Monarch butterfly migration

Monarch butterflies (Danaus plexippus) perform annual migrations across North America. Eastern/northeastern populations migrate from southern Canada and the United states to overwintering sites in central Mexico. Similarly, the western population migrate seasonally from regions between the Rocky Mountains and the coast of California. Monarchs also perform small distance migrations in Australia and New Zealand.

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.^[1] The media consistently reports that the monarch is endangered of becoming extinct and have been criticized for exaggerating.^[2][3][4] Reports of the monarch becoming extinct by the media have been criticized by scientists. "Monarchs are not in danger of extinction," states Lincoln Brower, a monarch conservation researcher.^[5][6]

Range of the migration

The eastern population of monarch butterflies migrates both north and south annually. But no individual makes the entire round trip. Female monarchs lay eggs for the next generation during the northward migration.^[7] 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.^[8]

Not all monarchs migrate. Migrating populations and non-migrating populations coexist in many areas.^[9] 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.^[10] The monarch population in Florida, a may be a result from migratory butterflies that do not to migrate north in the spring.^[11][9] 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. 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.^[12] In some instances monarchs from Arizona and New Mexico were found overwintering in California and in Mexico.^[12][13]

Fall-migrating monarchs are not the same ones that migrated northward approximately five months before. Instead the northern-migrating butterflies are at least five generations removed from overwintering sites. The eastern population migrates up to 4830 miles to overwintering sites in Mexico.^[14] One researcher calls it “one of the most spectacular natural phenomena in the world".^[15] Other insects show migratory behavior but not nearly for as long distances. The exception would be the desert locust, Schistocerca gregaria which was reported once in 1950 individual that swarms were seen migrating from the Arabian peninsula to over 5000 km to the west coast of Africa in seven weeks.^[16]

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 American 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.^[17] Roosting butterflies have been observed to roost in sumacs, locusts, basswood elm, oak, osage orange, mulberry, pecan, willow, cottonwood, and mesquite.^[18] 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 to early while it is still too cold in the north to stimulate the emergence of food plants and nectar plants^[11]

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 foodplants 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.^[19]

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.^{[20][21][22][23]}

For at least a century, monarchs were observed overwintering in California in the fog belt.^[24] 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.^[25]

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, Fred 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 coorelated to high pressure systems. He began the first successful tagging program which returned data. He and his volunteers recognized the existence of roosting behavior.^{[26]:290–296, 305, 306, 310}

The search for overwintering sites was initiated by Fred Urquhart when he advertised for 'interested persons' in the Mexican press. Catalina Trail and Ken 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.^[27][28][29] 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.^[30] Since 1976 multiple overwintering sites have been identified and their locations are public knowledge.^[31]

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. Monarchs migrate to other locations such as Cuba and Florida in the fall.^[32] Two migratory fly ways exist through 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 the Mexico, or they have a higher rate of mortality than those migrating inland.^[33] A few exceptions exist to the generally observed yearly S-SW migration routes. In 1998:

A tagged monarch in Cabell Geneva KY was recovered in Lindsborg KS a distance of 9 8miles in 2 0 days

A tagged monarch in Hartford CT was recovered in Camp Hill PA 9 8 miles in 5 days

A tagged monarch in Lincoln NE was recovered in Paullina IA Gehlsen MO 158miles in 18 days^[34]

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.^[35] 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.^[15][36]

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.^[35][37] The latter feature is essential in distinguishing diapause as a different phenomenon from other forms of dormancy such as stratification, and hibernation.^{[20][38][39][40]}

Part of a series on
Animal dormancy
Torpor Hibernation Hibernaculum HIT Aestivation Cryptobiosis Brumation Diapause Embryonic diapause Winter rest Critical thermal maximum Sleep (non-human) Developmental biology

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.^[36] Monarchs migrating to Mexico accumulate more lipids than those migrating to California. ^[41] Fats and lipids reduce water to provide energy reserves and prevent desiccation.^[42] These substances are used to maintain the insect throughout diapause and to provide fuel for development following diapause termination. It occurs at a genetically occurs well in advance of environmental stress.^[37] This considered a type of animal dormancy. It is a state resulting in the cessation of high-metabolic activities including reduced oxygen use.^[43][43]

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.^[37] 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 a 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.^[37]

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.^[44] Roosting reduces water loss, probably due to decreased surface area to volume ratios reducing evaporative water loss.^[45]

Other physiological changes

Migrating monarchs tend to have darker and larger wings.^[46] Monarchs that migrate often exhibit changes in the shape of their wings. They are larger, weigh more and contain more fat than monarchs that are not migrating. 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.^[47] Female monarchs lay eggs for the next generation during these migrations.^[7] 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.^[48]

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.^[12]

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.^[33]

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.^[49]

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. 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.^{[26]:88, 305–306} 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 on in inland areas and on non-native tree species.^[50]

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.^[51]:2 Overwintering sites have also been observed in coastal South Carolina along with ovapositing females.^[33]

At least twenty colonies exist in Mexico.^[51]:1

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 Montery 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. ^[52] Monarchs overwintering along the Gulf Coast and in Florida do not enter diapause and breed year-round.

Population and migratory study methods

Population counts "dramatically" vary year to year.^[53] The cause of the variations are attributed to natural occurrences, ^[41] Different methods are used to count migrating butterflies,^[33] 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.^[54] The Commission for Environmental Cooperation has determined that population variations require a long-term and large scale monitoring effort^[53] 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 populationc censuses in the Midwestern United States and Canada.^[55]

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.^[56] has been used to estimate the number of butterflies remigrating to Florida in the spring and overwintering in California.^[57][58]

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 mnonarchs are counted during their 'Thanksgiving Butterfly Count'.^[59] 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.^[11] Concentrations of migrating monarchs are consistently monitored by Cape May Bird Observatory,^[60] 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 spiecies observed during a count provides information about habitat changes. Publicized butterfly counts can generate interest.^[61][62]

Monarch butterfly counts from 1979-1990 revealed fluctuations. Some of these are attributed to severe weather effects, El Nino Southern Oscillation and volcanic eruption.^[61]

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.^[63]

Protocols used to conduct the censuses include:

• Driving Census
• Walking Census
• Roosting Counts
• Hawk-watch Observations^[64]

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.^[62][65]

Direct observations

Direct observation was the primary method used when monarch migration studies began.^[66] 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.^[53][46][67] Observers have begun to record their sightings via Google maps.^[68]

Observers

Most observers are laypersons (trained and untrained), individuals identified with the term ‘citizen scientist’ but also called "amateur naturalists".^[69] Anecdotal information by observers has been criticized and labelled as not "good science" and "not science at all".^[69] 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.^[70]

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. 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.^[26]:279Many organizations currently use tagging to study migration.^[71][72][73]

Monarch tagging is a popular educational project for students.^[74] Captive/commercially bred monarchs migrate to overwintering sites in Mexico. ^[75]

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.^[74]

New methods of studying the migration include the use of VHF transmitters and commercial aircraft.^[76] Isotopic tagging has been employed.^[77][78]

Migratory theory mechanisms

Theories that explain monarch migration are many. "Science has not yet offered a sufficient explanation for how that [the migration] happens."^[79] 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.^[80] The possibility of an inherited map has been posited suggesting that the butterflies may follow streams and recognize landmarks.^[81][82][83] Other studies provide evidence against the theory of an inherited map.^[84]

Geographical features, chemical markers

Migration theories take into account the terrain monarchs encounter during their migration. Mountains, rivers, lakes and oceans are credited with influencing the migration. ^[41] 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.^[49][84] One monarch tagged in Ontario was recovered on a oil rig 100 miles south of Galveston, Texas.^[85]

One recent hypothesis suggests that is that monarchs may be chemically marking certain trees, using an unknown substance and so orienting themselves when they return the following winter.^[86]

Chemical markers

One recent hypothesis suggests that is that monarchs may be chemically marking certain trees, using an unknown substance and so orienting themselves when they return the following winter.^[86]

Position of the sun

The migratory patterns may be based on a the position of the sun in the sky including its angle and spectrum changes that occur near the end of the summer breeding season.^[87][88] The proposed Sun compass depends upon a circadian clock based in their antennae.^[89][90] 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.^[91][92]

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^[93] or relieve pressure on their habitat.^[24] 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.^[94] 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.^[95]

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 Werner, professor emeritus of natural history at the University of California, Santa Barbara^[69]

Werner 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.

Conservation

Monitoring and conservation organizations can be organized by their efforts directed to each of the four stages in the monarch lifecycle.^[96]

“We have a lot of habitat in this country but we are losing it at a rapid pace. Development is consuming 6,000 acres a day, a loss of 2.2 million acres per year. Further, the overuse of herbicides along roadsides and elsewhere is turning diverse areas that support monarchs, pollinators, and other wildlife into grass-filled landscapes that support few species. The adoption of genetically modified soybeans and corn have further reduced monarch habitat. If these trends continue, monarchs are certain to decline, threatening the very existence of their magnificent migration.” O.R. Taylor ^[97]

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.^[98]

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".^[26]

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.^[99]

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.^[100]

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.^[98][101] Conservation efforts in and around the overwintering sites include the planting of native tree species on which the monarchs prefer to roost.^[102]

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.,^[103] 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

167 million acres of monarch habitat has been lost since 1996.^[104] The reduction in milkweed habitat in agricultural regions of North America has been cited as a major cause of population declines.^[105][106] Prior to the introduction of genetically altered corn and soybeans, milkweed was common in the crop fields. Conservationists cite the use of pesticides and herbicides as a cause of population decline. Public criticism of GMO crops continues of corn and soybeans which have Bacillus therigenes genes as part of their DNA, (pollen from these crops is thought to increase monarch mortality).^[101] that produce pollen that can fall onto larval host plants negatively impacts the survival of larvae. More acres of GMO crops are planted yearly, partly in demand for the ethanol that is required in gasoline, the so-called ethanol mandate, the Clean Energy Act of 2007^[107][108] The of a connection between the use of GMO crops and the decline in population has been called 'suggestive but not conclusive'.^[109] Milkweed habitat is also destroyed by the expansion of urban and suburban areas.^[110]

Conservationists also call attention to the decreased habitat that allows the growth of nectaring plants.^{[101][111][112][113]}

Man-made obstacles

Man-made obstacles include vehicular traffic near larval food plants and adult nectaring plants.^[101][114] One study suggests that the planting of non-native milkweed, Ascleepias curassavica in South Carolina has the potential to pull monarchs out of the migratory pool.^[33]

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.^[115]

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.

Organization or political entities	Monarch Conservation Programs												Database
	Health monitoring	Habitat restoration	Policy	Reserve	Education	Censuses	Grants-Rec'd or Granted	Research	Citizen Science Participation	Tagging	Regulation	Economic Development	Repository	Available to public
Monarch Watch		♦			♦	♦			♦	♦			♦	♦
Monarch Joint Venture			♦
Association for butterflies	♦				♦		G	♦	♦
Project Monarch Health	♦							♦	♦				♦
Pollinator Partnership		♦	♦		♦
UNESCO[116]		♦		♦
La Naturaleza Nos Llama		♦		♦		♦		♦				♦
National Park System		♦	♦	♦ [117]							♦
Executive Order - Presidental Memorandum [118]		♦	♦
Xerces			♦		♦	♦	R	♦	♦	♦			♦	♦
Volunteer Match		♦			♦				♦
Iowa Department of Natural Resources Iowa Prairie Resource Center		♦			♦				♦
California State Park system		♦		♦
City ordinance of Capitola, California			♦	♦							♦
The Coastal Zone Management Act, California[119]			♦								♦
Assessment and Status Report, Canada			♦								♦
Monarch Butterfly Fund					♦		G
Forest For Monarchs		♦ [120]					R					♦
Larson Juhl		♦										♦
Monarch Ecology Fund		♦
Plantit		♦
Global Climate Summit California Environmental Protection Agency		♦	♦				G
USDA			♦								♦
Medio Ambiente y Recursos Naturales			♦	♦			G				♦	♦
Texas Milkweeds and Monarchs		♦	♦	♦	♦			♦	♦		♦	♦	♦	♦
Wild Ones Wild for Monarchs		♦			♦
Notes

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^[121]
• Reforestation of overwintering habitat in Mexico.^[122]
• 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.^[123]
• the formation of specific organizations to educate the public about the migration and monarch biology^[124]
• the study of the effects of diseases, parasites and predators on populations ^[125]
• limiting activities at the overwintering sites (logging, tourism),^[49][126]
• payments to local residents to monitor forest habitats^[49]
• mass planting of milkweed and nectar plants. Concerned individuals governmental agencies, and organizations have made efforts to restore milkweed habitats to provide nectar and foodplants.^{[127][128][129][130][131][132]}
• 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^{[133][134][135]}
• the creation of media (websites, magazine articles, art, newspapers, movies, children’s books, documentaries, educational curricula) that provides information about monarch migration.

Economic influences related to the migration phenomena

Tourism around the overwintering sites in Mexico and California provides income for those who provide such services.^[136]

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.^[49]

Contributions are solicited to fund programs that support monarch conservation efforts.^[137][138] Some donations to conservation programs are directed toward fundraising for the organization.^[139]

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.^[140]

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^[141]

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.^{[51][142][143][144]}

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 ^[51]:11

Animal research in conservation has a role but it has little significance unless sociological, economic and political issues are satisfactorily resolved.^[141]

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.^[145] The world Wildlife Fund pays for the salaries of enforcement officers.^[49]

Presidential memorandum

President Obama recently directed his agencies via a presidential memorandum, to "Promote the Health of Honey Bees and Other Pollinators". The monarch butterfly was specifically mentioned in the memorandum.^[118]

Petition to designate the monarch endangered

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.^[146] 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^[147]

Scientific community

Not all researchers are in consensus regarding lobbying for federal government intervention, population censuses,^[55] 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.^[55] Some researchers have been critical of each other for not making their data available to the public and to each other.^{[148][54][53]} Like all scientic 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".^[69] Another researcher denies that the monarch migrates but instead is greatly affected by weather conditions to head south.^[69]

Local governments

Local governments are considering legislation to provide habitat for migrating monarchs.^[149]

See also

• Conservation biology
• Lepidoptera migration
• Monarch Butterfly Biosphere Reserve
• Peninsula Point Light, Michigan
• Catalina Trail

References

Bibliography

Books

• Halpern, Sue (2002). Four Wings and a Prayer. Kindle edition. New York, New York: Random House. ISBN 978-0-307-78720-0. 
• Oberhauser, Karen S.; Batalden, Rebecca; Howard, Elizabeth (2009). Monarch Butterfly Monioring in North America: Overviews and Protocols. Montreal, Quebec: The Commission for Environmental Cooperation. ISBN 978-2923358567. Retrieved September 17, 2014. 
• Oberhauser, Karen S.; Solensky, Michelle J (2004). The Monarch Butterfly: Biology and Conservation (First ed.). Ithaca NY: Cornell University Press. ISBN 978-0801441882. 
• Pyle, Robert Michael (2014). Chasing monarchs: Migrating with the butterflies of passage. Yale University Press. ISBN 978-0300203875. 
• Pyle, Robert Michael (2010). Mariposa Road:the first butterfly big year. New York: Houghton Mifflin Harcourt Publishing Company. ISBN 97-80618945399. 
• Pyle, Robert Michael (1981). National Audubon Society Field Guide to North American Butterflies. New York: Alfred A. Knopf. ISBN 978-0394519142. 

Journals

• Brower, Lincoln (1977). "Monarch Migration". Natural History 85 (6). 
• Brower, Lincoln P.; Fink, Linda S.; Brower, Andrew Van Zandt; Leong, Kingston; Oberhauser, Karen; Altizer, Sonia; Taylor, Orley; Vickerman, Danel; Calvert, William H.; Van Hook, Tonya; Alonso-Mejia, Alphonso; Malcolm, Stephen B.; Owen, Denis F.; Zalucki, Myron P. (September 1995). "On the dangers of interpopulational transfers of monarch butterflies". BioScience 45 (8): 540. doi:10.2307/1312699. JSTOR 1312699. 

• Davis, Andrew K. (June 20, 2011). "Are migratory monarchs really declining in easteren North America". Insect Conservation and Diversity 5 (2): x. doi:10.1111/j.1752-4598.2011.00158.x. 
• Davis, Andrew K. (2014). "Opinion: conservation of monarch butterflies (Danaus plexippus) could be enhanced with analyses and publication of citizen science tagging data". Insect Conservation and Diversity. doi:10.1111/icad.1284 (inactive 2015-03-29). 

External links

• Journey North
• Forests For Monarchs, Mexico

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