Habitat quality, urbanisation & pesticides influence bird abundance and richness in gardens.

Gardens are regularly portrayed as green oases, refuges for wildlife that has been displaced from the countryside by intensive farming practices which have reduced habitat availability. Pesticides are also commonly used in urban areas, but few studies have investigated their impacts. In this study, we explored how bird richness and abundance in gardens across the UK are influenced by habitat quality, urbanisation level and pesticide practices. To achieve this, we collaborated with the British Trust for Ornithology (BTO) which runs Garden Birdwatch, a citizen-science-based garden bird recording scheme. Participants in the study were asked to complete a questionnaire about their pesticide practice. From the 615 gardens that provided useful data, we found that 32.2 % applied pesticides in their gardens and that glyphosate comprised 53.3 % of these applications. We found that bird abundance and species richness was lower in suburban compared to rural gardens but positively influenced by measures of garden quality and by surrounding habitat quality. We show that there was an interaction between the habitat quality of the surrounding area and pesticide use: negative effects of pesticides on species richness were more pronounced in gardens in areas of high habitat quality compared to those surrounded by poor habitat. We found that pesticide use, and particularly glyphosate and metaldehyde, negatively predicted the abundance of house sparrows, a fast-declining bird species. The average house sparrow abundance was 12.1 % lower in gardens applying any pesticide, 24.9 % lower with glyphosate, and 38.6 % lower with metaldehyde. Overall, our study shows that garden bird abundance and richness is strongly influenced by both extrinsic and intrinsic factors, and suggests that garden management, particularly regarding pesticide use, has a significant effect on bird life.