Work on emerging infectious diseases and garden birds in the UK has been supported by citizen science projects, most notably Garden BirdWatch, Garden Wildlife Health and the Garden Bird Health Initiative – the latter now superseded by Garden Wildlife Health. Through these schemes, researchers have been able to carry out national surveillance of emerging diseases, including finch trichomonosis, Paridae pox and passerine salmonellosis. This paper, part of a special issue of Philosophical Transactions focusing on wildlife disease issues, reviews the work that has been carried out on these diseases over the past 25 years. It also takes a look at the occurrence of mycotoxin contamination of food residues in bird feeders, which also pose a risk to the health of wild birds. A citizen science approach provides a cost-effective means to undertake large-scale and year-round disease surveillance (Garden Wildlife Health), delivered in parallel to the monitoring of wildlife populations (Garden BirdWatch). By combining large-scale surveillance and targeted post-mortem examinations we can differentiate between the multiple diseases that result in non-specific clinical signs (e.g. lethargy and a fluffed-up appearance). The sample archive collected through post-mortem examination also enables future identification of other disease agents, including those – such as environmental pollutants – associated with non-infectious disease. Avian trichomonosis, caused by the protozoan parasite Trichomonas gallinae, has long been known to affect pigeons, doves and birds of prey. Its emergence in finches in 2005 led to a major population decline in Greenfinch and Chaffinch, reported in an earlier paper. While multiple strains of Trichomonas gallinae are known to infect pigeons and doves in the UK, a single clonal strain is responsible for the epidemic seen in finches. Quite why Greenfinch is so susceptible to the disease is unclear. It is likely that the disease spilled over into finches following the increase in use of garden feeding stations by Woodpigeon, a recent change that follows an increase in wider countryside populations. Avian poxvirus has been documented in a number of garden bird species and is most often seen in House Sparrow, Starling, Woodpigeon and Dunnock. Its emergence in UK tits saw a more severe form of the disease, resulting in pronounced skin lesions, some of which were likely to have hampered the individual’s ability to feed and to avoid predators. Sequence analysis of the poxvirus strains affecting garden birds revealed that a single clade is responsible for the disease seen in UK tits. This form has been known in Scandinavia since the 1950s, with incidents seen elsewhere in mainland Europe since 2005. Because UK tits are relatively sedentary in their habits, and because of the geographical pattern of disease spread seen, it is likely that the disease reached the UK via a biting insect – such as a mosquito, crossing the English Channel in a warm plume of air. Salmonellosis has been reported in wild birds since at least the 1950s, with the bacterium responsible known to be capable of persisting in the environment for many months. Greenfinch and House Sparrow are the two species in which the disease is most often seen. Passerine salmonellosis incidents have a clear seasonality, peaking in January. Interestingly, the prevalence of the disease in UK passerines has dropped sharply over recent years. This may reflect increased immunity to the particular form (DT56v) that had been seen here; or it may be that transmission is density-dependent, with the sharp decline in Greenfinch populations resulting in much lower rates of transmission. Mycotoxins, which include the aflatoxins and ochratoxin, are secondary metabolites produced by certain fungi of the genera Aspergillus and Penicillium. Exposure to the aflatoxins and ochratoxin can exert a range of adverse effects in birds, and the fungi involved and their toxins are known to occur on foodstuffs, including peanuts. Food residues from bird feeders were screened for the toxins as part of the current study, with detectable aflatoxin residues found in all seven samples, two of which greatly exceeded the maximum permitted limits set for such residues in peanuts destined for livestock feed, which includes wild bird food. It therefore seems likely that garden birds may be exposed to these toxins at levels associated with toxic effects in captive birds. This review underlines the great deal of new information that has been generated through these citizen science projects. It also highlights future research needs, particularly around the identification of risk factors, and that we need to understand the balance of risks and opportunities that garden bird feeding provides.

Currently non-native species are being introduced to countries at an unprecedented rate. These species can have severe detrimental effects on native biodiversity, human health and the economy. Due to population growth, increases in trade and tourism and global warming the likelihood of non-native species arriving and establishing in the UK will be higher in the future. A new study by BTO investigates whether it is possible to predict which non-native species are likely to establish in the UK based on the climate in their native range, thereby enabling early preventative action to be taken. Invasive species can have serious effects in their new home turf; they can be economically expensive, potentially cause health hazards, and they can have a large impact on the native biodiversity. Predicting whether invasive species are likely to colonise the UK is therefore an important priority. This study compared the suitability of the climate in the UK against the native range of 167 potentially invasive, or already established non-native bird species to see which species would be able to expand their range into the UK. Climate parameters that were used included temperature, precipitation and moisture. Values were used for both the current climate and the projected future climate. Results predicted that in the future, the UK climate will be suitable for more non-native species. Currently the UK climate was deemed suitable for 69 out of the 167 species included, but only 44 of those species actually currently occur in the UK. The results also showed that 85% of species that have colonised the UK successfully were found in climatically unsuitable areas. Many of these were usually found in areas that were wetter than their native range. In conclusion, there was no overall support that climate suitability is a reliable predictor of non-native bird species’ ranges, as there are many other contributing factors. Non-native populations are highly dependent on when and where introductions take place. Additionally, local availability of resources and competition with native flora and fauna may prevent establishment. Similarly, some birds which may not be climatically suited to the UK may be able to evolve rapidly to adjust to a different climate, or human influence (such as feeding) may provide them with the resources they need to survive. Regular surveying will be necessary to determine the effect climate change has on bird populations, and on where they may go in future.

The return of breeding Peregrines to former haunts, and the colonisation of urban sites such as industrial buildings and cathedrals, has not gone unnoticed by birdwatchers. It is only now, however, with the publication of the results from the latest national Peregrine survey, that we can put figures on the changing fortunes of this stunning bird of prey. The Peregrine breeding population in the UK and Isle of Man has been surveyed at intervals of 10 years since 1961/62. The first four surveys documented the recovery of the Peregrine population from the ‘crash’ of the 1960s (when numbers fell to less than half of the pre-war population) to the highest levels since recording began. The new national survey, carried out in 2014, sought to secure a new national population estimate and, in particular, to improve our knowledge of the species in lowland areas not traditionally regarded as being part of the Peregrine’s breeding range. The 2014 survey, co-ordinated by the BTO in partnership with many other raptor monitoring individuals and organisations, was made possible by the hard work of hundreds of volunteers. These fieldworkers surveyed a combination of known sites and randomly selected survey squares to secure evidence of occupation and breeding by Peregrines. The population estimate derived from the survey puts the UK Peregrine population at 1,769 breeding pairs, an increase of 22% on the previous survey (carried out in 2002). Most of the increase is accounted for by population growth in lowland England, with breeding Peregrines continuing to occupy new sites. Most of the inland breeding pairs utilise large cliffs, smaller crags or quarries, but an increasing proportion of pairs occupy man-made structures such as buildings, bridges, pylons and communication masks. Examination of the regional results reveals contrasting fortunes in Scotland, where there the population has declined overall. Worryingly, Peregrine populations are not doing well in the upland SPAs (Special Protection Areas) established to protect them, a pattern evident in both Scotland and northern England. Further losses of Peregrines from such areas might not pose a grave threat to the UK population, but could be important at a regional level. Possible factors associated with the poor performance of upland Peregrine populations may include prey abundance and availability, and illegal killing associated particularly with management of upland gamebirds for shooting, but also with recreational breeding and racing of domestic pigeons. Other factors may have affected Peregrine numbers at a local level; these include avoidance of Golden Eagles, oiling by Fulmars and exposure to a wide range of environmental pollutants. The findings of this survey provide an opportunity to investigate the effects of these and other issues, with complementary data sets – such as Bird Atlas 2007-11 or the RSPB’s data on upland land use – potentially of great value here.

A three-year study, supported by EDF Energy and the British Trust for Ornithology (BTO), has been able to identify that dry summer weather may be putting some of our favourite bird species at risk as it triggers a significant drop in the availability of earthworms close to the soil surface during the breeding season. The research was undertaken by thousands of schoolchildren in a nationwide science project to understand the effects of climate change on our soils and ecosystems, helping to inspire the next generation of ecologists. Nearly 15,000 school children from over 500 schools across the UK have been digging up small sections of their playing fields once a term in October, March and June, and counting and identifying the creatures they found living in the top 5cm of the turf. The results show that the invertebrate groups varied based on season and small-scale habitat factors. Earthworms were the most present group (93.1% of total invertebrate biomass) and were strongly associated with soil moisture, and therefore season. Other groups that were monitored included slugs and snails, woodlice, centipedes, spiders, beetles, ants, earwigs, Diptera larvae, beetle larvae and caterpillars, most of which became more common in spring and summer. The results suggest that climate change will not necessarily have large-scale impacts on soil invertebrate populations, but rather affect their availability through time. The project shows that large-scale citizen science at schools can be of tremendous value to scientific data collection. As the project continues, we hope to further expand our knowledge on the UK’s soil invertebrate communities with the help of schools across the country and link this knowledge to bird populations.

Ecology and Conservation of Forest Birds is a unique review of current understanding of the relationships between forest birds and their changing environments. Large ecological changes are being driven by forest management, climate change, introduced pests and pathogens, abiotic disturbances, and overbrowsing. Many forest bird species have suffered population declines, with the situation being particularly severe for birds dependent on attributes such as dead wood, old trees and structurally complex forests. With a focus on the non-tropical parts of the northern hemisphere, the text addresses the fundamental evolutionary and ecological aspects of forest birds using original data analyses and synthesising reviews. The characteristics of bird assemblages and their habitats in different European forest types are explored, together with the macroecological patterns of bird diversity and conservation issues. Ecology and Conservation of Forest Birds provides a valuable reference for ecologists, ornithologists, conservation professionals, forest industry employees, and those interested in birds and nature.

Large-scale population estimates of species are used for several reasons, including the assessment and protection of important sites. However, determining a national population requires extensive surveying and using methods that allow counts to be scaled up to the number of birds actually present and across a larger area. This new BTO study looks at different methods used to estimate the population of Nightingales in the UK. Nightingales have declined by 61% in the last 25 years and therefore determining which sites contain the largest populations is vital. The study focused on 2733 2x2 km squares, 2356 where Nightingales were known to be, as well as randomly-chosen squares whose selection was stratified based on habitat suitability. By using different analytical methods, the final population was estimated to be between 5094 and 5938 territorial males, of which only 55-65% were counted during the surveys. It is therefore important to consider how to fully control for variability in detection and for birds outside of surveyed areas when estimating national populations. The study also highlighted the importance of Lodge Hill SSSI for breeding Nightingales, which was designated for its nationally important population of the species, based on the results presented in this paper.

Initial findings suggest that Lesser Black-backed Gulls in north-west England fly within wind farms, but may avoid wind turbines once there. Offshore wind farms may affect birds in many ways, such as stopping them moving between places, or restricting access to areas where they feed. Collision risk is a key concern for seabirds, yet there has been little study to date of the use of wind farms by birds from known breeding colonies. This study, led by BTO, provides a first look at the movements of Lesser Black-backed Gulls at a colony in north-west England and their interaction with five operational offshore wind farms. The birds were tracked with GPS tags which recorded location, speed and height. Out of the 24 birds tracked, 15 visited wind farms, and in total spent 1.3% of their time there. A detailed look at the movements of two birds that visited wind farms most often, showed that their flight heights were greater within wind farms than outside, particularly during the day, potentially placing them at greater risk of collision. However, within wind farms, their use of the zone swept by the rotor blades was significantly less than expected. Although preliminary, these results suggest that Lesser Black-backed Gulls at this site may not avoid wind farms, but could avoid individual wind turbines once inside the wind farms. Further work is now being conducted to verify these patterns, which will be important in improving our understanding of the likely collision risk for seabirds.