Butterfly monitoring

Aims of BMS Finland

The monitoring scheme aims to produce annual estimates on the population changes of the more common Finnish butterfly species. In addition to this, the records can be analyzed to provide new insights on the ecology of our butterfly species, and to illustrate the effects of climate change on our nature.

BMS Finland has been running since 1999, making it the fourth oldest BMS in Europe. The work of voluntary recorders has been coordinated by the Finnish Environment Institute. The yearly number of monitoring sites has varied between 30 and 60, with an average of around 50. Over the years, recording has been done on a total of around 130 monitoring sites by almost as many voluntary recorders. 

The monitoring method

Butterfly records are collected using the widely known and recognized transect counting method. This means that on each monitoring site the butterflies are recorded by walking along a fixed route of around 1-3 kilometers, depending on the recorder's prefences. This walking route is kept the same on each count, as well as on successive years. Further on this route is divided into 5-20 sub-routes (sections), on which the numbers of all observed species are recorded separately. These sections are defined on the basis of varying habitats along the transect (a meadow patch, followed by a road verge etc.).

Butterflies are recorded from the transect with regular time intervals from late May to late August - preferably once every week, but at least twice a month. Butterflies are only recorded from a fixed area of 5x5x5 meters ahead of the recorder. After the counts, the volunteers should register their records into the online data service Laji.fi .

Results of monitoring

BMS Finland provides each year an estimate on the population change of our 51 most common butterfly species. In addition to these species indeces, we produce three composite indeces which provide more generalized information on the development of Finland's butterfly fauna:

• Generalized index on the average population change of our 45 most common resident butterfly species
• Total abundance of butterflies (all species combined), and
• Community Temperature Index (CTI) for the Finnish butterflies, reflecting the effects of climate change on our butterfly assemblages.

All results are reported annually in the Finnish Lepidopterologists' Society's Baptria -magazine (in Finnish, with an English abstract). In addition to this, two wider reports have been published presenting the results from the periods of 1999-2008 and 1999-2021 (in Finnish, with English abstracts). These wider reports can be downloaded from below.

Instructions and field sheets

Below you can download all the essential guidance documents and field sheets (for printing) that you'll need to participate in the monitoring. These documents are only available in Finnish. 

Annual reports and the two wider reports

All our annual reports are available below, archived into two larger documents including over ten annual reports each (each of them with an English abstract). The two published wider reports for the years 1999-2008 and 1999-2021 can be downloaded from here:

• Maatalousympäristön päiväperhosseuranta 1999-2008 (Helda; in Finnish)
• Maatalousympäristön päiväperhosseuranta 1999-2021 (Helda; in Finnish)

Join in!

All butterfly-enthusiasts with relatively good Finnish skills are welcome to join in as recorders for BMS Finland. For more information and assistance also in English, contact our main coordinator (see below).

Further information

Coordinator of BMS Finland: Janne Heliölä, Finnish Environment Institute, tel. +358-40 0148 654, firstname.lastname@syke.fi.