, is needed to determine whether invertebrate-rich agri-environment scheme habitats can influence colony size or improve the breeding success of this species.     

The state of play of farmland birds: population trends and conservation status of lowland farmland birds in the United Kingdom

Many bird species of lowland farmland have declined substantially in the United Kingdom over the past 30 years. Declines among farmland specialists are steeper than for generalists and were most rapid for these specialists in the 1970s and 1980s. These changes have been linked to increased agricultural intensification and are reflected in Red or Amber conservation concern status for many common farmland species, as well as for rarer ones. We review long- and short-term population trends and the conservation status of lowland farmland birds in the UK using the latest available information from bird surveys, and examine patterns among species. Analyses of demographic parameters suggest broadly that the key factor driving population changes of seed-eating and migrant birds is overwinter survival, whereas for many non-passerine species population growth appears to be limited by productivity. Population trends for a suite of lowland farmland species were first combined in the UK Government's headline wild bird indicator published in 1998. This 'Skylark index' as it is sometimes known was intended to reflect the health of the wider countryside and struck a chord with the public and decision-makers. We look at the behaviour of the composite indicator and explore the population dynamics of the increasing and declining species separately. Simple models of population growth in these groups are then used to explore plausible scenarios for delivering the Government's Public Service Agreement target to reverse the long-term decline in the number of farmland birds by 2020.     

Habitat associations of Eurasian Skylarks Alauda arvensis breeding on Irish farmland and implications for agri-environment planning

Capsule Skylarks breeding in Ireland prefer extensive grassland habitats and almost completely avoid tillage habitats.

Aims To describe the distribution and habitat use of breeding Skylarks in Ireland, particularly in lowland agricultural habitats, and to use this information to inform conservation measures for this species.

Methods Countryside Bird Survey (CBS) and Farmland Bird Project (FBP) data were examined to determine large-scale (national) distribution and habitat selection, in addition to smaller-scale (farm- and field-level) habitat use. The CBS is a national breeding bird monitoring scheme involving 397 1-km squares. The FBP collected detailed bird and habitat data from 122 farms.

Results CBS and FBP data both showed significant regional differences in breeding Skylark densities, with the highest relative abundances in the northwest and west. Dry grassland/grass moor habitats supported the highest densities of breeding Skylarks in the CBS, which were significantly higher than in improved grassland or tillage. At the farm-level, Skylark numbers were positively related to wetland habitats but negatively associated with trees in field boundaries, dense ground vegetation and overall density of farm boundaries. At the field-scale, larger fields and unimproved grasslands were preferred.

Conclusion Agri-environment measures tailored to region-specific requirements and to the relatively local habitat preferences of target species are required if population declines of species of conservation concern, including Skylarks, are to be reversed.     

Habitat associations of British breeding farmland birds

Capsule Territory distribution for ten species was most strongly positively influenced by the presence of hedges and woodland edge.

Aims To describe and rank the importance of different habitat predictors on the distribution of bird territories.

Methods We derived territory maps for ten bird species across 25 sites on English lowland farmland in 2002. We related habitat predictors to the distribution of these species using information theoretic methods.

Results Habitat predictors were ranked as follows (numbers in parentheses indicate the number of species with a strong effect): hedge presence (8), boundary height (7), woodland edge (6), tree presence in boundary (4), brassica (mainly oil seed rape) (3), within‐field vegetation height (3), boundary strip (3), boundary width (3), tilled fields (3), winter set‐aside (2), ditch (1), winter stubble fields (1).

Conclusions Non‐cropped habitats had the most consistent positive effects across all ten species, with crop types and their margins exerting smaller effects.     

Silent fields: the decline of farmland birds in Europe

Populations of many farmland birds appear to have collapsed across much of Europe. Agricultural intensification is driving populations down over huge areas and represents probably the greatest single threat to the continent's birds. Understanding the problem, however, is only the first step to putting farmland birds back in the countryside. The plight of these once-widespread birds highlights the need for improved monitoring across Europe.     

Evidence for the indirect effects of pesticides on farmland birds

Indirect effects of pesticides, operating through the food chain, have been proposed as a possible causal factor in the decline of farmland bird species. To demonstrate such a link, evidence is needed of (1) an effect of food abundance on breeding performance or survival; (2) an effect of breeding performance or survival on population change; and (3) pesticide effects on food resources, sufficient to reduce breeding performance or survival, and hence to affect the rate of population change. Evidence under all three categories is only available for one species, the Grey Partridge Perdix perdix , although data showing effects of pesticides on food resources and relationships between food resources and breeding performance are also available for some other species. This paper reports on recent work investigating the effects of pesticides on Yellowhammer Emberiza citrinella and Skylark Alauda arvensis during the breeding season. The probability of brood reduction in Yellowhammer was affected by the proportion of the foraging area around the nest which was sprayed with insecticide. No significant effects of pesticides were recorded on Skylark chick condition or growth rate, but sample sizes were small. Invertebrate food abundance affected chick condition (Skylark) and the number of chicks fledging (Yellowhammer and Corn Bunting Miliaria calandra ; relationship for the latter derived from re-analysis of data from an earlier study). Other recent work is briefly reviewed and the current evidence for the indirect effects of pesticides is summarized. Significant knowledge gaps are identified and some of the issues involved in resolving these are discussed.     

Reintroduction as a tool for population recovery of farmland birds

Conservation efforts in the United Kingdom have increasingly sought to restore the populations and ranges of birds affected by changes to their habitat or by direct human persecution. One approach is reintroduction, although this is likely to be appropriate in only a limited set of circumstances, involving a small number of species. This paper reviews the use of reintroduction as a tool for conserving birds associated with lowland farmland, highlighting the benefits of this approach to conservation, as well as the potential dangers. Two case studies are presented to illustrate how different reintroduction techniques are required, depending on the species involved and the donor stock available. The internationally agreed, though not legally binding, IUCN guidelines for reintroduction projects are summarized, together with the requirements of The Wildlife & Countryside Act (1981) in relation to the release of birds into the wild in Britain. Potential changes to current legislation are suggested, to prevent inappropriate and potentially damaging reintroduction projects from being carried out in the future.     

The optimal age of sown field margins for breeding farmland birds

The Europe‐wide decline in the populations and diversity of farmland birds has not been stopped despite dedicated conservation efforts such as agri‐environment schemes (AES). The main reason for the lack of success of AES is considered to be their low ecological quality and insufficient area. Understanding the effects of different management strategies on the ecological quality of AES is therefore important. Here, we investigate the relationship between breeding bird density and species richness and the age of sown field margins, a widely used type of AES, in southwestern Switzerland. Territories of breeding birds were mapped on 67 field margins between 2004 and 2011. Territory densities (for eight species) and species richness were analysed in relation to age of the field margin. A general negative correlation between size of the field margin and territory density indicated that territory density was higher when the birds could forage in adjacent cultivated land. Territory densities and species richness increased up to an age of 4–6 years after sowing, depending on the species, and declined thereafter. The results suggest that the co‐occurrence of newly sown margins and margins over 3 years old will have a positive effect on breeding bird densities and species diversity.