Monarch butterflies (Danaus plexippus) perform annual migrations across North America which have been called "one of the most spectacular natural phenomena in the world".
Starting in September and October, eastern/northeastern populations migrate from southern Canada and the United States to overwintering sites in central Mexico where they arrive around November. They start the return trip in March, arriving around July. No individual butterfly completes the entire round trip; female monarchs lay eggs for the next generation during the northward migration and at least four generations are involved in the annual cycle.
Similarly, the western populations migrate annually between regions west of the Rocky Mountains including northern Canada and overwintering sites at the coast of California.
Monarchs also perform small distance migrations in Australia and New Zealand. There are also some populations, for instance in Florida and the Caribbean, that do not migrate. Recently discovered overwintering sites have been identified in Arizona and northern Florida.
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Range of the migration
The western population overwinters in various coastal sites in central and southern California, United States, notably in Pacific Grove, Santa Cruz, and Grover Beach. Western monarchs also overwinter in Baja, California's central valley, and the Sierra Nevada foothills.
Not all monarchs migrate. Migrating populations and non-migrating populations coexist in many areas. Monarchs are year-round residents in Florida and monarchs migrate to Florida and Gulf coast areas, and can often continue to breed and survive the winter. The monarch population in Florida may be a result from migratory butterflies that do not to migrate north in the spring. These locations provide access to nectar plants. If there is a hard frost in these areas they do not survive. Asclepias curassavica, an introduced annual ornamental, provides larval food if native species are unavailable, although because of the risks to monarchs from the spread of the parasite, OE, this plant is not recommended for planting. Year-round breeding of resident monarch populations exist in the Caribbean, and in Mexico as far south as the Yucatán peninsula. Surprisingly, monarchs do not migrate over most of their global range. Tagging records demonstrate that the eastern and western populations are not entirely separate. Arizona butterflies have been captured at overwintering sites in both California and Michoacan, Mexico. In some instances monarchs from Arizona and New Mexico were found overwintering in California and in Mexico.
Fall-migrating monarchs are not the same ones that migrated northward approximately five months before. Instead the northern-migrating butterflies are at least four generations removed from overwintering sites. The eastern population migrates up to 4830 miles (7,778 km) to overwintering sites in Mexico. Other insects show migratory behavior but not nearly for as long distances. The exception would be the desert locust, Schistocerca gregaria: it was reported once in 1950 that individual swarms were seen migrating from the Arabian peninsula over 5,000 km (3,105 miles) to the west coast of Africa in seven weeks.
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Habitats
Ideal habitats have a profound effect on the migration of large numbers of monarchs. The single most influential factor is the weather. Ideal habitats promote the migration of large numbers of migrating monarchs.
Summer
The ideal summer breeding habitat will provide ample nectaring plants for the adults and abundant, healthy larval plants. Low populations of predators and parasites will also allow for more monarchs surviving into adulthood. A low prevalence of disease will improve the survival. Monarchs breed the fastest within a specific temperature range. An increase of the range of the breeding population is another indicator that the habitat is conductive to reproductive success.
Fall
In North America the ideal breeding habitat changes in late summer. The migration begins and the ideal habitat required for successful migration changes to a 'corridor' (to Mexico) of available nectaring plants, optimal temperatures, tailwinds and low precipitation. The butterflies must also remain hydrated. An early frost will kill migrating butterflies.
Winter
The ideal habitat for monarchs in winter exists in their overwintering sites. The factors influencing the habitat include: the condition of the forest canopy, precipitation, predation, availability of suitable trees on which to roost, sources of water, the ideal temperature range, sunlight, lack of rain and ice and human activity near the sites. Roosting butterflies have been observed to roost in sumacs, locusts, basswood elm, oak, osage orange, mulberry, pecan, willow, cottonwood, and mesquite. If conditions are too hot in the overwintering sites, the butterflies will use up their fat reserves and not survive until spring. High temperatures initiate reproductive behavior with the possibility of the butterflies leaving the overwintering areas too early while it is still too cold in the north to stimulate the emergence of food plants and nectar plants
Spring
The ideal habitat for monarchs migrating north from Mexico sites to Texas and Oklahoma is less studied. Presumably, tailwinds assist the migration north. Rainfall is critical in creating the ideal habitat for the returning monarchs which must have abundant, lush and healthy food plants available for larvae. Ideal growth of larval plants that emerge in succession as the breeding butterflies migrate north, is also critical. Drought is a big factor influencing the emergence of food plants.
If any of these habitats is less than ideal, the population of monarchs will be negatively affected though ideal conditions in the other habitats monarchs encounter make up for the 'losses'.
Historical accounts
Before 1975
As late as 1951, monarchs were thought to overwinter in northern latitudes as adults or pupae. Roosts of thousands were observed in southern regions of North America.
Migrating western populations of D. plexippus and their overwintering sites were known long before the winter sites in Mexico were located by Canadian and American researchers in the 1970s. Pre-Hispanic Native Americans, the Purépecha and Otomi once occupied this area and tied the harvest of corn to the arrival of the butterflies. Monarchs appear in legends of the people that live near overwintering areas. In the areas surrounding the overwintering sites in Mexico, local residents were quite aware of the overwintering behavior of monarch butterflies long before 1975. The local people, called the Mazahua, have lived near the overwintering sites for centuries. The arrival of the monarchs is closely tied to the traditional the Day of the Dead celebrations. Local residents today easily recall seeing the migrating butterflies prior to 1975.
For at least a century, monarchs were observed overwintering in California in the fog belt. Historical records of lepidopterists do not mention the existence of monarchs in their current western range that extends northward through Washington, Oregon and Canada possibly because milkweed was not available until human disturbance expanded its range.
After 1975
Formal studies began when Fred Urquhart graduated from the University of Toronto in 1935 and accepted a graduate fellowship in the field of entomology. In 1937, Urquhart began to plot the route taken by the migrating butterflies. He was the first to record that monarchs move S/SW in the fall and that these movements were correlated to high pressure systems. He began the first successful tagging program which returned data. He and his volunteers recognized the existence of roosting behavior.
The search for overwintering sites was initiated by Fred Urquhart when he advertised for 'interested persons' in the Mexican press. Catalina Trail and Kenneth C. Brugger responded to the ad and in January 1975 discovered one of the major overwintering sites. Urquhart, William Calvert, John Christian, and Lincoln P. Brewer cooperated to put together the details in this discovery of a major overwintering site of monarchs in 1976. At first, information on the discovery of the first major overwintering was suppressed due to the concerns that public knowledge might lead to endangerment of the butterflies. Since 1976 multiple overwintering sites have been identified and their locations are public knowledge.
Southern migration
By the end of October, the population of monarchs east of the Rocky Mountains migrates to the sanctuaries of the Mariposa Monarca Biosphere Reserve within the Trans-Mexican Volcanic Belt pine-oak forests in the Mexican states of Michoacán and México. They also overwinter in areas that are privately owned. Some monarchs migrate to other locations such as Cuba and Florida in the fall. Two migratory fly ways exist thrugh North America. One in the Central states leads to the Mexican overwintering areas and a smaller flyway along the eastern North American seaboard. The timing of the eastern flyway lags behind the more central flyway. Monarchs migrating along the coast are less likely of being recovered in Mexico. This suggests that butterflies migrating along the eastern seaboard are migrating to locations other than Mexico, or they have a higher rate of mortality than those migrating inland.
Initiation
Monarchs respond to different cues that promote the fall season, southern migration. These include the angle of light coming from the sun, the senescence of larval host plants, the decreasing day period and temperature drop. The migration begins at the northernmost summer range approximately in August. Migrating monarchs are thought to rely heavily on the nectar of fall flower composites that lie along the migration path.
Monarchs in diapause
Diapause is a physiological state found most often in arthropods, especially insects, and in embryos of fish that allows survival when conditions become harsh. Diapause is not only induced in an organism by specific stimuli or conditions, but once initiated, only certain other stimuli are capable of bringing the organism out of diapause. The latter feature is essential in distinguishing diapause from other forms of dormancy such as stratification, and hibernation.
When the adult monarch begins its southern migration, it enters diapause. Where other species in diapause remain fairly immobile, monarchs remain active. When diapause is initiated the butterflies accumulate and store lipids, proteins and carbohydrates. Monarchs migrating to Mexico accumulate more lipids than those migrating to California. Fats and lipids reduce water to provide energy reserves and prevent desiccation. These substances are used to maintain the insect throughout diapause and to provide fuel for development following diapause termination. It occurs at a genetically well in advance of environmental stress. It is a state resulting in the cessation of high-metabolic activities including reduced oxygen use.
Monarchs in diapause of the fall migrating population are physiologically distinct from those in active reproduction behavior in the spring and summer. In diapause, the measurement of fats and lipids levels a can be as high as 34%. The fat storage organ is substantially larger in migrating and overwintering monarchs compared to the summer generations. Samples of tissue excluding the fat body also show higher levels of free lipids in the hemeolymph. Females in diapause show little evidence of mature eggs. Mating is repressed and only occasionally observed among overwintering monarchs. This is thought to increase the survivability of winter populations and maintain fat reserves that will promote spring northward migration. At one site, the population stayed in diapause until the middle to the end of January. By the beginning of February the day length increases to just over 11 hours, the point at which monarchs come out of diapause. In addition to the required day length, monarchs in diapause must also have temperatures that promote the formation of eggs. When these two conditions are met, mating occurs and females migrate northward. While migrating, the monarch in diapause uses nectar along its migration to create a significant increase in its fat reserves. There are reports of monarchs laying eggs while traveling southward to overwintering sites. Eggs and larvae are killed by freezing temperatures. Migration ends at the first frost.
Diapause has distinct phases. While diapause varies considerably from one taxon of insects to another, these phases are characterized by series of metabolic processes and responsiveness of the insect environmental stimuli.
Decreasing day period and dropping temperatures have been found to initiate the production of juvenile hormone. This represses the development of gonadal activity, mating behaviors, and egg-laying. While in diapause new behaviors emerge such as the development of social nectaring groups and late afternoon formation of night-time clusters or roosts. Roosting reduces water loss, probably due to decreased surface area to volume ratios reducing evaporative water loss.
Other characteristics of migrant monarchs
Migrating monarchs tend to have darker orange and larger wings than they do during the breeding phase in the summer. In fact, the darkness of the orange color in monarch wings appears to be a visual indicator of their migratory ability. This has been shown in field and laboratory research. Wing size is a key element during the migration, and much research has shown how important it is for migrants to have large wings. Comparisons of migratory vs. non-migratory populations shows migrant populations are much larger than non-migrants, which suggests natural selection acts to keep migratory populations large. Two studies have used stable isotopes to infer natal origins of migrating monarchs captured at their wintering sites (eastern and western), and both showed that monarchs migrating from father distances tended to be larger, which also is consistent with the idea that long-distance migration selects for larger wings, or that small-winged butterflies tend not to be successful. One researcher summarized what the optimal size of migrant monarch wings should be, which is 51 mm in length or more.
There is other research around migrant wing size that shows how this differs between early and late migrants. This has to do with the fact that earlier migrants tend to be the more robust, healthier individuals, while late-migrating monarchs represent the ones that fell behind, presumably because they are less well-suited for migration. A study published in the journal, Animal Migration, showed that early-migrating monarchs tended to be redder, have larger, and more elongated wings, than those at the tail end of the migration. Another study that examined long-term records of tagging data from a site in South Carolina found early migrants tended to be larger.
In females the production of eggs ceases. Mating behavior is not observed presumably due to changing levels of hormones that promote breeding.
Colony dispersal and northern migration
Northern migration
There is a northward migration in the spring. Female monarchs lay eggs for the next generation during these migrations. Northward migration from Florida normally occurs from mid-March to mid-May and the initial wave of the migration may be the offspring of monarchs that have overwintered in Florida and along the northern Gulf Coast, not in central Mexico. Tagged monarchs from Tallahassee were recovered in Virginia and Georgia.
The distance and length of these journeys exceeds the normal lifespan of monarchs, which is less than two months for butterflies born in early summer. The first generation leaving the overwintering sites only migrates as far north as Texas and Oklahoma. The second, third and fourth generations return to their northern breeding locations in the United States and Canada in the spring.
Initiation
As with the initiation of the southern migration, a variety of cues trigger the cessation of diapause, the beginning of breeding activity and the movement north. In the case of the western population, the dispersal proceeds in a westerly and northwesterly direction. During this process, roosting sites sometimes move and the monarchs move to lower elevations. Rising temperatures and increasing daylengths influence the initiation of the northward migration. Temperature also has an effect. Mated females leave the overwintering sites before the males. Monarchs travelling north do not form roosts.
Rates of recolonization
Rates of recolonization have remained steady between 1997 and 2011. The recolonization of the breeding grounds in the United States and Canada is a two generation process. The pattern of recolonization of the northern breeding areas has not changed since monitoring began in 1997. The timetables of the re-colonization range is not correlated to the censuses of overwintering monarchs in Mexico.
Migration routes
Generally speaking, the eastern population migrates from southern Canada and the Midwest United States almost directly south toward Mexico. Monarchs from the Northeast tend to migrate in a southwesterly direction. Monarchs transplanted from the midwest to the east coast began migrating directly south but then reoriented their path to the southwest in one study. Geographical features affect the migration route.
In general, the western population of monarchs migrates from areas west of the Rocky Mountains including northern Canada to California. Australian monarchs that migrate travel from the west to eastern regions closer to the Pacific.
Roosting sites
During the migration, the eastern and western populations tend to group together during the migration and then at the overwintering sites. These roosts form along the migration routes, and scientists have used these roost locations to map out the flyways of the entire population. Prior to the discovery of the overwintering sites in Mexico, Fred Urquhart observed roosting behavior in south-migrating butterflies in Mexico and Michoacan. He documented 1500 monarchs roosting at lighthouse point Florida. In California, monarchs have been observed roosting in a wide variety of locations: Fremont, Natural Bridges Beach, golf courses, suburban areas. California roosts differ from those in Mexico. Roosts are observed in inland areas and on non-native tree species.
Overwintering sites
Overwintering sites in California, Northwestern Mexico, Arizona, the Gulf Coast, central Mexico and Florida share the same habitat characteristics: a moderating climatic conditions (thermally stable and frost free), are relatively humid, allow access to drinking water and have the availability of trees on which to roost and avoid predation. California has more than 200 overwintering sites. Overwintering sites have also been observed in coastal South Carolina along with ovapositing females.
At least twenty colonies exist in Mexico.
California overwintering sites exist in areas that are developed and are not considered especially forest-like. These sites have been referred to as having a uniform vegetation population of either Monterey pine or eucalyptus trees and are sometimes present in urban areas. Over wintering sites are dynamic in that tagged butterflies are observed in different roosts throughout the winter. Monarchs overwintering along the Gulf Coast and in Florida do not enter diapause and breed year-round.
Sex ratios
An unusual pattern has been observed in the sex ratios of monarchs in the eastern North American population, both during the fall migration and at the overwintering sites in Mexico. Normally during the breeding season, the ratio of males and females is roughly the same, but during the migration the ratio is skewed toward males. This persists during the overwintering period as well, likely because it's the same cohort that advances from migration to the overwintering sites. Scientists have examined records from the overwintering period over 30 years, and found that the skewed sex ratio has grown more pronounced in recent years, perhaps because of a loss of females. The ratio appears to be even more evident in observations of roosting or migrating monarchs, where fewer than 30% of the monarchs are females.
Population and migratory study methods
Population counts "dramatically" vary year to year. The cause of the variations are attributed to natural occurrences, different methods used to count migrating butterflies, and man-made changes to the habitat. The validity of the population census at overwintering sites in North America is questioned. The discrepancy between migrating populations and populations present at the overwintering sites suggests a significant adult mortality during the migration. The Commission for Environmental Cooperation has determined that population variations require a long-term and large scale monitoring effort Population estimates of adults, or of eggs and larva, and milkweed abundance, should correlate with the censuses at the overwintering sites. Data are currently unavailable at this time to determine these censuses but a current study by The Monarch Larva Monitoring Project is designed to determine whether or not population censuses in Mexico match the population censuses in the Midwestern United States and Canada.
Mark and recapture
This is the technique whereby a sample of the population is captured, tagged, and returned to the original location. After the tagged monarchs are released they are later re-captured. This procedure allows the determination of the total populations since the recaptured monarchs are directly proportional to the number in the whole population. An estimate of the total population size can be obtained by dividing the number of marked individuals by the proportion of marked individuals in the second sample. This method of population determination is useful because it is not practical to count all the individuals in the population. Other names for this method, or closely related methods, include capture-recapture, capture-mark-recapture, mark-recapture, sight-resight, mark-release-recapture, multiple systems estimation, band recovery, the Petersen method and the Lincoln method. has been used to estimate the number of butterflies remigrating to Florida in the spring and overwintering in California.
Butterfly counts
Monarch butterfly counts can be compared to bird counts. During a butterfly count, individuals and organized groups count the numbers of butterflies that they observe during a discrete time period and within a predetermined area. The western population of monarchs are counted during their 'Thanksgiving Butterfly Count'. Methods differ but can include consistent observations of butterflies traversing areas within predetermined limits, presumably along the migratory route measured in butterflies/hour sometimes with recording vectors. Data collected are likely to be accurate and become more accurate with the increasing number of samples. Concentrations of migrating monarchs are consistently monitored by Cape May Bird Observatory, Peninsula Point Light, Michigan, and Point Pelee National Park, Ontario, Canada.
Butterfly counts of monarchs serve many purposes. The results of the counts allow the determination of the range of the monarch. This includes what is known as 'accidental sightings'; sightings that occur out of the normally established range. Determining the range will reveal the expansion or contraction of the butterfly's normal range. The range of the monarch does vary year. Another result that is obtained during the butterfly count of the monarch is an estimate of the butterflies population. Butterfly counts of the monarch reflect effects of weather on the range and populations. Habitat change can impact a count; many assess habitat changes in the range of the monarch based upon the counts. The ratio of monarchs to other species observed during a count provides information about habitat changes. Publicized butterfly counts can generate interest.
Monarch butterfly counts from 1979-1990 revealed fluctuations. Some of these are attributed to severe weather effects, El Nino Southern Oscillation and volcanic eruption.
Migrating monarchs tend to congregate and form roosts on peninsulas that point south. Monitoring programs count the number of monarchs in roosts that develop along the migration route. Monitoring data from multiple sites correlate.
Protocols used to conduct the censuses include:
- Driving Census
- Walking Census
- Roosting Counts
- Hawk-watch Observations
Aerial and satellite observations
The condition of the Mexican forest habitats and progression of deforestation of overwintering roosts can be observable via satellite imagery. These images show the changes in and around the overwintering areas. Efforts to visual the satellite images for actual presence of the roosts of butterflies have not been successful. Small aircraft were used in one study, allowing views of the colonies. Aerial assessments of the areas surrounding the colonies revealed the presence of potential areas of colonization. After these efforts the costs out-weighed the benefits of high-altitude aerial photography. It was determined to be time-consuming and expensive and did not allow a reliable method for identifying or conducting a census of the colonies.
Direct observations
Direct observation was the primary method used when monarch migration studies began. These past sightings and recovery of tagged butterflies is information cited in publications even up to 2014. Direct observations are performed by laypeople, scientists and those residing close to overwintering sites.
Types of data collected
Direct observation usually means that an observer records data while the butterfly is one stage of its migration. This can include:
Use of data and availability
Recorded, anecdotal information is most often submitted to the sponsoring organization. Data has significantly accumulated over the years and is used by researchers. Scientific observations are sometimes treated like proprietary information and are not available to the public or other researchers. Observers have begun to record their sightings via Google maps.
Observers
Most observers are laypersons (trained and untrained), individuals identified with the term 'citizen scientist' but also called "amateur naturalists". Anecdotal information by observers has been criticized and labelled as not "good science" and "not science at all". Conservation organizations and scientists use observations in their research. Those who participate in organized butterfly counts also provide valid observations. Some regions in Texas are located in the flight path during the migration and the patterns, distributions, and populations are recorded by observers there.
Tagging
Tagging was done as early as 1796 on silk moths by Indian silk producers. It was discovered that the moths would migrate up to 100 miles (160 km). Prior to the tagging activity of Fred Urquart, other methods of monarch tagging included wing incisions, spots arrangements, colored spots, spraying with dyes, painted letters and numbers. The reason these methods resulted in no information about the migration was because there were no instructions to return or at least record the recovery.Many organizations currently use tagging to study migration.
Monarch tagging is a popular educational project for students. Captive/commercially bred monarchs have been known to migrate to overwintering sites in Mexico, although their success rate is much lower than it is for wild monarchs.
Scientists who study monarch migration have utilized monarch tagging records to answer a number of questions about monarch migration biology. A study from South Carolina showed, through tagging records, that monarchs with smaller and/or damaged wings tend to remain longer at stopover sites, which leads to them falling behind in the migration. Another study used tagging records to show how monarchs tagged in areas along the Atlantic coast have a lower migration success rate than do those tagged at inland locations. Collectively, the conservation value of tagging data are vast, yet one scientist argued that these data remain largely untapped.
Monarch tagging allows scientists to assess migration directions and speeds, by comparing the timing of the initial tag date and the date and location of the subsequent recovery of the tagged individual. For example:
A tagged monarch in Geneva, Kentucky, was recovered in Lindsborg, Kansas, a distance of 50 miles in 2 days.
A tagged monarch in Hartford, Connecticut, was recovered in Camp Hill, Pennsylvania, 98 miles in 5 days.
A tagged monarch in Lincoln, Nebraska, was recovered in Paullina, Iowa, 158 miles in 18 days.
The official record for the longest tag-recovery is for a monarch tagged by Don Davis, from Ontario, Canada. This record is listed in the Guinness Book of Records for the longest insect migration. It was a monarch tagged in southern Ontario during the fall of 1988, that traveled to Mexico and then north again in the spring where it was recovered in Texas, for a grand total of 4,635 km (2,880 miles). This record assumed the monarch traveled to Mexico and back north in the spring. Also, the straight line distance from the tag site to the overwintering site was 3,429 km (2,131 miles). In fall 2015, a new (unofficial) record was set by a tagger from Nova Scotia, Canada - Larry bogan, who tagged a monarch that was recovered in Mexico, for a distance of 4,330 km (2,690 miles). One monarch researcher argues the Nova Scotia monarch should be the record-holder, since its one-way migration was longer than the Ontario monarch's.
While the practice of transferring monarchs from place to place is generally not condoned by scientists, some reciprocal transfers of tagged monarchs have demonstrated that monarchs from east of the Rocky Mountains will migrate south if transferred west, in the range of the western population (rather than SW). Monarchs transferred from Nebraska to Oregon will also migrate south.
New methods of studying the migration include the use of VHF transmitters and commercial aircraft. Isotopic tagging has been employed.
Migratory theory mechanisms
Theories that explain monarch migration are many. "Science has not yet offered a sufficient explanation for how that [the migration] happens." Researchers often propose that multiple migratory mechanisms play a role. Not all who study monarch migration agree on the mechanisms that allow the migrating butterflies to find overwintering sites.
Instinct
It is proposed that the ability to find overwintering sites in California and Mexico is an inherited trait. It has also been called a genetic memory. The possibility of an inherited map has been posited suggesting that the butterflies may follow streams and recognize landmarks. Other studies provide evidence against the theory of an inherited map.
Geographical features
Migration theories take into account the terrain monarchs encounter during their migration. Mountains, rivers, lakes and oceans are credited with influencing the migration. Large roosts of migrating monarchs are often formed at a locations that act as obstacles impeding their movement S/SW. Roosting butterflies are thought to form these roosts to wait for ideal weather conditions that will aid them in crossing these landforms, such as lack of rain, temperature, tailwinds, and sunlight. Some years the roosting sites form predictably and consistently year to year. In other instances, roosting sites form in new areas on a transient basis. A roost of migrating monarchs can contain as few as four and as many as thousands. Other geographic features such as the Appalachian Mountains and the Sierra Madres in Mexico 'funnel' the migration, orienting it to the S/SW. One monarch tagged in Ontario was recovered on an oil rig 100 miles south of Galveston, Texas.
Chemical markers
One recent hypothesis suggests that monarchs may be chemically marking certain trees, using an unknown substance and so orienting themselves when they return the following winter.
Position of the sun
The migratory patterns may be based on the position of the sun in the sky including its angle and spectrum changes that occur near the end of the summer breeding season. The proposed Sun compass depends upon a circadian clock based in their antennae. The antennae contain cryptochrome, a photoreceptor protein sensitive to the violet-blue part of the light spectrum. In the presence of violet or blue light, it can function as a chemical compass.
Other theories
The Colombus Hypothesis is another theory that accounts for the phenomena of the mass migration of the eastern population of the monarch by examining historical records. This theory discusses how many butterflies engage in mass movements to expand their range or relieve pressure on their habitat. According to this theory, the eastern population did not have such an extensive range and did not migrate. Historical observations of animal life during the colonial period in America make no mention of monarch butterflies. Observations of monarchs began and seemed to be related to the deforestation of the Northeast. Monarchs were presumably residents of subtropical and tropical areas but began to move north to breed on the increased numbers of larval host plants that replaced the deforested areas. Populations found in other regions do not migrate over such long distances (in Australia, for example) This may suggest that the migratory behavior of the eastern population of the monarch butterfly developed after other populations of monarchs had become established in other regions.
Another theory denies the existence of the mass migration, but instead explains the movements of monarchs in the fall to weather conditions:
In the fall, monarch adults in Canada and the upper Midwest likely receive an environmental trigger (change in photoperiod or seasonal cold snap) and cease egg laying. When the main jets stream moves south out of Canada, high and low pressure cells become carried across extreme southern Canada and later across the US. At that time, monarchs need merely rise on thermals during clearing conditions and become carried toward the South out of the region in which they were reared. If they have reached sufficient altitude in their ride on thermals, the north winds can carry some of them considerable distance towards Mexico." Adrian Wenner, professor emeritus of natural history at the University of California, Santa Barbara
Wenner goes on to say that monarchs were found in Mexico in the winter simply because people expected they would be there. He contends that monarchs may be in other places, but just haven't been found yet.
Extinction
The range of the monarch is worldwide and while monarch butterflies are not endangered as a species, the migration of the eastern North American population may be an endangered phenomenon. The media consistently reports that the monarch is endangered of becoming extinct and have been criticized for exaggerating. Media reports of the monarch becoming extinct have been criticized by scientists. "Monarchs are not in danger of extinction," states Lincoln Brower, a monarch conservation researcher.
Conservation
Monitoring and conservation organizations can be organized by their efforts directed to each of the four stages in the monarch life cycle.
The winter roosts in both Mexico and California were declared to be threatened phenomena by the International Union for the Conservation of Nature and Natural Resources (IUCN) in the IUCN Invertebrate Red Data Book.
Historical conservation regulations began when the residents of Pacific Grove, CA passed an ordinance prohibiting the disturbance of the "peaceful occupation of the Monarch butterflies".
Adult mortality
Unknown factors that impact the numbers of migrating monarchs requires more research. Culling may occur during the migration due to high counts of infection with the parasite 'Ophryocystis elektroscirrha'. This parasite is known to cause reductions in flying ability, thus infected monarchs have a reduced chance of reaching the overwintering sites. Another source of mortality during migration is death from car-strikes. One researcher examined all evidence from the scientific literature on this and concluded that hundreds of millions of monarchs die on roadways each fall.
Overwintering sites
Work to protect the overwintering sites in Mexico began before 1975 and were initiated by local residents. Populations of overwintering monarchs in Mexico have been declining. It is expected that the numbers of monarchs will increase this winter (2014-15) due to favorable conditions that existed during the early spring migration and throughout the summer.
Gulf Coast areas and Florida
Overwintering sites exist along the Gulf Coast states and in Florida.
Mexico
Periodic disasters at the Mexican overwintering sites are the main reason for the population decline. Some sites have experienced losses of 30% to 90% during storms. Conservation efforts in and around the overwintering sites include the planting of native tree species on which the monarchs prefer to roost.
California
Overwintering monarchs in California have shown to have a slight preference to roost on native species but will also consistently choose introduced eucalyptus species, even when native species are present. Roosting sites in California are typically located close to the coastline, though some have been found further inland.
Reductions in milkweed and agricultural regions of the United States
Some conservationists blame the reductions in monarch overwintering numbers in Mexico on the loss of milkweeds in the Midwestern region of the United States. 167 million acres of monarch habitat has been lost since 1996. These conservationists argue that the reduction in milkweed habitat in agricultural regions of North America is a major cause of the declines in the number of monarchs that reach Mexico. However, other top researchers doubt this claim, because it is not consistent with data collected by several long-term butterfly monitoring programs in the United States. The data from these programs do not show evidence that the numbers of breeding adult monarchs has declined since the 1990s. Despite this evidence, some conservationists cite the use of pesticides and herbicides as a cause of the declines in overwintering monarchs. They state that prior to the introduction of genetically altered corn and soybeans, milkweed was common in the crop fields. The connection between the use of GMO crops and the decline in the numbers of overwintering monarchs has been called 'suggestive but not conclusive', as there are other factors such as deforestation and weather events that could be the cause. Milkweed habitat is also destroyed by the expansion of urban and suburban areas.
Based on the recent evidence that failed to show declines in the breeding season, coupled with the clear declines in the number of overwintering monarchs in Mexico, some of the leading monarch researchers have embraced the theory that the problem must lie en route to Mexico, i.e. that losses during migration is the reason that fewer monarchs are seen in Mexico in recent years. Conservationists also call attention to the decreased habitat that allows the growth of nectaring plants.
Other threats
Factors that have a negative effect on the migration are extreme weather, including colder winters in central Mexico, droughts in Texas, invasive (non--milkweed )flora on which monarchs lay eggs and the increased use of synthetic insecticides that are less biodegradable.
Conservation programs
There are many organizations and programs existing to promote the preservation of the monarch and its migration.
- Health monitoring contributes to conservation by studying the health of butterflies in all or various stages of its life cycle.
- Habitat restoration contributes to conservation by planting larval food plants, nectaring plants and overwinter plants necessary for winter survival.
- Policy contributes to the conservation by coordination of efforts across governmental and non-governmental organizations
- Reserves protect habitat for the butterfly.
- Education contributes to the conservation of the monarch by raising awareness and participation in conservation activities.
- Censuses of the monarch provide information regarding the migration routes, relative population comparisons between different populations.
- Grants are given and received to help foster new conservation programs and to fund research.
- Research provides information regarding the butterfly and its migration.
- Citizen science participation involves activities by lay-persons to promote conservation.
- Tagging and then recapturing monarchs provides information useful to provide information on migration.
- Regulations exit to protect the butterfly and its habitat
- Economic development promotes the development of alternative sources of income around Mexican overwintering sites to prevent the harvesting of trees used by overwintering butterflies
- Repository is the accumulated data produced by scientists and citizen scientists.
- Available to public indicates whether this data are shared freely to the public.
Proposed policies to conserve the migration
Much discussion exists concerning what actions may benefit the migration. Efforts to preserve this phenomenon include:
- continued discussion via the Trilateral Committee for Wildlife and Ecosystem Conservation and Management Summit to organize continent wide conservation actions
- Reforestation of overwintering habitat in Mexico.
- Promote the Farm Service Agency Conservation Reserve Program in which enrolled farmers receive yearly payments for removing environmentally sensitive areas from production and to promote species of plants that improve habitat.
- the formation of specific organizations to educate the public about the migration and monarch biology
- the study of the effects of diseases, parasites and predators on populations
- limiting activities at the overwintering sites (logging, tourism),
- payments to local residents to monitor forest habitats
- mass planting of milkweed and nectar plants. Concerned individuals governmental agencies, and organizations have made efforts to restore milkweed habitats to provide nectar and food plants.
- studies that involve the participation of citizen-scientists who monitor and apply tags to migrating monarchs
- the lobbying of lawmakers, corporations, highway departments, utilities and policy-makers to preserve habitat
- the creation of media (websites, magazine articles, art, newspapers, movies, children's books, documentaries, educational curricula) that provides information about monarch migration.
Tourism around the overwintering sites in Mexico and California provides income for those who provide such services.
Residents near the overwintering sites are concerned that their children do not have enough to eat so they are forced to continue illegal logging. Other residents take advantage of the months butterflies overwinter near their homes. Though they consider themselves quite poor, it is possible for them to generate enough income to last them through the year acting as guides, providing lodging and meals, selling crafts and souvenirs.
Overwintering monarchs roost in trees on privately owned land. Laws and regulations regarding the protection of the overwintering sites and habitat override the interests of land owners, farmer' cooperatives and local governing bodies.
In 1986, Mexico created sanctuaries for the winter months. Sections of the forest were closed to the local people who depended on lumber for their income. Small-scale logging operations continued though illegal. Conservation organizations pay residents to patrol the forest.
Contributions are solicited to fund programs that support monarch conservation efforts. Some donations to conservation programs are directed toward fundraising for the organization.
Politics
The scientific and conservation efforts require the involvement of the United States, Canada and Mexico. This has resulted in the formation of the North American Monarch Conservation plan. Conservation plans in Mexico have been suggested to be deficient.
Conservation has both practical and theoretical components, with the former often having little to do with science or biology. Education shapes attitudes, a sympathetic populace lobbies government, regulations are instituted, and where possible, land is set aside as reserves. Joel Berger, University of Nevada
Affected people groups
Indigenous people groups, residents, farmers and landowners surrounding the overwintering sites have made statements about their dissatisfaction with the involvement of Canadian and American conservationists concerning the enforcement of restricting the use of lands in and around preserves. Sustainable development in the areas surrounding overwintering colonies has been identified as a major factor in conservation efforts. It refers to the substitution of economic activities that have a negative effect on conservation efforts with economic opportunities that have a positive effect on conservation goals. Mexican communities have expressed concern with the limitations placed on their use of land and resources. Conservation proposals are met with 'little enthusiasm' if not inclusive of local interests.
Sustainable development and conservation today is a problem of marketing and financing, with real numbers and real mechanisms-not of good intentions. - Roberto Solis, Instituto Nacional de Ecologia, Mexico
Animal research in conservation has a role but it has little significance unless sociological, economic and political issues are satisfactorily resolved.
Access to overwintering colonies is tightly controlled by Mexico and monitored by Profepa, Universidad Nacional Autonoma de Mexico (UNAM), Instituto Politécnico Nacional (IPN), Monarch Butterfly Biosphere Reserve (MBBR), local and international volunteers. The world Wildlife Fund pays for the salaries of enforcement officers.
Presidential memorandum and national strategy
On June 20, 2014, President Barack Obama issued a presidential memorandum entitled "Creating a Federal Strategy to Promote the Health of Honey Bees and Other Pollinators". The memorandum established a Pollinator Health Task Force, to be co-chaired by the Secretary of Agriculture and the Administrator of the Environmental Protection Agency, and stated:
The number of migrating Monarch butterflies sank to the lowest recorded population level in 2013-14, and there is an imminent risk of failed migration.
In May 2015, the Pollinator Health Task Force issued a "National Strategy to Promote the Health of Honey Bees and Other Pollinators". The strategy lays out current and planned federal actions to achieve three goals, two of which are:
o Monarch Butterflies: Increase the Eastern population of the monarch butterfly to 225 million butterflies occupying an area of approximately 15 acres (6 hectares) in the overwintering grounds in Mexico, through domestic/international actions and public-private partnerships, by 2020.
o Pollinator Habitat Acreage: Restore or enhance 7 million acres of land for pollinators over the next 5 years through Federal actions and public/private partnerships.
Many of the priority projects that the National Strategy identifies will focus on the I-35 corridor extending for 1,500 miles (2,400 km) from Texas to Minnesota that provides spring and summer breeding habitats in the monarch's key migration corridor.
Efforts to designate the monarch as endangered
Both the United States and Canada have taken steps to move closer to providing federal protection for the monarch, although these efforts come with some controversy. In the United States, based on the 20-yr declines seen in the numbers of monarchs that reach Mexico each fall, the Center for Biological Diversity, The Center for Food Safety, The Xerces Society and Lincoln Brower have filed a petition to the Interior Department (USA) to protect the monarch by having it declared as an endangered species. The environmental activist Robert Kennedy has endorsed the petition but has said the designation should be 'threatened', not 'endangered'. Critics state monarchs are not threatened and do not need Federal protection. Listing the monarch could divert funding take attention away from rarer species at greater risk of extinction. Critics also are concerned about what the petition does not say.
... it could create a backlash. Fear of regulation, he said, could make landowners into opponents. He pointed out the petition calls for the "designation of critical habitat" via the powers of the act, but doesn't spell out what that means. Chip Taylor, Monarch Watch
In fall 2016, the Committee on the Status of Endangered Wildlife in Canada recently proposed that the monarch be listed as endangered in Canada, as opposed to its current listing as a 'species of concern' in that country. This move, once enacted, would protect critical monarch habitat in Canada, such as major fall accumulation areas in southern Ontario, but it would also have implications for citizen scientists who work with monarchs, and for classroom activities. If the monarch were federally protected in Canada, these activities could be limited, or require federal permits.
Scientific community
Not all researchers are in consensus regarding lobbying for federal government intervention, population censuses, steps to take to conserve the migration, and the possible endangered status of the monarch. They have been critical of the data generated by citizen scientists calling it 'inappropriate'. Differences in opinions by researchers are common. Some researchers have been critical of each other for not making their data available to the public and to each other. Like all scientific research, opinions are voiced, sometimes explicitly. One scientistist is critical of the first tagging efforts by Fred Urquhart calling it an "amateurish self-serving approach to biology that isn't science". Another researcher denies that the monarch migrates but instead is greatly affected by weather conditions to head south.
Local governments
Local governments are considering legislation to provide habitat for migrating monarchs.
Source of the article : Wikipedia
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