Butterflies, as many other insects, are suffering a decline in their populations and a lost in their habitats. It is necessary to have a proper monitoring of the different species in order to know the real causes of their decline and act to restore the situation.
The initial method to assess the butterfly decline was recording the area of distribution and the changes over time. It is important to know perfectly the butterfly distribution and recording the presence of different butterfly species the distribution could be quite accurate. However the population information, what is happening with the number of individuals, is missing. The first signals of butterflies decline are showed in their abundances before they disappear from an area.
Therefore, it is better to count abundances of butterflies and with that information calculate the population trends.
Butterflies can be monitored by anyone who has the time and is familiar with the butterfly species at the place where the counts have to be made. In this page, diverse methods of butterfly monitoring schemes are explained to count their abundances.
Transect Counts - Pollard Walks
A transect is a fixed route (walk) established at a site where butterflies are recorded, weekly, over a number of years following some basic rules. The majority of transects are chosen by the walker and they decide which route to choose. Some schemes provide advice about areas to record to get even coverage of land cover/ habitat types as well as ensuring that a good range of the species present in a country are sufficiently monitored.
You can do the counts as part of a team: it is more fun to share experiences of what you saw and you can replace each other during holidays. There is just a few rules to follow for doing a transect:
- Transects are typically about 1km long and divided into sections that correspond to different habitat areas.
- Butterflies are counted when they are flying, flight period of butterflies. Depending on the country and the region, the flight period of butterflies will be longer or shorter.
- The transect is ideally walked every week during the butterfly season. If it is not possible, count as often as possible, every two weeks or 10 days. Don't leave more than 3 weeks between one visit and another.
- Count butterfly adults in an imaginary box of 2.4m to each side, 5m high and 5m ahead.
- The visits should be done with good weather: sunny and warm, with no rain and not too windy.
This type of monitoring is used to obtain butterfly abundances and it has been used for monitoring rare species and butterflies with specific behaviors. This method is basically based on monitoring in an specific area for a determine minutes, for example 15 minutes.
Keeping the same time in areas with similar extension, it will produce standardised results which you can obtain butterfly abundances. This method is used for the butterflies Mellicta athalia and Argynnis adippe in the United Kingdom.
There are species which are difficult to see adult flying and it requires to count the eggs being more effective. Typical examples are Phengaris (Maculinea) alcon and Thecla betulae. Normally the counts are done during the winter, looking for the eggs in the host plants. It is essential that the area is indicated by coordinates.
If you want to have more information of these methodologies, you could find it in the Manual for Butterfly Monitoring and in the Butterfly Transect Counts Manual. There are many other methodologies used for butterfly monitoring based on the purpose of the research and required results. For studies on specific species or populations is necessary more precise and complex methods. Check the list of references to find more information and other techniques use in butterfly monitoring.