The project

In 1994 a project to monitor butterfly populations was launched, with the support of the Generalitat de Catalunya: the Catalan Butterfly Monitoring Scheme (abbreviated CBMS). Its philosophy and methodology fully coincide with the well-known British BMS from which it takes its name. Its aim is to monitor in detail the changes in the abundance of butterflies using weekly visual censuses along fixed transects in order to relate population fluctuations with different environmental factors. The use of butterflies in these projects responds to their proven bioindicator character, their popularity and charisma, and the fact that they have recently experienced widespread regressions throughout Europe.

Initially, the monitoring network consisted of 11 sampling stations located in northeast Catalonia. This number has been increasing annually and by 2023 (after the end of season number 30) 240 stations have provided data. The geographical coverage has also improved dramatically and it currently includes much of Catalonia, the Balearic Islands and Andorra. Although in this latter country there is the separate BMSAnd, the Andorran BMS monitoring program, the information it provides is integrated into the CBMS database.

Over these years, the structural aspects of the project have also improved significantly. A database closely linked to a geographical information system (GIS) has been developed to efficiently store and exploit all the information. In addition, basic information on the plant communities occurring at the study sites is regularly collected and updated for documenting environmental changes at transect level.

Why a monitoring network?

As a result of severe anthropogenic pressure and the profound and rapid transformations the environment has undergone in recent decades, animal and plant communities have experienced important changes, in many cases clearly negative. Although no one doubts that these changes are taking place, it is much more difficult to establish exactly their direction and identify the trends that affect individual species. However, there is a need for managers of protected areas to assess the suitability of measures adopted for improving biodiversity. This is one of the main aims of the so-called monitoring of bioindicator groups.

Briefly, we can say that monitoring can be used to obtain data on the abundance of an organism (or a group of organisms) over time and therefore to assess how populations fluctuate in the study area. Bioindicator taxa need to satisfy a number of conditions such as sensitivity and quick responders to environmental change, easy to identify and consisting of a wide range of species with different environmental needs and habitat preferences. The ideal bioindicator group varies depending on the type of environment studied. For example, aquatic invertebrates accurately reflect the quality of a river and have traditionally been chosen as bioindicators of riparian ecosystems. Lichens are very sensitive to air pollution and are, therefore, used in some studies as bioindicators of air quality. In terrestrial environments, apart from birds, there is a growing interest in butterflies.

Indeed, day-flying Lepidoptera (butterflies or Rhopalocera) have certain advantages that make them an excellent bioindicator group:

• They show a great sensitivity to the composition and structure of vegetation: in their larval stage they feed exclusively on a small number of host plants and when these plants disappear or become scarce, butterfly populations undergo rapid declines. It is often not even necessary for the host plant to disappear as butterflies respond to changes in microclimatic conditions or the type of management they are subject to. For example, the introduction or removal of an element such as grazing can radically change the conditions of a meadow and its accompanying butterfly fauna.
• A large number of butterfly species are highly sedentary and are severely affected by habitat fragmentation. The connection between nearby populations decreases rapidly if barriers are created or favourable habitat disappears, and this progressive isolation leads, sometimes in a very short time, to a high frequency of local extinctions.
• They are extraordinarily sensitive to climate and respond conspicuously to global warming and variations in thermo-pluviometric regimes with changes in phenology, abundance and distribution.
• They play a key role in the ecosystem, both as primary consumers (herbivores) and as a source of food for many secondary consumers (predators and parasitoids). Therefore, whatever affects butterflies will, in turn, also affect many other organisms.
• Finally, their great aesthetic value and the relative ease of identification have made butterflies a popular group of insects. Many naturalists observe them regularly and are able to reliably identify the species living in their activity areas, something completely unthinkable for other groups of invertebrates.

It is thus not surprising that butterflies have played an outstanding role in the development of monitoring techniques. In the mid-1970s, a group of researchers from the Institute of Terrestrial Ecology (England), led by E. Pollard and J.A. Thomas, developed a simple method to objectively assess changes in butterfly abundance: the Butterfly Monitoring Scheme. The technique was based on repeating visual censuses along fixed transects, and soon gained great popularity among scientists and amateurs, and was adopted as a standard method for monitoring butterflies across the country. Subsequently, many other European countries have set up comparable butterfly monitoring networks (see http://www.bc-europe.eu). In Catalonia, the BMS has become successfully consolidated since the early 1990s and is currently the longest-running biodiversity monitoring project in the country.

Conservation state of the species

Species sheets include information on their conservation status in Catalonia according to the IUCN category proposed in the Guide of Butterflies of Catalonia (Vila, Stefanescu & Sesma, 2018):

• RE (Regionally Extinct)
• CR (Critically Endangered)
• EN (Endangered)
• VU (Vulnerable)
• NT (Near Threatened)
• LC (Least Concern)
• NA (Not Evaluated)

For species in the CR and EN categories, the abundance indices and exact location of populations are not shown to guarantee their protection. These species are also hidden from the list of species appearing in a given itinerary. For any query concerning CR and EN species, please contact us by email.

Recommended references

• Vila, R., Stefanescu, C., & Sesma, J. M. 2018. Guia de les papallones diürnes de Catalunya. Lynx edicions.
• Hanski, I., 1999. Metapopulation Ecology. Oxford University Press, Oxford.
• Parmesan, C., Ryrholm, N., Stefanescu, C., Hill, J.K., Thomas, C.D., Descimon, H., Huntley, B., Kaila, L., Kullberg, J., Tammaru, T., Tennent, W.J., Thomas, J.A. & Warren, M., 1999. Poleward shifts in geographical ranges of butterfly species associated with regional warming. Nature, 399: 579-583.
• Pollard, E. & Yates, T.J., 1993. Monitoring butterflies for ecology and conservation. Chapman and Hall, London
• Stefanescu, C., Peñuelas, J. & Filella, I., 2003. Effects of climatic change on the phenology of butterflies in the northwest Mediterranean Basin. Global Change Biology, 9: 1494-1506.
• Thomas, J. A., 2005. Monitoring change in the abundance and distribution of insects using butterflies and other indicator groups. Philosophical Transactions of the Royal Society B, 360: 339-357.
• Van Swaay, C. A. M., Nowicki, P., Settele, J. & Strien, A.J., 2008. Butterfly monitoring in Europe: methods, applications and perspectives. Biodiversity and Conservation, 17: 3455–3469.