![\"butterflies](\"https:\/\/uwm.edu\/field-station\/wp-content\/uploads\/sites\/380\/2024\/03\/monarch18-23brz.webp\")
<\/a><\/figure>\n\n\n\nEvery fall, most of the Monarch Butterflies east of the Rockies set their compass for a small patch of mountains just northwest of Mexico City.\u00a0This winter\u2019s count of eastern Monarch Butterflies (Danaus plexippus plexippus<\/em>) overwintering in the oyamel fir forests of central Mexico was the second lowest since annual censusing began in 1993. In the 1990\u2019s, the eastern Monarch Butterfly population was estimated at 70 million, and today\u2019s numbers represent an 80% decline in population.<\/p>\n\n\n\n The census is not an actual nose-count of the butterflies themselves but is a measurement of the area they occupy.\u00a0They\u2019re densely concentrated on their wintering grounds — scientists estimate between 20 and 30 million Monarchs per hectare (about 2.5 acres).\u00a0The lowest area, 0.67 hectares (1 66 acres), occurred 10 years ago, and the largest ever, in 1996-97, found 45 acres occupied.\u00a0This year, Monarchs were seen on 0.9 hectares (2.2 acres), down 59% from the 2022-2023 season (Dr. Karen Oberhauser, founder and director of the Monarch Larva Monitoring Project<\/a>, points out that 2.2 acres is smaller than two football fields).\u00a0It\u2019s felt that almost 15 acres of overwintering butterflies are needed to maintain a healthy eastern population.\u00a0\u201cMonarch populations [are] at a level that most scientists suggest is not sustainable,<\/em>\u201d says Dr. Oberhauser.\u00a0Western Monarchs, residents and migrants along the Pacific Coast, are treated as a separate population. \u00a0\u00a0<\/p>\n\n\n\n Migration is expensive, energy-wise, and is dangerous, and the list of hazards is long.\u00a0Land use changes and habitat loss, herbicides and pesticides, loss of milkweed, car-butterfly collisions, climate change that brings harsh winter conditions to central Mexico or storms as the butterflies prepare to depart, or that puts migrating butterflies out of sync with nectar plants on their spring migration, high temperatures that reduce the nutritional value of milkweed plants, and severe drought along the fall migration route through \u201cthe Texas Funnel\u201d have all been suggested as factors.<\/p>\n\n\n\n The integrity of the fir forests themselves is critical, but the illegal logging that has reduced the forest size and cover in the past was held to a minimum last year.\u00a0The butterflies depend on a dense forest to act as insulation so they don\u2019t have to expend as much energy staying warm, dry, and hydrated.\u00a0<\/p>\n\n\n\n Quick review of Monarch biology and migration — there are four or five generations annually, and the last brood of the year is extraordinarily long-lived for a butterfly. It emerges in August or September, and while the earlier generations are reproductively active, this final generation is not. Signaled by decreasing day length, lowering angle of the sun, cool nights, and increasingly leathery milkweed leaves, their reproductive organs don\u2019t mature.\u00a0Instead, they apply their energy to a journey – a leisurely trip that can cover more than two thousand miles and take two months.\u00a0The butterflies feed on nectar from a wide variety of flowers as they wend their way south, and while a newly-emerged Monarch in Wisconsin has about 20 mg of fat in its body, a Monarch newly-arrived in the oyamel fir forests of Mexico may carry 125 mg of fat.\u00a0They eat little on their wintering grounds.\u00a0<\/p>\n\n\n\n With the warming temperatures of late March, they become reproductively ready and head north through northern Mexico and our Southern states, laying eggs as they go, careful not to get ahead of the emerging milkweed plants.\u00a0Their young — the first-generation offspring of the Mexican butterflies — keep moving and recolonize the north, often arriving in Wisconsin in mid-May and in Canada shortly after that (Southern summers are too hot for the caterpillars to thrive).<\/p>\n\n\n\n Their<\/em>\u00a0offspring \u2013 the second generation out of Mexico, continue to lay eggs and may fly a little farther north, but most have reached their destinations by the end of June.\u00a0The \u201cjob\u201d of this short-lived generation (and of the next generation, if there\u2019s time for one) is to stay put and use their energy to build up the population. The migratory final generation, sometimes called Gen 5 or the Super Generation, is the only one that is tagged.\u00a0<\/p>\n\n\n\n This complicated dance depends on good weather, milkweeds for caterpillars, and abundant nectar plants for adults. Monarchs will lay their eggs on a variety of milkweed species, but Common milkweed is the favorite.\u00a0<\/p>\n\n\n\n Follow the northward wave of Monarchs<\/a>.<\/p>\n\n\n\n There have been passionate efforts in past years to list the Monarch as an Endangered Species under the Endangered Species Act (ESA).\u00a0Classification under the ESA is a lengthy process, there are many other deserving candidates, and listing requires both a recovery plan and a dedicated budget<\/a>.\u00a0 \u00a0<\/p>\n\n\n\n Monarch populations are subject to wide swings, but a low year followed by another low year lessens the possibility of a speedy comeback.\u00a0Overall population levels in the summer of 2023 were not alarming, but severe heat and drought in the Texas Funnel migratory corridor probably resulted in fewer Monarchs finishing their journey to Mexico.\u00a0<\/p>\n\n\n\n Based on a few recent studies, there are voices, even voices within the Monarch Butterfly community, that suggest (counterintuitively) that there\u2019s no need to change the Monarch\u2019s status, citing past population plunges and recoveries.\u00a0The International Union for Conservation of Nature (IUCN), a leading scientific authority on the status of species, recently downgraded Monarchs on their Red List of Threatened Species from Endangered to Vulnerable.\u00a0<\/p>\n\n\n\n Some of the arguments are historical. Monarchs like milkweeds, and milkweeds like sunshine, and the treeless Great Plains is thought by some to be the historical center of both Monarch and milkweed populations.\u00a0Too, there was lots of sunshine during the long postglacial period while trees moved back north after the most recent glacier pushed them south, and some speculate that milkweeds and Monarchs took that opportunity to push east and increase their numbers before the forests regrew.\u00a0<\/p>\n\n\n\n The early settlers cut down swathes of America\u2019s Great Eastern Forest to establish villages and farms, making the area sunnier and more Monarch\/milkweed-friendly, and some say that Monarch populations are larger now than they were 200 years ago.\u00a0Today, they say, Monarchs are adapting to modern stressors, and they\u2019re establishing some non-migratory breeding communities in Florida and around the Gulf Coast.\u00a0Monarchs, some scientists say, are not at risk, but the eastern Monarch\u00a0migration<\/em>\u00a0may be (a distinction without a difference to Monarch lovers). \u00a0\u00a0<\/p>\n\n\n\n Did the Monarch\u2019s eastward expansion into a glacially-modified landscape and later into a human-modified landscape artificially boost their numbers, so that what\u2019s happening today is just a \u201ccourse correction?\u201d Should we base the butterfly\u2019s status on the wintering numbers rather than the summertime population?\u00a0On today\u2019s numbers vs long-time averages?\u00a0Is it better to err on the side of caution?\u201d\u00a0Will there, as Chip Taylor of Monarch Watch says\u00a0\u201calways be Monarchs<\/em>?\u201d<\/p>\n\n\n\n Only time \u2013- and more research — will tell who\u2019s got it right. In the meantime, what can we do to help?\u00a0<\/p>\n\n\n\n The BugLady<\/em><\/p>\n\n\n Note: Most links leave to external sites. Howdy, BugFans, The BugLady wrote this for an upcoming newsletter of the Lake Michigan Bird Observatory (an organization that would love your support). It started out as a simple report about this year\u2019s …<\/p>\n","protected":false},"author":32664,"featured_media":14705,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":"","uwm_wg_additional_authors":[]},"categories":[8],"tags":[607,41,158,614,456,589,486,768],"class_list":["post-14704","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-bug-of-the-week","tag-bugs","tag-butterflies","tag-caterpillars","tag-insects","tag-milkweed","tag-monarch-butterfly","tag-monarch-caterpillar","tag-monarchs"],"yoast_head":"\n<\/a><\/figure>\n\n\n\n<\/a><\/figure>\n\n\n\n<\/a><\/figure>\n\n\n\n<\/a><\/figure>\n\n\n\n\n