Dawn E. Balmer

Survival rates of hirundines in relation to British and African rainfall

The BTOs Retrapping Adults for Survival scheme is designed to monitor survival rates of species of conservation concern that are monitored relatively poorly by other forms of ringing. Here we present temporal trends in survival rates for three hirundine species, Barn Swallow Hirundo rustica, House Martin Delichon urbicum and Sand Martin Riparia riparia. Estimates of apparent survival rate were similar to those found in previous studies and were correlated with rainfall on the African wintering grounds, but not with rainfall in Britain, suggesting that overwinter food resources may be more limiting.

Cetti's Warbler Cettia cetti: analysis of an expanding population

Capsule Productivity in the UK Cettis Warbler population is constant, but overwinter survival has become increasingly dependent on winter temperatures. Aims To demonstrate how constant effort (CE) ringing can be used to estimate productivity of breeding populations, using the expanding Cettis Warbler population as an example. Methods A logistic generalized linear model is developed from an established method of estimating abundance to generate an annual index of productivity from CE catches. Dispersal of birds from ring–recapture data is modelled using a simple exponential model of dispersal. Results The number of Cettis Warblers on CE sites has increased markedly, particularly since 1998, but productivity has remained largely constant. The rate of population increase has slowed in recent years, in part because of an increasing sensitivity of the population to cold winters. Juveniles disperse further than adults, and the distance over which they disperse has increased. Conclusions CE catching provides a way of easily measuring whole-season productivity. The future of Cettis Warblers in Britain looks secure, but the population may be approaching its maximum size under current conditions.

Bird ringing in Britain and Ireland in 2003

This is the 67th annual report of the British Trust for Ornithologys Ringing Scheme, covering work carried out, and data received, in 2003. During the year, reports of ringed birds were used to assess the post‐release survival of rehabilitated individuals. Varying proportions of different species were able to re‐enter the population, with Mute Swan Cygnus olor being the most successful. The origins and age structure of Guillemots Uria aalge ringed in Britain & Ireland and found dead after five major oil spills in European waters were found to vary depending on the location of the oil spill. More immature birds and birds from eastern colonies tended to be found after spills that were further south, whereas spills in the north had a greater effect on adults and birds from western colonies. Work on mass gain strategies in Blackbirds Turdus merula showed that they put on mass in winter, when the threat of starvation is greatest, as well as changing mass through the day, again probably in response to the likelihood of starvation. A study of the survival of passerines in the few weeks after fledging found that the survival rate during this critical period is only aboutone sixth of the rate in the rest of the first year of life. A study of the demography of Spotted Flycatcher Muscicapa striata showed that changes in post fleding survival were the most likely mechanism for the observed population decline. Data gathered as part of the Constant Effort Sites (CES) Scheme showed that adult abundance among resident species was generally high, following a good breeding season in 2002. When compared to 2002, fledgling productivity in 2003 was lower, probably as a resultof cold, wetweather during the breeding season. A total of 111 Retrapping Adults for Survival (RAS) studies submitted data covering 43 species. Target species for future workwere identified. Continuing work on the winter movements of farmland passerines showed variations in the distances moved by different species. Over 11,000 Swallows Hirundo rustica were ringed aspartofthe Swallow Roost Project. The total number of birds ringed (848,532) increased for the second year and was 5% above the mean of the previous five years (1998–2002). The recovery total (11,554) was also 5% up on the five‐year mean (1998–2002). Recoveries of 180 BTO‐ringed birds and 76 ringed abroad are presented in the report; those included confirm known or suspected movement patterns or are unexpected movements.

Migration Watch: an Internet survey to monitor spring migration in Britain and Ireland

The arrival patterns of summer visitors to Britain and Ireland were monitored from 2002 to 2004 using large numbers of birdwatching lists collected by Migration Watch, an Internet-based survey. Records were only accepted from registered observers, and procedures for data validation were implemented. We show here how data on the frequency of occurrence from birdwatching lists can be analysed to estimate the timing and duration of the migration period. Aerial insectivores showed clear species-specific arrival patterns, with sand martins arriving first, followed in succession by swallows, house martins and finally swifts. Wheatears showed two peaks of arrivals, one for the British population and one for passage migrants from Greenland. The progression of arrivals from south to north and variation in arrival timing between years were also demonstrated. The method offers considerable potential for studying migration phenology at large spatial scales, and within Britain and Ireland it is now being applied throughout the year within the BTO/RSPB/BWI BirdTrack project. It could potentially be implemented at a continental scale, at which it would provide an important tool for measuring the growing impacts of global climate change on bird populations.

Bird ringing in Britain and Ireland in 2004

This is the 68th annual report of the British Trust for Ornithologys Ringing Scheme, covering work carried out, and data received, in 2004. During the year, changes in bird survival in relation to winter weather were studied. In almost all cases, there was a greater influence of weather on first‐year than adult survival. A paper providing guidelines to help those setting up demographic monitoring schemes for waders was produced, with ringing as a key component. Concern about a reduction in reporting rates of ringed birds led to a study of the changes. Declines were found across nearly all taxonomic groups and may reflect a combination of changes in reporting behaviour, ringing behaviour or bird behaviour. A study of the timing of muirburning used the ringing dates of pulli in conjunction with nest record data to assess its possible effect on breeding birds. There appears to be little reason for differences in cut‐off dates for muirburning in different regions and at different altitudes, but further work is required to quantify more fully the effects on moorland birds. Data gathered as part of the Constant Effort Sites (CES) Scheme showed increases in the numbers of adults of several, mainly migrant, species, possibly as a result of high rainfall in Africa south of the Sahara. Productivity was good for most species. Cettis Warbler Cettia cetti was added to the list of species covered and a study of habitat on CE sites showed that vegetation management mitigates the effect of habitat progression on catching rates. Data for 117 Retrapping Adults for Survival (RAS) studies were submitted. Over 12,000 Swallows Hirundo rustica were ringed as part of the Swallow Roost Project. The total number of birds ringed (881, 920) was the highest ever, showing an 18% increase on the mean of the previous five years (1999–2003). The recovery total (11,930) also increased (by 9% compared to the mean of the previous five years). Recoveries of 154 BTO‐ringed birds and 102 ringed abroad are presented in the report. They include records that confirm suspected or known migration patterns as well as the more unexpected movements

Bird ringing in Britain and Ireland in 2002

This is the 66th annual report of the British Trust for Ornithologys Ringing Scheme covering work carried out and data received in 2002. The BTO continues to work to understand the causes of bird population declines. During the year a major report on the demography of House Sparrows† and Starlings was completed. The work showed that while the decline in House Sparrows is likely to be due to a decline in the survival rate of first‐year birds, changes in productivity (the number of young birds entering the population) appear to have helped to halt the decline in recent years. For Starlings, changes in survival of first‐year birds was the best way of explaining the population decline, although changes in adult survival rate may also be implicated in eastern Britain. Work on wader age ratios showed that the proportion of juvenile waders in flocks caught in winter in Britain & Ireland may provide information about breeding success of high arctic species. Such data are hard to gather on the breeding grounds because of their remoteness and the dispersed nature of the breeding birds. A novel analysis of recoveries was able to show that the origins of Willow Warblers moving through Dungeness Bird Observatory in the autumn varied through the migration period and that the patterns of movement had changed in recent years. Data from the Constant Effort Sites (CES) Scheme showed that adult abundance in 2002 was generally lower than in 2001 following poor productivity in that year. Of nine significant changes in catches of adult birds between 2001 and 2002 eight were decreases (Blackbird, Sedge Warbler, Reed Warbler, Garden Warbler, Willow Warbler, Blue Tit, Great Tit and Chaffinch), with one increase (Bullfinch). Productivity generally improved when compared to 2001 with 18 species showing a statistically significant increase between the two years (Wren, Dunnock, Robin, Blackbird, Sedge Warbler, Reed Warbler, Whitethroat, Blackcap, Chiffchaff, Willow Warbler, Long‐tailed Tit, Blue Tit, Great Tit, Treecreeper, Chaffinch, Greenfinch, Bullfinch and Reed Bunting). Data sets for 110 studies of 42 species were submitted as part of the Retrapping Adults for Survival (RAS) Project. The number of birds ringed (791,074) increased, after the drop in 2001 as a result of some land access restrictions imposed due to Foot and Mouth Disease, and was 4% above the mean of the previous five years (1997–2001). The recovery total (11,042) was similar to the five‐year mean (1997–2001). Recoveries of 130 BTO‐ringed birds and 63 ringed abroad are presented in the report; those selected for inclusion confirm known breeding or wintering areas or migration routes and also show a number of significant or unusual movements.

Bird ringing in Britain and Ireland in 2001

This is the 65th annual report of the British Trust for Ornithologys Ringing Scheme covering work carried out and data received in 2001. As part of the BTOs production of the landmark Migration Atlas: movements of the birds of Britain & Ireland, which will review movements of birds using Britain & Ireland, novel approaches to the investigation of the movement patterns and distances were developed. These allow the objective comparison of whether different species are sedentary, short‐distance or long‐distance migrants and the investigation of differential migration between birds of different age and sex. The BTO continues to carry out a programme of work investigating the declines in bird populations. In 2001, an investigation of Song Thrush population dynamics showed that the survival rates of young birds was key in the population decline; reduction in survival rates also seemed to have driven the fall in numbers of Marsh Tits. Work on movements of waders between roosts on the Moray Basin showed little movement for most species; important information when the possible effects of disturbance are being considered. An investigation of the biometrics of the Redshank wintering on Severn Estuary found that the proportions of Icelandic and British breeders varied between sites; again an important factor in assessing the possible consequences of disturbance. A pilot project, which is investigating the collection of data on movements and demography of farmland passerines in winter is described. Data collected as part of the Constant Effort Sites (CES) Scheme showed significant changes in the numbers of seven species between 2000 and 2001. Of these, five resident species (Blackbird, Blue Tit, Great Tit, Chaffinch and Greenfinch) and one migrant (Whitethroat) showed increases. Only one species (Willow Warbler) decreased. By contrast, productivity tended to be low with 11 species, both residents (Dunnock, Robin, Blackbird, Long‐tailed Tit, Blue Tit, Greenfinch and Reed Bunting) and migrants (Sedge Warbler, Reed Warbler, Blackcap and Chiffchaff) showing significant declines. Progress on the EURO‐CES project, which aims to develop standard protocols for CES fieldwork and data capture across Europe is reported. Data sets for 86 studies of 42 species were submitted as part of the Retrapping Adults for Survival (RAS) Project. The first detailed analysis of Pied Flycatcher data from RAS‐type studies showed that survival rates vary between different areas of the country and confirms the value of this project. The numbers of birds ringed in 2001 (648,936) was 16% below the mean of the previous five years (1996–2000), largely as a result of Foot and Mouth Disease, which restricted the areas ringers had access to. The recovery total (10,692) was 6% lower than the five‐year mean (1996–2000). Recoveries of 195 BTO‐ringed birds and 77 birds ringed abroad are presented in the report and include a number of unusual or significant movements. Of particular note are the first recovery of a Great White Egret involving Britain & Ireland, the first recoveries of BTO‐ringed Honey Buzzards, a BTO‐ringed American Golden Plover recovered in Italy, an Hungarian‐ringed Knot found in England and the first foreign‐ringed Yellow‐browed Warbler (from Norway) to be reported in Britain & Ireland.

On Adjusting for Missed Visits in the Indexing of Abundance from “Constant Effort” Ringing

Producing accurate, reliable indices of abundance, enabling the status of breeding bird populations to be monitored is of interest to government, conservation groups and other bodies. Indices for Sedge Warblers Acrocephalus schoenobaenus from 1983 to 2002 were produced using catch data from the British Trust for Ornithology’s (BTO) Constant Effort Scheme (CES). This is a ringing programme based on standardised mist-netting across up to 12 annual visits to each of a large number of sites. A feature of these data is that some yearly site counts are “censored” due to visits missed within certain years. Peach et al. (1998) developed an intuitive, non-parametric method for correcting for missed visits, prior to model-fitting in the form of a Poisson regression model with an additive offset. In this paper a novel Bayesian approach is introduced, which produces annual indices of abundance whose uncertainty also incorporates a component due to the correction for missed visits. We describe the method in detail, applied to the Sedge Warbler data and to simulated data, and compare the results with those from the current method of Peach et al. (1998).

Identification of marsh warblers Acrocephalus palustris and reed warblers a. scirpaceus on autumn migration through the eastern Mediterranean

Published criteria for the separation of Reed Warbler Acrocephalus scirpaceus and Marsh Warbler A palustris in the hand were found to be of limited value in identifying these species in samples captured during autumn migration through the island of Lesvos in the Aegean Sea. This is probably because Reed Warbler morphology varies clinally with birds in eastern Europe (likely to be migrating through Lesvos) being more similar to Marsh Warblers than are populations in western Europe from which existing identification criteria were calculated. However, a modified biometric index did separate a sample of 364 birds captured during August and September 1994–1996 and 1998 into two clear‐cut groups along the morphological gradient which is known to distinguish the two species. We were therefore confident that these two groups comprised Marsh and Reed Warblers. Linear Discriminant Function Analysis confirmed that this index could be used to identify approximately 95% of the birds in our sample. The index also correlates well with independent assessments of bare part colouration (eg leg colour) which are known to be of use in distinguishing the two species. We suggest that this index will be useful for identifying Reed and Marsh Warblers wherever migrating populations of the two species drawn from a wide geographical area occur together.

Bird ringing in Britain and Ireland in 2005

This is the 69th annual report of the British Trust for Ornithologys Ringing Scheme, covering work carried out, and data received, in 2005. Important research on Oystercatchers Haematopus ostralegus in North Wales showed that survival of adults, recruitment of juveniles and mass of both adults and juveniles were lower during winters when there was mechanised dredging for shellfish. A study of weight changes of House Sparrows Passer domesticus in autumn and winter found that they spread their weight gain through the day, thus potentially decreasing their risk of predation, but increasing their risk of starvation. Data gathered as part of the Constant Effort Sites (CES) Scheme showed an annual increase in adult numbers for five species (one migrant and four residents) and an annual decrease for five species (four migrants and one resident). Productivity was variable with 11 species having above‐average productivity and 13 below‐average. Work began to develop methods to produce annual survival trends by integrating CES data from the 350 sites that have taken part in CES over the last 21 years. Data for 110 Retrapping Adults for Survival (RAS) studies were submitted. Over 13,000 Swallows were ringed as part of the Swallow Roost Project, which ran until 2006. The total number of birds ringed (873,581) was exceeded only in 2004 and was a 12% increase on the mean of the previous five years (2000–04). The recovery total (12,658) was the second highest in the last decade, being exceeded only in 2004, and was 9% higher than the mean of the previous five years. A total of 236 selected recoveries are presented in the report. They include unexpected movements and others that confirm suspected or known migration patterns.