Conclusions
♦ Important using flexible dates when monitoring. . ♦ Repeted visits to the same site over the season necessary. . ♦ No effect of wind speed. . ♦ When overall cloudiness > 50 %, it should be at least 22 °C. . ♦ When proportion of count carried out in sunshine < 80 %, it should be at least 19 °C. . ♦ Transect counts should be performed ~ 8.30 - 17. . ♦ No inter-observer differences. . ♦ Power analysis showed that a 20 % change in species richness could be detected when using power 0.8, α 0.05 % and a sample size of 5.

Monitoring of butterflies in semi-natural grasslands – phenology, daily variation and weather effects
Linnea Wikström
Final Thesis International Master Programme Applied Biology 2006

Acknowledgements I would like to thank my supervisors Karl-Olof Bergman and Per Milberg for all their support and encouragement during this study. I am also very grateful to Stiftelsen Oscar och Lilli Lamms Minne who have supported this work financially, and to all landowners who kindly have let me work on their property. Last but not least I would like to thank Dennis Jonason, Martin Planthaber, Joakim Sandell and Victor Johansson for their participation in the inter-observer study.

For more information please contact: Linnea Wikström linvi186@gmail.com +46706194379 Or visit my homepag: http://cms.ifm.liu.se/biology/master_ projects/2007/linvi186/

Background
Declining populations The abundances of many butterfly species have declined rapidly during the last decades as a result of habitat loss and fragmentation caused by changes in land use and agricultural intensification. Since many butterfly species are sensitive to changes in the local habitat quality and show rapid response to environmental change they can be used as indicators when looking at habitat status, biodiversity and climate change. This, in addition with their importance as pollinators and the well known natural histories of many species make them especially appropriate for monitoring activities.
Monitoring methods The development of accurate, repeatable and cost-effective methods is crucial when monitoring butterfly diversity and changes in abundances. The line transect method (Pollard 1977) is widely used in butterfly monitoring, and it states criteria which should be followed in order to provide a degree of uniformity. However, many of these criteria have not been thoroughly tested.
Aim The aim of my study was to investigate inter-observer differences, variations within a day and variations due to weather conditions in recorded butterfly species richness and abundances using the line transect method. The phenology of butterflies during the season was also investigated and power analysis carried out.

Results
Phenology The study highlights the importance of using flexible dates when monitoring, since emergency dates and flight periods may be affected by variation in the weather. Ideally, monitoring should be performed at points in the season that are phenologically as similar as possible between years. Since the phenology differ between butterfly species, repeated visits to the same site during the season were shown to be essential when the aim is to investigate the entire species richness. If five visits were made to the same site during a season, 85 % of the total number of species was found on average.
Impacts of weather The activity of butterflies is to a high extent limited by temperature since most butterflies require a high and restricted range of body temperature in order to fly. Cloudiness has been shown to affect counts, and to inhibit flight activity of some butterfly species. My study shows the effects of cloudiness on two levels, the overall cloudiness of the sky and the proportion of time during transect walk made in sunshine. The number of butterflies showed a drastic fall when the cloudiness exceeded 50 % unless the temperature was at least 22 °C. During the actual time for recording, there was a sharp decline in butterflies at temperatures below 19 °C if the proportion of sunshine was below 80 %. No effect of wind speed, up to five on the Beaufort scale, on observed numbers of butterflies was found.

Variation within a day The findings of my study show that the number of observed individuals of a species might fluctuate greatly over the course of the day, and that there can be large differences in daily rhythms of flight activity between species. In order to counter some of the influence of these differing activity profiles, monitoring is recommended to start after 08.30, and be finished before 17.
Inter-observer differences No significant differences in the number of recorded butterfly species and individuals, between different observers were found, even though one of the observers had considerable more experience than the others. This strengthens previous suggestions that results from different observers can be used without problems of observer bias (Pollard 1977).
Detecting changes Power analysis were done using estimates of SD for species richness and abundances, to appreciate the number of sites needed to detect an average change estimated at two points in time. A change in species richness with about 20 % could be detected when using power 0.8, α 0.05 % and a sample size of five. However, this data must be interpreted with care, since power analysis based on data from other sites and longer time periods, including between season variations, are likely to produce larger minimal detectable differences. Reference: Pollard E (1977) A method for assessing changes in the abundance of butterflies. Biological Conservation 12, 115-134.