Trends in butterfly populations in UK gardens—New evidence from citizen science monitoring

• Published in: Insect conservation and diversity Vol. 17; no. 2; pp. 345 - 357
• Main Authors: Plummer, Kate E., Dadam, Daria, Brereton, Tom, Dennis, Emily B., Massimino, Dario, Risely, Kate, Siriwardena, Gavin M., Toms, Mike P.
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01.03.2024; Wiley Subscription Services, Inc
• Subjects: biodiversity; Butterflies & moths; gardens; Gardens & gardening; insect declines; invertebrates; Lepidoptera; Migratory species; population trends; Refugia; Statistical analysis; Trends; urban; wildlife monitoring; United Kingdom > UK
• ISSN: 1752-458X; 1752-4598
• DOI: 10.1111/icad.12645

Private gardens are recognised as potentially important refugia for butterflies. Yet little is known about how gardens might be contributing to butterfly conservation, as their restricted accessibility has meant that garden habitats are not well‐represented in traditional monitoring schemes. Garden BirdWatch (GBW) is the UK's largest structured bird survey, comprising over 25 years of weekly bird counts from more than 14,000 gardens, predominantly occupying suburban and rural locations. Since 2007, a subset of GBW participants have additionally recorded the weekly abundances of butterflies. Using data for 14 seasons (2007–2020) from 7971 gardens with consistent butterfly monitoring, we present the first garden‐specific, national trends for 22 widespread butterfly species (37% of all UK butterflies). Half of the species investigated increased significantly in abundance in gardens between 2007 and 2020. Conversely, only one species, Wall (Lasiommata megera), showed a marginal reduction, though this change was not statistically significant. A strong, positive association between these new, habitat‐focused trends and those for UK butterflies more broadly, previously reported by the UK Butterfly Monitoring Scheme (UKBMS), indicates that patterns of abundance in gardens are largely a reflection of the changes that are occurring nationally. However, butterflies do appear to be faring better in gardens compared to the wider landscape. Averaging trends across non‐migratory species revealed that GBW recorded significantly greater increases over time than UKBMS. Effective monitoring of butterflies in gardens can produce reliable and informative population trends, and it provides important evidence of the significant role gardens play in sustaining butterfly populations. We present abundance trends for 22 butterfly trends in UK gardens from 2007 to 2020, based on newly analysed data collected through the BTO Garden BirdWatch survey. Eleven species showed moderate to strong, statistically significant increases over time. In addition, non‐migrant species showed significantly larger increases in gardens, on average, compared to in countryside habitats. These findings show that commonly occurring butterflies have found a haven in gardens, signalling an opportunity for gardeners to contribute to their conservation through positive actions that enhance garden habitats.