SCORES & OUTDOORS – Monarch butterflies on the decline: what caused the death of this one?
Monarch butterfly.
by Roland D. Hallee
One day last week, as we were backing out of our driveway, I noticed something hanging from the front door knob. I stopped, and my wife jumped out to see what it was. What else but a political notice to vote “No” on Question 1. That is not the subject of this column. What is that on her way back to the car, at the base of a pine tree, she picked up a dead monarch butterfly. What had caused its demise?
I have seen a handful of monarchs this summer.
The monarch butterfly is the most widely recognized of all American butterflies with its distinct orange, black, and white wings. While beautiful, this coloring actually sends a warning to predators that the monarch is foul tasting and poisonous. Found throughout the United States, as well as Mexico and Canada, one of the most notable characteristics about the monarch is the astonishing 3,000 mile journey some will make in the fall to their wintering grounds in the Sierra Nevada Mountains of Mexico or to southern California, depending on which part of the United States or Canada they migrate.
Millions of monarch butterflies make the trip down to Mexico to roost for the winter. During the migration tens of thousands will land on a single tree in certain areas along their migratory path.
Monarchs can travel between 50 – 100 miles a day; it can take up to two months to complete their journey to winter habitats.
Wherever there is milkweed there will be Monarch butterflies. The monarch is widely distributed across North America, from Central America northwards to southern Canada, and from the Atlantic to the Pacific coasts.
Milkweed produces glycoside toxins to deter animals from eating them, but monarchs have evolved immunity to these toxins. As they feed, monarch caterpillars store up the toxins in their body, making them taste bad, which in turn deters their predators.
Monarchs can produce four generations during one summer. The first three generations will have life spans from 2 – 6 weeks and will continue moving north. During this time they will mate and have the next generation that will continue the northward migration. The fourth generation is different and can live up to nine months. These are the butterflies that will migrate south for winter to either Mexico or southern California.
It is predicted that one of the many effects of climate change will be wetter and colder winters. If they are dry, monarchs can survive below freezing temperatures, but if they get wet and the temperature drops they will freeze to death. Because hundreds of millions of monarchs are located in such a small area in the Sierra Nevada of Mexico during the winter, a cold snap there could be devastating.
Monarch butterflies cannot fly if their body temperature is less than 86 degrees. They will sit in the sun or “shiver” their wings to warm up.
As the world warms, suitable habitat will begin to move northward resulting in a longer migration. This means the monarchs may be forced to adapt and produce another generation to reach further north. It is uncertain whether they will be able to do so. Therefore, few monarchs may be able to make the longer trip back to Mexico for winter.
Other threats to the monarch include habitat loss and loss of milkweed which they depend upon as larva to survive. Illegal logging remains a problem today in Mexico in protected areas and is devastating monarch winter habitat.
Whether monarchs are present in a given area within their range depends on the time of year. They are one of the few migratory insects, traveling great distances between summer breeding habitat and winter habitat where they spend several months inactive.
From September into early October, fall southern migration to Mexico begins, with the majority of monarchs following the reverse path south along the central migratory corridor. Monarchs from the Northeast head south along the Atlantic coast, concentrating in the states that make up the Delmarva Peninsula between the Atlantic Ocean and the Chesapeake Bay on the journey. Florida is a stop for many monarchs before they fly over the Gulf Coast to Mexico. A much smaller population of monarch butterflies lives west of the Rocky Mountains.
There are populations of monarchs in Hawaii, Puerto Rico, and some islands of the Caribbean, as well as in New Zealand. Monarchs may have been blown to these places in storms or naturally dispersed there by island-hopping, or they may have been introduced by humans. These populations are not part of the annual migrations on the North American mainland.
The monarch migration is one of the greatest phenomena in the natural world. Monarchs know the correct direction to migrate even though the individuals that migrate have never made the journey before. They follow an internal “compass” that points them in the right direction each spring and fall. A single monarch can travel hundreds or even thousands of miles.
The monarch population has declined by approximately 90 percent since the 1990s. Monarchs face habitat loss and fragmentation in the United States and Mexico. For example, over 90 percent of the grassland ecosystems along the eastern monarch’s central migratory flyway corridor have been lost, converted to intensive agriculture or urban development. Pesticides are also a danger. Herbicides kill both native nectar plants where adult monarchs feed, as well as the milkweed their caterpillars need as host plants. Insecticides kill the monarchs themselves. Climate change alters the timing of migration as well as weather patterns, posing a risk to monarchs during migration and while overwintering. The U.S. Fish & Wildlife Service is currently reviewing the species’ status.
One easy way to help monarchs is to participate in the National Wildlife Federation’s Garden for Wildlife program by planting a pesticide-free monarch habitat garden filled with native milkweed and nectar plants. North America has several dozen native milkweed species, with at least one naturally found in any given area.
The International Union for Conservation of Nature (IUCN) has designated the monarch migration a threatened phenomenon. In 1986, the Mexican government created the Monarch Butterfly Biosphere Reserve which protects 62 square miles of forests in the Sierra Madres where hundreds of million of monarchs spend each winter. The Biosphere Reserve was expanded to include 217 square miles in 2000. Local organizations are also working to stop the illegal harvesting of trees on the reserve to protect wintering habitat.
I guess we’ll never know what killed this particular monarch.
Roland’s trivia question of the week:
Name the two NFL teams that have a human face on the sides of their helmets.
