This year marks the sixth continuous loss in the past seven years for the Monarch butterflies, since monitoring of the insects began 20 years ago.
The brightly coloured orange and black species, which spend their winter clustered around trees in central Mexico, were dramatically smaller in number this season, according to the annual census of insects released this week.
Scientists believe the pattern is part of a long-term downward trend, threatening the extraordinary annual migration phenomenon that sees the butterflies travel back and forth between their Mexican winter sanctuary and their feeding and breeding grounds across the United States and Canada – a process that takes place over the course of several generations.
There is now only one-fifteenth as many butterflies as there were in 1997 and the decline is of such magnitude that it can no longer be disregarded simply as seasonal or yearly changes, experts warned.
Though, they differ on the probable causes of the dramatic decline.
“Extreme climate fluctuations in the spring and summer in the United States and Canada, affect the survival and reproductive ability of the adults,” said Omar Vidal, director in Mexico of the World Wildlife Fund (WWF) – which carries out the annual census of insects in collaboration with the Mexican government.
The WWF believes the destruction of milkweed, the monarch’s main source of food, through the use of herbicides as well as climate change and extreme weather patterns, had contributed greatly to the dramatic decline.
Fingers have also been pointed at rampant and illegal small-scale logging in the reserve Mexican fir forests. Established for the winter refuge of the butterflies, logging of these forests is also partly to blame. Logging has been found to affect the overall temperatures, humidity and amount of direct sunlight exposure to butterflies, which can be fatal for them.
However, the experts and scientists do agree on one thing: when it comes to the alarming decline in the Monarch butterfly population, it is the shared responsibility of all three countries – Mexico, the United States and Canada – to address the problem and the activities that are contributing to this great environmental loss.