The BirdTrends 2020 report is a one-stop shop for authoritative information about the population status of the common breeding birds of the wider UK countryside. The report is based on data gathered by the many thousands of volunteers who contribute to BTO-led surveys.

Population estimates of birds have a wide range of practical conservation uses, as well as being of enduring interest to many birdwatchers. Following previous reports by the Avian Population Estimates Panel (APEP), in 1997 and 2006, we present the third collation of population estimates of birds in Great Britain and the United Kingdom. This report follows previous reports by the Avian Population Estimates Panel (APEP), in 1997 and 2006. There are now thought to be about 84 million breeding pairs of birds in the UK. The ten commonest species contribute 57% of this total, with Wren Troglodytes troglodytes alone providing one in ten of our breeding birds. In all, 23 species exceed one million breeding pairs. The individual population estimates come from a wide variety of sources, many from extrapolation of previous estimates by recognised trend measures, others from new surveys and novel analytical approaches developed since the last report. Despite the exceptional level of detail available for some species, many gaps in our knowledge remain. Recommendations are made to allow a continuing improvement in our understanding of the numbers of birds in GB and the UK. There are many opportunities for volunteer and amateur birdwatchers to make a significant contribution.

Although many of us provide food for garden birds, especially in winter, we are still only in the early stages of understanding exactly how this affects wild bird populations. One possibility is that winter food enhances birds’ ability to invest in future reproduction. However, it is likely that the type of nutrients a bird receives from supplementary food will be an important factor in determining whether this is the case. A new study by scientists at the University of Exeter, in collaboration with the BTO and the University of Turin, has shown exactly that. In a three year study of woodland Blue Tit populations, researchers examined the consequences of providing different winter food supplements for egg production. Their results showed that provisioning with fat alone resulted in smaller relative yolk mass, and reduced yolk carotenoid concentrations in early breeders. This suggests that females which utilised a fat-rich diet in winter were less able to acquire some of the important resources needed to form yolk during egg production. However, the addition of vitamin E to the fat mitigated the negative effects of a fat-rich diet. It is thought that this may be because, as an antioxidant, vitamin E provides protection against oxidative damage which could result from increased metabolism after eating fatty foods. These findings suggest that birds require a balanced diet, much like we do, to aid their reproduction, and it underlines the importance of considering the nutritional value of provisioned foods. This study highlights that much more research is needed to fully understand the impacts of winter feeding, in particular how it affects individual survival.