Showing papers by "Royal Society for the Protection of Birds published in 2001"

Agricultural intensification and the collapse of Europe's farmland bird populations

Abstract: The populations of farmland birds in Europe declined markedly during the last quarter of the 20th century, representing a severe threat to biodiversity. Here, we assess whether declines in the populations and ranges of farmland birds across Europe reflect differences in agricultural intensity, which arise largely through differences in political history. Population and range changes were modelled in terms of a number of indices of agricultural intensity. Population declines and range contractions were significantly greater in countries with more intensive agriculture, and significantly higher in the European Union (EU) than in former communist countries. Cereal yield alone explained over 30% of the variation in population trends. The results suggest that recent trends in agriculture have had deleterious and measurable effects on bird populations on a continental scale. We predict that the introduction of EU agricultural policies into former communist countries hoping to accede to the EU in the near future will result in significant declines in the important bird populations there.

The importance of arable habitat for farmland birds in grassland landscapes

Abstract: Summary 1 Over the last 25 years, populations of seed-eating birds have declined severely over most of western Europe Local extinctions have occurred in grassland-dominated areas in western Britain, which may be influenced by loss in habitat diversity and a decline in the amount of arable cultivation 2 We used the large-scale British Breeding Bird Survey of 1998 to investigate the importance of arable habitat within grassland landscapes for 11 common seed-eating birds and four similar sized insectivores Generalized linear models were used to model the number of birds recorded in agricultural habitat within survey squares as a function of the amount of arable habitat present 3 Numbers of grey partridge Perdix perdix, skylark Alauda arvensis, tree sparrow Passer montanus, corn Miliaria calandra and reed buntings Emberiza schoeniclus, yellowhammer Emberiza citrinella and whitethroat Sylvia communis increased with the amount of arable habitat present in a survey square; the numbers of house sparrow Passer domesticus, four finch species, dunnock Prunella modularis, robin Erithacus rubecula and blackcap Sylvia atricapilla did not 4 The positive association between numbers of some species and arable habitat within 1-km squares was strongest where arable habitat was rare in the surrounding area, and weakest or even reversed when arable habitat was common These results demonstrate the scale-dependence of bird–habitat associations in agricultural landscapes, only demonstrable where data are available at fine grain over large geographical areas 5 These results support the hypothesis that range contractions (ie local extinctions) of some granivorous species have occurred because of contraction in arable cultivation The loss of arable habitat where it is scarce may be causing declines in some areas, even though intensification of arable management is thought to be the main cause of declines elsewhere Agri-environment schemes may need to vary between regions, for example to encourage arable cultivation in pastoral areas

The effects of flooding lowland wet grassland on soil macroinvertebrate prey of breeding wading birds

Abstract: Summary 1 Lowland wet grassland in western Europe is often managed for breeding wading birds, especially lapwing Vanellus vanellus, redshank Tringa totanus, snipe Gallinago gallinago and black-tailed godwit Limosa limosa. Recommended conservation management often entails introducing winter flooding, and in Britain there is government funding to encourage this through the Environmentally Sensitive Area scheme. 2 Soil macroinvertebrates are important prey for breeding wading birds on lowland wet grassland. This study quantified the response of soil macroinvertebrates to flooding, their ability to survive in flooded grassland, and changes in the abundance and physical availability of soil macroinvertebrates for feeding wading birds as flood water subsides. 3 Unflooded grasslands contained high biomasses of soil macroinvertebrates, comprising mainly Tipulidae larvae and earthworm species that are widespread in pastures. Grasslands with a long history of winter flooding contained much lower biomasses of soil macroinvertebrates, comprising mainly a limited range of semi-aquatic earthworm species. 4 Introducing winter flooding to previously unflooded grassland greatly reduced soil macroinvertebrate biomass. This was mainly due to the majority of earthworms vacating the soil soon after the onset of flooding. However, when earthworms were artificially confined in flooded soils, most species were capable of surviving periods of at least 120 days continual submergence. Winter flooding also expelled large numbers of overwintering arthropods from the soil. 5 Soil macroinvertebrates were slow to recolonize winter-flooded grassland when it was re-immersed in spring. Consequently, prey biomass for breeding wading birds remained low in areas that had been flooded during the preceding winter. However, winter flooding probably benefited breeding snipe by helping keep the soil soft enough for them to probe for prey. It also probably benefited breeding lapwings and redshank by helping keep the sward short and open enough for them to feed in during the latter part of their breeding season. Pools of winter flood water that remained in spring and early summer also provided a source of aquatic invertebrate prey for breeding wading birds. 6 We suggest that the best feeding conditions for breeding snipe will be provided by keeping the upper soil soft enough for them to probe in but without reducing soil macroinvertebrate biomass by flooding it beforehand. Optimal conditions for breeding lapwings and redshank will probably be provided by creating a mosaic of unflooded grassland, winter-flooded grassland and shallow pools.

The effect of management for red grouse shooting on the population density of breeding birds on heather‐dominated moorland

Abstract: Summary 1 Breeding birds, vegetation and moorland management were surveyed in 320 1-km squares on 122 estates in upland areas of eastern Scotland and northern England where red grouse shooting is a widespread land use. We assessed whether population densities of 11 species of breeding birds differed between heather-dominated moorland managed for red grouse shooting and other moorland with similar vegetation. 2 We classified estates that had a full-time equivalent moorland gamekeeper as grouse moors. The mean density of red grouse shot per year was four times higher and the mean density of gamekeepers was three times higher on grouse moors than on other moors. Rotational burning of ground vegetation covered a 34% larger area on grouse moors than on other moors. 3 Selection of heather-dominated squares resulted in similar composition of vegetation on grouse moors and other moors (about 76% heath, 12% grass, 8% bog, 2% flush and < 1% bracken on both types). However, grouse moors tended to have less tall vegetation than other moors and differed significantly in some other characteristics of the vegetation, topography and soil type. 4 Densities of breeding golden plover and lapwing were five times higher and those of red grouse and curlew twice as high on grouse moors as on other moors, while meadow pipit, skylark, whinchat and carrion/hooded crow were 1·5, 2·3, 3·9 and 3·1 times less abundant, respectively, on grouse moors. The differences in density between moorland types remained significant (P < 0·001) for golden plover and crow and approached significance (P < 0·10) for lapwing and meadow pipit after allowing for variation among regions. 5 We used Poisson regression models to relate bird density to vegetation cover, topography, climate and soil type. After adjusting for significant effects of these habitat variables, significant differences in bird density between the two moorland types remained for six species, although their magnitude was reduced. 6 Correlations of adjusted bird density with measures of different aspects of grouse moor management provided evidence of a possible positive influence of predator control (assessed using crow density) on red grouse, golden plover and lapwing. The control of crows by gamekeepers is the most probable cause of the low densities of crows on grouse moors. There was evidence of a positive effect of heather burning on the density of red grouse and golden plover and a negative effect on meadow pipit. Multiple Poisson regression indicated that predator control and heather burning had significant separate effects on red grouse density. Significant relationships between adjusted breeding bird densities and the abundance of raptors and ravens were few and predominantly positive. 7 The results provide correlative evidence that moorland management benefits some breeding bird species and disbenefits others in ways that cannot readily be explained as effects of differences in vegetation type or topography. However, experimental manipulations of numbers of some predators and heather burning are required to test these findings.

Predicting shorebird mortality and population size under different regimes of shellfishery management

Abstract: Human interests often conflict with those of wildlife. In the coastal zone humans often exploit shellfish populations that would otherwise provide food for populations of shorebirds (Charadrii). There has been considerable debate on the consequences of shellfishing for the survival of shorebirds, and conversely the effects of shorebird predation on the shellfish stocks remaining for human exploitation. Until now, it has been difficult to determine the impact of current shellfishery practices on birdsor to investigate how possible alternative policies would affect their survival and numbers. One long-running contentious issue has been how to manage mussel Mytilus edulis and cockle Cerastoderma edule shellfisheries in a way that has least effect on a co-dependent shorebird, the oystercatcher Haematopus ostralegus, which also consumes these shellfish. This study used a behaviour-based model to explore the effects that the present-day management regimes of a mussel (Exe estuary, UK) and a cockle (Burryinlet, UK) fishery have on the survival and numbers of overwintering oystercatchers. It also explored how alternative regimes might affect the birds. The model includes depletion and disturbance as two possibly detrimental effects of shellfishing and some of the longer-term effects on shellfish stocks. Importantly, model birds respond to shellfishing in the same ways as real birds. They increase the time spent feeding at low tide and feed in fields and upshore areas at other times. When shellfishing removes the larger prey, birds eat more smaller prey. The results suggest that, currently, neither shellfishery causes oystercatcher mortality to be higher than it would otherwise be in the absence of shellfishing; at present intensities, shellfishing does not significantly affect the birds. However, they also show that changes in management practices, such as increasing fishing effort, reducing the minimum size of shellfish collected or increasing the daily quota, can greatly affect oystercatcher mortality and population size, and that the detrimental effect of shellfishing can be greatly increased by periods of cold weather or when prey are unusually scarce. By providing quantitative predictions of bird survival and numbers of a range of alternative shellfishery management regimes, the model can guide management policy in these and other estuaries.

Habitat use and diet of skylarks Alauda arvensis wintering on lowland farmland in southern Britain

Abstract: Summary 1 The habitat use and diet of skylarks wintering on lowland farms were studied to assess whether changes in agricultural practice could have reduced their most favoured wintering habitats or foods. Faecal samples were collected and soil seed densities were estimated. Skylarks in 122 cereal stubble fields in Oxfordshire were counted monthly to examine habitat use. 2 Cereal stubble fields were more likely to be occupied than other crops, and densities of birds in occupied fields were high. Barley stubbles were significantly more likely to be occupied than wheat stubbles. Growing cereals were weakly selected. Sugar beet stubbles held high densities of birds. Rotational set-aside was occupied more frequently and held higher densities than non-rotational set-aside. 3 Field size affected field occupancy independently of crop type, with larger fields more likely to be occupied. Fields enclosed by hedges or trees tended to be avoided. Cereal and set-aside fields that were occupied by skylarks in at least 1 month held significantly higher soil seed densities than fields that were not occupied. 4 Differences in occupancy between crops could be explained by diet. Birds in cereal stubbles fed largely on cereal grain, whereas those in winter cereals fed largely on cereal leaves. Broad-leaved weed leaves were strongly selected as food in cereal crops and farmland grass fields. In grass fields, the proportion of the diet made up by broad-leaved weeds was positively correlated with their availability. Broad-leaved weed seeds did not make up a significant dietary component in any crop. 5 Our results show that the shift from spring to autumn sowing of cereals has led to a loss of the skylark’s most strongly selected wintering habitat and best food source. In winter cereals and in grass there was a high selectivity for relatively scarce, and probably declining, food resources. Our results suggest that the retention of weed-rich cereal (particularly barley) and sugar beet stubbles through the winter, particularly in large open blocks, will improve conditions for skylarks in winter. Whole-field rotational set-aside, particularly as naturally regenerating cereal stubbles, provides good winter food resources for skylarks.

Experimental removal of introduced hedgehogs improves wader nest success in the Western Isles, Scotland

Abstract: Summary 1 Introduced predators are a major threat to island avifaunas world-wide. In the Western Isles of Scotland, recently introduced hedgehogs Erinaceus europaeus have become a serious predator of bird eggs and are an important cause of declines of some waders (Charadrii). 2 Experiments at two sites in 1998 measured the effect on wader nest success resulting from hedgehog removal from fenced exclosures. The nest success of waders inside the plots (where hedgehog densities were zero or low) was approximately 2·4 times that of birds nesting in the adjacent control areas (where hedgehog densities were high). There was no evidence of a compensatory increase in egg loss to native avian predators. 3 The experiment was an integral part of a research programme to support wader conservation efforts. On the basis of the experiment it can be predicted that the removal of hedgehogs on a larger scale would result in a large increase in nest success. 4 The study also tested the practicalities of using relatively cheap fences against hedgehogs. Fences were generally effective, but on dry sandy ground rabbits Oryctolagus cuniculus burrowed under fences, enabling some hedgehogs to re-enter plots. Well-designed fences could be used as a conservation tool, both as a barrier to protect key sites, and to aid the trapping and removal of hedgehogs. However, fences cannot be seen as a long-term solution to the problem. 5 Radio-tagged hedgehogs removed from the plots and released nearby all attempted to re-enter the plots. Two tracking methods revealed that displaced hedgehogs followed fences for distances up to 500 m looking for an entry point. There was no evidence that hedgehogs were able, or even attempted, to climb over or dig under fences. 6 The establishment of hedgehogs in the Western Isles provides an example of a threat to biodiversity following human-mediated redistribution of a species native to the UK to parts of the UK (Scottish islands) outside the species’ natural range, an activity not currently prohibited by law. Policy action to deter or control species introduction should consider ecological range even within national boundaries.

Predicting population responses to resource management

Abstract: The use of limited funding to optimal effect in conservation depends on the costs and benefits of different approaches to predicting population responses to management action. Resource management based on predictions from various classes of population-level model has had success in increasing populations of at-risk species. However, such models might not meet policy demand for more accurate predictions of the extent of population recovery. This is because, by necessity, they often extrapolate from known data to predict the effect of new environmental conditions. Behaviourally structured population models could deliver greater prediction accuracy because they can truly predict population-level responses to novel situations. If such an approach can be applied to new situations, it could play an increasing role in the prediction of population recovery following management.

The effects of forestry on golden eagles on the island of Mull, western Scotland

Abstract: Summary 1 The afforestation of previously open habitats continues to involve conservation organizations in assessing effects on important species. We investigated the effects of commercial afforestation on golden eagles Aquila chrysaetos on the island of Mull, western Scotland, using long-term data on eagle reproductive success and occupancy on 30 home ranges, largely during 1981–99. 2 We modelled home range parameters in a geographical information system (GIS) that gave geographical location and predicted range use as a percentage of the total use. Resolution was to 50 × 50-m (equivalent) pixels, each with a predicted value of percentage use. Forest cover was created as a separate GIS layer set to be temporally dynamic and to reflect the stage at which commercial plantations made open ground unsuitable for golden eagles by canopy closure (12 years). 3 The layers for forest cover and range use were overlapped in the GIS to produce year-on-year estimates of the extent of open canopy forest (trees < 12 years), closed canopy forest (trees ≥ 12 years), semi-natural woodland, and open ground within each golden eagle range. 4 Based on their history of productivity, golden eagle ranges were classified using cluster analysis as either productive or unproductive. These two groups did not differ significantly in range size, mean elevation, variation in elevation, terrain ruggedness or mean cover of closed canopy forest. Nor was productivity related to these measures on ranges unaffected by commercial forestry. 5 Two golden eagle ranges were apparently abandoned by breeding eagles as a result of afforestation, but these losses were balanced by the formation of new ranges elsewhere. However, on ranges where forests were planted, standardized values of golden eagle productivity fell significantly after canopy closure. 6 Temporal trends in eagle productivity on ranges where forest had been planted differed significantly from ranges where no forest was planted. The productivity of forested ranges declined markedly in the mid-1990s when forest cover exceeded 10–15% of the areas probably used by range-holding golden eagles. 7 In a general linear model, using ranges with commercial forestry, productivity after canopy closure was positively associated with productivity before closure. Productivity after canopy closure was unrelated to range size, and only weakly related to the change in forest cover (P = 0·09, 13 ranges). Changes in eagle productivity due to increased forest cover were thus too variable on individual ranges to be predicted with confidence. 8 This study demonstrates that commercial forestry can adversely affect the productivity of golden eagles but the exact scale of effect is difficult to predict as even small plantations can have an adverse influence. Vacant neighbouring ranges may also influence the response of golden eagles to increasing forest cover. We caution against using set criteria of the extent of forest cover to predict whether a range will be abandoned.

Microsatellite and mitochondrial DNA homogeneity among phenotypically diverse crossbill taxa in the UK.

Abstract: Genetic differentiation within and between the three morphologically divergent crossbill species extant in the UK was assessed by comparison of allele frequencies at five unlinked microsatellite loci and DNA sequence variation across the mitochondrial control region. No significant differences in microsatellite allele frequency were found either between different populations of the same species or between the crossbill species themselves. A similar lack of genetic divergence was apparent from the mitochondrial sequence data. We resolved 33 different haplotypes, separated by low levels of sequence divergence (0–0.15%). Levels of divergence within and between species were not significantly different. Haplotypes formed a polyphyletic phylogeny, indicating that the crossbill species do not form genetically separate clades. Discordance between neutral DNA polymorphisms and adaptive morphological variation is discussed in relation to defining the systematic relationship between crossbill forms. If adaptive differences have arisen without a concomitant divergence in neutral DNA then attempting to define crossbill types from microsatellite and mitochondrial DNA without recourse to ecology and behaviour may be misleading.

Flexibility and the use of indicator taxa in the selection of sites for nature reserves

Abstract: 'Minimum' sets of complementary areas represent all species in a region a given number of times. In recent years, conservation assessments have centred around the evaluation of these 'minimum' sets. Previous research shows little overlap between 'minimum' sets and existing nature reserves and between 'minimum' sets for different taxonomic groups. The latter has been used as an argument to discount the use of indicator taxa in the selection of sites for nature reserves. However, these 'minimum' set analyses have only considered a single set for each taxonomic group when there are, in fact, a large number of equally valid 'minimum' sets. We present new methods for evaluating all of these alternative 'minimum' sets. We demonstrate that if all of the sets are evaluated, significantly higher levels of overlap are found between 'minimum' sets and nature reserves, and pairs of 'minimum' sets for different taxonomic groups. Furthermore, significantly higher proportions of species from non-target taxonomic groups are recorded in the 'minimum' sets of target groups. Our results suggest that previous conservation assessments using 'minimum' sets may have been unduly pessimistic.

Body condition, growth rates and diet of Skylark Alauda arvensis nestlings on lowland farmland

Abstract: Factors affecting the diet, body condition and growth rates of Skylark chicks were assessed to examine their relationship to their agricultural environment during a critical period in the life cycle of this rapidly declining species. Rainfall explained the greatest amount of variation in body condition and growth rates and had a negative effect on both. Body condition indices were a good predictor of the likelihood of future partial brood loss to starvation. Low body condition in grass fields was related to a low diversity in the diet. Chicks fed insect larvae had higher body condition indices than those not fed larvae. Larger broods tended to have higher growth rates than smaller ones, whereas smaller broods tended to have higher body condition indices. Natural brood size reduction through the non-hatching of eggs resulted in higher body condition indices than were found in nests with the same number of chicks where all eggs hatched, this effect being independent of absolute brood size. There was no significant difference between crop types in the distance adult birds flew to forage for food for nestlings and foraging crop destination had no effect on chick development. Differences between crop types in chick diet could be related to the documented effects of pesticides on different prey species. We suggest that recent agricultural changes have affected diet and possibly body condition, but that these effects are unlikely to have been an important factor in recent population declines.

Microsatellite variation in the yellowhammer Emberiza citrinella: population structure of a declining farmland bird.

Abstract: In recent years, there has been much concern in the UK about population declines of widespread species in agricultural habitats. Conservation-orientated research on declining birds has focused on vital rates of survival and productivity. However, the environmental factors which may influence movements between populations of widespread species is poorly understood. Population genetic structure is an indirect description of dispersal between groups of individuals. To attempt to develop an understanding of genetic structuring in a widespread, but declining, farmland bird, we therefore investigated the yellowhammer, Emberiza citrinella, population in England and Wales using microsatellite data. Our first aim was to investigate whether there was genetic substructuring in the population. A second aim was to investigate if there was a relationship between genetic distances and various environmental variables. Finally, we analysed the microsatellite data for evidence of loss of genetic variation due to population decline. Our data showed a slight but significant structure within the yellowhammer population. This therefore cannot be considered a panmictic population. Our example from South Cumbria implies that high-altitude barriers may have a slight influence on population structure. However, on the whole, genetic distances between sample sites were not significantly correlated with geographical distances, degrees of population connectivity, high altitudes, or differences in precipitation between sites. Finally, we detected departures from mutation-drift equilibrium (excess heterozygosity), which is indicative of a loss of genetic variation through recent decline.

Factors affecting the distribution of landbirds on the Falkland Islands

Abstract: A high proportion of island birds are threatened with extinction as a result of their vulnerability to introduced predators, habitat destruction, and fragmentation/isolation effects. In order to conserve island species effectively, it is necessary to disentangle these effects on distribution and abundance. We attempt to do this for the nine native passerines in the Falkland (Malvinas) Islands, using a database of presence/absence on 59 offshore islands in the archipelago, linked to data for each island on mammal presence, habitat modification, and isolation. Falklands native passerines are of considerable conservation importance, comprising one endemic globally threatened species, several endemic subspecies, and several restricted range species. Presence of rats on islands was by far the most important predictor of passerine presence, overriding the effect of habitat modifications. The globally threatened endemic Cobb's Wren Troglodytes cobbi was absent from all islands containing rats. Some species were more likely, and others less likely to occur on islands where tussac Poa flabellata grassland had been destroyed by grazing. The former species were primarily those adapted to dwarf-heath vegetation, and/or that thrive around human settlements. Island size and isolation were important predictors of occurrence for several bird species. The analyses show that, if vegetation restoration in the Falklands is to meet conservation aims, then it should be accompanied by introduced mammal control. Secondly, they indicate that biogeographical effects on bird distribution among islands in the Falklands are important, and need to be considered when assessing the conservation status of species, and when considering conservation action.

Land-use and the conservation of Sharpe's Longclaw Macronyx sharpei in central Kenya

Abstract: The highland grasslands of central Kenya hold a suite of restricted-range bird species, including several of global conservation concern These grasslands occur almost entirely on private land with no formal protection, and have received little conservation attention This paper describes land-use change on the Kinangop Plateau, Kenya, and considers the implications for grassland bird species, especially Sharpe's Longclaw Macronyx sharpei The Kinangop Plateau is an area of montane grassland east of the Rift Valley, used primarily for dairy farming since human settlement in 1964 However, dairy farming (which retains grassland as pasture) has given way to other forms of land-use, especially cultivation of crops In March 1996, a questionnaire was administered to 50 landowners to investigate community attitudes towards birds and their conser vation, the extent of present land-use changes and likely future land-use patterns The mean acreage of landholding was decreasing, and more grassland was rapidly being converted into cultivated land, with 32% being ploughed up during the six months from November 1995 to May 1996 Farmers expressed a preference for crop farming (66%) over livestock farming (26%) or other land uses Thirty-two per cent expressed a positive attitude, and 60% were indifferent, towards birds Most (76%) were not aware of biodiversity values or conservation Though 64% were aware of declining bird populations around them, 82% of this group did not realize that their activities might be contributing to this decline Sixty-eight per cent of landowners planned to convert all or part of their grassland holdings Although landowners' interests seemed generally incompatible with grassland conservation, a substantial proportion (44%) were prepared to consider opportunities to enhance the area's conservation value An informal follow-up survey in March 1999 concluded that prospects for the dairy industry and for grassland habitats on Kinangop were not as bleak as the initial survey suggested, but confirmed the delicate conservation status of Sharpe's Longclaw and its habitat We suggest a variety of actions that might help to secure the future of Sharpe's Longclaw while promoting sustainable agricultural development on Kinangop, and propose several topics where further research is needed Species such as Sharpe's Longclaw will only survive if we can develop ways of managing their habitats in a manner that is consistent, rather than in conflict, with the needs of the agricultural community

A method for ageing adult Corncrakes Crex crex

Abstract: The shapes of the tips of Corncrake Crex crex secondary remiges grown by chicks and adults were compared. Measurements of secondaries of birds of known age were obtained from wild Corncrakes in Britain and captive‐bred birds originating from Germany and Poland. The tips of secondaries grown in the hatching year were more pointed than those grown in subsequent years in both samples. Secondaries grown in the hatching year are retained until the autumn of the next calendar year. Consequently the average shape of the tips of secondaries of one year old adults was different from that of older birds. The sum of the angles measured at the tips of secondaries 3 to 6 inclusive (numbered ascendantly) was used to quantify this difference. The angle sum scores of known first‐years and older birds overlapped, but it is possible to estimate the proportions of the two age classes in a sample of adults of unknown age by assuming that the distribution of scores is the combination of two normal distributions with means and...