Researchers announced Tuesday that winter populations of western monarch butterflies along the California coast have rebounded for the second year in a row after a dramatic decline in 2020, but the numbers of these colorful insects are significantly lower.
Volunteers visiting locations in California and Arizona around the Thanksgiving holiday counted more than 330,000 butterflies, the highest number of these insects in six years. It was a promising rebound after fewer than 2,000 individuals were registered in the annual winter 2020 count. In 2021, 247,000 butterflies were registered.
“I think we can all celebrate it, it’s really exciting,” said Emma Pelton, a conservation biologist with the Xerces Society, an environmental nonprofit that focuses on invertebrate conservation. “Last year we were very relieved because we had about 250,000 butterflies and you see that number going up a bit this year and it’s a good sign that we have a second chance.”
Pelton said it’s not clear at this time why the butterfly population has increased, but one explanation could be that eastern monarchs, which typically winter in Mexico, may be mixing with their western counterparts.
“There may be some kind of leaking going on, but I don’t think we understand the system well enough to tell what it is,” he said. “But I guess you can’t say everything is fine or that we’ve all taken human actions that magically improve everything.”
The population is well below records from the 1980s, when monarchs numbered in the millions.
Scientists say the butterfly’s levels are critically low in the western United States due to destruction of milkweed’s habitat along its migratory route in the form of urbanization and the use of pesticides and herbicides in its region.
Along with agriculture, climate change is one of the main factors threatening the extinction of the monarch butterfly, disrupting its 4,828-kilometre (3,000 mi) annual migration that is synchronized with northern spring and the blooming of wildflowers. Is.
Western monarchs migrate northwest to California each winter, returning to the same locations and even the same trees where they congregate for the summer.
During a journey of thousands of miles, monarchs nurse several generations before reaching California, where they typically arrive in early November. They move east as soon as the warm weather arrives in March.
East of the Rocky Mountains, another population of monarchs travel thousands of miles from southern Canada and the northeastern United States to winter in central Mexico. Scientists estimate that monarch populations have declined by 80% in the eastern United States since the mid-1990s, but the decline has been most marked in the western United States.
Adult monarchs live for a few weeks, while monarchs that overwinter in groups of trees and moult in late summer and early fall may live up to nine months. When temperatures rise, monarch butterflies return to their breeding areas, where their reproductive cycle begins anew.
Western Monarch Butterfly Counts are conducted by trained volunteers over several weeks around the Thanksgiving holiday. This practice has been going on since 1997 and has registered a population loss of more than 95%, which according to previous studies, reached a few million specimens.
Overwintering sites for these insects along the central California coast have also been affected by heavy rains this year, according to a statement from the Xerces Society, and have seen volunteers separated from their groups and exposed to more cold, humidity and prey.
The group usually holds the second count after the new year. This year’s results will be released in February and will help determine the impact of winter storms on the butterflies, according to Isis Howard, an endangered species conservation biologist with the Xerx Society.
Howard explained that New Year’s follow-up counts typically show a 30% to 50% drop in butterflies from the Thanksgiving count.
“Because the storms have been so intense and so close together this year, it is logical to assume that there could be an increase in mortality this winter, leading to a smaller population starting the breeding season next spring and summer.” ”
