Monarch Habitat Loss
Logging in their winter grounds in Mexico is
shrinking monarch habitat there. Loss of farmland fields and natural
areas to residential and commercial development in the United States
has reduced habitat for milkweed because manicured lawns and
ornamental beds (not to mention pavement) supplant native species.
Also, the widespread-use of herbicide-resistant soybeans and corn in
modern agriculture has increased the use of non-selective herbicides
that effectively eliminate butterfly-friendly plant species that may
have survived applications of other herbicides.
But loss of habitat is not the only problem facing
monarchs. Eastern monarchs pass through the state of Texas on their
way to and from Mexico, and Texas is in the grip of a multi-year
drought. Fifty-four percent of rangeland and pastures there have
been rated as being in “poor or very poor” condition, and some parts
of the state have been in “extreme drought” (as rated by the United
States Drought Monitor) since 2010. The drought and periodic
wildfires have severely reduced milkweed populations in Texas. Given
that milkweed species are the only larval food for monarchs, reduced
milkweed populations mean reduced monarch populations.
Monarch migration is a carefully choreographed dance
that requires the coordination of three or four generations.
Generation four adults are those we see (or should see) at this time
of year, and are those that make the perilous journey from western
Pennsylvania to Mexico where they overwinter. They are the
longest-lived generation, with a typical lifespan of six to eight
months. Although monarchs travel to their winter grounds in a single
generation, it takes three or four generations for them to return to
the northern United States and Canada the following year, with each
generation pushing further north. These generations have much
shorter life spans than generation four, perhaps four to six weeks.
Monarchs are dependent on finding sufficient milkweed populations
along the way. When drought, agriculture and/or development has
eliminated milkweed along their route, that may be as far north as
they can go that year.
the Monarch Butterflies
Despite the fact that the 2012-13 overwintering
monarch population in Mexico was 59 percent smaller than the year
before, butterfly experts are not suggesting they are headed for
extinction. Like most insects, monarchs reproduce rapidly and their
population can recover from such crashes. Planting pollinator
gardens that include species of milkweed is one the best things
humans can do to help.
Help the Bees & Butterflies