Mike P. Toms

Emerging Infectious Disease Leads to Rapid Population Declines of Common British Birds

Emerging infectious diseases are increasingly cited as threats to wildlife, livestock and humans alike. They can threaten geographically isolated or critically endangered wildlife populations; however, relatively few studies have clearly demonstrated the extent to which emerging diseases can impact populations of common wildlife species. Here, we report the impact of an emerging protozoal disease on British populations of greenfinch Carduelis chloris and chaffinch Fringilla coelebs, two of the most common birds in Britain. Morphological and molecular analyses showed this to be due to Trichomonas gallinae. Trichomonosis emerged as a novel fatal disease of finches in Britain in 2005 and rapidly became epidemic within greenfinch, and to a lesser extent chaffinch, populations in 2006. By 2007, breeding populations of greenfinches and chaffinches in the geographic region of highest disease incidence had decreased by 35% and 21% respectively, representing mortality in excess of half a million birds. In contrast, declines were less pronounced or absent in these species in regions where the disease was found in intermediate or low incidence. Also, populations of dunnock Prunella modularis, which similarly feeds in gardens, but in which T. gallinae was rarely recorded, did not decline. This is the first trichomonosis epidemic reported in the scientific literature to negatively impact populations of free-ranging non-columbiform species, and such levels of mortality and decline due to an emerging infectious disease are unprecedented in British wild bird populations. This disease emergence event demonstrates the potential for a protozoan parasite to jump avian host taxonomic groups with dramatic effect over a short time period.

The emergence and spread of finch trichomonosis in the British Isles.

Finch trichomonosis, caused by the protozoal parasite Trichomonas gallinae, was first recognized as an emerging infectious disease of British passerines in 2005. The first year of seasonal epidemic mortality occurred in 2006 with significant declines of greenfinch Carduelis chloris and chaffinch Fringilla coelebs populations. Here, we demonstrate that large-scale mortality, principally of greenfinch, continued in subsequent years, 2007–2009, with a shifting geographical distribution across the British Isles over time. Consequent to the emergence of finch trichomonosis, the breeding greenfinch population in Great Britain has declined from ca 4.3 million to ca 2.8 million birds and the maximum mean number of greenfinches (a proxy for flock size) visiting gardens has declined by 50 per cent. The annual rate of decline of the breeding greenfinch population within England has exceeded 7 per cent since the initial epidemic. Although initially chaffinch populations were regionally diminished by the disease, this has not continued. Retrospective analyses of disease surveillance data showed a rapid, widespread emergence of finch trichomonosis across Great Britain in 2005 and we hypothesize that the disease emerged by T. gallinae jumping from columbiforms to passeriforms. Further investigation is required to determine the continuing impact of finch trichomonosis and to develop our understanding of how protozoal diseases jump host species.

Evidence of Spread of the Emerging Infectious Disease, Finch Trichomonosis, by Migrating birds

Finch trichomonosis emerged in Great Britain in 2005 and led to epidemic mortality and a significant population decline of greenfinches, Carduelis chloris and chaffinches, Fringilla coelebs, in the central and western counties of England and Wales in the autumn of 2006. In this article, we show continued epidemic spread of the disease with a pronounced shift in geographical distribution towards eastern England in 2007. This was followed by international spread to southern Fennoscandia where cases were confirmed at multiple sites in the summer of 2008. Sequence data of the ITS1/5.8S/ITS2 ribosomal region and part of the small subunit (SSU) rRNA gene showed no variation between the British and Fennoscandian parasite strains of Trichomonas gallinae. Epidemiological and historical ring return data support bird migration as a plausible mechanism for the observed pattern of disease spread, and suggest the chaffinch as the most likely primary vector. This finding is novel since, although intuitive, confirmed disease spread by migratory birds is very rare and, when it has been recognised, this has generally been for diseases caused by viral pathogens. We believe this to be the first documented case of the spread of a protozoal emerging infectious disease by migrating birds.

Bird ringing in Britain and Ireland in 1996

This is the 60th annual report of the British Trust for Ornithologys Ringing Scheme, presenting the data received in 1996. The development and implementation of a Scientific Strategy for the Ringing Scheme is discussed, together with examples of future work and data analysis. The strategy provides a coherent approach to the collection of data needed for future analytical work on bird populations within Britain and Ireland, ensuring that questions of conservation importance are addressed. The number of birds ringed during the current period (851,237) was slightly down on that for 1995, but remained some 2.8% up on the mean for the previous five years. For several species there were changes in the number of individuals ringed (when compared with previous years) which could not be explained by changes in ringing effort. These included increases for Firecrest, Fieldfare and Barn Owl and a decrease for Crossbill. The total number of recoveries for the period (12,342) is nearly 5% down on the mean for the prev...

Sparrowhawk Accipiter nisus presence and winter bird abundance

The decline and subsequent re-colonisation of the Sparrowhawk Accipiter nisus in the UK has allowed an examination of its potential impacts on passerine abundance through analysis of long-term garden bird monitoring data. Weekly counts in gardens in winter have been collected annually since the early 1970s, a period when Sparrowhawks were initially rare but recolonised to a point in the 1990s when they were recorded in the majority of gardens. Change in bird count from year-to-year for 10 common prey species from up to 483 survey sites were analysed in relation to Sparrowhawk re-colonisation, the number of feeding units per site (e.g. bird tables, hanging bird feeders) and, for a subset of the data, minimum temperature. Year-to-year change increased with Sparrowhawk re-colonisation in Great Tit Parus major, Blue Tit Cyanistes caeruleus and Collared Dove Stretopelia decaocto, but decreased in Starling Sturnus vulgaris, Chaffinch Fringilla coelebs and Greenfinch Carduelis chloris. Positive associations may suggest a behavioural response to predators, or an attraction of predators to increased prey caused by confounding effects of improvement in site quality. The significant negative effects detected suggest that there is a temporal matching between increased predation pressure and decreases in bird abundance for certain species. However, there was no strong evidence that Sparrowhawk re-colonisation was linked to long-term declines in population size.

Importance of Sitka Spruce Picea sitchensis seed and garden bird-feeders for Siskins Carduelis spinus and Coal Tits Periparus ater

Capsule Siskins and Coal Tits were present in gardens more often in years of poor Sitka Spruce cone crops, with synchrony across the UK. Aims To examine how the relative abundances of Siskins and Coal Tits in a garden in western Scotland varied annually with the size of the spruce cone crop, and to determine whether this pattern was similar nationally. Methods A ten-year mist-netting data set from Tarbet, Argyll and Bute was used to test the hypothesis that some species utilize supplementary food in gardens more often in years with poor cone crops than in years when crops are large. Annual peaks in the relative abundances of four species (two that ate conifer seed and two that did not) in Tarbet were correlated with a Sitka Spruce masting index. BTO Garden BirdWatch data from six regions of the UK were correlated with the Tarbet data, the cone index and each other to determine the extent of synchrony. Results Both Siskins and Coal Tits were present more often in the Tarbet garden in years with poor cone crops, with relative abundances significantly negatively correlated with cone crop for both species (r = −0.739 and −0.832, respectively). Correlations between regions using BTO data showed abundances of species in gardens to be broadly similar across the UK. Independent scores of cone abundance in Kielder and Galloway were correlated. Correlations between BTO data, cone index and Tarbet garden data were mostly high and almost all in the same direction, also indicating a degree of synchrony in cone production across the UK. Conclusion Both Siskins and Coal Tits appear to be influenced by changes in cone abundance, switching to feed on supplementary food in gardens more often in years with few cones than in mast years. While such a relationship has been shown previously for Siskins, for Coal Tits this is a novel result.

Bayesian hierarchical modelling of continuous non-negative longitudinal data with a spike at zero: An application to a study of birds visiting gardens in winter

The development of methods for dealing with continuous data with a spike at zero has lagged behind those for overdispersed or zero‐inflated count data. We consider longitudinal ecological data corresponding to an annual average of 26 weekly maximum counts of birds, and are hence effectively continuous, bounded below by zero but also with a discrete mass at zero. We develop a Bayesian hierarchical Tweedie regression model that can directly accommodate the excess number of zeros common to this type of data, whilst accounting for both spatial and temporal correlation. Implementation of the model is conducted in a Markov chain Monte Carlo (MCMC) framework, using reversible jump MCMC to explore uncertainty across both parameter and model spaces. This regression modelling framework is very flexible and removes the need to make strong assumptions about mean‐variance relationships a priori. It can also directly account for the spike at zero, whilst being easily applicable to other types of data and other model formulations. Whilst a correlative study such as this cannot prove causation, our results suggest that an increase in an avian predator may have led to an overall decrease in the number of one of its prey species visiting garden feeding stations in the United Kingdom. This may reflect a change in behaviour of house sparrows to avoid feeding stations frequented by sparrowhawks, or a reduction in house sparrow population size as a result of sparrowhawk increase.

Bayesian hierarchical modelling of continuous non-negative longitudinal data with a spike at zero

The development of methods for dealing with continuous data with a spike at zero has lagged behind those for overdispersed or zero‐inflated count data. We consider longitudinal ecological data corresponding to an annual average of 26 weekly maximum counts of birds, and are hence effectively continuous, bounded below by zero but also with a discrete mass at zero. We develop a Bayesian hierarchical Tweedie regression model that can directly accommodate the excess number of zeros common to this type of data, whilst accounting for both spatial and temporal correlation. Implementation of the model is conducted in a Markov chain Monte Carlo (MCMC) framework, using reversible jump MCMC to explore uncertainty across both parameter and model spaces. This regression modelling framework is very flexible and removes the need to make strong assumptions about mean‐variance relationships a priori. It can also directly account for the spike at zero, whilst being easily applicable to other types of data and other model formulations. Whilst a correlative study such as this cannot prove causation, our results suggest that an increase in an avian predator may have led to an overall decrease in the number of one of its prey species visiting garden feeding stations in the United Kingdom. This may reflect a change in behaviour of house sparrows to avoid feeding stations frequented by sparrowhawks, or a reduction in house sparrow population size as a result of sparrowhawk increase.

Using citizen science to investigate the role of productivity in House Sparrow Passer domesticus population trends

Capsule Seasonal variation in garden House Sparrow numbers provides a tool to examine overall annual productivity, measuring the combined success of multiple breeding attempts and post-fledging survival. Aims To develop a metric to use British Trust for Ornithology (BTO) Garden BirdWatch (GBW) data to measure annual productivity in House Sparrows across regions and habitats exhibiting contrasting population trends. Methods We examine variation in annual productivity by quantifying the height of the seasonal peak of garden House Sparrows relative to pre-breeding numbers. We use BTO Nest Record Scheme (NRS) data to explore the demographic drivers of variation in this metric and relate differences to BTO/Joint Nature Conservation Committee/Royal Society for Protection of Birds Breeding Bird Survey regional population trends. Results GBW annual productivity was similar between rural and urban gardens but was lower in the south and the east of Britain (1.32 fledglings per adult), where populations are declining, than in the north and west where populations are stable (1.37 fledglings per adult). Analysis of NRS data showed similar regional variation in clutch and broods sizes. Conclusion The intensity of effort required to measure breeding success directly through nest monitoring has limited the scale of data collection but these results suggest that Garden BirdWatch (GBW) data can provide a measure of annual productivity across multiple sites. Regional variation in annual productivity (primarily driven by reduced clutch sizes) mirrors population trends, suggesting that reduced breeding success may be influencing House Sparrow population recovery.

Urbanization and time of arrival of common birds at garden feeding stations

Capsule Birds appeared at garden feeding stations later in the morning in urban areas than in rural areas during winter.