British Breeding Birds Research Articles

The monitoring of British breeding birds: a success story for conservation science?

For almost four decades the British Trust for Ornithology has monitored populations of the commoner 35–50% of species of British breeding birds. The monitoring involves surveillance of numbers, breeding output and survival rates across the whole of the United Kingdom. A formal alert system allows serious declines to be identified and brought to the attention not only of conservationists and those responsible for countryside policy but also the general public. Demographic modelling, the gathering of ancillary information and linked research programmes allow the causes of declines to be identified. The paper details the operation of the programme, illustrated by examples. The system has resulted in the widespread declines in farmland birds that occurred in the last quarter of the 20th century being brought to the attention of conservation scientists, campaigners, policy-makers, politicians and the public. From this (and from the associated understanding of the causes of the declines) have stemmed policies aimed at reducing the problems and a commitment by government to halt the declines. The success of the programme rests on scientifically rigorous design and analysis, on a partnership between volunteer birdwatchers (who do most of the fieldwork) and professional ecologists (responsible for design and analysis) and on effective interaction between scientists and policy makers.

The importance of arable habitat for farmland birds in grassland landscapes

Summary 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. 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. 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. 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. These results support the hypothesis that range contractions (i.e. 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.

Spatial patterns of range contraction in British breeding birds

We use ornithological atlas data to assess evidence for the existence of a number of spatial patterns of range contraction in British breeding birds. For 18 of the 25 species which suffered the greatest range contractions between 1968 and 1991, there wais a greater likelihood of local extinction in areas where the species was initially less widespread, so ranges tended to contract towards their cores. However there was evidence for a number of other patterns, with some species having a greater likelihood of local extinction in the centres of their ranges and others suffering random local extinctions throughout their range. The different spatial patterns identified were largely independent of the overall range contraction suffered by each species nationally. We suggest that range contractions in British birds can generally be explained better by a general decline in habitat quality or other factors than by contagious anthropogenic effects, as might be expected in a country with a long history of human environmental modification.

Self‐Similarity and the Relationship between Abundance and Range Size

Patterns in the relationships among the range, abundance, and distribution of species within a biome are of fundamental interest in ecology. A self-similarity condition, imposed at the community level and previously demonstrated to lead to the power-law form of the species-area relationship, is extended to the species level and shown to predict testable power-law relationships between range size and both species abundance and area of census cell across scales of spatial resolution. The predicted slopes of plots of log(range size) versus log(abundance) are shown to be in good agreement with data from British breeding bird and mammal censuses and with data on the distribution of fern species in old-growth forest. The predicted slopes of plots of log(range size) versus log (area of census cell) are consistent with the limited available data for British plant species. Self-similarity provides a testable theoretical framework for a unified understanding of patterns among the range, abundance, and distribution of species.

Self-Similarity and the Relationship between Abundance and Range Size

Patterns in the relationships among the range, abundance, and distribution of species within a biome are of fundamental interest in ecology. A self‐similarity condition, imposed at the community level and previously demonstrated to lead to the power‐law form of the species‐area relationship, is extended to the species level and shown to predict testable power‐law relationships between range size and both species abundance and area of census cell across scales of spatial resolution. The predicted slopes of plots of $$\mathrm{log}\,( \mathrm{range}\,\,\mathrm{size}\,) $$ versus $$\mathrm{log}\,( \mathrm{abundance}\,) $$ are shown to be in good agreement with data from British breeding bird and mammal censuses and with data on the distribution of fern species in old‐growth forest. The predicted slopes of plots of $$\mathrm{log}\,( \mathrm{range}\,\,\mathrm{size}\,) $$ versus $$\mathrm{log}\,( \mathrm{area}\,\,\mathrm{of}\,\,\mathrm{census}\,\,\mathrm{cell}\,) $$ are consistent with the limited available data for British plant species. Self‐similarity provides a testable theoretical framework for a unified understanding of patterns among the range, abundance, and distribution of species.

Explanations of commonness and rarity in British breeding birds: separating resource use and resource availability

Two of the most prominent explanations for a positive interspecific relationship between local abundance and regional distribution are the resource breadth and the resource availability hypotheses. Here we test these hypotheses by characterising habitat use of British breeding birds using extensive census and environmental data. A group of 85 bird species was considered for study along with 34 land use or environmental variables, which were used to generate four ordination axes by Canonical Correspondence Analysis. Measures of niche breadth and position were derived from these synthetic environmental axes using standard procedures. Across species, none of five measures of abundance and distribution chosen were correlated with niche breadth, whereas four out of five of these measures were correlated negatively with niche position. Repeating the analyses using a method designed to control for phylogenetic non‐independence confirmed these general patterns. Birds that tended to use resources that were more atypical of the environment tended to be rarer and thinly distributed, while those using typical resources were common and widely distributed. Performing the analyses on subsets of the data based on species sample sizes did not alter the conclusions. On the assumption that our analyses properly capture patterns of niche use by birds, we find little support for the resource breadth hypothesis, but considerable support for the resource availability hypothesis.

Changes in the biomass of birds breeding in Great Britain, 1968–88

Using published data, this study assesses whether population changes in British breeding birds over the 20-year period, 1968–88, have led to an overall change in biomass. Because of uncertainty in the population estimates, the most extreme estimates of biomass changes are a 6% increase and a 71% decrease. However a parsimonious mid-range estimate suggests that, excluding seabirds and Common Eider Somateria mollissima, bird biomass in Great Britain has fallen from 14 200 tonnes in 1968 to 12742 tonnes in 1988, a decrease of 10%. If the Pheasant Phasianus colchicus is excluded from the calculations, the decrease becomes 29%. While most of the species contributing to the decrease are associated with farmland, the species that have increased in biomass form a more heterogenous group, many being commensal with humans.

Determinants of geographical range sizes: a test using introduced New Zealand birds

Summary1. The 34 species of birds that have been successfully introduced to New Zealand offer a unique opportunity to study patterns of variation in geographical range sizes, and to test mechanisms that may be responsible for that variation, because the New Zealand range sizes have established within the last 160 years and because there are data on the starting conditions, including the year of first recorded release and the subsequent effort put into the introduction of each species.2. We collated data on geographical range sizes, life history traits, dates of introduction and initial introduction effort for the birds successfully introduced to New Zealand. To test whether range size–life history correlations show a consistent pattern between regions, we collated further data on geographical range sizes and life history traits for British breeding birds.3. The geographical range sizes of birds introduced to New Zealand did not depend on the length of time since they were introduced. Instead, large geographical ranges were exhibited by species whose preferred habitat is widespread in New Zealand, species with life history traits associated with higher rates of population growth (high fecundity, fast development and small body size), species that are partial migrants in part of their natural range, and species that were initially introduced more often and in greater numbers to New Zealand.4. The strength and direction of geographical range size–life history correlations in introduced New Zealand and British breeding birds were very similar. There was also a strong positive correlation between the geographical range sizes of the species introduced to New Zealand from Britain and their geographical range sizes in Britain. However, the similarity of the correlations between life history traits and geographical range sizes in both regions was not a simple consequence of this; the similarity persisted when species introduced from Britain were excluded from the New Zealand data.5. We discuss the implications of these results for understanding variation in geographical range sizes in the introduced New Zealand avifauna.

Macroecological patterns in British breeding birds: covariation of species’geographical range sizes at differing spatial scales

The availability of high quality data on the distribution and abundance of British birds at the national scale means that this fauna is the basis for a growing body of macroecological study. Nevertheless. questions remain about how representative of wider patterns the distributions and abundances of birds in Britain may be. Here, we use data on the British. European and global breeding distributions of British birds to show that species that are widespread in Britain also tend to be widespread across larger regions. These results hold for both residents and migrants separately, and when controlling for the phylogenetic related ness of species. Species with wide latitudinal spans in Europe also tend to have large British ranges, with the largest British ranges exhibited by species inhabiting mid‐latitudes in Europe. These results demonstrate that the distributions of birds within Britain are not simply idiosyacratic. but do reflect aspects of their broader distributions.

The anatomy of the interspecific abundance–range size relationship for the British avifauna: II. Temporal dynamics

In a companion paper, we started an examination of the anatomy of the interspecific relationship between local abundance and geographical range size in the British avifauna by analysing its spatial dynamics. Here, we use the same data to extend this study to a consideration of the temporal dynamics of the relationship. Most species of British breeding bird show a positive intraspecific abundance–range size relationship through time: i.e. in years when a species is locally more abundant it also occupies a higher proportion of census sites. However, the majority of such relationships are not statistically significant, and other relationships that are statistically significant are negative. Therefore, intraspecific abundance–range size relationships do not simply mirror the relationship across species. Where they do arise, positive relationships are more likely to be associated with positive intraspecific relationships between range size and maximum rather than minimum abundance. The interspecific abundance–range size relationship is remarkably consistent across years, and is always significantly positive. The relationships for woodland and farmland census sites show correlated variation, so that in years when the linear regression slope and coefficient of determination are high across species on farmland plots, they also tend to be high across species on woodland plots. Common species tend to be common on both farmland and woodland plots, and tend to be common in all years. Likewise, rare species tend to be rare in all habitats and years. This concordance means that the positive interspecific abundance–range size relationship can be viewed as occurring largely independently of intraspecific relationships. It follows from the above that developing an understanding of intraspecific abundance–range size relationships may be of only limited value in ascertaining the determinants of positive interspecific abundance–range size relationships. We conclude that for interspecific relationships, it will be important to know why some species are consistently common and others rare, whereas for intraspecific relationships it will be important to understand the dynamic links between local abundances across sites.

Interspecific differences in intraspecific abundance‐range size relationships of British breeding birds

A general positive interspecific relationship between local abundance and geographic range size in animals has prompted speculation that a similar relationship might exist intraspecifically, such that a species is widespread at times when it is locally abundant, and more restricted in distribution when it is locally rare. Current evidence suggests that intraspecific relationships often are positive, but that there is considerable variation in the pattern exhibited by species. Here, we use data on British birds to test the hypotheses that species showing a high mean or wide spread of local densities or range sizes will be more likely to show strong intraspecific relationships between abundance and geographic range size. These data show only inconsistent support for an effect of the range of densities or of occupancies on intraspecific abundance‐range size relationships. However, the strength of an intraspecific relationship does seem to be related to the mean occupancy of species, and whether or not a species exhibits temporal trends in density, with the strongest relationships found in species with simultaneous trends in both density and occupancy. We suggest that these results are explained by time lags in the loss or gain of species at occupied sites in response to reductions or increases in density.

Of mice and wrens: the relation between abundance and geographic range size in British mammals and birds

We examine the relation between population size and geographic range size for British breeding birds and mammals. As for most other assemblages studied, a strong positive interspecific correlation is found in both taxa. The relation is also recovered once the phylogenetic relatedness of species has been controlled for using an evolutionary comparative method. The slope of the relation is steeper for birds than for mammals, but this is due in large part to two species of mammals that have much higher population sizes than expected from their small geographic ranges. These outlying mammal species are the only ones in Britain to be found only on small offshore islands, and so may be exhibiting density compensation effects. With them excluded, the slope of the abundance–range size relation for mammals is not significantly different to that for birds. However, the elevation of the relation is higher for mammals than for birds, indicating that mammals are approximately 30 times more abundant than birds of equivalent geographic range size. An earlier study of these assemblages showed that, for a given body mass, bats had abundances more similar to birds than to non–volant mammals, suggesting that the difference in abundance between mammals and birds might be due to constraints of flight. Our analyses show that the abundance–range size relation for bats is not different for that from other mammals, and that the anomalously low abundance of bats for their body mass may result because they have smaller than expected geographic extents for their size. Other reasons why birds and mammals might have different elevations for the relation between population size and geographic range size are discussed, together with possible reasons for why the slopes of these relations might be similar.

Phylogeny and relations among abundance, geographical range and body size of British breeding birds

Links between bird phylogeny and abundance, geographical range and body size relations were examined with use of a newly published data set on the numbers and distribution of British breeding birds. There was a negative correlation between abundance (and geographical range) and body size across species, but no significant correlations within non-passerine and passerine taxa considered separately. Abundance correlated positively with geographical range across species and within non-passerines and passerines. Three measures of phylogenetic relatedness of bird tribes were considered, termed ‘rootedness’, ‘date of origin’ and ‘radiation d ate’. The date at which a tribe originated (measured as rootedness or date of origin) had a consistent but weak influence on the form of the relation between abundance and body size. Phylogeny was not implicated in the relation between geographical range and body size. Phylogenetically isolated tribes were more likely to show a positive correlation between abundance and body size than more recently evolved tribes. Results are discussed in the context of previous studies of both regional and local bird assemblages and the hypotheses suggested to explain associations with phylogeny.

Some new approaches to conservation monitoring of British breeding birds

It is important to monitor bird populations both in their own right and as indicators of the general health of wildlife habitats. The objectives of the British Trust for Ornithology's Integrated Population Monitoring programme relate to breeding bird populations in Britain and Ireland and involve the estimation of demographic parameters as well as assessment of numbers. Current programmes for monitoring bird numbers cover the majority of British species; it would be feasible to monitor most of the rest. A new Breeding Bird Survey has been developed to provide effective coverage of all regions and all major habitats in Britain through random sampling, allowing for the marked geographical variation in volunteer observer density. The final choice of a random sample stratified by observer density (with some professional support in regions with few volunteer observers) was based on comparison with alternative stratifications, using data from a 2‐year pilot study to assess the number of species adequately covered under various alternatives. A method of assessing whether or not targets are being achieved at any time has been developed: it involves looking back through the data at intervals of 1‐year, 4‐year, 16‐year and longer spans. It will be possible to refine this by incorporating environmental and density‐dependent effects into predictive models. The method is illustrated here using Common Birds Census data. We discuss associated problems of statistical inference and of taking decisions under uncertainty. The data provide evidence for large declines in some species, particularly in farmland; the value of birds as general indicators of habitat health is clear. The results of monitoring can be used to illuminate possible causes of problems and to guide both practical steps to ameliorate the problems and research aimed at better understanding the causes. Examples of such research are discussed.

Species abundance patterns of British birds

Species abundances tend to follow lognormal frequency distributions, and samples often appear to be skewed to the right of the veil line. It has been suggested that the underlying distribution is likely to be skewed to the left, and that the left-hand tail would only be revealed by increasing sampling effort. Preliminary data for British birds have shown abundances to be significantly skewed to the left, and further, the degree of skew was compatible with a `sequential stick breaking' model of species abundances. Here I report an analysis of a newly published data set on British breeding birds which confirms the original findings in demonstrating a left skew to bird abundances, although the degree of skew is less than previously reported and not significantly different from zero. This result is quantitatively compatible with both the previous theoretical model and one based on independent draws from a lognormal distribution. This raises the possibility that species abundances may follow roughly symmetrical lognormal distributions; the problem in demonstrating such patterns may be the existence of extensive data sets which are free of bias.

Migration of dunlincalidris alpina:A worldwide overview

Ringing recoveries have been used to determine the winter quarters for the different breeding populations of Dunlin. These are Greenlandic, Icelandic, and British breeding birds to north‐west Africa; those from the Baltic to north‐west Africa, the Mediterranean and Persian Gulf; Lapplandic to the British Isles south to north‐west Africa; western Russian to the British Isles, the Mediterranean, the Caspian and Abrabian Gulf; eastern Russian and northern Alaskan to the Asian Pacific coast; western Alaskan to the North American Pacific coast; arctic Canadian to the North American Atlantic coast. Populations that breed in different areas occupy greatly overlapping regions in winter throughout much of the range.

The Red-backed Shrike: A Vanishing British Species

Within the next decade the Red-backed Shrike may cease to exist as a British breeding bird. The picture painted by this latest survey of its status is a gloomy one. It would appear that the combined pressures of an adverse climatic trend, the fragmentation of its habitat in the name of ‘development’, and not least over-collecting of its eggs, have reduced the population to a dangerously low level.

Birds, Game, and Trees 1

MR. KEARTON'S books on British birds (1) are so well, and deservedly, known, that the new edition of his work entitled “British Birds Nests” calls for only a brief notice. The original edition first saw the light in the autumn of 1895, and was the first book of its kind to be illustrated throughout by means of photographs taken direct from nature, and was declared by the late Dr. Bowdler Sharpe to “mark a new era in natural history.” This was followed in 1891 by another volume, entitled, “Our Rarer British Breeding Birds.” The present revised and enlarged edition of the first work contains the best of the pictures that appeared in the pages of the second, together with numerous photographs secured during the intervening years. To give an idea of the time and labour expended in gathering materials for this book, it may be mentioned that Mr. Richard Kearton, with his brother, Mr. Cherry Kearton, to whom, we understand, most of the photography is entrusted, have travelled more than thirty thousand miles and exposed more than ten thousand plates to secure the necessary illustrations of nesting sites and birds. In addition to the photographs, the book is illustrated with fifteen coloured plates of eggs.