Winter habitat associations of seed-eating passerines on Scottish farmland

CapsuleExtensive surveys highlighted the importance of weedy fodder brassicas, stubbles and open farmland landscapes to declining birds.

Aims To determine habitat associations of seed-eating passerines on Scottish farmland in winter, and recommend appropriate conservation measures.

Methods Transect surveys were carried out on farmland in 100 1-km squares, containing 2885 fields, across Scotland. Birds, crops, field boundary features and weeds were recorded on three visits. Bird–habitat associations were examined using logistic regression models.

Results Seed-eating passerines were highly concentrated: 100 fields (1.4% of the area surveyed) held half the total count. The highest field densities of birds were recorded in fodder brassica crops and stubbles, averaging 12 and 3.3 birds/ha respectively. In fodder crops, weedier fields held many more birds. Multiple regression analysis emphasized the importance of fodder crops, stubbles and farmyards and suggested that declining bird species preferred more open landscapes. Several bird species were associated with fields containing very weedy patches, and/or weeds of the family Chenopodiaceae. These features were commonest in fodder brassicas. Many of the crop types found to be important as bird habitats in winter have declined in area in Scotland; the availability of seed food in such habitats may also have diminished. Such changes may partly explain recent population declines.

Conclusions Agri-environment measures for seed-eating passerines should support the widespread provision of small areas of seed-rich wintering habitats, such as weedy fodder brassicas and stubbles, especially in open (0–10% woodland and scrub) landscapes in areas with mild winters.     

Indexing winter gull numbers in Great Britain using data from the 1953 to 2004 Winter Gull Roost Surveys

Capsule Winter Gull Roost Survey data spanning 50 years were used to generate population indices.

Aims To evaluate how wintering numbers of five gull species have changed in Great Britain over the last five decades.

Methods Generalized linear models were used to relate gull numbers to habitat, site and year factors, and so derive species‐specific indices for nine regions of Great Britain. Regional models considered data from different timescales depending on coverage.

Results Patterns of change varied by species and region. All species showed increases in number over the period 1953 to 2004. In most regions, Black‐headed Gull Chroicocephalus ridibundus numbers have declined since peaks between 1973 and 1993; Common Gulls Larus canus have also declined recently in some regions. Lesser Black‐backed Gull L. fuscus numbers have increased dramatically since 1953, whereas numbers of Herring Gull L. argentatus showed large declines between 1963 and 1983. Great Black‐backed Gull L. marinus numbers have increased in the west and the Midlands, but recently declined in eastern regions.

Conclusions Numbers of wintering gulls in Great Britain have shown rapid changes over the last five decades, reflecting changes in the sizes of breeding populations. These changes are likely to be associated with changes in human activities and resource availability.     

Using repeated winter surveys to estimate changes in abundance of seed‐eating passerines

Capsule Winter Atlas surveys of 16 species on lowland farmland revealed significant changes in count for four species.

Aims To estimate changes in abundance between the early 1980s and late 1990s, of wintering seed‐eating passerines, in ‘core’ areas of lowland Scotland.

Methods Ninety‐five Scottish 10‐km squares were selected that held high numbers of seed‐eating passerines in the 1981–84 Atlas of Wintering Birds in Britain and Ireland. The same survey methods were used to resurvey these in winters 1997/98 and 1998/99, and visits were matched as closely as possible for duration and date. Analyses compared counts between the two survey periods for 16 species of seed‐eating passerines and, for 12 of these, differences were also compared with national breeding population trend information for the same period.

Results Mean Corn Bunting Emberiza calandra count per visit declined by 62% between the early 1980s and late 1990s, a difference which was statistically significant (P = 0.026). Significant increases were recorded for Yellowhammer Emberiza citrinella (up 62%), Common Linnet Carduelis cannabina (up 3.4‐fold) and European Goldfinch Carduelis carduelis (up 13‐fold). For 12 species for which national breeding population trend data were available, trends were weakly positively correlated (r _s = 0.43, P = 0.08) with those from our results, but several species trends were more positive in our study. This difference was particularly marked for Eurasian Tree Sparrow Passer montanus, Goldfinch and Linnet.

Conclusion Repeating Winter Atlas surveys offers a useful additional method for assessing population trends. They are particularly useful in a region with low observer coverage and for species that are poorly covered by long‐term bird monitoring data sets. It would be valuable to validate this approach at a regional level, especially in a region for which detailed long‐term bird monitoring data are available.     

Fit is fat: winter body mass of Atlantic Puffins Fratercula arctica

Capsule: Atlantic Puffins Fratercula arctica from Scottish and Norwegian populations were significantly heavier in winter than when rearing chicks.

Aims: To compare body masses of Atlantic Puffins on their wintering grounds off the Faroe Islands with those of birds rearing chicks at colonies in Scotland and Norway.

Methods: We took standardized measurements of wing length and body mass of Atlantic Puffins during the summer chick-rearing period and on the wintering grounds near the Faroe Islands. These measurements were used to estimate seasonal changes in body mass for the two breeding populations. In three cases data were available for individuals weighed both at the colony and on the wintering grounds.

Results: On average, Atlantic Puffins breeding in Scotland and Norway increased their body mass by 20–30% between the chick-rearing period and winter. The very limited individual level data accorded well with the population level estimates.

Conclusions: Our results provide the first estimates of the order of magnitude in mass change between two key life history stages in this species. They indicate that gains in body mass between chick-rearing and winter are at least double the decline in mass previously recorded between incubation and chick-rearing. Given the Atlantic Puffin’s deteriorating conservation status, improved information on seasonal changes in body condition should help determine the underlying causes of die-offs in major wreck incidents such as those reported in recent years.     

Long-term population declines in Danish trans-Saharan migrant birds

Capsule Long-distance migrant birds show less favourable trends than sedentary/short-distance species.

Aims To use breeding bird surveys to contrast population trends amongst common species according to their migration pattern.

Methods Changes in abundance of 62 Danish breeding sedentary, short-distance (Europe/North Africa) or long-distance (trans-Saharan) migrants were described by fitting log linear regression models to point-count census data gathered during 1976–2005.

Results Trans-Saharan migrants declined by 1.3% per annum during this period, while short-distance migrants and sedentary species increased by 1.4% and 1.0% per annum, respectively. There were no significant decadal declines amongst species using different summer breeding habitats, except for wetlands, and there was no consistent variation in trends associated with wintering regions or habitats or diet.

Conclusions More information is urgently needed on diet, feeding ecology, habitat requirements, winter distribution and intra-African movements of the commoner European summer visitors to identify causes of the declines and highlight when in the annual cycle detrimental effects occur. Studies linking individuals on their breeding, staging and wintering grounds are especially needed. Danish trends resemble those from elsewhere in Europe, confirming that restoration to favourable conservation status requires inter-continental action to meet European and global targets to reduce or halt biodiversity loss.     

Status of the Nightingale Luscinia megarhynchos in Britain at the end of the 20th Century with particular reference to climate change

Capsule The population level may be unchanged but the range has contracted.

Aims To establish the current status of the Nightingale in Britain and explore causes for any changes.

Methods Over 3000 sites where Nightingales were known to have occurred since 1980 were surveyed by volunteers between mid-April and early June 1999. A selection of 135 random tetrads were also surveyed to gauge the efficiency of the volunteer survey in locating Nightingales.

Results The survey located 4565 singing male Nightingales while the random tetrad surveys suggest that c. 32% of birds occur away from known sites, increasing the estimate for the British Nightingale population to 6700 males (95% confidence limits 5600–9350) in 1999. A higher proportion of Nightingales was found in scrub (46.7%) than in 1976 (28.4%), suggesting a recent shift in habitat use.

Conclusion There is little evidence of a change in the size of the British Nightingale population, probably because earlier surveys underestimated numbers. The range has contracted markedly over the last few decades and numbers outside the core areas in southeast England are now low. Changes in habitat quality and increasing deer populations have caused decreases on a local scale. Changes in climate on the breeding grounds and general changes in climate or habitat suitability on the African winter quarters are likely to be important in influencing the distribution within England. Models of the effects of future climate change on Nightingale distribution in Britain predict that numbers and range should increase over the next few decades.     

Distribution shifts in wintering Golden Plover Pluvialis apricaria and Lapwing Vanellus vanellus in Britain

Capsule The winter distribution of Golden Plover and Lapwing has shifted east since the mid-1980s, perhaps in response to climate change.

Aims To combine analyses of winter trends on wetlands and flocks on farmland to assess the current status of Golden Plover and Lapwing in one of their main wintering regions.

Methods Winter trends were derived from monthly counts on estuaries and wetlands for the period 1974–2002 (the Wetland Bird Survey). Winter distribution on farmland was assessed using casual records of large flocks and surveys of a stratified random sample of 1-km squares (the Winter Farmland Bird Survey).

Results Regional trends showed a pronounced increase in numbers of both species since 1974 on the east coast, with a smaller increase on the south coast. Numbers in the west and north tended to decline. Flocks on farmland were concentrated in eastern Britain unlike the situation in the 1980s.

Conclusions The winter distribution of Golden Plover and Lapwing has shifted to the east, resulting in large numbers on the east coast and in the arable east of Britain. The implications of this shift, especially in relation to known habitat associations, are discussed.     

Evaluation of an Aerial Survey to Estimate Abundance of Wintering Ducks in Mississippi

Abstract: Researchers have successfully designed aerial surveys that provided precise estimates of wintering populations of ducks over large physiographic regions, yet few conservation agencies have adopted these probability-based sampling designs for their surveys. We designed and evaluated an aerial survey to estimate abundance of wintering mallards (Anas platyrhynchos), dabbling ducks (tribe Anatini) other than mallards, diving ducks (tribes Aythini, Mergini, and Oxyurini), and total ducks in western Mississippi, USA. We used design-based sampling of fixed width transects to estimate population indices (Ǐ), and we used model-based methods to correct population indices for visibility bias and estimate population abundance (Ň) for 14 surveys during winters 2002–2004. Correcting for bias increased estimates of mallards, other dabbling ducks, and diving ducks by an average of 40–48% among all surveys and contributed 48–61% of the estimated variance of Ň. However, mean-squared errors were consistently less for Ň than Ǐ. Estimates of Ň met our goals for precision (CV ≤ 15%) in 7 of 14 surveys for mallards, 5 surveys for other dabbling ducks, no surveys for diving ducks, and 10 surveys for total ducks. Generally, we estimated more mallards and other dabbling ducks in mid- and late winter (Jan-Feb) than early winter (Nov-Dec) and determined that population indices from the late 1980s were nearly 3 times greater than those from our study. We developed a method to display relative densities of ducks spatially as an additional application of survey data. Our study advanced methods of estimating abundance of wintering waterfowl, and we recommend this design for continued monitoring of wintering ducks in western Mississippi and similar physiographic regions.     

The population status of Capercaillie Tetrao urogallus in Scotland during winter 2015–16

Capsule: The population size of Western Capercaillie Tetrao urogallus in Scotland was estimated at 1114 individuals with 95% confidence intervals (CIs) of 805–1505.

Aim: To produce an updated estimate of Capercaillie population size in Scotland, with improved precision from, but retaining comparability with, previous surveys.

Methods: A random sample of 2?km long line transects was surveyed throughout the current range of the Capercaillie, during winter 2015–16, with sampling in three separate strata. Multi-covariate distance sampling was used to fit detection functions to the Capercaillie data, deriving national, regional and sex-specific estimates of density and abundance.

Results: Across 741 transects, 136 Capercaillie were recorded in 120 separate encounters, giving rise to a population estimate of 1114 individuals (95% CIs: 805–1505). This estimate is 13% lower than that from the previous survey in 2009–10 but the difference is not statistically significant. Most of the population (83%) was estimated to occur in Strathspey, with much smaller numbers in the rest of the range.

Conclusion: The Capercaillie population in Scotland remains at a critically low level. Further evidence of decline in edge of range subpopulations raises serious concern over the viability of Capercaillie in these areas, whereas numbers appear stable in the core of the range in Strathspey. The use of a revised survey design, with greater sampling in the core of the range, improved estimate precision.     

Spatial distribution of the active surveillance of sheep scrapie in Great Britain: an exploratory analysis

Background  

This paper explores the spatial distribution of sampling within the active surveillance of sheep scrapie in Great Britain. We investigated the geographic distribution of the birth holdings of sheep sampled for scrapie during 2002 – 2005, including samples taken in abattoir surveys (c. 83,100) and from sheep that died in the field ("fallen stock", c. 14,600). We mapped the birth holdings by county and calculated the sampling rate, defined as the proportion of the holdings in each county sampled by the surveys. The Moran index was used to estimate the global spatial autocorrelation across Great Britain. The contributions of each county to the global Moran index were analysed by a local indicator of spatial autocorrelation (LISA).     

Sources and extent of human disturbance to waterbirds in the UK: an analysis of Wetland Bird Survey data, 1995/96 to 1998/99

Capsule Less than 32% of counters record disturbance at their site, with differences in causes between coastal and inland sites.

Aim Wetland Bird Survey (WeBS) data were reviewed to investigate the sources and scale of potential disturbance to waterbirds in the UK.

Methods Between 1995/96 and 1998/99, WeBS volunteer counters recorded human activity and perceived waterbird disturbance during co-ordinated counts at wetland sites across the UK.

Results Over 68% of counters recorded no disturbance at their site and only a small proportion of these (< 2%) indicated very high levels. The frequency of disturbance peaked during the late summer. Just over 26% of disturbance events were attributed to human activities. The most perceived human-related disturbance was caused by people using motor-driven machines and shooters. Coastal waterbirds were more likely to be disturbed by walkers, shooters and large aircraft whereas those inland were more likely to be disturbed by motor-driven machines and unpowered boats.

Conclusions Volunteer-based surveys can be useful in monitoring the sources and distribution of potentially disturbing activities over large spatial scales.     

Breeding status of Merlins Falco columbarius in the UK in 2008

Capsule The third national Merlin survey estimated a UK population of 1162 breeding pairs (95% CI: 891–1462).

Aims To estimate the number of breeding Merlins (with associated 95% confidence intervals) in the UK and the four countries (Scotland, England, Wales and Northern Ireland), and to compare these with the relevant estimates from the 1993–94 Merlin survey. In addition, to calculate estimates of change for several regional populations with complete survey coverage during both national surveys.

Methods A subset of 10-km squares (Raptor Study Group squares and randomly sampled squares) was surveyed across the breeding distribution of Merlins in the UK using standardised methods devised during the 1993–94 national survey.

Results The population estimate for Merlins in the UK was 1162 breeding pairs, and in Britain was 1128 pairs (95% CI: 849–1427), which although 13% lower, was not significantly different from the British estimate of the 1993–94 survey. Scotland held the bulk (733 pairs) of the UK Merlin population, and smaller numbers of 301 pairs, 94 pairs and 32 pairs were estimated for England, Wales and Northern Ireland, respectively. The population estimate for Wales may have been biased upwards by low coverage in the south of the country. Marked declines were noted in several regional Merlin populations, particularly in areas of northern England.

Conclusions The 2008 Merlin survey suggests that the population in Britain has remained relatively stable since 1993–94, but with local declines, particularly in northern England. Currently, little is known about important drivers of regional population change in Merlins, but changes in land-use, prey populations and climate are likely to be important factors.     

A survey and GIS-based estimate of the breeding population of Great Snipe Gallinago media in Central Norway

Capsule By using a GIS-model to identify suitable breeding habitats for Great Snipe in Central Norway, we estimated a total of 276 leks holding approximately 2700 males.

Aim To estimate the size of the Great Snipe population in central parts of the species remaining breeding areas in Western Europe.

Methods GIS-analysis identified an area of 528?km² as suitable habitat for Great Snipe in the total study area (22?000?km²). Complete surveys were made in 8% of these habitats by using a subset of 53 sampling areas.

Results A total of 28 Great Snipe leks were found within the sampling areas. Ten of these were found in previously known lek areas, while 18 leks were found in areas with no previous knowledge of leks. Extrapolating the lek density and the lek size found in the surveyed areas, resulted in a total estimate of 276 Great Snipe leks holding approximately 2700 lekking males. The leks were found on open fens along the forest edge and were mainly situated on base-rich bedrocks. Mean altitude of the leks was 570?m.

Conclusion The total population of Great Snipe in Norway was previously assumed to comprise 5000–15?000 lekking males or ‘pairs'. By extrapolating the densities of leks found in Central Norway to a national scale, we expect the true breeding population of Great Snipe to be approximately 13?500 males. Changes in the elevation of the tree limit and increased overgrowth, as a result of reduced grazing pressure and/or global warming, are possible threats that may reduce the availability of preferred Great Snipe habitats and increase population fragmentation.     

The geographical range of British birds expands during 15 years of warming

Capsule Abundance monitoring data suggest that the short-term response of breeding birds to recent warming in Great Britain has been range expansion, caused by poleward shifts of leading range margins and no significant shifts of trailing range margins.

Aims To quantify latitudinal and elevational shifts of breeding bird populations in Great Britain and test for differential shifts in range margins during a period of warming (1994–2009).

Methods We modelled the population density of 80 species as a smooth function of latitude, longitude, elevation and year. Reference points on the distribution curve were used to describe latitudinal and elevational shifts.

Results Across species, poleward shifts in the leading range margin were greater than in the range-centre. The trailing range margin was largely static, providing evidence for significant range expansion. The magnitude of latitudinal range shift lagged behind the equivalent shift in temperature, suggesting that species may be accumulating a climatic debt. There was no evidence for consistent elevational shifts.

Conclusion Contrary to the generally expected long-term consequences of climate change of range contraction, we show that the short-term response to recent warming has been range expansion. This suggests the mechanisms of short-term and long-term consequences of climate change may differ.     

Status of breeding Dotterel Charadrius morinellus in Britain in 1999

Capsule A minimum of 220 male Dotterel nested in Britain in 1999, which after correction for missed birds led to an estimated 630 breeding males.

Aims To provide a reliable population estimate of Dotterel against which past and future estimates could be compared.

Methods Over half of the potential breeding habitat in Britain, selected randomly and to cover protected sites and former breeding sites for Dotterel, was surveyed through a single visit when Dotterel had young chicks.

Results After correcting for missed birds, 750 males were estimated to be breeding in Britain in 1999. An alternative method led to an estimated 510 males. Both methods had their drawbacks – 630 males probably represented the best estimate. Almost 93% of males bred in three regions: central, east and north Highlands. Around a third of surveyed sites were occupied by breeding birds. The national population estimate was significantly higher in 1987/88 but numbers were probably greatest in 1989 and declined in the 1990s. In 1999 Dotterel distribution had contracted to those sites with the highest densities in the late 1980s.

Conclusion It is unlikely that changes in numbers between surveys were due to changes in the British breeding grounds. They may be due to adverse influences away from the breeding grounds or, because Dotterels can move across large distances between breeding attempts, a redistribution of birds away from Scotland to breeding sites elsewhere in the Palearctic.     

Do bridge construction activities influence birds using the River Mersey,in northwest England?

Capsule: Bridge construction works over a major river did not adversely impact the overall wintering and breeding bird assemblage, although contrasting species-specific trends in breeding number were noted.

Aims: To determine whether the wintering water-bird and breeding bird assemblage using the River Mersey, in northwest England, was influenced by bridge construction works.

Methods: Common bird census and wintering bird surveys were carried out before and during construction of the Mersey Gateway bridge. The species abundance and richness of wintering water-birds, assigned to a group (‘Waterfowl’, ‘Wader’, ‘Wetland species’ and ‘Gull’) and breeding birds, assigned to a group (‘Salt marsh species’, ‘Waterfowl species’, ‘Wader species’, ‘Warbler species’ and ‘Other passerine species’), were separately compared before and during the works.

Results: We found little evidence that the bridge construction displaced wintering water-birds and instead found that for most bird groups, their assemblages were higher during the construction works, compared to before. Similarly, we found no evidence that the bridge construction reduced breeding density of any bird group. Contrasting species-specific trends were, however, noted, with some species only recorded breeding during the construction works, and other species recorded in higher breeding densities before the works.

Conclusion: The inadvertent increase in the mud-flats around the bridge structure since the works resulted in more mud-flat being exposed for a greater amount of time, and thus increased the foraging opportunities for many birds. This may at least partly explain why overall wintering bird abundance and richness increased since the works began. Although most breeding birds either increased or remained stable, in number since the works, a small number reduced. This may have been a consequence of the removal of suitable nesting habitat. This study provides a preliminary assessment of the influence of bridge construction on birds.     

Distribution and population development of introduced Ring-necked Parakeets Psittacula krameri in Britain between 1983 and 1998

Capsule Of the three subpopulations, only the one west of London was increasing, with little spread.

Aims To investigate the distribution and population dynamics of feral Ring-necked Parakeets in Great Britain.

Methods County bird report records (from 1983–95) were collated and analysed to determine distribution and population trends. Roost counts were undertaken monthly from September 1996 to September 1998 to determine minimum population counts and trends.

Results The parakeets were distributed in three subpopulations: west of London, southeast London and in Thanet, Kent. The total population increased during the period, with little spread, except for a slight westward range expansion. Flock size did not increase, and population growth was only apparent from maximum counts at communal roosts. The roosts were largest in the early autumn when, in each of the three years, minimum total population counts were obtained. The west of London population was large and growing, while the southeast London and Thanet populations were smaller and not increasing. The yearly total population counts were 1508, 1880 and 2060.

Conclusion The population is still relatively small and range expansion is slow, suggesting that agricultural areas are not yet threatened by this potential pest species.     

Stable isotope ratios in winter‐grown feathers of Great Reed Warblers Acrocephalus arundinaceus,Clamorous Reed Warblers A. stentoreus and their hybrids in a sympatric breeding population in Kazakhstan

Analyses of the stable isotope composition of feathers can provide significant insight into the spatial structure of bird migration. We collected feathers from Great Reed Warblers Acrocephalus arundinaceus, Clamorous Reed Warblers A. stentoreus and a small sample of their hybrids in a sympatric breeding population in Kazakhstan to assess natural variation in stable isotope signatures and delineate wintering sites. The Great Reed Warbler is a long‐distance migrant that overwinters in sub‐Saharan Africa, whereas the Clamorous Reed Warbler performs a short‐distance migration to the Indian sub‐continent. Carbon (δ¹³C), nitrogen (δ¹⁵N) and deuterium (δD) isotope signatures were obtained from winter‐grown feathers of adult birds. There were highly significant differences in δD and less significant differences in δ¹³C between Great and Clamorous Reed Warblers. Thus, our results show that the stable isotope technique, and in particular the deuterium (δD) signal, resolves continental variation in winter distribution between these closely related Acrocephalus species with sympatric natal origin. The isotope signatures of hybrid Great × Clamorous Reed Warblers clustered with those of the Great Reed Warblers. Hence, a parsimonious suggestion is that the hybrids undergo moult in Afrotropical wintering grounds, as do the Great Reed Warblers. The observed δD values fell within the range of expected values based on available precipitation data collected at precipitation stations across the wintering continents of each species. However, the power to predict the winter origin of birds in our study system using these data was weak as the expected values ranged widely at this broad continental scale.     

Fine-scale habitat associations of Oklahoma's longspurs

Overwintering is a key demographic stage for migratory birds but remains poorly understood, especially among multiple declining grassland bird species. The non-breeding ranges all 4 species of longspur (i.e., chestnut-collared [Calcarius ornatus], Smith's [C. pictus], Lapland [C. lapponicus], thick-billed [Rhynchophanes mccownii]) overlap in Oklahoma and the Texas Panhandle, USA, making this region ideal to study their wintering ecology. We evaluated the relationship between wintering longspur occurrence and fine-scale habitat characteristics using a combination of standardized bird surveys and vegetation plot sampling. Our study encompassed large, representative tracts of 3 prairie ecosystems (i.e., shortgrass, mixed-grass, and tallgrass prairies) that intersect within the Southern Great Plains, during winters of 2018–2019 and 2019–2020. Using randomization tests and classification trees, we characterized longspur habitats and compared these associations across the 3 prairie ecosystems. Fine-scale winter habitats (horizontal structure, vertical structure, and species compositions) varied among all 4 longspur species, varied at very fine scales, and differed between grassland types. Our findings can be applied to the management of grasslands such as decreasing vegetation height in mixed-grass prairies for chestnut-collared longspurs or removing woody vegetation in shortgrass prairies for thick-billed longspurs to help develop full-life cycle conservation for longspurs, which have experienced population declines.     

Recent population declines in Afro‐Palaearctic migratory birds: the influence of breeding and non‐breeding seasons

Aim

Recent, rapid population declines in many Afro‐Palaearctic migratory bird species have focussed attention on changing conditions within Africa. However, processes influencing population change can operate throughout the annual cycle and throughout migratory ranges. Here, we explore the evidence for impacts of breeding and non‐breeding conditions on population trends of British breeding birds of varying migratory status and wintering ecology.

Location

Great Britain (England & Scotland).

Methods

Within‐ and between‐species variation in population trends is quantified for 46 bird species with differing migration strategies.

Results

Between 1994 and 2007, rates of population change in Scotland and England differed significantly for 19 resident and 15 long‐distance migrant species, but were similar for 12 short‐distance migrant species. Of the six long‐distance migrant species that winter in the arid zone of Africa, five are increasing in abundance throughout Britain. In contrast, the seven species wintering in the humid zone of Africa are all declining in England, but five of these are increasing in Scotland. Consequently, populations of both arid and humid zone species are increasing significantly faster in Scotland than England, and only the English breeding populations of species wintering in the humid zone are declining.

Main conclusions

Population declines in long‐distance migrants, especially those wintering in the humid zone, but not residents or short‐distance migrants suggest an influence of non‐breeding season conditions on population trends. However, the consistently less favourable population trends in England than Scotland of long‐distance migrant and resident species strongly suggest that variation in the quality of breeding grounds is influencing recent population changes. The declines in humid zone species in England, but not Scotland, may result from poorer breeding conditions in England exacerbating the impacts of non‐breeding conditions or the costs associated with a longer migration, while better conditions in Scotland may be buffering these impacts.