Threats to monarchs begin in their overwintering sites and extend all along their migration routes and into their summer breeding ranges. Just as protecting the overwintering sites determines how many monarchs fly north each spring, protecting the migration routes and breeding areas determines how many fly south each fall. The survival of the migration depends on protecting all of these areas, not just one. In addition to weather, disease and predators, man is one of the greatest threats to migrating monarchs. Let’s look at just some of the things we are doing that adversely affect this natural phenomena.
Milkweed is often damaged by exposure to ozone. The dark spots on the leaves caused by this damage are called " stipples."
The fate of the monarch migration in Mexico depends to a great extent on the fate of the oyamel forest in which monarchs shelter for the winter. They depend of the integrity of this forest to protect them from winds, rain and freezing temperatures. With a growing human population, and few other resources to draw on, there has been relentless lumbering in and around the sanctuaries. Although persistent lumbering is lamentable and may prove tragic in the end, Mexico is actually doing more than their northern neighbors. They have at least expanded the sanctuary and begun reforestation efforts.
It’s estimated that almost half of the monarch population breeds in the Midwest, with most of them in agricultural areas. What happens in those areas has the greatest effects on the monarch population. Although monarchs in all stages can be killed directly by insectacide, its milkweed host plant is also at risk. The problem is that development and especially the widespread adoption of Monsanto’s Roundup Ready® corn and soybeans have caused the loss, by Monarch Watch’s estimate, of more than 80 million acres of monarch habitat in recent years. These Roundup Ready crops are designed to survive repeated dousing of Roundup® that kill other plants including milkweed.
Many open areas throughout the US and Canada are being covered by everspreading developments, reducing the habitat for milkweed. In California it’s not just the milkweed at risk because most overwintering sites are located in beautiful settings near the coast. These areas are also subject to intense and sustained developmental pressure.
Monarch Watch estimates that "development (subdivisions, factories, shopping enters, etc.) in the U.S. is consuming habitats for monarchs and other wildlife at a rate of 6,000 acres per day— that’s 2.2 million acres each year, the area of Delaware and Rhode Island combined!"
One of our most wasteful practices is the use of herbicides and repeated mowing along roadsides. This has turned this habitat into grasslands the don’t provide much, if any, food and shelter for wildlife. Monarch Watch reports that although some states have started to increase the diversity of plantings along roadsides, including milkweeds, these programs are small.
In urban and suburban areas another problem is spraying to control mosquitoes. When New York City sprayed insecticide to kill mosquitoes that may carry encephalitis, the New York Times reported “Edward Spevak, the curator of invertebrates at the Bronx Zoo, said he received a call last week from a jogger who had found a number of dead monarch butterflies in Central Park shortly after the spraying. ‘She was running shortly after the truck passed,’ he said, ‘and she started noticing all these monarchs dropping around her.’ He cautioned that it would be ‘very difficult to determine’ if malathion had killed the butterflies. But he said that Bronx Zoo officials have asked the city not to spray over the zoo because of the danger to its Butterfly Zone exhibit, a caterpillar-shaped tent that houses hundreds of butterflies from around the world. Instead, zoo workers have sprayed specific trouble spots themselves, Dr. Spevak said.”
One of the most bizarre threats to monarchs is the practice of buying live monarchs for release at weddings and other events. How could something so innocent sounding be bad? Let us count the ways.
One of the many things we don’t know is what impact wind turbines have on migrating monarchs.
Global climate change is happening at an ever accelerating rate. Over time, it will have lasting effects on monarchs, just as it will on everything else. One dire prediction is that it will cause habitat loss for migrating monarchs by making their wintering site in Mexico wetter, and their California and Midwestern breeding grounds hotter. In addition, climate changes may affect the seasonality of milkweed. To study this, Monarch Watch is starting a Milkweed and Nectar Plant Phenology Project which you can join as a citizen scientist. (The term phenology refers to the study of the seasonal progression of natural events involving plants and animals.) In the case of monarchs, Monarch Watch is interested in recording a series of “firsts” (first emergence of shoots, first flower bud, and so on) of milkweed and other selected plants. This will help them monitor the effects of climate change on the plants that monarchs depend on.