Monarch butterfly migration
Monarch butterfly migration is the phenomenon, mainly across North America, where the subspecies Danaus plexippus plexippus migrates each summer and autumn to and from overwintering sites on the West Coast of California or mountainous sites in Central Mexico. Other subspecies perform minor migrations or none at all. This massive movement of butterflies has been called "one of the most spectacular natural phenomena in the world".
The monarchs begin their southern migration September to October. Eastern and northeastern populations, originating in southern Canada and the United States, travel to overwintering sites in central Mexico. They arrive at their roosting sites in November. They remain in their roosts during the winter months and then begin their northern migration in March. No individual butterfly completes the entire round trip. Female monarchs lay eggs for a subsequent generation during the northward migration. Four generations are involved in the annual cycle.
Similarly, the western populations migrate annually from regions west of the Rocky Mountains to overwintering sites on the coast of California.
Not all monarch populations make major migrations. Monarchs migrate short distances in Australia and New Zealand. There are some populations, for instance in Florida and the Caribbean, that do not migrate, as well as another subspecies distributed in the Caribbean, Central America and northern South America. Additional overwintering sites have been identified in Arizona and northern Florida.
As late as 1951, monarchs were mistakenly thought to overwinter as adults or pupae. Roosts of thousands were observed in southern regions of North America.
Migrating western populations of Danaus plexippus and their overwintering sites were known long before the Mexican winter sites were discovered 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. Historical records kept by lepidopterists do not mention the presence of monarchs in their current western range extending northward through Washington, Oregon and Canada. Female Monarchs lay their eggs almost exclusively on milkweeds, which provide the caterpillars and later adults with protection from predators, and it is speculated that milkweed may not have been available until western lands were cultivated, resulting in the expansion the butterfly.
More formal migration 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 in a south to southwest direction during the North American 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.:290–296, 305, 306, 310
Fred Urquhart advertised for 'interested persons' in the Mexican press to assist him in locating the roosting sites. Catalina Trail and Kenneth C. Brugger responded and in January 1975 they led him to one of the major overwintering sites. Urquhart, William Calvert, John Christian, and Lincoln P. Brower collaborated to publish the details in this discovery in 1976. There was some concern at the time that public knowledge would endanger the butterflies. Since 1976, multiple overwintering sites have been identified and their locations are public knowledge.
Although the exact dates change each year, 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 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 Mexico, or they have a higher rate of mortality than those migrating inland.
Monarch butterflies are thought to 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. Research is ongoing.
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.
In most individual adult butterflies, diapause begins with its southern migration, but unlike other insects in this state, it remains 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 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 hemolymph. 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.
Diapause has distinct phases. Decreasing day period and dropping temperatures inhibit the production of juvenile hormone. This represses the development of gonadal activity, mating behaviors, and egg-laying. 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.
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.
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 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.
Roosting and overwintering sitesEdit
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. 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.: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 in inland areas and on non-native tree species.
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.:2 Overwintering sites have also been observed in coastal South Carolina along with ovipositing females. On the US East Coast, they have overwintered as far north as Lago Mar, Virginia Beach, Virginia.
At least twenty colonies exist in Mexico.: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 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.
Range and characteristics of migrating butterfliesEdit
The western population of migrating monarchs overwinters in 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 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.
Migrating monarchs tend to have darker orange and larger wings than they do during the breeding phase in the summer. The darkness of the orange color in monarch wings appears to be a visual indicator of their migratory ability. The monarchs migrating south are larger in size and weight  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 longer distances tended to be larger. Wing size differs between early and late migrants. Earlier migrants tend to be more robust, healthier individuals, while late-migrating monarchs represent the ones that fell behind, presumably because they are less well-suited for migration. Early-migrating monarchs tended to be redder, have larger, and more elongated wings, and larger bodies, than those at the tail end of the migration.
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 methodsEdit
Initially, direct observation was the primary method used to assess monarch migration. More sophisticated methods have been developed since 1975.
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 recaptureEdit
Tagging and recapture allows the determination of the total population of monarchs. The recaptured monarchs are directly proportional to the number in the whole population. This procedure allows an estimate of the total population size by dividing the number of marked individuals by the proportion of marked individuals in the second sample. Other 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. The northern migration from Florida and the disbursement of roosts in California have been studied using these methods.
The migration of the Monarch butterfly is documented and studied during annual butterfly counts. During the southward migration, concentrations of migrating monarchs are consistently monitored by the Cape May Bird Observatory,Peninsula Point Light, Michigan, and Point Pelee National Park, Ontario, Canada. Other protocols used to conduct the censuses include: Driving Census, Walking Census, Roosting Counts, and Hawk-watch Observations. 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. The ratio of monarchs to other species observed during a count provides information about habitat changes. Yearly fluctuations are attributed to severe weather effects, El Nino Southern Oscillation and volcanic eruption.
Aerial and satellite observationsEdit
Satellite imagery has been used to assess changes in and around the Mexican overwintering areas. Researchers have determined that an accurate count of the butterflies using satellite images is not possible, though aerial assessments of the areas surrounding the colonies reveals potential areas of colonization. After these efforts, the costs out-weighed the benefits of high-altitude aerial photography and it was determined to be time-consuming and expensive.
Types of data collectedEdit
Direct observation usually means that an observer records data while the butterfly is one stage of its migration. These data can include:
- Historical accounts.
- flight vectors
- appearance in the northern breeding range
- appearance in overwintering sites
- location of overwintering sites
- wing condition
- butterfly counts (butterfly sightings/minute)
- emergence of host plants
- local frosts
- estimations of populations and densities
- wind direction
- cloud cover
- parasite loads
Use of data and availabilityEdit
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.
Most of those who participate in the study of Monarch migration are laypersons (trained and untrained) and are sometimes referred to as 'citizen scientist'. Anecdotal information by observers has been criticized and called 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.
Though the tagging of Lepidoptera was done as early as 1796 on silk moths, Fred Urquart initiated monarch butterfly tagging and used wing incisions, spots arrangements, colored spots, spraying with dyes, painted letters and numbers to mark the butterflies. These methods were unsuccessful as there were no instructions to return the butterfly or record the recovery.:279 Currently, many organizations study migration by tagging. New methods of studying the migration include the use of VHF transmitters and commercial aircraft. Isotopic tagging has been employed.
Migratory theory mechanismsEdit
There are many theories that attempt to explain monarch migration. "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.
Time-Compensated sun compass theoryEdit
Time-Compensated sun compassEdit
The sun plays an integral role in the monarchs’ migratory patterns: they travel during the day and use a circadian clock based on the sun's position in the sky to orient themselves. This clock mechanism is time compensated, where each butterfly entrains to the light-dark cycle of its surroundings and thereby knows how to interpret the changing light patterns throughout the day. Various studies have shown this behavior both in natural systems and laboratory settings. Yet there remains much to be researched about the underlying mechanisms for interpreting the orientation and timing cues that lead to the migratory patterns of the monarchs.
Among the better understood areas of the sun compass is the neural and anatomical layout of the underlying mechanism in the butterfly. Light is first perceived by the monarch's compound eyes, hitting the retina which registers the azimuthal angle of the light. The light polarization, which is used by various insects for navigation, is then detected by the dorsal rim area, a specialized feature of the compound eye. These cues are then passed on to the central complex of the brain, where they are interpreted. Here, single neurons combine the azimuthal location of the sun and the e-vector angle (angle of polarized skylight). This information is then processed and further combined with other locational and orientational cues in order to produce migratory behavior. Overall, studies agree that the neural processing underlying the monarch's sun compass occurs in the brain's central complex; the neural structure found there indicates the butterflies engage in spatial learning, memory and awareness. Further research is needed in order to model the neuronal network and fully understand how spatial cues are modeled and stored in the brain.
While neural processing may occur in the monarch's brain, research indicates that the actual circadian clock underlying the migratory patterns is located in the butterfly's antennae. Butterflies with their antennae removed showed no consistent group orientation in their migratory patterns: first exposed to a consistent light-dark cycle prior to release, antennae-less monarchs would show consistent individual directional flight, but no clear cardinal directionality as a group, unlike intact monarchs. Painting the antennae black, thereby causing a free running circadian rhythm, led to altered orientation patterns as well. Examination of various genes and proteins involved in circadian rhythms showed that the antennae exhibited their own circadian fluctuations, even when removed from the butterfly and studied in vitro. Overall, the study of antennae-less Monarchs as well as the in vitro analysis of the antennae indicate that the antennae are both necessary for the proper functioning of the time-compensated sun compass and contain their own circadian clocks that function even without the butterfly's brain.
The importance of the circadian clock in the function of this time-compensated sun compass system has led to investigation into the molecular basis of the clock mechanism in monarchs, resulting in a well-defined model of both central and secondary clocks. Similarly to Drosophila and mammals, the core mechanism of the monarch circadian clock relies on a transcriptional-translational auto-regulatory negative feedback loop that drives rhythms in the mRNA and protein levels of core circadian clock components. However, the monarch mechanism has been found to be unique because it diverges from other clock mechanisms in the functions of its elements, some which reflect that of a Drosophila clock and some which reflect that of a mammalian clock. The most unique aspect of the monarch clock mechanism is that it involves two cryptochrome proteins – CRY1 and CRY2 – with differing functions. CRY1 is much like the Drosophila CRY in that it functions as a photoreceptor, while CRY2 is similar to the mammalian CRY in that it functions as one of the major repressors in the feedback loop.
In the major monarch clock mechanism, CRY1 functions as a blue light photoreceptor, providing the clock with a means to entrain to light-dark cycles. The proteins CLOCK (CLK) and CYCLE (CYC) function as transcription factors which drive transcription of the period (per), timeless (tim), and cry2 genes. The translated PER, TIM, and CRY2 proteins form complexes in the cytoplasm and, after a delay, translocate back into the nucleus, allowing CRY2 to repress transcription.
In addition to the core feedback loop, a second modulatory feedback loop has also been identified in monarchs. This feedback loop is much like the Drosophila second feedback loop and includes genes that encode orthologs of VRILLE and PDP1, which are known to regulate CLK transcription in Drosophila.
Bi-directionality of sun compassEdit
Monarchs are known to use their time-compensated sun compass during both the southern migration in the fall and the northern remigration in the spring. The change in directionality necessary to re-orient the monarchs has been shown to depend on the cold temperatures that the monarchs experience while overwintering in the coniferous forests of Mexico. The change in sun compass direction does not depend on the change in photoperiod experienced during the winter months, but this change is likely to affect the timing of the northern remigration in the spring.
An experiment demonstrating the importance of cold exposure for remigration utilized fall monarchs with and without cold temperature exposure in the laboratory. The monarchs that experienced cold temperatures during the winter months successfully changed the direction of their sun compass and oriented north in the spring. In contrast, the monarchs that never experiences the cold temperatures during the winter months oriented south in the spring, and thus did not experience a change in sun compass direction to accompany their migration. Therefore, the cold exposure experienced while overwintering is required for the monarch's migration cycle.
During the northern remigration of monarchs in the spring, the time-compensated sun compass uses the same substrates as used in the fall. However, the mechanistic differences in these substrates that allows for a switch in the directionality of the compass is still unknown. RNA-sequencing differences found between the fall and spring butterflies is one avenue of research that could locate the mechanism responsible for the recalibration, which may utilize a temperature sensor to start the switch.
Genetic memory theoryEdit
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.
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.
The Columbus 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.
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.
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
There is debate between researchers and citizen scientists who study the migration regarding the possible local extinction of the Monarch. The species is distributed worldwide and is not endangered. Still, there is concern that the migration of the eastern North American population may be at risk. Media reports of the monarch's forthcoming extinction have been criticized by scientists. "Monarchs are not in danger of extinction," states Lincoln Brower, a leading monarch conservation researcher.
Monitoring and conservation organizations can be organized by their efforts directed to each of the four stages in the monarch life cycle.
- "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 
The winter roosts in both Mexico and California were declared to be threatened 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".
Work to protect the overwintering sites in Mexico began before 1975 and were initiated by local residents. Populations of overwintering monarchs declined significantly when the 1992 counts are compared to more recent censuses. Overwintering sites exist along the Gulf Coast, Arizona and Florida.
Periodic disasters at the Mexican overwintering sites are often credited with 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.
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 acreageEdit
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 factors that may 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.
There are many organizations and programs that exist to promote the preservation of the monarch and its migration. 3-letter codes, explained in the linked footnotes, are used to head the table compactly.
|Organization or political entities||Monarch conservation programs||Database|
| Monarch Joint Venture
| Association for butterflies
|Project Monarch Health||♦||♦||♦||♦|
| Pollinator Partnership
|La Naturaleza Nos Llama||♦||♦||♦||♦||♦|
|National Park System||♦||♦||♦ ||♦|
|Executive Order – Presidential Memorandum ||♦||♦|
|Iowa Department of Natural Resources Iowa Prairie Resource Center||♦||♦||♦|
|California State Park system||♦||♦|
|City ordinance of Capitola, California||♦||♦||♦|
|The Coastal Zone Management Act, California||♦||♦|
|Assessment and Status Report, Canada||♦||♦|
|Monarch Butterfly Fund||♦||G|
|Forest For Monarchs||♦ ||R||♦|
|Monarch Ecology Fund||♦|
|Global Climate Summit California Environmental Protection Agency||♦||♦||G|
|Medio Ambiente y Recursos Naturales||♦||♦||G||♦||♦|
|Texas Milkweeds and Monarchs||♦||♦||♦||♦||♦||♦||♦||♦||♦||♦|
|Wild Ones Wild for Monarchs||♦||♦|
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.
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 groupsEdit
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 :11
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.
Local people groups, municipalities, government and non-governmental organizations have proposed policies to preserve the migration. A trilateral effort involving Mexico, Canada and the United States was established to organize conservation efforts. One policy that has been implemented is the mass planting of milkweed and nectar plants.
Mexico has developed other policies to help preserve the migration. Payments to local residents to monitor forest habitats have been considered. Another policy is to encourage reforestation of overwintering habitat. Efforts to limit activities at the overwintering sites (logging, tourism) that may disturb the monarchs roosts have been attempted.
In the US, the Farm Service Agency Conservation Reserve Program enrolls farmers in a program in which they receive yearly payments for removing environmentally sensitive areas from production and to promote species of plants that improve habitat promoting food and nectar plants. The University of Minnesota co-ordinates studies across North America to monitor the health and populations of monarch larvae. Other organizations lobby lawmakers, corporations, highway departments, utilities and policy-makers to preserve habitat.
US National strategyEdit
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.
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 protect Monarch butterflies and other pollinators:
- 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.
- Pollinator Habitat Acreage: Restore or enhance seven million acres of land for pollinators over the next five 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.
Endangered species designationEdit
Both the United States and Canada have considered 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.
Differences in opinions by researchers are common and not all researchers are in agreement regarding lobbying for federal government intervention, 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'. 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.
- 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 (G) and received (R) 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.
- Morris, Gail. "Status of Danaus plexippus in Arizona" (PDF). Southwest Monarch Study. Retrieved 2016-01-09.
- Pyle 1981, pp. 712–713.
- Morris, Gail M.; Klein, Christopher; Morris, Scott M. (2015). "Status of Danaus plexippus population in Arizona" (PDF). Journal of the Lepidopterists' Society. 69 (2): 91–107. doi:10.18473/lepi.69i2.a10.CS1 maint: Uses authors parameter (link)
- Klots, Alexander B. (1951). A Field Guide to the Butterflies of North America, East of the Great Plains (Tenth ed.). Boston: Houghton Mifflin. pp. 78, 79. ISBN 978-0-395-07865-5.
- Brower 1977, p. 41.
- "The Monarchs' Arrival in Mexico and Mexican Traditions". Retrieved August 26, 2014.
- "Mexico's Monarchs Return". Retrieved August 26, 2014.
- Lowery, Linda (2004). Day of the Dead. Minneapolis, Minnesota. pp. 28–29. ISBN 978-0-87614-914-0.
- Pyle 2014, p. 7.
- Pyle 2014, p. 15.
- Urquhart, Fred A. (1960). The Monarch butterfly. University of Toronto Press.
- Brower 1977, p. 43.
- Sanchez Reyna, Ramon (2008). Turiguía:Michoacán [Tour Guide: Michoacán] (in Spanish). Mexico City: Grupo Azabache, S.A. de C.V. p. 152. ISBN 978-607-7568-08-7.
- "Historic Rendezvous of Those Who Located Monarch Butterfly Roosting Sites Draws Crowd of 200". Texas Butterfly Ranch. 2014-03-28. Retrieved 2015-03-10.
- Brower 1977, p. 54.
- "The Location of the Monarch Overwintering Sites in Mexico". Journey North. Retrieved 2015-03-10.
- Taylor, O.R.; Jim Lovett; Cathy Walters; Sarah Schmidt (2002). "2001 Season Summary". Monarch Watch. Retrieved July 17, 2014.
- McCord, John W.; Davis, Andrew K. (2010). "Biological Observations of Monarch Butterfly Behavior at a Migratory Stopover Site: Results from a Long term Tagging Study in Coastal South, Carolina". Journal of Insect Behavior. 23 (6): 405–418. doi:10.1007/s10905-010-9224-x.
- The Insects; Structure and Function, 4th Edition. R.F. Chapman, Cambridge University Press, 1998. ISBN 0-521-57048-4, p 404.
- Brower 1977, p. 52.
- Oberhauser 2009, p. 9.
- "The Incredible Journey of the Butterflies, airdate January 27, 2009". PBS Nova Series.
- Kostal, V. (2006). "Eco-physiological phases of insect diapause". Journal of Insect Physiology. 52 (2): 113–127. doi:10.1016/j.jinsphys.2005.09.008. PMID 16332347.
- Glen E. Collier; William J. Murphy (August 1997). "A molecular phylogeny for aplocheiloid fishes (Atherinomorpha, Cyprinodontiformes): the role of vicariance and the origins of annualism". Mol. Biol. Evol. 14 (8): 790–9. doi:10.1093/oxfordjournals.molbev.a025819. PMID 9254916.
Annual aplocheiloid killifish embryos possess a rare ability among vertebrates to enter stages of developmental arrest (diapause) when subjected to adverse environmental conditions.
- The Insects; Structure and Function, 4th Edition. R.F. Chapman, Cambridge University Press, 1998. ISBN 0-521-57048-4, p 403.
- Tauber, M.J., Tauber, C.A., Masaki, S. (1986) Seasonal Adaptations of Insects. Oxford University Press, 414 pp.
- Brower et al. 1995, p. 542.
- Epicuticular Wax Secretion in Diapause and Non-diapause Pupae of the Bertha Army worm, Author: HEGDEKAR, B. M., Source: Annals of the Entomological Society of America, Volume 72, Number January 1, 15, 1979 , pp. 13–15(3)Publisher: Entomological Society of America
- The Insects; Structure and Function, 4th Edition. R.F. Chapman, Cambridge University Press, 1998. ISBN 0-521-57048-4, pp. 403–404
- Herman, 1981, Biological Bulletin Vol 160,No1,pp 89-106
- Denlinger, D.L. (1986). "Dormancy in tropical insects". Annual Review of Entomology. 31: 239–264. doi:10.1146/annurev.en.31.010186.001323. PMID 3510585.
- Yoder, J.A.; Denlinger, D.L.; Wolda, H. (1992). "Aggregation promotes water conservation during diapause in the tropical fungus beetle, Stenotarsus rotundus". Entomologia Experimentalis et Applicata. 63 (2): 203–205. doi:10.1111/j.1570-7458.1992.tb01574.x.
- "Chill turns monarchs north". Science News. 2014-04-14.
- Rubino, Richard (March–April 2014). "Some Observations on Monarch Migration". MonarchNet News – A Citizen Science Newsletter (2): 2.
- Pyle 2014, p. x.
- Howard, E. and A.K. Davis. 2009. The fall migration flyways of monarch butterflies in eastern North America revealed by citizen scientists. Journal of Insect Conservation 13(3): 279–286.
- Davis, A.K., N.P. Nibbelink and E. Howard. 2012. Identifying large- and small-scale characteristics of migratory stopover sites of monarch butterflies with citizen-science observations. International Journal of Zoology, Article ID 149026, 9 pages.
- Pyle 2010, pp. 15,16 290.
- "1997 North American Conference on the Monarch Butterfly". Roundtable Discussions and Priority Actions (in English and Spanish). U.S. Fish and Wildlife Service, Officeof International Affairs. Commission for Environmental Cooperation. November 10–14, 1997. p. 3,4,10,18.
- "Monarch Butterfly Journey North". Annenberg Learner.
- Brower 1977, p. 44.
- Pyle 2014, p. 3.
- Zhan, Shuia; Zhang, Wei; Niitepold, Kristjan; Hsu, Jeremy; Haeger, Juan Fernandez; Zalucki, Myron P.; Altizer, Sonia; de Roode, Jacobus C.; Reppert, Stephen M.; Kronforst, Marcus R. (2014-10-16). "The genetics of Monarch butterfly migration and warning coloration". Nature. 514 (7522): 317–321. Bibcode:2014Natur.514..317Z. doi:10.1038/nature13812. PMC 4331202. PMID 25274300.
- Taylor, O.R.; Lovett, Jim; Walters, Cathy; Schmidt, Sarah (2002). "2001 Season Summary". Monarch Watch. Retrieved July 17, 2014.
- Oberhauser 2009, p. 10.
- Monarch Joint Venture. 2016. Potential risks of growing exotic (non-native) milkweeds for monarchs. This 'potential' risk does not have solid scientific support. If cared for properly, and iif the Monarch eggs laid on it,are brought in to be raised through their life cycle, these Monarch butterflies can have an infestation rate as low as 5%. There has been no scientific study that includes this data of the low rate of O.e. in Monarchs raised from eggs. http://monarchjointventure.org/images/uploads/documents/Oe_fact_sheet.pdf
- "Monarch Migration Studies". Retrieved March 26, 2014.
- Oberhauser 2004, p. 79.
- Tipping, Christopher (May 8, 1995). "Chapter 11: The Longest Migration". Gainesville, FL: Department of Entomology & Nematology University of Florida, Gainesville, FL. Retrieved September 2, 2014.
- Davis, A. K. (2009). "Wing color of monarch butterflies (Danaus plexippus) in eastern North America across life stages: migrants are 'redder' than breeding and overwintering stages". Psyche. 2009: 1–5. doi:10.1155/2009/705780.
- Davis, Andrew K.; Chi, Jean; Bradley, Catherine; Altizer, Sonia (2012). Chiao, Chuan-Chin (ed.). "The Redder the Better: Wing Color Predicts Flight Performance in Monarch Butterflies". PLoS ONE. 7 (7): e41323. Bibcode:2012PLoSO...741323D. doi:10.1371/journal.pone.0041323. PMC 3405115. PMID 22848463.
- Altizer, Sonia; Davis, Andrew K. (2009). "Populations Of Monarch Butterflies With Different Migratory Behaviors Show Divergence In Wing Morphology". Evolution. 64 (4): 1018–1028. doi:10.1111/j.1558-5646.2009.00946.x.
- Altizer, S.M., K.A. Hobson, A.K. Davis, J.C. de Roode, and L.I. Wassenaar. 2015. Do healthy monarchs migrate farther? Tracking natal origins of parasitized vs. uninfected monarch butterflies overwintering in Mexico. PLoS One 10(11): DOI: 10.1371/journal.pone.0141371
- Yang et al. 2015. Intra-population variation in the natal origins and wing morphology of overwintering western monarch butterflies Danaus plexippus. Ecography
- Satterfield, Dara A.; Davis, Andrew K. (2014). "Variation in wing characteristics of monarch butterflies during migration: Earlier migrants have redder and more elongated wings". Animal Migration. 2 (1). doi:10.2478/ami-2014-0001.
- McCord J. W., Davis A. K., Biological observations of monarch butterfly behavior at a migratory stopover site: results from a long-term tagging study in coastal South Carolina, Journal of Insect Behavior, 2010, 23, 405–418
- Davis, A.K. and E. Rendon-Salinas. 2010. Are female monarch butterflies declining in eastern North America? Evidence of a 30-year change in sex ratios at Mexican overwintering sites. Biology Letters 6: 45–47. PDF
- Oberhauser 2009, p. 5.
- Urqhart, Fred A.; Urqhart, N. A. (1976). "A Study of the Peninsular Florida Populations of the Monarch Butterfly (Danaus p. plexippus, Danaidae)". Journal of the Lepidopterists' Society. 30 (2): 73–87.
- Davis 2011, pp. 1–5.
- Brower, Lincoln P.; Taylor, Orley R.; Williams, Ernest H. (2012). "Response to Davis: choosing relevant evidence to assess monarch population trends". Insect Conservation and Diversity. 5 (4): 327–329. doi:10.1111/J.1752-4598.2011.00176.x.
- Knight, Amy; Brower, Lincoln P.; Williams, Ernest H. (1999). "Spring remigration of the monarch butterfly, Danaus plesippus (Lepidoptera: Nymphhalidedae) in north-central Florida: estimating population parameters using mark-recapture". Biological Journal of the Linnean Society. 68 (4): 531–556. doi:10.1111/j.1095-8312.1999.tb01187.x. Retrieved September 17, 2014.
- "Rincon Biologist Volunteers for Annual Monarch Butterfly Event". Rincon Consultants. Retrieved September 17, 2014.
- "Parks Canada – Point Pelee National Park – Monarch Migration". Parks Canada. Retrieved September 17, 2014.
- "The Xerces Society Western Monarch Thanksgiving Count". The Xerces Society for Invertebrate Conservation. Retrieved September 17, 2014.
- Walton, Dick. "Monarch Monitoring Project". Cape May Bird Observatory. Retrieved September 17, 2014.
- Oberhauser 2009, pp. 30–31.
- Davis, Andrew K.; Garland, Mark S. (2002). "An Evaluation of Three Methods of Counting Migrating Monarch Butterflies in Varying Wind Conditions" (PDF). Southeastern Naturalist. Retrieved 11 July 2018.
- Oberhauser 2009, pp. 29–30.
- Oberhauser 2009, p. 26.
- "terrace-ave-bolinas – The Monarch Program". Retrieved September 17, 2014.
- "Ikonos_2004_2008_Animated_Combined.gif (1000×1361)". Journey North. Retrieved September 17, 2014.
- Davis, Andrew (2014). "Opinion: conservation of monarch butterflies (Danaus plexippus) could be enhanced with analyses and publication of citizen science tagging data". Insect Conservation and Diversity. 8 (2): 103–106. doi:10.1111/icad.12084.
- "Southwest Monarch Study, Data Access Policy". Southwest Monarch Study. Retrieved 2014-09-19.
- Pais, Miguel. "Northwestern African sightings of D.plexippus, Maroc>Pappilons>Danaus plexippus". Google Maps. Retrieved 2014-09-19.
- Halpern 2002.
- "Map of Fall Monarch Migration Through Texas". Texas Monarch Watch. Retrieved 2014-10-07.
- Pyle 2014, p. 22.
- "Southwest Monarch Study". Southwest Monarch Study. Retrieved 2014-09-19.
- "Monarch Monitoring Project". New Jersey Audubon. Retrieved 2014-09-19.
- "United Using Planes to Track Butterflies and Birds". Retrieved June 30, 2014.
- "Tracking with isotopes". Retrieved September 13, 2014.
- Wassenaar, L. I.; Hobson, K. A. (December 22, 1998). "Natal origins of migratory monarch butterflies at wintering colonies in Mexico: New isotopic evidence". Proceedings of the National Academy of Sciences. 95 (26): 15436–15439. Bibcode:1998PNAS...9515436W. doi:10.1073/pnas.95.26.15436. PMC 28060. PMID 9860986.
- Halpern, Sue (2002). Four Wings and a Prayer. Kindle edition. New York City: Random House. ISBN 978-0-307-78720-0.
- Reppert, Steven M.; Zhu, Haisun; White, Richard H. (2004). "Polarized Light Helps Monarch Butterflies Navigate". Current Biology. 14 (2): 155–158. doi:10.1016/j.cub.2003.12.034. ISSN 0960-9822.
- Guerra, Patrick A.; Merlin, Christine; Gegear, Robert J.; Reppert, Steven M. (2012). "Discordant timing between antennae disrupts sun compass orientation in migratory monarch butterflies". Nature Communications. 3 (1): 958. Bibcode:2012NatCo...3E.958G. doi:10.1038/ncomms1965. ISSN 2041-1723. PMC 3962218. PMID 22805565.
- Merlin, C.; Gegear, R. J.; Reppert, S. M. (2009-09-25). "Antennal Circadian Clocks Coordinate Sun Compass Orientation in Migratory Monarch Butterflies". Science. 325 (5948): 1700–1704. Bibcode:2009Sci...325.1700M. doi:10.1126/science.1176221. ISSN 0036-8075. PMC 2754321. PMID 19779201.
- Mouritsen, H.; Frost, B. J. (2002-07-09). "Virtual migration in tethered flying monarch butterflies reveals their orientation mechanisms". Proceedings of the National Academy of Sciences. 99 (15): 10162–10166. Bibcode:2002PNAS...9910162M. doi:10.1073/pnas.152137299. ISSN 0027-8424. PMC 126641. PMID 12107283.
- Perez, Sandra M.; Taylor, Orley R.; Jander, Rudolf (May 1997). "A sun compass in monarch butterflies". Nature. 387 (6628): 29. Bibcode:1997Natur.387...29P. doi:10.1038/387029a0. ISSN 0028-0836.
- Reppert, Steven M.; Guerra, Patrick A.; Merlin, Christine (2016-03-11). "Neurobiology of Monarch Butterfly Migration". Annual Review of Entomology. 61 (1): 25–42. doi:10.1146/annurev-ento-010814-020855. ISSN 0066-4170. PMID 26473314.
- Labhart, Thomas; Baumann, Franziska; Bernard, Gary D. (2009-10-30). "Specialized ommatidia of the polarization-sensitive dorsal rim area in the eye of monarch butterflies have non-functional reflecting tapeta". Cell and Tissue Research. 338 (3): 391–400. doi:10.1007/s00441-009-0886-7. ISSN 0302-766X. PMC 2779342. PMID 19876649.
- Zhan, Shuai; Merlin, Christine; Boore, Jeffrey L.; Reppert, Steven M. (November 2011). "The Monarch Butterfly Genome Yields Insights into Long-Distance Migration". Cell. 147 (5): 1171–1185. doi:10.1016/j.cell.2011.09.052. ISSN 0092-8674. PMC 3225893. PMID 22118469.
- Cyran, Shawn A.; Buchsbaum, Anna M.; Reddy, Karen L.; Lin, Meng-Chi; Glossop, Nicholas R.J.; Hardin, Paul E.; Young, Michael W.; Storti, Robert V.; Blau, Justin (February 2003). "vrille, Pdp1, and dClock Form a Second Feedback Loop in the Drosophila Circadian Clock". Cell. 112 (3): 329–341. doi:10.1016/s0092-8674(03)00074-6. ISSN 0092-8674.
- Guerra, Patrick A.; Reppert, Steven M. (March 2013). "Coldness Triggers Northward Flight in Remigrant Monarch Butterflies". Current Biology. 23 (5): 419–423. doi:10.1016/j.cub.2013.01.052. ISSN 0960-9822. PMID 23434279.
- Guerra, Patrick A; Reppert, Steven M (October 2015). "Sensory basis of lepidopteran migration: focus on the monarch butterfly". Current Opinion in Neurobiology. 34: 20–28. doi:10.1016/j.conb.2015.01.009. ISSN 0959-4388. PMC 4514576. PMID 25625216.
- Halpern, Sue (2002). Four Wings and a Prayer. Kindle edition location 1565. New York City: Random House. ISBN 978-0-307-78720-0.
- "How Do Monarchs Find the Overwintering Sites?". University of Minnesota Monarch Lab. Retrieved September 9, 2014.
- Mouritsen (April 30, 2014). "An experimental displacement and over 50 years of tag-recoveries show that monarch butterflies are not true navigators (pre-published paper provided by author)". PNAS. 110 (18): 7348–7353. Bibcode:2013PNAS..110.7348M. doi:10.1073/pnas.1221701110. PMC 3645515. PMID 23569228.
- "The Incredible Journey of the Butterflies, airdate January 27, 2009". PBS Nova Series.
- Davis, Donald (2014-11-27). "DPLEX-L:59250 The possibility of a trans-Gulf migration, oil rigs, Dr. Gary Ross, and more" (mailing list). Monarch Watch, University of Kansas.
- "The lonely flight of the monarch butterfly". NewsAdvance.com, Lynchburg, Virginia Area. Retrieved 2014-10-07.
- "Rates of Deforestation & Reforestation in the U.S." Seattle PI. Retrieved August 27, 2014.
- Vane-Wright, Richard I. The Columbus Hypothesis: ... An Explanation for Dramatic 19th Century Range Expansion of the Monarch Butterfly Stephen B. Malcom and Zalucki, Myron P., Eds 1993 Biology and Conservation of the Monarch Butterfly From,. the 2nd International Conference on the Monarch Butterfly Natural History Museum of Los Angeles County. Los Angeles, CA.Pp. 183–185.
- Plumer, Brad (January 29, 2014). "Monarch butterflies keep disappearing. Here's why". The Washington Post. Retrieved September 2, 2014.
- Malcolm, Stephen B. (1993). "Conservation of monarch butterfly migration in North America: An endangered phenomenon". In Malcolm, S.B.; Zalucki, M.P. (eds.). Biology and Conservation of the Monarch Butterfly. Science Series No.38. Natural History Museum of Los Angeles County. pp. 357–361.
- Gore, Bob. "Iowa Associations Working On Preserving the Dying Breed of Monarch Butterfly Against Extinction". Empire State Tribune. Retrieved 2015-03-10.
- "Are GMOs causing monarch butterflies to become extinct?". Tampa Bay Times. Retrieved 2015-03-10.
- Ball, Nicole. "Monarch Butterfly Garden Workshop". Hamlet Hub (Rye, NY). Retrieved 2015-03-10.
- "Are GMOs causing monarch butterflies to become extinct?". Tampa Bay Times. Retrieved 2015-03-10.
- LaCapra, Véronique. "Saving The Monarch's Migration: A Conversation With Ecologist Lincoln Brower". St. Louis Public Radio. Retrieved 2015-03-10.
- Oberhauser 2009, p. 13.
- "Bring Back The Monarchs". Retrieved August 26, 2014.
- Crolla, Jeffrey P.; Lafontaine, J. Donald. "Monarch Watch : Reading Room : Articles : Status Report on the Monarch Butterfly (Danaus plexippus) in Canada". Retrieved September 4, 2014.
- Bartel, Rebecca; Oberhauser, Karen; De Roode, Jacob; Atizer, Sonya (February 2011). "Monarch butterfly migration and parasite transmission in eastern North America". Ecology. 92 (2): 342–351. doi:10.1890/10-0489.1. PMID 21618914.
- Bradley, C. and S. Altizer. 2005. Parasites hinder monarch butterfly flight: implications for disease spread in migratory hosts. Ecology Letters 8: 290–300
- Davis 2014, p. 1.
- http://www.forestsformonarchs.org/ Forest For Monarch
- Griffiths, Jessica; Villablanca, Francis (July 2013). "Management of Monarch butterfly (Danaus plexippus) overwintering habitat: recommendations based on patterns of tree use". White Paper Prepared for the Xerces Society.
- Marriott, David. "Where To See The Monarchs In California" (PDF). Monarch Watch. The Monarch Program. Retrieved 29 September 2017.
- Taylor, Chip (January 29, 2014). "Monarch Population Status". Monarch Watch. Retrieved 2014-10-06.
- "The lonely flight of the monarch butterfly". NewsAdvance.com, Lynchburg, Virginia Area. Retrieved 2014-10-07.
- "Monarch Butterfly's Reign Threatened by Milkweed Decline". National Geographic Society. 2014-08-20. Retrieved 2014-10-06.
- Inamine, Hidetoshi; Ellner, Stephen P.; Springer, James P.; Agrawal, Anurag A. (2016). "Linking the continental migratory cycle of the monarch butterfly to understand its population decline". Oikos. 125 (8): 1081. doi:10.1111/oik.03196
- "Are GMOs causing monarch butterflies to become extinct?". Tampa Bay times. Retrieved 2015-03-10.
- "Monarch Butterfly". The Native Plant Herald. Retrieved 2014-10-06.
- "Monarch ESA Petition – Center for Biological Diversity" (PDF). Center for biological diversity. Retrieved 2014-10-06.
- "Monarchs in Migration : The Humane Society of the United States". the Humane Society. Retrieved 2014-10-06.
- Drouin, Roger. "Monarch Butterflies at the Center of a Continent-Wide Conservation Effort". Scientific American. doi:10.1038/scientificamerican1014-22. Retrieved 2014-10-08.
- "Monarch Watch". www.monarchwatch.org. Retrieved 2018-07-05.
- Venture, The Monarch Joint. "Home | The Monarch Joint Venture". monarchjointventure.org. Retrieved 2018-07-05.
- This includes more than acres 1273.51 acres in national monuments and 23,019,204 acres in national parks
- Obama, President Barack (2014-06-20). "Presidential Memorandum – Creating a Federal Strategy to Promote the Health of Honey Bees and Other Pollinators". Office of the Press Secretary. Washington, D.C.: The White House. Archived from the original on 2014-07-02. Retrieved 2015-06-02.
- cities and counties are required to develop legislative Local Coastal areas and programs
- Reforestation of monarch reserve areas in Mexico.
- "Petition to protect the Monarch butterfly (Danaus plexippus plexippus) under the endangered species act" (PDF). Xerces Society. Retrieved August 3, 2018.
- "Donations". Retrieved August 26, 2014.
- "Monarch Butterflies". The Xerces Society For Invertebrate Conservation. Retrieved September 4, 2014.
- "The Xerces Society, Inc., Notes To Financial Statements" (PDF). The Xerces Society For Invertebrate Conservation. December 31, 2013. Retrieved September 4, 2014.
- Oberhauser 2009, p. 4.
- Berger, Joel (1994). "Science, Conservation, and Black Rhinos". Journal of Mammalogy. 75 (2): 298–308. doi:10.2307/1382548. JSTOR 1382548.
- Ramírez, Maria Isabel; Azcárate, Joaquín G.; Luna, Laura (2003). "Effects of human activities on Monarch Butterfly habitat in protected mountain forests, Mexico". Forestry Chronicle. Canadian Institute of Forestry. 79 (2): 242–246. doi:10.5558/tfc79242-2.
- Tucker, Catherine (2004). "Community Institutions and Forest Management in Mexico's Monarch Butterfly Reserve". Society and Natural Resources. Routledge. 17 (7): 569–587. doi:10.1080/08941920490466143. ISSN 1521-0723. Retrieved 2014-10-10.
- "Región Mariposa Monarca" [Monarch Butterfly Region] (in Spanish). Mexico: World Wildlife Fund Mexico. 2007. Archived from the original on January 4, 2011. Retrieved December 19, 2010.
- Oberhauser 2009, p. 32.
- Drouin, Roger. "Monarch Butterflies at the Center of a Continent-Wide Conservation Effort". Scientific American. doi:10.1038/scientificamerican1014-22. Retrieved 2014-10-08.
- Malkin, Elisabeth (2014-02-14). "North American Leaders Urged to Restore Monarch Butterfly's Habitat". The New York Times. Retrieved March 25, 2014.
- "Project Milkweed". Retrieved June 29, 2014.
- "The lonely flight of the monarch butterfly". NewsAdvance.com, Lynchburg, Virginia Area. Retrieved 2014-10-07.
- "CMBG becomes 'Monarch Butterfly Waystation'". The Times Record. Retrieved 2014-10-08.
- "Forests For Monarchs-Reforestation Program, Mexico". Forests For Monarchs. Retrieved 2014-10-17.
- "Conservation Reserve Program". US Department of Agriculture, Farm service agency. Retrieved 2014-10-08.
- "Monarch Larva Monitoring Project". University of Minnesota. Retrieved August 3, 2018.
- Pollinator Health Task Force (2015-05-19). "National Strategy to Promote the Health of Honey Bees and Other Pollinators" (PDF). Washington, D.C.: The White House. Archived from the original (PDF) on 2015-05-21. Retrieved 2015-05-30.
- "The lonely flight of the monarch butterfly". Lynchburg, Virginia: NewsAdvance.com. Retrieved 2014-10-07.
- Davis, Andy (December 18, 2016). "Monarchs to be listed as endangered in Canada – is this the beginning of the end for citizen science". monarchscience. Retrieved 2018-05-26.
- Brower et al. 1995, p. 544.
- "Dwindling monarch butterflies in Cape May County has legislators worried". pressofAtlanticCity.com: Upper Cape May. Retrieved 2014-10-08.
- Halpern, Sue (2002). Four Wings and a Prayer. Kindle edition. New York City: 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 978-2-923358-56-7. 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 978-0-8014-4188-2.
- Pyle, Robert Michael (2014). Chasing monarchs: Migrating with the butterflies of passage. Yale University Press. ISBN 978-0-300-20387-5.
- Pyle, Robert Michael (2010). Mariposa Road:the first butterfly big year. New York: Houghton Mifflin Harcourt Publishing Company. ISBN 978-0-618-94539-9.
- Pyle, Robert Michael (1981). National Audubon Society Field Guide to North American Butterflies. New York: Alfred A. Knopf. ISBN 978-0-394-51914-2.