Wondrous Wildlife
By Vern and Lori Gieger
Mexico Migrations

     Mexico is one of the most important countries in the world in terms of biological richness, covering one percent of the Earth’s land area, but containing about 10 percent of all the species known to science. Half of these species can only be found in Mexico.
     The convergence of Neartic and Neotropical biotic regions, topography, location and climate influence this extraordinary biological diversity. Mexico harbors a richness of ecosystems and ecological diversity, including temperate and tropical forests, arid and semi-arid wild lands, alpine meadows, and wetlands.
     Many of its ecosystems play a vital role in providing stopover and wintering habitats for migratory species that breed as far north as Alaska and Canada and migrate south to Mexico’s most remote ecosystems. Every autumn, thousands of ducks and geese, thrushes, warblers, raptors and hummingbirds congregate along the Gulf Coast from Texas to Florida in preparation for the nonstop flight across the gulf to the Yucatan Peninsula. Likewise, millions of monarch butterflies from Canada and the United States converge on forests in Mexico’s central mountains to winter.
     One of the most amazing migratory feats is that of the monarch butterfly. In North America they begin to make massive southward migrations starting in August until the first frost. By the end of October, the populations of the Rocky Mountains migrate to the sanctuaries of the Mariposa Monarca Biosphere Reserve in the Mexican states of Michoacán and México. The length of these journeys exceeds the normal lifespan of most monarchs, which is less than two months for butterflies born in early summer. The last generation of the summer enters into a non-reproductive phase known as diapause and may live seven months or more. During this time they fly to a wintering site.
     The generation that over-winters generally does not reproduce until it leaves its migratory site sometime in February and March. It is thought that the over-winter population of that of east of the Rockies may reach as far north as Texas and Oklahoma during the spring migration. However it is the second, third and fourth generations that return to their northern locations in the United States and Canada in the spring. How the species manages to return to the same locations over a gap of several generations is still a subject of research; their flight patterns appear to be inherited.
     When the phrase migratory species is mentioned most think of birds, perhaps a few think of the amazing monarchs. But, each year, during spring and summer, an estimated 150 million Mexican free-tailed bats emerge from their maternity colonies in a dozen caves in Texas, New Mexico, Oklahoma and Arizona. These are the populations that migrate back from wintering grounds in Mexico and play a vital role in maintaining critical ecological processes, necessary for total ecosystem health and biological diversity.
     These migratory bats act as pollinators, seed dispersers, and regulators of insect pests. In the U.S., farmers spend an estimated 500 million dollars annually on pesticides, yet insect pests will still destroy tens of millions of dollars’ worth of crops. Without bats, the damage would be even greater. A million bats can devour ten tons of insects nightly. Unfortunately, bats are killed in massive numbers due to lack of understanding of their critical function and services.
     Mexico and the United States share a border of more than 2,000 miles, presenting many conservation challenges and opportunities. The unique biological diversity in the border region and the stopover and wintering habitats Mexico provides for migratory species make this partnership one of special importance.