[ad_1]
this New discovery This suggests that changes in migratory habitat are unlikely to be the primary cause of population declines and that monarchs still have good migratory habitat, especially in Mexico.
The study used data and expertise from the United States and Mexico to help paint a picture of habitat changes throughout the life cycle of the eastern migratory monarch butterfly population.
“This is an important example of international scientific collaboration,” Jay Diffendorfer, research ecologist at the U.S. Geological Survey and lead author.
Monarch butterflies are known for their impressive annual migration. Not all monarchs migrate, but for those that do, the journey can be as long as 3,000 miles, a long distance for an insect that weighs only half a gram. Each spring, the eastern migratory population of monarchs flies north from their overwintering grounds in central Mexico to mate and lay eggs on milkweed in Texas, then die. Subsequent generations of monarchs migrate to the central and eastern United States and southern Canada and continue to reproduce. In the fall, the last generation of monarchs gives up breeding and flies south to their overwintering grounds in Mexico, passing through Texas, completing the annual cycle.
Monarch butterfly populations in their overwintering habitat in Mexico have declined dramatically since the 1990s, with last winter recording the second-lowest number in an annual survey led by the World Wildlife Fund.
Diefendorfer was in Mexico when the latest monarch population counts were released, and his field observations reflect the latest data.
“It was really shocking to be there — you’re in a beautiful fir forest at 10,000 feet — and there were almost no monarchs,” he said. “It was pretty sobering, to say the least.”
The wintering population has dropped sharply Connected Milkweed disappeared from the Midwestern United States due to the rapid introduction of herbicide-tolerant genetically modified corn and soybeans. The accompanying use of glyphosate herbicides has largely eliminated milkweed in and around Midwestern farmlands.
However, there is still disagreement about the cause of the monarch butterfly’s decline, with some scientists suggesting that fewer monarchs are surviving the long fall migration to Mexico. While the loss of milkweed and other changes to the monarchs’ summer breeding habitat have been Researched Widelyfew studies have examined how land use and land cover changes affect milkweed and nectar availability in migratory habitats in Mexico and Texas.
The researchers found few major changes in migratory habitat from 2001 to 2020, with an estimated 2.9% decline in milkweed in Texas and almost no change in Mexico. Fall and spring nectar resources declined by less than 1% in both regions. Overall, they found that monarch habitat in Mexico and Texas appears to be relatively intact compared to monarch habitat in agricultural areas of the Midwestern United States.
These findings suggest that habitat loss in the migration region studied is unlikely to be the primary cause of monarch declines, weakening support for the idea that monarchs are unable to survive their fall migration.
“If there had been a large-scale change like what we’re seeing in the Midwest, we would have picked it up,” Diefendorfer said. “The hypothesis that losses are occurring during migration may still be true, but it’s not because of the type of habitat changes we measured.”
Despite this year’s low numbers, the study highlights how much intact monarch habitat remains in Mexico and Texas.
“This study provides foundational information for strengthening conservation actions from the Mexican perspective.” Víctor Sánchez-Cordero, a professor at the Institute of Biology at the National Autonomous University of Mexico and co-author of the study, said“This justifies the idea of expanding conservation efforts along the Mexican monarch flyway, where land use has remained virtually unchanged for decades. For example, a network of protected areas could connect enacted protected areas with newly identified priority areas to protect the Mexican monarch migratory corridor during fall and spring migration.”
this study It was published in Nature Scientific Reports on March 20.
# # #
The U.S. Geological Survey provides scientific data for a changing world. For more information, visit United States Geological Survey Or follow us on Facebook @USGeologicalSurveyYoutube @U.S. Geological SurveyInstagram @U.S. Geological Surveyor Twitter @U.S. Geological Survey.
[ad_2]
Source link
