Chaffinch Appeal

In just eleven years from 2007–2018, the UK Chaffinch population fell by a staggering 30%. This appeal helped us make the best use of BTO’s data resources and investigate the causes of the decline, enabling us to inform conservation solutions.

Please note that this appeal is now closed to donations. If you’d like to support our work, you can donate to a current appeal >

Summary

Research funded by this appeal included analysis of Garden BirdWatch trends, and integrated population modelling that combined BTO’s bird abundance and demographic datasets.
Our work suggests that the disease trichomonosis is likely responsible for Chaffinch declines, and conservation solutions for Chaffinches may lie in managing disease transmission risks.
Our research also showed that guidelines for feeding wildlife should include disease mitigation strategies, to ensure that the benefits to target species outweigh the risks of disease transmission.

Why we launched the Chaffinch Appeal

This appeal, launched in 2020, was inspired by a marked decline in Chaffinch populations – in just 11 years from 2007–2018, the UK Chaffinch population fell by a staggering 30%. We suspected these declines were driven by the disease trichomonosis, which is thought to have caused a similar decline previously in Greenfinches.

We wanted to make the best use of BTO’s data resources to properly investigate the causes of the decline, so we could inform conservation solutions and help restore Chaffinch populations.

Findings of the Chaffinch Appeal research project

In the first strand of our research, we used Garden BirdWatch data to illustrate long-term trends in garden birds for spring and winter numbers, adapting data processing and analysis approaches used in other monitoring schemes. This required novel approaches to extract data so that we could consistently describe populations in different seasons. In particular, for the Chaffinch trichomonosis case, we wanted to learn whether variations in trends between regions, and differences between those for different species susceptible to the disease, suggest that the declines are indeed caused by the disease.

This research approach could be applied to a wide range of ecological questions, and one of the purposes of this project was to enable such studies in the future. Work on this part of the project is now being finalised to complete a scientific paper for publication.

Our second strand of research showed that both Chaffinch and Greenfinch declines were driven primarily by reduced adult survival, with the greatest reductions occurring in areas around human habitation, where supplementary food provision is common. Examinations of dead adult birds, conducted by Garden Wildlife Health, showed a proportional increase in Chaffinch trichomonosis cases around the same time as the population decline. Our results support the hypothesis that supplementary feeding can increase parasite transmission frequency within and between common species.