The results of my study show a great crash of the population of the large blue as an effect of the drought. This can be seen in the maps below. The marked squares are the hectares that has been part of the survey all four years. Yellow squares indicate that butterflies has been found there, and blue squares are empty of individuals. As you can see, the number of occupied squares differ greatly between 2018 and 2019. This is most likely an effect of the drought in 2018. The dots indicate butterflies outside of the continuously searched areas.
When all of the GPS points were analysed, they showed that individuals of P. arion has been using different parts of the area different years. My results show that they spent more time in areas with higher tree and bush cover in 2018, but in 2020 they spent more time in areas with higher Ground moisture (See pictures a-c).
The habitat choice for 75 individual P. arion gave four significant results. The probability of finding a P. arion decreased with overall cover of bushes and trees. Higher nectar quantity significantly increased the probability of finding a P. arion. There was a significant higher probability of finding P. arion in areas sheltered by woody vegetation below three meters in the north-east direction at the same time as the cover of woody vegetation below three meters was low in south-west direction. So this result shows that they prefer an open flower rich area with some clustered bushes to give protection from wind.
When i compared areas where Phengaris arion survived all years I focused on the squares where they survived the drought. What we can see in these areas is that they had a much higher ground moisture and tree cover than the other areas. This indicates that individuals survived because there were areas that had a higher ground moisture index than individuals normally use. Bush cover was approximately the same, or at least no big differences can be seen. For the cover of T. serpyllum the cover was actually lower in areas where individuals survived the drought. This is probably an indication that the areas where they survived the drought are not optimal for their survival, but are a good option during a shorter period, such as a seasonal drought (see box plots below).
