Antony J. Morris

A review of the abundance and diversity of invertebrate and plant foods of granivorous birds in northern Europe in relation to agricultural change

Abstract This study reviews the diet of 26 granivorous bird species of European temperate farmland, and evidence for the effects of agricultural practices on their invertebrate and plant foods, in order to assess whether the latter could have contributed to recent widespread population declines of farmland birds. Cereal grain and seeds of Polygonum (knotgrasses and persicarias), Stellaria (chickweeds) and Chenopodium (goosefoots) are important for the bird species considered. Seeds and green material of Asteraceae, Fabaceae, and Brassicaceae are also widely used, the seeds of Asteraceae particularly by cardueline finches. Declining bird species are not associated with particular plant foods, but reductions in overall diversity and abundance of food plants have taken place in intensively managed arable land. Grassland intensification has reduced floral diversity, and the quantity and diversity of grass and broad-leaved seed produced, but some plant species of value to granivorous birds benefit from high-nitrogen environments and may increase in availability (e.g., Stellaria – chickweeds). During the breeding season, Acrididae (grasshoppers), Symphyta (sawflies), Araneae (spiders), Chrysomelidae (leaf-beetles), Curculionidae (weevils), Lepidoptera (butterflies and moths and their larvae), Aphididae (aphids) and Tipulidae (crane-flies and their larvae) are important foods. The first four are associated with the diet of declining bird species, and all are sensitive to insecticide applications. Herbicide applications, increasing specialisation of farmland, loss of uncultivated field margin habitats, and ploughing are also associated with generally detrimental effects on invertebrate groups in arable habitats. In intensively managed grassland, loss of grasshoppers, ants, spiders and lepidopteran larvae removes an important source of food for younger chicks of a wide range of species. Some phytophagous taxa and predators, however, may be more abundant due to the greater standing biomass of plant material. Overall, intensification and specialisation of arable and grassland systems is likely to have reduced the availability of key invertebrate and seed foods for birds. However, there is also evidence that reversal of intensification, especially in arable systems can result in rapid recovery of these resources. In intensively managed farmland, uncultivated field margins, hedgerows, ditches and road verges are likely to become increasingly important sources of seed and invertebrate food for birds.

Habitat characteristics affecting use of lowland agricultural grassland by birds in winter

Almost a third of the bird species designated as Species of European Conservation Concern exploit agricultural grasslands, yet few studies have focused on their use as foraging habitats for birds. This study investigated the influence of variation in sward structure, grassland management and landscape variables on the use of 77 grass fields by 14 field-feeding bird species wintering on lowland mixed farmland in southern England. Multiple logistic regression was used to model the proportion of bird-count visits in which each species was encountered as a function of the recorded habitat variables for each field. Variation in sward height and density were associated with frequency of occurrence for 12 bird species and larger areas of bare earth and occurrence of winter grazing by stock animals were correlated with greater frequency of occurrence by 11 bird species. Two rapidly declining species, skylark (Alauda arvensis) and yellowhammer (Emberiza citrinella), were recorded more frequently on fields with higher numbers of seeding grasses. We suggest that mosaics of fields managed as short-term leys and permanent pastures with low-intensity cattle grazing over the autumn and winter would provide the combination of heterogeneous sward structure, areas of bare earth and presence of some seeding plants necessary to maximise the range of bird species able to use a given area of agriculturally improved grassland throughout the winter.

Use of set-aside land in winter by declining farmland bird species in the UK

Between 1992 and 1993 over 600 000 ha of arable farmland in the UK were set aside under a production control mechanism of the Common Agricultural Policy (CAP) of the European Union. One of the management options for this set-aside land was to leave it as an over-winter fallow with a naturally regenerated green cover. This study was designed to test whether such land was used by seed-eating bird species, populations of many of which have undergone recent severe declines. Five out of six declining species recorded in the study were found in significantly greater numbers on this habitat than would be expected if the birds were randomly distributed over the farmland landscape. The results of this study, covering a wide geographical area, reinforce previous findings of the importance of winter food sources, particularly over-winter stubble fields, to declining farmland seed-eaters. Proposed changes to the CAP under Agenda 2000 include the reduction of the obligatory set-aside rate to zero. These results sugges...

Foraging habitat selection by yellowhammers (Emberiza citrinella) nesting in agriculturally contrasting regions in lowland England

Fine-scale habitat use by yellowhammers (Emberiza citrinella) searching for food to provision nestlings was compared in three agriculturally contrasting regions of lowland England. Log-linear modelling was used to test for significant overall variation in habitat use and significant differences in relative use between pairs of habitats. Yellowhammers provisioned nestlings non-randomly with respect to habitat availability. Habitat selection was found to be generally consistent across the three regions; field boundary structures and barley crops were the most selected foraging habitats, while intensively-managed grass fields were avoided relative to virtually all other habitats. The observed patterns of habitat selection are likely to result from an interaction of food abundance and varying accessibility to food, mediated by sward structure. The geographical generality of the results allows reasons to be suggested for the recent rapid population decline of the species and general conservation recommendations to be made with respect to lowland farmland.

Use of field margins by foraging yellowhammers Emberiza citrinella

Abstract Some agri-environment schemes promote the creation and management of a variety of non-crop habitats on farmland in the UK, yet there has been relatively little monitoring to assess how species, particularly birds, use these habitats. The present study deals with a declining UK farmland bird species, yellowhammer Emberiza citrinella , and considers to what extent grass margins of arable fields are used as a foraging habitat when feeding nestlings. Studies were carried out in lowland mixed farmland in southern England. Grass margins and other non-crop field boundary habitats, such as hedgerows and ditches, were selected relative to cropped areas by yellowhammers. No significant difference was found between use of cut and uncut grass margins. Studies have shown that grass margins support high densities of invertebrates and their provision at the edge of arable fields would benefit yellowhammers during the breeding season both as habitat for prey and as nesting habitat. During the breeding season from May to August, management should create cut and uncut grass margins in close proximity to each other. This could be achieved by cutting only the outer edge of the grass margin, maintaining cover next to the hedgerow. Cut areas would provide easier access to food resources for birds and prevent weed encroachment to the crop, whilst adjacent uncut areas would maintain invertebrate sources and provide nesting cover for yellowhammers.

Chaffinch Fringilla coelebs foraging patterns, nestling survival and territory distribution on lowland farmland

Numbers of many bird species which breed on farmland, and are reliant on cropped land for feeding or nesting, declined between the 1960s and 1990s. In contrast, Chaffinch Fringilla coelebs numbers increased on farmland over the same period. This study investigates the influence of both cropped and non-cropped land on Chaffinches foraging for nestlings, nestling survival and territory density. The study was carried out on nine mixed lowland farms in south central England in 1996 and 1997. Chaffinches made little use of cropped areas when foraging for young (less than 9% of foraging visits, despite cropped areas covering 93% of study areas). Instead, trees and bushes influenced foraging patterns and breeding success. Extensive use was made of trees and bushes by adults searching for food for nestlings (75% of foraging visits were to hedges and trees within boundaries or fields, despite these areas covering <3% of study areas). Oaks (69% of visits) and Willows (15% of visits) were found to be the most favoured species of tree for foraging. In one year of the study, chick starvation was less frequent in nests located on field boundaries with Oak trees than in nests on boundaries without Oaks. Successful nests also tended to be closer to Oak or Willow trees than those where nestlings starved. Territory density was not related to hedgerow structure, presence or absence of Oaks and Willows in field boundaries, or adjacent cropping. Our findings on nest survival were supported by analysis of British Trust for Ornithology nest record data which revealed that nests associated with trees had better brood survival rates than sites not located close to trees. The use of trees and shrubs for feeding and nesting in the farming landscape and the ability to utilize unkempt hedgerows may have contributed to the ability of Chaffinches to persist on farmland despite wide-scale agricultural change in recent decades.

The status and distribution of Nightjars Caprimulgus europaeus in Britain in 1992. A report to the British Trust for Ornithology

In 1992 the British Trust for Ornithology and the Royal Society for the Protection of Birds organized a national survey of Nightjars. A total of 3093 churring males was located and the British population was estimated to be approximately 3400 males. This represents an increase in numbers of more than 50% since the last national survey in 1981. Possible reasons for this partial recovery after a long period of decline are discussed.

Trichomonad parasite infection in four species of Columbidae in the UK

Trichomonas gallinae is an emerging pathogen in wild birds, linked to recent declines in finch (Fringillidae) populations across Europe. Globally, the main hosts for this parasite are species of Columbidae (doves and pigeons); here we carry out the first investigation into the presence and incidence of Trichomonas in four species of Columbidae in the UK, through live sampling of wild-caught birds and subsequent PCR. We report the first known UK cases of Trichomonas infection in 86% of European Turtle Doves Streptopelia turtur sampled, along with 86% of Eurasian Collared Doves Streptopelia decaocto, 47% of Woodpigeons Columba palumbus and 40% of Stock Doves Columba oenas. Birds were more likely to be infected if the farm provided supplementary food for gamebirds. We found three strains of T. gallinae and one strain clustering within the Trichomonas tenax clade, not previously associated with avian hosts in the UK. One T. gallinae strain was identical at the ITS/5.8S/ITS2 ribosomal region to that responsible for the finch trichomonosis epizootic. We highlight the importance of increasing our knowledge of the diversity and ecological implications of Trichomonas parasites in order further to understand the sub-clinical impacts of parasite infection.

The protozoan parasite Trichomonas gallinae causes adult and nestling mortality in a declining population of European Turtle Doves, Streptopelia turtur

Studies incorporating the ecology of clinical and sub-clinical disease in wild populations of conservation concern are rare. Here we examine sub-clinical infection by Trichomonas gallinae in a declining population of free-living European Turtle Doves and suggest caseous lesions cause mortality in adults and nestlings through subsequent starvation and/or suffocation. We found a 100% infection rate by T. gallinae in adult and nestling Turtle Doves (n = 25) and observed clinical signs in three adults and four nestlings (28%). Adults with clinical signs displayed no differences in any skeletal measures of size but had a mean 3.7% reduction in wing length, with no overlap compared to those without clinical signs. We also identified T. gallinae as the suggested cause of mortality in one Red-legged Partridge although disease presentation was different. A minimum of four strains of T. gallinae, characterized at the ITS/5.8S/ITS2 ribosomal region, were isolated from Turtle Doves. However, all birds with clinical signs (Turtle Doves and the Red-legged Partridge) carried a single strain of T. gallinae, suggesting that parasite spill over between Columbidae and Galliformes is a possibility that should be further investigated. Overall, we highlight the importance of monitoring populations for sub-clinical infection rather than just clinical disease.

Influence of agri-environment scheme options on territory settlement by Yellowhammer (Emberiza citronella) and Corn Bunting (Emberiza calandra)

Conserving farmland birds is a key objective for agri-environment schemes (AES) across Europe, with a number of management options aimed at providing invertebrate food and nesting habitats. We analysed territory settlement by two widespread but declining farmland buntings with contrasting nesting requirements: the Yellowhammer Emberiza citrinella, a boundary-nesting species, and the Corn Bunting Emberiza calandra, a ground-nesting species. The study was conducted on farms participating in the English Higher Level Stewardship scheme to test whether territory settlement is influenced by the provision of key arable AES options. Both species settled preferentially in localities containing sown arable field margins, while Corn Bunting also settled in localities containing nectar flower mixtures. These preferences are likely to reflect foraging rather than nesting habitat requirements. Yellowhammer selected territories containing hedgerows under AES management, which are nesting rather than foraging habitat but may also provide food. Uptake by land owners of several AES options likely to provide limiting resources for farmland birds was very low, and because uptake at the landscape scale is also low, wider-scale population level benefits are likely to be constrained. However, this is one of few studies demonstrating selection of widely applied arable AES options by breeding farmland birds.ZusammenfassungUmweltschutzprogramme in der Landwirtschaft und ihr Einfluss auf die Besiedlung durch Goldammern (Emberiza citronella) and Grauammern (Emberiza calandra) Die Erhaltung der Vogelwelt von Agrarlandschaften ist überall in Europa ein primäres Ziel landwirtschaftlicher Umweltschutzprogramme und beinhaltet eine ganze Reihe von Management-Optionen zur Erhaltung von Nistarealen und auch von Wirbellosen als Futterquelle. Wir analysierten die Besiedelung von Farmland bei zwei weit verbreiteten, jedoch rückläufigen Ammernarten mit unterschiedlichen Nestbau-Anforderungen: die Goldammer, eine Art, die an Waldrändern und im Gebüsch nistet, und die bodenbrütende Grauammer. Unsere Untersuchung wurde auf Farmen durchgeführt, die am English Higher Level Stewardship-Programm teilnehmen. In diesem Programm soll festgestellt werden, ob eine Besiedlung durch die Vögel von der Umsetzung spezieller landwirtschaftlicher Umweltschutzprogramme beeinflusst wird. Beide Ammernarten siedelten sich bevorzugt in solchen Arealen an, in denen die Ackerraine eingesät worden waren, während die Grauammern auch in Arealen mit einer Mischung unterschiedlicher Blütenpflanzen siedelten. Diese Vorlieben spiegeln aber wohl eher Anforderungen an die Nahrungssuche als an Nistareale wider. Die Goldammern bevorzugten Flächen mit Hecken, die im Rahmen von Umweltschutzprogrammen angelegt worden waren und sich eher als Nistgebiete eignen, aber für die Nahrungssuche ebenfalls gut sind. Nur sehr wenige Landbesitzer in der Landwirtschaft waren bereit, ausgewählte Schutzprogramme umzusetzen, die Feldvögeln begrenzte Ressourcen geboten hätten, und da die Bereitschaft auch auf Landschaftsebene recht niedrig ist, sind positive Auswirkungen für größere Populationen vermutlich eher begrenzt. Nichtsdestotrotz ist dies eine von nur wenigen Untersuchungen, die zeigt, dass Feldvögel bestimmte, weit verbreitete Umweltschutzmaßnahmen im landwirtschaftlichen Bereich für die Besiedlung bevorzugen.