@article{236,
  keywords = {Lepidoptera, Biodiversity, indicators, log-linear model, statistical power, UK butterfly monitoring scheme, wider countryside},
  author = {Roy D. B. and Rothery Peter and Brereton Tom M.},
  title = {Reduced-effort schemes for monitoring butterfly populations},
  abstract = {<ol>
	<li>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.</li>
	<li>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.</li>
	<li>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.</li>
	<li>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.</li>
	<li>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.</li>
</ol>
},
  year = {2007},
  journal = {Journal of Applied Ecology},
  volume = {44},
  pages = {993-1000},
  month = {2007},
  isbn = {1365-2664},
  doi = {10.1111/j.1365-2664.2007.01340.x},
  language = {en},
}