Mon . 19 Apr 2019

Monarch butterfly migration

monarch butterfly migration, monarch butterfly migration map
Monarch butterflies Danaus plexippus perform annual migrations across North America which have been called "one of the most spectacular natural phenomena in the world"

Starting in September and October, eastern/northeastern populations migrate from southern Canada and the United States to overwintering sites in central Mexico where they arrive around November They start the return trip in March, arriving around July No individual butterfly completes the entire round trip; female monarchs lay eggs for the next generation during the northward migration and at least five generations are involved in the annual cycle

Similarly, the western populations migrate annually between regions west of the Rocky Mountains including northern Canada and overwintering sites at the coast of California

Monarchs also perform small distance migrations in Australia and New Zealand There are also some populations, for instance in Florida and the Caribbean, that do not migrate Recently discovered overwintering sites have been identified in Arizona and northern Florida

Contents

  • 1 Range of the migration
  • 2 Habitats
  • 3 Historical accounts
    • 31 Before 1975
    • 32 After 1975
  • 4 Southern migration
    • 41 Initiation
    • 42 Monarchs in diapause
    • 43 Other physiological changes
  • 5 Colony dispersal and northern migration
    • 51 Northern migration
      • 511 Initiation
    • 52 Rates of recolonization
  • 6 Migration routes
  • 7 Roosting sites
  • 8 Overwintering sites
  • 9 Population and migratory study methods
    • 91 Mark and recapture
    • 92 Butterfly counts
    • 93 Aerial and satellite observations
    • 94 Direct observations
      • 941 Types of data collected
      • 942 Use of data and availability
      • 943 Observers
    • 95 Tagging
  • 10 Migratory theory mechanisms
    • 101 Instinct
    • 102 Geographical features
    • 103 Chemical markers
    • 104 Position of the sun
    • 105 Other theories
  • 11 Extinction
  • 12 Conservation
    • 121 Adult mortality
    • 122 Overwintering sites
    • 123 Reductions in milkweed and agricultural regions of the United States
    • 124 Man-made obstacles
    • 125 Other threats
  • 13 Conservation programs
  • 14 Proposed policies to conserve the migration
  • 15 Economic influences related to the migration phenomena
  • 16 Politics
    • 161 Affected people groups
    • 162 Presidential memorandum and National Strategy
    • 163 Petition to designate the monarch endangered
    • 164 Scientific community
    • 165 Local governments
  • 17 See also
  • 18 References
  • 19 Bibliography
  • 20 External links

Range of the migration

The western population overwinters in various coastal sites in central and southern California, United States, notably in Pacific Grove, Santa Cruz, and Grover Beach Western monarchs also overwinter in Baja, California's central valley, and the Sierra Nevada foothills

Not all monarchs migrate Migrating populations and non-migrating populations coexist in many areas Monarchs are year-round residents in Florida and monarchs migrate to Florida and Gulf coast areas, and can often continue to breed and survive the winter The monarch population in Florida may be a result from migratory butterflies that do not to migrate north in the spring These locations provide access to nectar plants If there is a hard frost in these areas they do not survive Asclepias curassavica, an introduced annual ornamental, provides larval food if native species are unavailable 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

Overwintering monarchs cluster on oyamel trees in a preserve outside of Angangueo, Michoacan, Mexico; one tree is completely covered in butterflies roosting, overwintering butterflies in Pacific Grove, California Monarchs roosting during fall in central Texas

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 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

Habitats

Ideal habitats have a profound effect on the migration of large numbers of monarchs The single most influential factor is the weather Ideal habitats promote the migration of large numbers of migrating monarchs

Summer

The ideal summer breeding habitat will provide ample nectaring plants for the adults and abundant, healthy larval plants Low populations of predators and parasites will also allow for more monarchs surviving into adulthood A low prevalence of disease will improve the survival Monarchs breed the fastest within a specific temperature range An increase of the range of the breeding population is another indicator that the habitat is conductive to reproductive success

Fall

In North America the ideal breeding habitat changes in late summer The migration begins and the ideal habitat required for successful migration changes to a 'corridor' to Mexico of available nectaring plants, optimal temperatures, tailwinds and low precipitation The butterflies must also remain hydrated An early frost will kill migrating butterflies

Winter

The ideal habitat for monarchs in winter exists in their overwintering sites The factors influencing the habitat include: the condition of the forest canopy, precipitation, predation, availability of suitable trees on which to roost, sources of water, the ideal temperature range, sunlight, lack of rain and ice and human activity near the sites Roosting butterflies have been observed to roost in sumacs, locusts, basswood elm, oak, osage orange, mulberry, pecan, willow, cottonwood, and mesquite If conditions are too hot in the overwintering sites, the butterflies will use up their fat reserves and not survive until spring High temperatures initiate reproductive behavior with the possibility of the butterflies leaving the overwintering areas too early while it is still too cold in the north to stimulate the emergence of food plants and nectar plants

Spring

The ideal habitat for monarchs migrating north from Mexico sites to Texas and Oklahoma is less studied Presumably, tailwinds assist the migration north Rainfall is critical in creating the ideal habitat for the returning monarchs which must have abundant, lush and healthy 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

Migrating western populations of D plexippus and their overwintering sites were known long before the winter sites in Mexico were located by Canadian and American researchers in the 1970s Pre-Hispanic Native Americans, the Purépecha and Otomi once occupied this area and tied the harvest of corn to the arrival of the butterflies Monarchs appear in legends of the people that live near overwintering areas In the areas surrounding the overwintering sites in Mexico, local residents were quite aware of the overwintering behavior of monarch butterflies long before 1975 The local people, called the Mazahua, have lived near the overwintering sites for centuries The arrival of the monarchs is closely tied to the traditional the Day of the Dead celebrations Local residents today easily recall seeing the migrating butterflies prior to 1975

For at least a century, monarchs were observed overwintering in California in the fog belt Historical records of lepidopterists do not mention the existence of monarchs in their current western range that extends northward through Washington, Oregon and Canada possibly because milkweed was not available until human disturbance expanded its range

After 1975

Formal studies began when Fred Urquhart graduated from the University of Toronto in 1935 and accepted a graduate fellowship in the field of entomology In 1937, Urquhart began to plot the route taken by the migrating butterflies He was the first to record that monarchs move S/SW in the fall and that these movements were correlated to high pressure systems He began the first successful tagging program which returned data He and his volunteers recognized the existence of roosting behavior: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 Kenneth C Brugger responded to the ad and in January 1975 discovered one of the major overwintering sites Urquhart, William Calvert, John Christian, and Lincoln P Brewer cooperated to put together the details in this discovery of a major overwintering site of monarchs in 1976 At first, information on the discovery of the first major overwintering was suppressed due to the concerns that public knowledge might lead to endangerment of the butterflies Since 1976 multiple overwintering sites have been identified and their locations are public knowledge

Southern migration

By the end of October, the population of monarchs east of the Rocky Mountains migrates to the sanctuaries of the Mariposa Monarca Biosphere Reserve within the Trans-Mexican Volcanic Belt pine-oak forests in the Mexican states of Michoacán and México They also overwinter in areas that are privately owned Some monarchs migrate to other locations such as Cuba and Florida in the fall Two migratory fly ways exist 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 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 50 miles in 2 days

A tagged monarch in Hartford CT was recovered in Camp Hill PA 98 miles in 5 days

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

Initiation

Monarchs respond to different cues that promote the fall season, southern migration These include the angle of light coming from the sun, the senescence of larval host plants, the decreasing day period and temperature drop The migration begins at the northernmost summer range approximately in August Migrating monarchs are thought to rely heavily on the nectar of fall flower composites that lie along the migration path

Monarchs in diapause

Diapause is a physiological state found most often in arthropods, especially insects, and in embryos of fish that allows survival when conditions become harsh Diapause is not only induced in an organism by specific stimuli or conditions, but once initiated, only certain other stimuli are capable of bringing the organism out of diapause The latter feature is essential in distinguishing diapause from other forms of dormancy such as stratification, and hibernation

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