Reduced-effort schemes for monitoring butterfly populations

TitleReduced-effort schemes for monitoring butterfly populations
Publication TypeJournal Article
Year of Publication2007
AuthorsRoy, DB, Rothery, P, Brereton, TM
JournalJournal of Applied Ecology
Date Published2007
ISBN Number1365-2664
KeywordsBiodiversity, indicators, Lepidoptera, log-linear model, statistical power, UK butterfly monitoring scheme, wider countryside
  1. Butterflies are one of the few insect groups that can be monitored effectively and have the potential to develop national and Europe-wide trends in abundance.
  2. For 20 widespread butterfly species, we assess the relative efficiency of reduced-effort schemes compared to the existing design and estimate the number of sites required to detect changes of given magnitudes over specified periods of time.
  3. A scheme restricted to three counts during July and August requires twice as many monitored sites on average to achieve comparable precision to the existing 26-week scheme in the United Kingdom. Such a scheme requires 430 monitoring sites on average to achieve 80% power (5% significance level) for detecting a 25% decline in abundance over 10 years.
  4. Such a reduced-effort scheme may also mean that volunteers are more willing to record in areas where they are likely to see only a few individuals of a few common species (such as on intensively farmed areas). This could potentially help to ensure that butterfly monitoring schemes achieve a more even geographical coverage and less of a bias towards areas rich in butterflies.
  5. Synthesis and applications. Schemes with few sampling visits per year are cost-effective for expanding butterfly monitoring across Europe, and can be applied to national monitoring programmes and lead to effective assessment of continent-wide trends in populations.