Anthony Morton
Well-known member
Tim Allwood said:
Tim,
Agreed - but I prefer to look at it as a possible indication that the perceived scientific opinion regarding songbird predation is perhaps not set in tablets of stone after all.
Anthony
-
Welcome to BirdForum, the internet's largest birding community with thousands of members from all over the world. The forums are dedicated to wild birds, birding, binoculars and equipment and all that goes with it.
Please register for an account to take part in the discussions in the forum, post your pictures in the gallery and more.
Who To Believe? (1 Viewer)
- Thread starter Anthony Morton
- Start date
Tim,
Agreed - but I prefer to look at it as a possible indication that the perceived scientific opinion regarding songbird predation is perhaps not set in tablets of stone after all.
Anthony
Anthony Morton said:
Anthony - can you provide a a quote from this report that actually determines that songbird population decine is as a result of predation. The quotes the magazine use only say that predation affects breeding success in those areas, it does not say that this has an influence on population decline.
Richard
Nightranger
Senior Moment
Anthony Morton said:
Hi Anthony,
Another good question but this is where we can get to the root of the problem. Evidence suggests that all habitats are at carrying capacity and despite a greater proportion of birds surviving the winter, there is no corresponding rise in the number of breeding pairs. The classic example is the house sparrow because we know habitat loss (for breeding) is one factor that has applied over urban and rural habitats albeit for different reasons. Food supplies are also an issue but I want to leave that to one side because the analogies are not so close for the two habitats (one being winter food and the other being summer food - there is a study into the latter underway BTW). A change of emphasis in farming means that a lot of old farm buildings are redundant and are being redeveloped whereas housing in urban areas has been heavily modernised in recent years. Both have led to a loss of nesting sites for sparrows (although nest boxes may eventually ameliorate this in urban areas when the trend catches on). Interestingly, house sparrows have up to 4 broods in a year and the better the summer whether, the better chance of all 4 broods being fledged successfully. The problem is, sparrows may be colonial but they have a rank of dominance and so should be considered as territorial birds to some extents. Ask anyone who has sparrows whether they saw extra nests and I can guarantee that they did not. Ask anyone who has not had sparrows whether there has been a sudden arrival in the last few years and some will tell you yes, but numbers are low and are not present all year. House sparrows do not seem to have a juvenile dispersal phase like the related tree sparrow but they cannot manufacture nest sites that do not already exist. I have only really dealt with birds that are declining here and we should never forget that some species are increasing, notably the blue tit and great tit. It is not just coincidence either because these two species are the two that benefit most from nest boxes and garden feeding (tighter nesting territories, for example). The most noticeable element of the increase is the expansion into urban areas, putting them firmly in contact with cats, magpies and squirrels yet the increase has not been arrested. I cannot see how this infers that predators have any bearing because blue tits have probably the highest predation pressures of any species (cats, squirrels, sparrowhawks, crows, jackdaws, magpies, jays, great spotted woodpeckers and weasels as primaries and hedgehogs, foxes and merlins as secondaries).
Ian
Last edited:
James Lowther
Well-known member
Anthony Morton said:
It would be interesting to know whether the authors think their work 'contradicts the accepted science on magpie predation'.
Jane Turner
Well-known member
Tim Allwood said:
Sorry if this bores anyone... but I did a little reseach this lunch time on papers on the decline of Song Thrush. If you want to get to the punch line read the last one
Papers suggestion possible role of Corvids:
Large-scale spatial variation in the breeding performance of song thrushes Turdus philomelos and blackbirds T. merula in Britain
Emmanuel Paradis*, Stephen R. Baillie*, William J. Sutherland, Caroline Dudley*, Humphrey Q.P. Crick* and Richard D. Gregory*§
Journal of Applied Ecology Volume 37, Issue s1, Page 73-87, September 2000
Discusses effect of Corvids on reproductive output, NOT population trends:
"We developed a method to predict spatial variation in reproductive output. Brood size and nest failure rates during the incubation and nestling periods were related to environmental factors using generalized linear models. Predicted values obtained from these models were combined to give values of number of fledglings produced per nesting attempt for 10-km squares throughout Britain. Reproductive output in both species was affected mainly by factors that vary on a small spatial scale. Nest failure rate during incubation increased significantly where corvids were more abundant, suggesting a role for avian nest predators in determining spatial variation in reproductive output."
Papers suggesting possible role of habitat/climate change
Demographic and environmental causes of the decline of rural Song Thrushes Turdus philomelos in lowland Britain
WILL J. PEACH1*, ROB A. ROBINSON2 & KATHRYN A. MURRAY3
Ibis Volume 146 Issue s2 Page 50 - November 2004
"Increased mortality during the first year of life (from fledging to recruitment) is highlighted as a potential demographic mechanism having driven the population decline.
Increasing dryness of agricultural soils and the loss of grassland from eastern arable counties have probably both contributed to the declines of rural Song Thrushes in Britain. Loss of hedgerows and scrub, and the degradation of woodland may also have contributed to population declines but the role of predators remains unclear. Recovery of rural Song Thrush populations requires challenging new policy initiatives that should aim to restore nesting cover (scrub and woodland understorey), grazed grassland in arable-dominated areas and damper soils in summer".
Summer diet and body condition of Song Thrushes Turdus philomelos in stable and declining farmland populations
Derek Gruar, Will Peach* & Roy Taylor
Ibis Volume 145 Issue 4 Page 637 - October 2003
Changes in agricultural practices have probably caused a major reduction in the availability of key summer food resources for Song Thrushes on lowland farmland, and we speculate that breeding thrushes mitigate the impacts of food shortage on chicks by confining their nesting attempts to localities and periods where invertebrate food resources are adequate to raise a brood of young.
Habitat selection by song thrushes in stable and declining farmland populations
Will J. Peach, Matthew Denny, Pete A. Cotton*, Ian F. Hill, Derek Gruar, David Barritt, Andrew Impey and John Mallord
Journal of Applied Ecology Volume 41 Issue 2 Page 275 - April 2004
Lack of woodland and grassland, and the faster drying of surface soils in the arable landscape, combined to limit the availability to thrushes of key summer invertebrate prey. Loss of hedgerows, scrub and permanent grassland with livestock, and the wide-scale installation of under-field drainage systems, have probably all contributed to the decline of song thrushes on UK arable farmland. New agri-environment measures may be needed to provide the nesting cover adjacent to invertebrate-rich damp soils that song thrushes require to sustain annual productivity
Thrushes now largely restricted to the built environment in eastern England
Christopher F. Mason
Diversity & Distributions Volume 6 Issue 4 Page 189 - July 2000
Song thrush was significantly associated with scrub within the urban boundary. With all three species largely absent from farmland, residential habitats can be considered as habitat refuges. The consequences of this for conservation and planning are discussed.
Demographic mechanisms of the population decline of the song thrush Turdus philomelos in Britain
Robert A. Robinson*, Rhys E. Green, Stephen R. Baillie*, Will J. Peach and David L. Thomson*§
Journal of Animal Ecology Volume 73 Issue 4 Page 670 - July 2004
Survival of first-year birds was correlated negatively with the duration of the longest run of frost days and the survival of adults was correlated negatively with the duration of the longest summer drought. Variation among blocks in mean PMR was correlated with block means of the duration of runs of frost days and drought days, but significant correlations between PMR and both post-fledging and first-year survival remained after allowing for the influence of weather on survival.
Large-scale habitat use of some declining British birds
R. D. Gregory & S. R. Baillie
Journal of Applied Ecology Volume 35 Issue 5 Page 785 - September 1998
Large-scale habitat use of eight species of breeding birds was considered using data collected across Britain. The species were skylark Alauda arvensis (L.), dunnock Prunella modularis (L.), blackbird Turdus merula (L.), song thrush Turdus philomelos (L.), starling Sturnus vulgaris (L.), linnet Carduelis cannabina (L.), bullfinch Pyrrhula pyrrhula (L.) and reed bunting Emberiza schoeniclus (L.). All are linked by roughly synchronous population declines over the last 25 years in southern Britain (and mostly in farmland landscapes). Discussion is limited to the conservation status of these species.
For most species considered, farmland holds a high proportion of their population (in excess of 50% for four species), reflecting the predominance of this land use across Britain. This suggests that sympathetic changes in farming practices are likely to provide the best mechanism for improving the status of these species.
I could go on... but I need to go swimming!
Edward woodwood
Member
game over?
again....
again....
Jane Turner
Well-known member
and
Ibis
Volume 146 Issue 1 Page 1 - January 2004
The potential for interactions between predation and habitat change to cause population declines of farmland birds
K. L. Evans*
Population declines are often attributed to either habitat change or increased predation rates, without a full consideration of the potential for these two factors to interact. This may lead to an inaccurate diagnosis of the causes of population decline and thus the selection of inappropriate management solutions. Here mechanisms through which habitat change and predation could interact are reviewed. Examples of how these may have contributed to population declines are provided, focusing on European farmland birds. However, very few appropriate studies have been conducted that allow the role of such interactions to be assessed accurately. To remedy this situation experimental designs that could detect the presence of interactive mechanisms are described. When habitat change and predation interact, conservation managers are provided with the opportunity to control predation impacts through habitat management rather than predator removal, which may provide a more cost-effective management strategy.
Ibis
Volume 146 Issue 4 Page 579 - October 2004
doi:10.1111/j.1474-919X.2004.00375.x
The recent declines of farmland bird populations in Britain: an appraisal of causal factors and conservation actions
Ian Newton*
In this paper, the main aspects of agricultural intensification that have led to population declines in farmland birds over the past 50 years are reviewed, together with the current state of knowledge, and the effects of recent conservation actions. For each of 30 declining species, attention is focused on: (1) the external causes of population declines, (2) the demographic mechanisms and (3) experimental tests of proposed external causal factors, together with the outcome of (4) specific conservation measures and (5) agri-environment schemes. Although each species has responded individually to particular aspects of agricultural change, certain groups of species share common causal factors. For example, declines in the population levels of seed-eating birds have been driven primarily by herbicide use and the switch from spring-sown to autumn-sown cereals, both of which have massively reduced the food supplies of these birds. Their population declines have been associated with reduced survival rates and, in some species, also with reduced reproductive rates. In waders of damp grassland, population declines have been driven mainly by land drainage and the associated intensification of grassland management. This has led to reduced reproductive success, as a result of lowered food availability, together with increased disturbance and trampling by farm stock, and in some localities increased nest predation. The external causal factors of population decline are known (with varying degrees of certainty) for all 30 species considered, and the demographic causal factors are known (again with varying degrees of certainty) for 24 such species. In at least 19 species, proposed causal factors have been tested and confirmed by experiment or by local conservation action, and 12 species have been shown to benefit (in terms of locally increased breeding density) from options available in one or more agri-environment schemes. Four aspects of agricultural change have been the main drivers of bird population declines, each affecting a wide range of species, namely: (1) weed-control, mainly through herbicide use; (2) the change from spring-sown to autumn-sown cereal varieties, and the associated earlier ploughing of stubbles and earlier crop growth; (3) land drainage and associated intensification of grassland management; and (4) increased stocking densities, mainly of cattle in the lowlands and sheep in the uplands. These changes have reduced the amounts of habitat and/or food available to many species. Other changes, such as the removal of hedgerows and 'rough patches', have affected smaller numbers of species, as have changes in the timings of cultivations and harvests. Although at least eight species have shown recent increases in their national population levels, many others seem set to continue declining, or to remain at a much reduced level, unless some relevant aspect of agricultural practice is changed.
Conservation Biology
Volume 14 Issue 5 Page 1441 - October 2000
doi:10.1046/j.1523-1739.2000.98246.x
Bird Communities of Prairie Uplands and Wetlands in Relation to Farming Practices in Saskatchewan
Dave Shutler,*§ Adele Mullie,* and Robert G. Clark*
Abstract: Modern farm practices can vary in their emphasis on tillage versus chemicals to control weeds, and researchers know little about which emphasis has greater ecological benefits. We compared avifaunas of uplands and wetlands in four treatments: conventional farms, conservation farms (contrasting those that minimized frequency of tillage [minimum tillage] with those that eliminated chemical inputs [organic]), and restored or natural (wild) sites in Saskatchewan, Canada. Of 37 different upland bird species encountered during surveys, one made greater use of farms, four made greater use of wild sites, and the remaining species showed no preference. When all upland species were combined, higher relative abundance occurred on wild than on farm sites, and on minimum tillage than on conventional farms. Wild upland sites also had more species than did conventional farms. Of 79 different species encountered during surveys of wetlands and their margins, most had similar encounter probabilities among treatments, although seven were more common on either organic farms or wild sites. Higher relative abundances were documented in wetland habitat of wild sites and organic farms than of minimum tillage or conventional farms. Wetlands of wild sites had more species than did minimum tillage or conventional farms. Overall, in terms of both avifaunal density and diversity, small treatment effects could be ascribed to differences between conventional and conservation farms, whereas larger effects were due to differences between farms and wild sites. Wetlands were heavily used by birds in all treatments, suggesting high conservation priority regardless of context.
Conservation Biology
Volume 14 Issue 2 Page 522 - April 2000
doi:10.1046/j.1523-1739.2000.98564.x
Influence of Landscape Scale on Farmland Birds Breeding in Semi-Natural Pastures
Bo Söderström* and Tomas Pärt
Abstract: Little attention has been paid to fragmentation effects on organisms living in open habitats in which species may have high mobility and generalized habitat use. We investigated landscape effects on 23 farmland bird species breeding in 72 semi-natural dry pastures distributed equally among three landscape types (agricultural-dominated, mosaic, and forest-dominated) in southcentral Sweden. There were generally higher local abundances of farmland birds in pastures located in agricultural-dominated and mosaic landscapes than in forest-dominated landscapes. Species feeding on a mixed diet as well as resident species and temperate migrants were most numerous in pastures located in agricultural-dominated landscapes and least numerous in forest-dominated landscapes. While controlling for the effects of local pasture area and vegetation structure, we found that the local abundance of 18 ( 78%) farmland bird species was significantly associated with the composition and structure of the surrounding landscape. The landscape distance that explained the largest part of local variation in abundance varied among species according to the size of their breeding territories or foraging home ranges. Our results suggest that habitat use of farmland birds breeding in pastures is affected both by suitable foraging habitats in the surrounding landscape and by nest sites within local pastures. Despite the generally higher abundances of farmland birds in pastures located in agricultural-dominated landscapes, most species of European and Swedish conservation concern had higher abundance in pastures located in more forested landscapes. Thus, the rapid loss of semi-natural dry pastures in forest-dominated landscapes is a serious threat to the future of these species in Sweden.
Journal of Applied Ecology
Volume 37 Issue 1 Page 128 - February 2000
doi:10.1046/j.1365-2664.2000.00484.x
The importance of variation in the breeding performance of seed-eating birds in determining their population trends on farmland
Gavin M. Siriwardena, Stephen R. Baillie, Humphrey Q.P. Crick and Jeremy D. Wilson*
Summary
1. Changes in agriculture have been linked to widespread declines in farmland bird populations. One approach to the identification of the causes of observed population changes is to investigate historical changes in national demographic rates.
2. We analysed the British Trust for Ornithology's nest records database to investigate whether long-term farmland population trends could have been driven by changes in several components of the annual breeding performance of 12 granivorous bird species. Clutch size, brood size, chick : egg ratio and daily nest failure rates were analysed with respect to blocks of years during which abundance (as measured by the Common Birds Census) was increasing, stable or declining. The individual components of breeding performance were combined to provide estimates of the production of fledglings per breeding attempt.
3. Most species' population declines were not associated with poor breeding performance per attempt. Effects of environmental change on this parameter therefore cannot be a general mechanism behind the major population declines seen.
4. A fall in linnet Carduelis cannabina fledgling production per attempt, driven primarily by increased nest failure rates during the egg period, represented the strongest evidence for an important effect of breeding performance on abundance. This change could have driven the principal population decline (197586) for this species.
5. Conversely, at least for the declining turtle dove Streptopelia turtur, skylark Alauda arvensis, tree sparrow Passer montanus, yellowhammer Emberiza citrinella and corn bunting Miliaria calandra, breeding performance per attempt was higher while populations declined.
6. Variation in annual survival and fledgling production per breeding attempt alone could not explain changes in abundance for at least seven species. This may suggest that changes in post-fledging survival rates and/or the number of breeding attempts per year could have been important.
7. Management to improve over-winter survival may be critical in reversing the population trends of most declining species, but such management might still best be directed at the breeding season. Post-fledging survival rates and the number of breeding attempts made within a season are little-studied demographic variables that are high priorities for future research and long-term monitoring.
Ibis
Volume 146 Issue s1 Page 48 - September 2004
doi:10.1111/j.1474-919X.2004.00327.x
The impact of climate change on birds (full document attached)
Humphrey Q. P. Crick*
Weather is of major importance for the population dynamics of birds, but the implications of climate change have only recently begun to be addressed. There is already compelling evidence that birds have been affected by recent climate changes. This review suggests that although there is a substantial body of evidence for changes in the phenology of birds, particularly of the timing of migration and of nesting, the consequences of these responses for a species' population dynamics is still an area requiring in-depth research. The potential for phenological miscuing (responding inappropriately to climate change, including a lack of response) and for phenological disjunction (in which a bird species becomes out of synchrony with its environment) are beginning to be demonstrated, and are also important areas for further research. The study of climatically induced distributional change is currently at a predictive modelling stage, and will need to develop methods for testing these predictions. Overall, there is a range of intrinsic and extrinsic factors that could potentially inhibit adaptation to climate change and these are a high priority for research.
Journal of Applied Ecology
Volume 38 Issue 3 Page 647 - June 2001
doi:10.1046/j.1365-2664.2001.00626.x
The management of lowland neutral grasslands in Britain: effects of agricultural practices on birds and their food resources
J.A. Vickery*, J.R. Tallowin, R.E. Feber§, E.J. Asteraki, P.W. Atkinson*, R.J. Fuller* and V.K. Brown¶
Summary
1. The effects of agricultural intensification on biodiversity in arable systems of western Europe have received a great deal of attention. However, the recent transformation of grassland systems has been just as profound.
2. In Britain, the management of grassland has changed substantially in the second half of the 20th century. A high proportion of lowland grassland is managed intensively. The major changes include a doubling in the use of inorganic nitrogen, a switch from hay to silage, and increased stocking densities, particularly of sheep. Structurally diverse and species-rich swards have been largely replaced by relatively dense, fast-growing and structurally uniform swards, dominated by competitive species.
3. Most of these changes have reduced the suitability of grassland as feeding and breeding habitat for birds.
4. The most important direct effects have been deterioration of the sward as nesting and wintering habitat, and loss of seed resources as food. Short uniform swards afford poor shelter and camouflage from predators, whereas increased mowing intensities and trampling by stock will destroy nests and young. Increased frequency of sward defoliation reduces flowering and seed set, and hence food availability for seed-eating birds.
5. The indirect effects of intensification of management on birds relate largely to changes in the abundance and availability of invertebrate prey. The effects of management vary with its type, timing and intensity, and with invertebrate ecology and phenology, but, in general, the abundance and diversity of invertebrates declines with reductions in sward diversity and structural complexity.
6. Low input livestock systems are likely to be central to any future management strategies designed to maintain and restore the ecological diversity of semi-natural lowland grasslands. Low additions of organic fertilizer benefit some invertebrate prey species, and moderate levels of grazing encourage sward heterogeneity.
7. There is now a need to improve understanding of how grassland management affects bird population dynamics. Particularly important areas of research include: (i) the interaction between changes in food abundance, due to changes in fertilizer inputs, and food accessibility, due to changes in sward structure; (ii) the interaction between predation rates and management-related changes in habitat; and (iii) the impact of alternative anti-helminithic treatments for livestock on invertebrates and birds.
Journal of Applied Ecology
Volume 37 Issue 5 Page 789 - October 2000
doi:10.1046/j.1365-2664.2000.00552.x
Habitat associations and breeding success of yellowhammers on lowland farmland
Richard B. Bradbury*, Antonios Kyrkos*, Antony J. Morris*, Stéphanie C. Clark*, Allan J. Perkins* and Jeremy D. Wilson*
1. Yellowhammers began to decline on British lowland farmland in the late 1980s and losses are presently 10% per year. This study examined variation in the habitat selection and breeding success of yellowhammers, allowing an evaluation of whether Britain's yellowhammer decline might have been caused by recent changes in agriculture.
2. Yellowhammer territories were associated with hedgerows, vegetated ditches and wide uncultivated grassy margins around fields. Pasture and silage leys were avoided. Nests were built among herbaceous vegetation in ditches or in the shrubby vegetation of hedgerows.
3. Breeding started slightly earlier on organic farms than on intensively managed farms, but no measure of breeding success differed between farm types. Predation was the cause of most (64%) nest failures. A maximum of three breeding attempts (two successful) was observed per pair, with a mean clutch size of 3·3, a Mayfield nest success rate of 0·46, and 2·6 nestlings fledged per successful brood. These data, together with published estimates of adult yellowhammer survival and of post-fledging survival among other passerines, suggest that breeding productivity is too low to maintain a stable population.
4. The removal of hedgerows or abandonment of hedge management, filling or clearing of ditches, intensification of grassland management and cropping or grazing right up to the field edge, are all likely to have adversely affected yellowhammers on lowland farmland in southern England. Policy reforms that redirect subsidy support to environmentally beneficial management of field margin habitats and retention of winter-feeding sites such as stubbles should assist in restoring populations of breeding yellowhammers on lowland farmland.
5. Our data expand further the array of farmland bird species for which interactions between agricultural change and population change are increasingly understood.
Ibis
Volume 146 Issue 1 Page 1 - January 2004
The potential for interactions between predation and habitat change to cause population declines of farmland birds
K. L. Evans*
Population declines are often attributed to either habitat change or increased predation rates, without a full consideration of the potential for these two factors to interact. This may lead to an inaccurate diagnosis of the causes of population decline and thus the selection of inappropriate management solutions. Here mechanisms through which habitat change and predation could interact are reviewed. Examples of how these may have contributed to population declines are provided, focusing on European farmland birds. However, very few appropriate studies have been conducted that allow the role of such interactions to be assessed accurately. To remedy this situation experimental designs that could detect the presence of interactive mechanisms are described. When habitat change and predation interact, conservation managers are provided with the opportunity to control predation impacts through habitat management rather than predator removal, which may provide a more cost-effective management strategy.
Ibis
Volume 146 Issue 4 Page 579 - October 2004
doi:10.1111/j.1474-919X.2004.00375.x
The recent declines of farmland bird populations in Britain: an appraisal of causal factors and conservation actions
Ian Newton*
In this paper, the main aspects of agricultural intensification that have led to population declines in farmland birds over the past 50 years are reviewed, together with the current state of knowledge, and the effects of recent conservation actions. For each of 30 declining species, attention is focused on: (1) the external causes of population declines, (2) the demographic mechanisms and (3) experimental tests of proposed external causal factors, together with the outcome of (4) specific conservation measures and (5) agri-environment schemes. Although each species has responded individually to particular aspects of agricultural change, certain groups of species share common causal factors. For example, declines in the population levels of seed-eating birds have been driven primarily by herbicide use and the switch from spring-sown to autumn-sown cereals, both of which have massively reduced the food supplies of these birds. Their population declines have been associated with reduced survival rates and, in some species, also with reduced reproductive rates. In waders of damp grassland, population declines have been driven mainly by land drainage and the associated intensification of grassland management. This has led to reduced reproductive success, as a result of lowered food availability, together with increased disturbance and trampling by farm stock, and in some localities increased nest predation. The external causal factors of population decline are known (with varying degrees of certainty) for all 30 species considered, and the demographic causal factors are known (again with varying degrees of certainty) for 24 such species. In at least 19 species, proposed causal factors have been tested and confirmed by experiment or by local conservation action, and 12 species have been shown to benefit (in terms of locally increased breeding density) from options available in one or more agri-environment schemes. Four aspects of agricultural change have been the main drivers of bird population declines, each affecting a wide range of species, namely: (1) weed-control, mainly through herbicide use; (2) the change from spring-sown to autumn-sown cereal varieties, and the associated earlier ploughing of stubbles and earlier crop growth; (3) land drainage and associated intensification of grassland management; and (4) increased stocking densities, mainly of cattle in the lowlands and sheep in the uplands. These changes have reduced the amounts of habitat and/or food available to many species. Other changes, such as the removal of hedgerows and 'rough patches', have affected smaller numbers of species, as have changes in the timings of cultivations and harvests. Although at least eight species have shown recent increases in their national population levels, many others seem set to continue declining, or to remain at a much reduced level, unless some relevant aspect of agricultural practice is changed.
Conservation Biology
Volume 14 Issue 5 Page 1441 - October 2000
doi:10.1046/j.1523-1739.2000.98246.x
Bird Communities of Prairie Uplands and Wetlands in Relation to Farming Practices in Saskatchewan
Dave Shutler,*§ Adele Mullie,* and Robert G. Clark*
Abstract: Modern farm practices can vary in their emphasis on tillage versus chemicals to control weeds, and researchers know little about which emphasis has greater ecological benefits. We compared avifaunas of uplands and wetlands in four treatments: conventional farms, conservation farms (contrasting those that minimized frequency of tillage [minimum tillage] with those that eliminated chemical inputs [organic]), and restored or natural (wild) sites in Saskatchewan, Canada. Of 37 different upland bird species encountered during surveys, one made greater use of farms, four made greater use of wild sites, and the remaining species showed no preference. When all upland species were combined, higher relative abundance occurred on wild than on farm sites, and on minimum tillage than on conventional farms. Wild upland sites also had more species than did conventional farms. Of 79 different species encountered during surveys of wetlands and their margins, most had similar encounter probabilities among treatments, although seven were more common on either organic farms or wild sites. Higher relative abundances were documented in wetland habitat of wild sites and organic farms than of minimum tillage or conventional farms. Wetlands of wild sites had more species than did minimum tillage or conventional farms. Overall, in terms of both avifaunal density and diversity, small treatment effects could be ascribed to differences between conventional and conservation farms, whereas larger effects were due to differences between farms and wild sites. Wetlands were heavily used by birds in all treatments, suggesting high conservation priority regardless of context.
Conservation Biology
Volume 14 Issue 2 Page 522 - April 2000
doi:10.1046/j.1523-1739.2000.98564.x
Influence of Landscape Scale on Farmland Birds Breeding in Semi-Natural Pastures
Bo Söderström* and Tomas Pärt
Abstract: Little attention has been paid to fragmentation effects on organisms living in open habitats in which species may have high mobility and generalized habitat use. We investigated landscape effects on 23 farmland bird species breeding in 72 semi-natural dry pastures distributed equally among three landscape types (agricultural-dominated, mosaic, and forest-dominated) in southcentral Sweden. There were generally higher local abundances of farmland birds in pastures located in agricultural-dominated and mosaic landscapes than in forest-dominated landscapes. Species feeding on a mixed diet as well as resident species and temperate migrants were most numerous in pastures located in agricultural-dominated landscapes and least numerous in forest-dominated landscapes. While controlling for the effects of local pasture area and vegetation structure, we found that the local abundance of 18 ( 78%) farmland bird species was significantly associated with the composition and structure of the surrounding landscape. The landscape distance that explained the largest part of local variation in abundance varied among species according to the size of their breeding territories or foraging home ranges. Our results suggest that habitat use of farmland birds breeding in pastures is affected both by suitable foraging habitats in the surrounding landscape and by nest sites within local pastures. Despite the generally higher abundances of farmland birds in pastures located in agricultural-dominated landscapes, most species of European and Swedish conservation concern had higher abundance in pastures located in more forested landscapes. Thus, the rapid loss of semi-natural dry pastures in forest-dominated landscapes is a serious threat to the future of these species in Sweden.
Journal of Applied Ecology
Volume 37 Issue 1 Page 128 - February 2000
doi:10.1046/j.1365-2664.2000.00484.x
The importance of variation in the breeding performance of seed-eating birds in determining their population trends on farmland
Gavin M. Siriwardena, Stephen R. Baillie, Humphrey Q.P. Crick and Jeremy D. Wilson*
Summary
1. Changes in agriculture have been linked to widespread declines in farmland bird populations. One approach to the identification of the causes of observed population changes is to investigate historical changes in national demographic rates.
2. We analysed the British Trust for Ornithology's nest records database to investigate whether long-term farmland population trends could have been driven by changes in several components of the annual breeding performance of 12 granivorous bird species. Clutch size, brood size, chick : egg ratio and daily nest failure rates were analysed with respect to blocks of years during which abundance (as measured by the Common Birds Census) was increasing, stable or declining. The individual components of breeding performance were combined to provide estimates of the production of fledglings per breeding attempt.
3. Most species' population declines were not associated with poor breeding performance per attempt. Effects of environmental change on this parameter therefore cannot be a general mechanism behind the major population declines seen.
4. A fall in linnet Carduelis cannabina fledgling production per attempt, driven primarily by increased nest failure rates during the egg period, represented the strongest evidence for an important effect of breeding performance on abundance. This change could have driven the principal population decline (197586) for this species.
5. Conversely, at least for the declining turtle dove Streptopelia turtur, skylark Alauda arvensis, tree sparrow Passer montanus, yellowhammer Emberiza citrinella and corn bunting Miliaria calandra, breeding performance per attempt was higher while populations declined.
6. Variation in annual survival and fledgling production per breeding attempt alone could not explain changes in abundance for at least seven species. This may suggest that changes in post-fledging survival rates and/or the number of breeding attempts per year could have been important.
7. Management to improve over-winter survival may be critical in reversing the population trends of most declining species, but such management might still best be directed at the breeding season. Post-fledging survival rates and the number of breeding attempts made within a season are little-studied demographic variables that are high priorities for future research and long-term monitoring.
Ibis
Volume 146 Issue s1 Page 48 - September 2004
doi:10.1111/j.1474-919X.2004.00327.x
The impact of climate change on birds (full document attached)
Humphrey Q. P. Crick*
Weather is of major importance for the population dynamics of birds, but the implications of climate change have only recently begun to be addressed. There is already compelling evidence that birds have been affected by recent climate changes. This review suggests that although there is a substantial body of evidence for changes in the phenology of birds, particularly of the timing of migration and of nesting, the consequences of these responses for a species' population dynamics is still an area requiring in-depth research. The potential for phenological miscuing (responding inappropriately to climate change, including a lack of response) and for phenological disjunction (in which a bird species becomes out of synchrony with its environment) are beginning to be demonstrated, and are also important areas for further research. The study of climatically induced distributional change is currently at a predictive modelling stage, and will need to develop methods for testing these predictions. Overall, there is a range of intrinsic and extrinsic factors that could potentially inhibit adaptation to climate change and these are a high priority for research.
Journal of Applied Ecology
Volume 38 Issue 3 Page 647 - June 2001
doi:10.1046/j.1365-2664.2001.00626.x
The management of lowland neutral grasslands in Britain: effects of agricultural practices on birds and their food resources
J.A. Vickery*, J.R. Tallowin, R.E. Feber§, E.J. Asteraki, P.W. Atkinson*, R.J. Fuller* and V.K. Brown¶
Summary
1. The effects of agricultural intensification on biodiversity in arable systems of western Europe have received a great deal of attention. However, the recent transformation of grassland systems has been just as profound.
2. In Britain, the management of grassland has changed substantially in the second half of the 20th century. A high proportion of lowland grassland is managed intensively. The major changes include a doubling in the use of inorganic nitrogen, a switch from hay to silage, and increased stocking densities, particularly of sheep. Structurally diverse and species-rich swards have been largely replaced by relatively dense, fast-growing and structurally uniform swards, dominated by competitive species.
3. Most of these changes have reduced the suitability of grassland as feeding and breeding habitat for birds.
4. The most important direct effects have been deterioration of the sward as nesting and wintering habitat, and loss of seed resources as food. Short uniform swards afford poor shelter and camouflage from predators, whereas increased mowing intensities and trampling by stock will destroy nests and young. Increased frequency of sward defoliation reduces flowering and seed set, and hence food availability for seed-eating birds.
5. The indirect effects of intensification of management on birds relate largely to changes in the abundance and availability of invertebrate prey. The effects of management vary with its type, timing and intensity, and with invertebrate ecology and phenology, but, in general, the abundance and diversity of invertebrates declines with reductions in sward diversity and structural complexity.
6. Low input livestock systems are likely to be central to any future management strategies designed to maintain and restore the ecological diversity of semi-natural lowland grasslands. Low additions of organic fertilizer benefit some invertebrate prey species, and moderate levels of grazing encourage sward heterogeneity.
7. There is now a need to improve understanding of how grassland management affects bird population dynamics. Particularly important areas of research include: (i) the interaction between changes in food abundance, due to changes in fertilizer inputs, and food accessibility, due to changes in sward structure; (ii) the interaction between predation rates and management-related changes in habitat; and (iii) the impact of alternative anti-helminithic treatments for livestock on invertebrates and birds.
Journal of Applied Ecology
Volume 37 Issue 5 Page 789 - October 2000
doi:10.1046/j.1365-2664.2000.00552.x
Habitat associations and breeding success of yellowhammers on lowland farmland
Richard B. Bradbury*, Antonios Kyrkos*, Antony J. Morris*, Stéphanie C. Clark*, Allan J. Perkins* and Jeremy D. Wilson*
1. Yellowhammers began to decline on British lowland farmland in the late 1980s and losses are presently 10% per year. This study examined variation in the habitat selection and breeding success of yellowhammers, allowing an evaluation of whether Britain's yellowhammer decline might have been caused by recent changes in agriculture.
2. Yellowhammer territories were associated with hedgerows, vegetated ditches and wide uncultivated grassy margins around fields. Pasture and silage leys were avoided. Nests were built among herbaceous vegetation in ditches or in the shrubby vegetation of hedgerows.
3. Breeding started slightly earlier on organic farms than on intensively managed farms, but no measure of breeding success differed between farm types. Predation was the cause of most (64%) nest failures. A maximum of three breeding attempts (two successful) was observed per pair, with a mean clutch size of 3·3, a Mayfield nest success rate of 0·46, and 2·6 nestlings fledged per successful brood. These data, together with published estimates of adult yellowhammer survival and of post-fledging survival among other passerines, suggest that breeding productivity is too low to maintain a stable population.
4. The removal of hedgerows or abandonment of hedge management, filling or clearing of ditches, intensification of grassland management and cropping or grazing right up to the field edge, are all likely to have adversely affected yellowhammers on lowland farmland in southern England. Policy reforms that redirect subsidy support to environmentally beneficial management of field margin habitats and retention of winter-feeding sites such as stubbles should assist in restoring populations of breeding yellowhammers on lowland farmland.
5. Our data expand further the array of farmland bird species for which interactions between agricultural change and population change are increasingly understood.
Nightranger
Senior Moment
Jane has partly beaten me to it and Richard has already pointed out that the paper looks at breeding success and not population trends. Interestingly, Stephen Baillie is also a co-author on a far more relevant paper to the topic of the thread.
The widespread declines of songbirds in rural Britain does not correlate with the spread of their avian predators. - Thompson, David L., Green, Rhys E., Gregory, Richard D., Baillie, Stephen R. Proceedings: Biological Sciences Volume 265 pages 2057-2062 Nov 1998.
Effectively, the original quoted paper does not go against conventional scientific thinking as Anthony claimed anyway and only looks at two species (blackbird and song thrush).
Ian
The widespread declines of songbirds in rural Britain does not correlate with the spread of their avian predators. - Thompson, David L., Green, Rhys E., Gregory, Richard D., Baillie, Stephen R. Proceedings: Biological Sciences Volume 265 pages 2057-2062 Nov 1998.
Effectively, the original quoted paper does not go against conventional scientific thinking as Anthony claimed anyway and only looks at two species (blackbird and song thrush).
Ian
Last edited:
Jane Turner
Well-known member
Tim Allwood said:
Except its not a game.. its blinking serious
Jane Turner
Well-known member
Ian Peters said:
Couldn't get that one online! and I only scratched the surface above... I expect you have had enough by now anyway.
Edward woodwood
Member
it's a shame people have to spend their time doing all this...those articles are all available to everyone via university libraries etc.....
maybe some folk will now understand why a few of us get a bit frustated from time to time.
any serious points contradicting the data above or references to papers in quality journals saying the opposite would of course be welcome.... hearsay not quite so welcome....
maybe some folk will now understand why a few of us get a bit frustated from time to time.
any serious points contradicting the data above or references to papers in quality journals saying the opposite would of course be welcome.... hearsay not quite so welcome....
Jane Turner
Well-known member
That was only the first few of around 500 hits I got on factors affecting bird populations btw.
I did see one other suggesting predator effects on breeding success..... in that case mammalian predators ..... on Curlew in Northern Ireland
I did see one other suggesting predator effects on breeding success..... in that case mammalian predators ..... on Curlew in Northern Ireland
Jane Turner
Well-known member
Tim Allwood said:
Not even any need to go to a University... you can get a long way sat on your bum at a computer... if you want to that is
http://www.sciencedirect.com/
James Lowther
Well-known member
David Bryant said:
I know this isn't exactly relevant to the way the thread has subsequently developed, but i've thought about it (!) and come up with a couple of completely hypothetical explanantions for this apparent paradox.
1) the adhesive allele arose as a result of a mutation in a gene for an existing secretory protein. Without the solvent, the mutation was fatal for homozygous individuals, but conferred sufficient advantage to heterozygotes that the allele remained circulating in the population. Subsequently, a mutation in another gene for an existing protein led to the development of the solvent producing mechanism. This development removed the competitive disadvantage previously incurred by the homozygous adhesive-producers - end result; sticky squid.
2) the adhesive started life as a very slightly sticky substance. A mutation leading to the production of a weak solvent allowed the evolution of a slightly more sticky adhesive, which in turn precipitated the evolution of a slightly more rapid solvent and so on and so forth, with the two mechanisms evolving cooperatively - end result; sticky squid
Now i'd like to point out that i have no particular knowledge of the biochemistry or genetics of either this or any other species of squid, and am not for one moment suggesting that the mechanism actually evolved in either of these ways, merely illustrating my opinion that this particular animal (as far as i can gather from David's explanation) doesn't seem like an insurmountable challenge to evolutionary theory.
James
p.s. sorry for diverting the thread!! :flowers:
Jane Turner
Well-known member
Anthony Morton
Well-known member
Good grief, talk about trying to blind people with science. Yet at the end of it all I'm still not overly impressed, because each of the various authors quoted only gives their personal version of what's already happened. Not one of them offers any suggestion as to what needs to be done to put matters right to reverse the decline in songbird numbers.
That's why I can't help thinking that when it comes to results StevieEvans' home-spun localised action has at least done more to increase songbird numbers than all this combined paper wisdom put together.
Perhaps there is a case for going back to basics and allowing land managers to manage the land without all this unnecessary interference. Surely they can't make things any worse than they are now, can they?
That's why I can't help thinking that when it comes to results StevieEvans' home-spun localised action has at least done more to increase songbird numbers than all this combined paper wisdom put together.
Perhaps there is a case for going back to basics and allowing land managers to manage the land without all this unnecessary interference. Surely they can't make things any worse than they are now, can they?
Edward woodwood
Member
er no...
Hello
Jane has pointed you to the facts as they are best understood by some of our best ecologists. If you are 'blinded' by them, take a little more time to digest them.
you don't HAVE to believe it of course....
and don't start changing the suject pleeeeesee!!!
Hello
Jane has pointed you to the facts as they are best understood by some of our best ecologists. If you are 'blinded' by them, take a little more time to digest them.
you don't HAVE to believe it of course....
and don't start changing the suject pleeeeesee!!!
David Bryant
Registered User
Awwwwwww! But Sticky Squids are soooooooooooo cute!
StevieEvans
Well-known member
Hello fellow wild bird lovers,
I have a question:-
If you saw a pr of Magpie in the process of 'raiding' a nest of fledgling thrushes outside your front window....would you stand back & watch nature take its course?, OR would you rap on the window?
I'd certainly scare them off.
Knocking the Mag no's down with trapping lessens the chance of this happening. I know thats simplistic but thats the way i view this one aspect of the Magpies behaviour.
SE.
I have a question:-
If you saw a pr of Magpie in the process of 'raiding' a nest of fledgling thrushes outside your front window....would you stand back & watch nature take its course?, OR would you rap on the window?
I'd certainly scare them off.
Knocking the Mag no's down with trapping lessens the chance of this happening. I know thats simplistic but thats the way i view this one aspect of the Magpies behaviour.
SE.
Anthony Morton said:
GOOD GRIEF, absolutely the right words! Mr Morten, this discussion arose in post 29 with your following submission based on a scientific paper ... "they are extracts from an interesting article published in the April 2002 edition of THE FIELD magazine under the title: 'If You Want Songbirds, Kill Magpies' based on the scientific paper referred to below and which was published in the Journal Of Applied Ecology".
People now point out, and provide papers illustrating, that the vast majority of ecologists are of the same opinion that most people on this thread have been trying to explain! Is this trying to blind people with science? Is there a whiff of selective use of data going on here - one scientific paper that appears to support one view is not blinding people with science, yet a ton provided to counter the view is deemed so? Good grief!!!
The thread is titled 'Who to believe?' Have to say, I would be tempted to listen to the leagues of respected ecologists who strangely enough seem to have reached the same conclusion! Of course, one or two people can never be pursuaded, whatever the thread or whatever the topic.
