In the absence of a month for spring to arrive, Rob Wilson restarted a routine that has been doing since 2018: the last weekend of February he went to the countryside from Colmenar Viejo (Madrid), where he lives. Since then and until the end of summer, sometimes alone, sometimes replaced by his colleague Juan Pablo Cancela, he always takes a walk, always the same, from the nearby stream to the mountain, looking for butterflies. The enough years have not passed for their impression to have scientific validity, but every time he sees less. Of the rarest species, not even that. Its impression is a global trend. In the rest of Spain, in Europe, in the United States, where there are reliable data, the landscape is the same :.
“The easiest thing is to choose a place near your home. I have one in Colmenar Viejo, ”says Wilson entomologist at. “You go to that same place between March and September every week. And you travel a route between one kilometer and two kilometers with an imaginary box of two and a half meters on each side and five meters in front of you. Basically, you are taking note of all the butterflies that enter your imaginary box. That is what is called a transect, ”says Wilson. Cancela, also entomologist at the MNCN, follows the explanation: “Many species are easy to identify while flying, but some are more complicated. For them, we carry a hunting, we have a permission from the Community of Madrid, and if there is any difficult species to identify, we capture it, identify it and release it. ” This is how they estimate the abundance of lepidoptera in Colmenar and in the rest of the world. “To see trends we need more years, but in these eight, the species that were abundant, are no longer and others that were rare at first, we no longer see them,” says the British ecologist of Colmenar Viejo.
In the United States, dozens of scientists such as Wilson and Cancela, more hundreds of volunteers have been doing the same since the beginning of the century. The results of their walks with their imaginary boxes have just published them today in and are dramatic: for the 342 species that had statistically significant data, the US landscape has lost 22% of its butterflies since 2000. For 107 species, the casualties exceeded half of its troops. The losses are occurring in all latitudes and bioclimates, but are more pronounced in the southern regions, the most affected by heat and droughts fueled by. This connection is confirmed by the few species that have prospered (only 3% grow significantly). Two thirds of those that have grown in number have their main geographical range in Mexico.
The biologist at the Washington State University (United States), Washington State University, is the first author of this huge work. They have supported 76,957 transects in almost 2,500 sites in which 12.6 million butterflies of 554 species were counted. “Many of those that are increasing are mainly in Mexico and/or Central America,” he recalls and adds: “This coincides with our finding that butterflies species tended to prosper at the north ends of their distribution limits, something we would expect to see in the northern hemisphere in a warmer climate.” That is, they are subtropical species that conquer the north.
The decline seen in the United States is even worse in Europe. Where there are temporary series, the longer, the butterflies has gone worse. Since 1992, in Belgium, one third of their species have become extinct and the populations of the rest have diminished by 30%. In the United Kingdom, with a long tradition of lepidopterologists, since 1976 8% of its species and the. But it is the Netherlands that anticipate a world without butterflies. In the country of Tulipanes, a work published in 2019 used the archives of the Museums of Natural Sciences to estimate the abundance of these animals since 1890. Their conclusion, reinforced by counts in the most recent decades, is that. The three Atlantic countries have in common the triad of traditional enemies of butterflies: densities of very high human populations, that is to say, the very high rate of urbanization that has reduced its habitat, an intensification of agriculture, whose monocultures do not help the diversity of species, and the use and abuse of pesticides. To these threats have joined new such as climate change and.
The Spanish Cristina González, from the Institute for the Conservation of butterflies from the Netherlands, also leads the project. “In the west, the main cause of the decline has been the intensification of agriculture, in other areas, such as the east European, it is the abandonment of traditional agriculture and livestock, which is scrubbing The open areas, ”he says. Its organization is responsible for the so -called Prairie butterflies indicator, an index that the European Commission uses to know the state of biodiversity, in this case of insects. His latest data shows that Lepidoptera populations have been reduced by 32% in the Union and up to 36% in Europe as a whole. “For Spain we only have data for the last 10 years, which is not enough to see trends. We do not know of its state in the 70s or 80s of the last century, ”explains the ecologist. In Catalonia they do have more back data.
Constantí Stefanescu, Ecologist at Creaf, has been studying butterflies in Catiples in Catiples in Mediterranean and states that their results are similar to those obtained in the United States. “In these 30 years, the population has decreased between 30 and 40%,” says the researcher at the Museum of Natural Sciences of Granollers and responsible for the Catalan butterfly monitoring scheme (BMS), there are BMS throughout Europe and everyone has butterflies such as Rob Wilson in Colmenar Viejo. But in Catalonia they have been studying evolution systematically since 1994. “Among the prairie species, there are species that have lost half of their troops. Among the forest, some have won, but the average is a loss of 20%, ”adds Stefanescu.
With fewer years of study, the thing is worse in the Cantabrian mountain range. Amparo Mora, researcher at the Picos National Park in Europe, the first protected space in Spain, adds to traditional threats one that might seem contradictory: “The abandonment of the countryside makes the medium closing. This rewilding [renaturalización] It is harming biodiversity, ”he says. The vast majority of butterflies are of meadow, up to 90%, and need, like most insects, open spaces full of flowers. But the lack of large herbivores, whether wild or livestock, is making them close. Mora has been doing transects in the Cantabrian Park for nine years. There they fly or flew 137 species, 60% of those in the Iberian Peninsula. But at this time, “abundance has collapsed by 45%; You have to wait another five or ten years, but the numbers are saying something, ”says the researcher.
In the southern end, in Sierra Nevada, more than half of the Iberian species also fly. There they are also telling them, but the period is still too short to know their future. José Miguel Barea’s doctoral thesis, which has been studying the Lepidoptera of the Penibetics, showed unequal results. Of the 125 documented species, 13% are increasing their population significantly, while another 19% are diminishing it. Another 8% remain stable. But there is 60% for which the trend is “uncertain.” Here, climate change is causing a double process: on the one hand, the most general butterflies are replacing specialists who depend on very specific microhabitats, on the other, every year they see the same species above. In this they follow an universal law of adaptation: migrate to the north or (in the case of the mountains) or (in the seas).
Yolanda Melero and her colleague Pau Colom, both of Creaf, just published a job that points the same thing they have seen in the mountains, but in. Melero leads a project that is studying the situation of urban butterflies. His work is carried out in parks and green areas of Madrid and Barcelona, such as La Casa de Campo or Montjuich. But what interests them is to know the interaction between threats, in this case urbanization and climate change. “We have observed, in general, that the most specialist species, species with less dispersion capacity have it worse,” says the researcher. For its part, Colom acknowledges that there are some species that “can even be seen beneficiaries, such as the thermophilites, which are colonizing cold sites, which could not live.” But he adds: “When you look at the trends for the whole of the butterflies community in a site, most species go down.” In addition, the city’s island effect could turn them into even more inhospitable places.
Miguel López Munguara, from the Biodiversity Research Center and Global Change of the Autonomous University of Madrid, was the thesis director of Barea and his butterflies of Sierra Nevada. He has been studying them for more than 40 years. He was one of those responsible for the group of specialists who developed the Atlas of the Day butterflies of the Iberian Peninsula and Balearic Islands of 2004. They are already giving him, which may come out next year. “Between 2004 and 2025 we have not lost any species, but we will lose them,” “But we are losing many populations in many places,” he adds. In the face of the future, he believes that “a cataclysm awaits them if nothing is done.” And they are too fragile for such a powerful enemy. “Climate change has joined changes in land use, where the intensification of agriculture has occurred, with its pesticides, which is bad, or the abandonment of agriculture, which is also harmful to animals that need open spaces.”
