Monitoring butterflies in Finnish agricultural landscapes

What is the status of butterflies in Finland?

Modern agricultural practices have drastically reduced the areas of meadows and semi-natural grasslands, which are most important habitats for butterflies. Many of the Finnish butterfly species have declined respectively.

Changes in the abundances of butterfly species need to be monitored in order to focus the conservation measures to the most relevant species. In 1999 Finnish Environment Institute started to construct a butterfly monitoring network in the southern half of Finland. Between 2010-2017 this network has annually included 40-60 sites.

European collaboration in butterfly monitoring is advancing

Currently there are active butterfly monitoring schemes in over 15 European nations, all using similar methodology.  During the last few years collaboration between these national monitoring schemes has increased considerably. This co-operation has been coordinated by Butterfly Conservation Europe, and it has resulted with several European-level indicators on the current trends in butterfly diversity:

• The European Butterfly Indicator for Grassland Species: 1990-2011  (PDF; EEA report 11/2013)
• The European Butterfly Indicator for Grassland Species: 1990-2007 (PDF)
• Developing a methodology for a European Butterfly Climate Change Indicator (PDF)
• The European Butterfly Indicator for grassland species:1990-2009 (PDF)
• The European Butterfly Indicator for grassland species: 1990-2013 (PDF)
• The European Butterfly Indicator for grassland species: 1990-2015 (PDF)
• Impact of climate change on butterfly communities 1990-2009 (PDF)

Monitoring method

Butterflies are monitored with the widely used transect walking method, which was originally developed in the Great Britain by E. Pollard. Today it is also used for butterfly monitoring in several other EU-countries, such as the Netherlands, Belgium, Germany and Catalonia in Spain.

Butterflies are recorded from a 5x5 meter area ahead of the observer. The butterfly count is conducted repeatedly during the summer along the same walking route, which is also kept constant from year to year. 

In Finland the suggested mininum number of annual counts has been seven, conducted once a fortnight from late May to late August. Weekly counts are recommended, and usually done on ca. half of the transects.  However, due to our northern location the butterfly season is typically no longer than ca. 16 weeks, and in the northernmost transects less than ten weeks.

Monitoring sites

During 1999-2017 butterflies have been recorded on a total of 106 voluntary transects. Their number has varied annually between 30 and 60. Locations of the transects in 2014 are shown below. Most of the sites are concentrated to the southern half of Finland. This means that the observed population trends may not be representative for the whole country.

Trends in butterfly abundances 1999-2014

Population changes have been estimated for 51 Finnish butterfly species using the TRIM software (TRends and Indeces for Monitoring, CBS Netherlands). Monitoring results have been reported annually in the Baptria -magazine published by the Finnish Lepidopterological Society. Reports for the years 2013 and 2014 can be downloaded below (in Finnish with English abstract).

The two graphs below present some general trends derived  from the individual species indices. Annual variation in  butterfly abundances has been considerable, but so far there has been no clear trend of either increase or decrease. The last three years (2012-2014) have been quite miserable for butterflies, and 2014 scored the lowest year during the whole monitoring period.

Observed butterfly and moth species

A total of  89 butterfly species and 824 804 individuals have been recorded during the monitoring period. Moths have also been recorded along with butterflies on ca. third of the transects, with a total of 334  species and 149 887 individuals observed. All butterfly species and 50 most numerously observed moth species for 1999-2014 have been listed in the attachments below.

• Observed butterfly species in BMS Finland (1999-2014)
• 50 most numerous moth species in BMS Finland (1999-2014)

Annual reports

Below you can download two of our latest annual reports (2012 and 2013). They are in Finnish, but with an abstract in English. Figures 1-5 are similar in both reports, and their contents are described below.

• BMS Finland, annual report for the year 2012
• BMS Finland, annual report for the year 2013
• Figure 1: Location of the monitored transects.
• Figure 2: y-axis, mean temperature during counts; x-axis, calendar week.
• Figure 3: y-axis, mean density of butterflies (ind/km); x-axis, fortnightly counts from late May to late August.
• Figure 4: y-axis, geometric mean of indeces for 45 species, separately for all species (Yhteensä) and for species favouring grasslands (Niittylajit), forest edges (Reunalajit) and open field margins (Peltolajit).
• Figure 5: y-axis, number of species in each trend class (- - = strong decline, ... + + = strong increase).
• Table 2: The observed butterfly species, with columns from left to right: rank in the current and previous year; species name; total individuals; number of sites where observed; change of the TRIM index (%) compared to the previous year and the average for the previous decade.

Basic facts about the Finnish BMS

First for the year 2014, then averages for the previous decade, and last, totals for the whole period of 1999-2014.

Further information

Janne Heliola, tel. +358 400 148654, firstname.surname@syke.fi