Emma Pelton & Stephanie McKnight, XERXES.ORG
During the 24th Western Monarch Thanksgiving Count, nearly 100 volunteers donned their masks and practiced social distancing to carefully survey groves of trees on the California and Northern Baja coast for monarch butterflies. Despite the challenges of conducting field work during a pandemic, volunteers surveyed 246 sites, three more sites than last year. Unfortunately, to the surprise and dismay of many, only 1,914 monarchs were counted at all the sites. This is a shocking 99.9% decline since the 1980s.
The Western Monarch Thanksgiving Count has been done every year since 1997. It happens during the three-week period centered on Thanksgiving and is coordinated by the Xerces Society and Mia Monroe. It is the primary way that the western monarch population is assessed and has built up a body of data than demonstrates the long-term collapse of the monarch migration in western North America.
Iconic and beloved monarch overwintering sites like Pismo Beach and Natural Bridges reported only a few hundred monarchs during the count. More startling, Pacific Grove, which goes by the name “Butterfly Town, USA” because of its overwintering sites, had no monarchs at all. Each of these sites normally host thousands—in some years, tens of thousands—of butterflies during the winter months, and are locations where visitors travel to experience the marvel of glittery orange monarch clusters.
We had indications that there might be a significant decline this year. In 2017, when monarch populations were still in the hundreds of thousands, researchers used Thanksgiving Count data to develop a population viability analysis and posited that the extinction threshold for the western monarch migratory population was 30,000 butterflies. It seems that, unfortunately, this prediction was right. The 30,000-butterfly threshold was reached during the last two years (2018 and 2019), and the population has crashed further this year. We may be witnessing the collapse of the western migration of monarch butterflies. A migration of millions of monarchs reduced to two thousand in a few decades.
The decline of the monarch isn’t just happening in the West. During the spring and summer, monarchs reach towns, cities, and rural areas across the Lower 48, making it probably the country’s most widely recognized butterfly. However, sightings are not as common as they once were. The eastern migratory population has also declined by more than 80% since monitoring began in the 1990s.