Tag Archives: World Wildlife Fund Mexico

EASTERN MONARCH POPULATION COUNT DOWN FOR OVERWINTERING BUTTERFLIES 2022-2O23

Leave a reply

The presence of the Eastern Monarch population in Mexico’s transvolcanic mountain forests was 22 percent less this winter compared to last winter, according to the World Wildlife Fund (WWF) annual count.

Rather than counting individual butterflies, the Monarchs are counted by the number of hectares they occupy. This past winter, the Monarchs occupied 2.21 hectares, down from 2.84 hectares in 2021-2022. A hectare is approximately 2.47 acres. A threshold of at least 6 hectares is recommended to sustain the eastern population.

 

For more precise information on how the Monarchs are counted read more from Monarch Joint Venture –

Estimating the Number of Overwintering Monarchs in Mexico

Contributors: Gail Morris, Karen Oberhauser, Lincoln Brower

Every year we anxiously await news of the monarch overwintering population count from Mexico. When are they done and how are the monarchs counted?

Monarchs go through four phases while overwintering in Mexico: their arrival, the establishment of an overwintering colony, colony movement and finally the spring dispersal.

The first fall migrating monarchs usually arrive at the overwintering sites in late October through mid-November. In this early phase, the monarchs are largely scattered and diffuse in their flight, moving frequently through an area and eventually creating small clusters at night, while still continuing to move through the forest. During the day, their movement is common and widespread, as they search for the perfect sheltered location to spend the winter.

As temperatures dip colder, monarchs begin to form larger and denser clusters, settling into smaller and protected areas at elevations of 2900-3300 meters (9,500 to 10,800 feet.) This usually occurs from mid-December through early February and the monarchs principally roost in oyamel trees although they use pines and other trees as well. This is the coldest time of the year where monarchs are most compact and stationary in their clusters, a time of winter survival with little movement.

By mid-February, temperatures are gradually climbing and the monarchs begin expanding their clusters. They slowly begin to move down the mountain on warm, sunny days searching for water to drink in nearby creeks. They return to the safety of the nearby forest as temperatures drop. The final phase is the monarch dispersal as the population gradually begins its movement north.

The traditional time of the annual overwintering count in Mexico is in late December when the clusters are most compact and movement is minimal. So how are the estimates done? How do you estimate how many monarchs there are in an area?

The World Wildlife Fund and the MBBR have measured the monarch population each year since the winter of 2004-2005. The occupied trees are mapped in each colony. Beginning with the highest tree in the periphery, the counters use a measuring tape or distance meter and compass to measure the perimeter using a series of lines connecting trees along the boundary. The enclosed area is then calculated in hectares.

Researchers have estimated that there are approximately 21.1 million butterflies per hectare, although this number most certainly varies with the time of the winter as the colonies contract, expand, and move. It also varies with the density and size of the trees in the colony. Based on this estimate the largest population of monarchs occurred in 1996-1997 when the colonies covered over 18 hectares and contained an estimated 380 million butterflies. To date the lowest population recorded was in 2013-2014 with 0.67 hectares and approximately 14 million monarchs.

While population estimates are recorded back to the winter of 1976-1977, long term counts of monarchs previously occupying the overwintering sites for comparison are limited due to a lack of complete data.

Keep in mind that the monarch overwintering estimates in Mexico are done when the monarchs are most compact in the trees. While counts continue biweekly during the time the monarchs are in the area, the end of December counts are used for comparison from year to year.

HIGHER NUMBERS GIVE HOPE FOR MONARCHS

1 Reply

By Kim Smith

January 31, 2019

The World Wildlife Fund Mexico and Monarch Butterfly Biosphere Reserve (MBBR) announced on January 30th that this year the Monarch Butterfly population has increased significantly.

Each year the orange and black winged beauties return to the oyamel fir and pine tree forests, which are located in the heart of Mexico’s trans volcanic mountain belt. In December and January, Lepidoptera population specialists and citizen scientists measure the area the Monarch colonies cover at their over wintering sites. This year (2018-2019) the butterflies are blanketing 6.05 hectares (approximately 15 acres), up from an all-time low of only 0.67 hectares (1.65 acres) during the winter of 2013-2014.

Not since 2006-2007 has this great an area been covered by the butterflies, although the numbers are still quite low when compared to the numbers recorded in the late 1970s when the butterfly’s winter roosts were first discovered by Dr. Fred Urquhart.

I have been following the butterfly counts around the US as they were reported. The Monarch population has been decimated in California. This year only about 30,000 butterflies were counted, down from several million just two decades ago. There is the very real possibility that the Monarch butterfly will become extirpated (extinct from an area) on the West coast. The winter count is down drastically in Florida as well.

It was clear though that east of the Rockies–the Midwest and Northeast regions of the US, as well as southern provinces of Canada–there were many more Monarchs in gardens and on the wing than in recent previous summers.

Leading Monarch scientists are reluctant to become excited about the increase, and justifiably so. Last spring the weather was slightly cooler in Texas, which allowed more Monarch eggs to hatch, which in turn allowed more caterpillars to mature. A greater number of butterflies emerged and set the stage for a strong breeding season throughout the summer. That scenario, along with the overall good weather during the summer of 2018, also helped create ideal conditions. It was a true “goldilocks” summer, not too hot, not too cold, but just right.

In autumn of 2018, the Monarchs arrived to Mexico about a week later than usual, but once they began to arrive, a kaleidoscope of butterflies poured into their winter roosting grounds.

The 2018-2019 Eastern population count is a reprieve from the past ten years of heartbreaking news, but one good year does not change what the butterflies need most, which is protection for the Monarchs under the Endangered Species Act.

Monarch and Mexican Sunflower (Tithonia)

There is disagreement among scientists whether planting milkweed has any bearing on the health of the Monarch butterfly population. Does creating corridors of Monarch habitat help mitigate the death and destruction caused by climate change, modern agricultural practices, the devastating use of pesticides and herbicides, and the planting of GMO crops (corn, sorghum, and soybeans, for example) that were engineered to withstand the deadly poisons, but which wildflowers and caterpillars cannot?

Monarch Butterflies and New England Aster, Gloucester, 2018

The answer to that question is a resounding yes! Monarchs are a bellwether species. The love for this one butterfly has helped shape a consciousness towards all species at risk. An uncomplicated stand of milkweed and asters can make every public walkway, park, community center, church, school, and backyard a haven for Monarchs and together we can bring about a conservation victory for the pollinators.