<P> A study in 2015 examined a preserved collection of male and female monarch specimens from eastern North America to evaluate the sex - based differences in fine - scale wing and body structure . The study found significant differences in overall wing size and in the physical dimensions of wings . Males tended to have larger wings than females, and were heavier than females, on average . Both males and females had similar thorax dimensions (wing muscles are contained in the thorax). Female monarchs tended to have thicker wings, which is thought to convey greater tensile strength . This would make female wings less likely to be damaged during migration . Also, females had lower wing loading than males (wing loading is a value derived from the ratio of wing size to body weight), which would mean females require less energy to fly . A table with the average measurements of each variable is shown . </P> <P> The range of the western and eastern populations of the monarch butterfly expands and contracts depending upon the season . The range differs between breeding areas, migration routes, and winter roosts . However, no genetic differences between the western and eastern monarch populations exist; reproductive isolation has not led to subspeciation of these populations, as it has elsewhere within the species' range . </P> <P> In North America, the monarch ranges from southern Canada through northern South America . It has also been found in Bermuda, Cook Islands, Hawaii, Cuba, and other Caribbean islands the Solomons, New Caledonia, New Zealand, Papua New Guinea, Australia, the Azores, the Canary Islands, Gibraltar, the Philippines, and North Africa . It appears in the UK in some years as an accidental migrant . </P> <P> Overwintering populations of D. plexippus are found in Mexico, California, along the Gulf Coast, year round in Florida, and in Arizona where the habitat has the specific conditions necessary for their survival . On the US East Coast, they have overwintered as far north as Lago Mar, Virginia Beach, Virginia . Their wintering habitat typically provides access to streams, plenty of sunlight (enabling body temperatures that allow flight), and appropriate roosting vegetation, and is relatively free of predators . Overwintering, roosting butterflies have been seen on basswoods, elms, sumacs, locusts, oaks, osage - oranges, mulberries, pecans, willows, cottonwoods, and mesquites . While breeding, monarch habitats can be found in agricultural fields, pasture land, prairie remnants, urban and suburban residential areas, gardens, trees, and roadsides--anywhere where there is access to larval host plants . Habitat restoration is a primary goal in monarch conservation efforts . Habitat requirements change during migration . During the fall migration, butterflies must have access to nectar - producing plants . During the spring migration, butterflies must have access to larval food plants and nectar plants . </P>

Where do monarch butterflies live in the world
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