| 05 July 2010
Monarch butterflies are not an endangered species but their migration is considered an endangered phenomenon. Their population is at an all time low. For the first time in 16 years of monitoring the Monarch butterflies scientists have noticed a dramatic decline this year.
The area of forest covered by Monarchs last year was 5.06 hectares or 12.5 acres, compared to 1.92 hectares, or 4.74 acres this year – less than half of the migratory population from last year. The annual monitoring of the Monarch butterflies began in 1994. It’s like an annual check-up of the overall health, which is used to estimate the annual winter migratory population. The number reflects survival and reproductive success over the past year.Twelve major monarch butterfly sanctuaries in Mexico are measured every winter and their results announced in January. Their unique winter habitat is found only on 12 mountaintops on the planet. In February the butterflies are at their winter refuge deep in central Mexico, roosting in Oyamel fir forests at an elevation of 2400 to 3600 meters (nearly 2 miles above sea level). The mountain hillsides of Oyamel forest provide an ideal microclimate for the butterflies, at temperatures ranging from 0 to 15 degrees Celsius. If the temperature is lower, the monarchs will be forced to use their fat reserves. The humidity in the Oyamel forest assures the monarchs won’t dry out allowing them to conserve their energy.
Did you know that the monarchs are the only butterflies known to make a two-way migration as birds do? They cannot survive the cold winters of northern climates, unlike other butterflies that can remain dormant as larvae, pupae, or even as adults. Using environmental cues, the monarchs know exactly when to travel south for the winter.
The spring migration begins in March, and an announcement comes from Mexico that the monarchs are on their way. After living off their fat reserves all winter, tens of millions of monarch butterflies head northward. With just a few weeks to live, they race to produce the next generation, using a combination of air currents and thermals to travel long distances. Some fly as far as 3,000 miles to reach their winter home.
The monarch’s story is one of nature’s most incredible examples of adaptation and survival.
Monarchs usually lay a single egg on a plant, often on the bottom of a leaf near the top of the plant. It’s difficult to tell just how many eggs each female lays during her life, but the average is probably from 100 to 300. The eggs hatch about four days after they are laid. They begin life by eating their eggshell, and then from the plant on which they were laid. Common Milkweed, which produces abundance of sweet-scented lavender flowers in mid-summer, is the main food source for the caterpillars who feast on the leaves.
I was lured into the world of Monarch butterflies on a hot summer’s day in June while touring the grounds of Saltus School with two enchanted young students. They took me to a small plot of their school garden, which looked like a caterpillar playground. The adorable creatures with green and black stripes were voraciously feasting on the vegetation as you see in these images captured by my camera.
When the caterpillar has become too large for its skin it moults, or sheds its skin. At first, the new skin is very soft, and provides little support or protection. The new skin soon hardens and the caterpillar often eats the shed skin before starting in a new on plant food. Within 10-14 days they moult five times and transform into a pupa or chrysalis. This is where they sulk into a deep slumber inside this beautiful silk cocoon, a silky shell like structure. The transformation from larva to adult is completed during the chrysalis stage.
Pupae are much less mobile than larvae or adults, but they often exhibit sudden movements if they are disturbed. Like other butterflies, Monarch pupae are well-camouflaged, since they have no other means of defence against predators. I got a glimpse of three of them dangling under a cement structure in the school compound. Within 10-14 days they transform into a beautiful butterfly.
And just as I spotted an adult monarch I was summoned into the gymnasium to present the four part miniseries that the BEA had produced on Bermuda’s conservation efforts. Reluctantly I walked into the room and to my amazement within a few minutes the adult Monarch butterfly entered in strutted it’s wings for a brief second and exited, leaving me curious. After the presentation I found the same butterfly in the same spot.
I began to wonder if monarchs, like many other creatures, are declining. According to scientists they have dramatically declined this year, as revealed in their latest winter migratory monitoring. So what is causing this drastic decline? Climate change and habitat destruction caused by illegal logging being blamed. Conservation of overwintering habitat is very important for the survival of monarchs. The Mexican Government recognized the importance of Oyamel forests to monarch butterflies and created the Monarch Butterfly Biosphere Reserve in 1986.
How closely do monarchs follow after milkweed becomes available in the spring? Monarch biologist Dr. Lincoln Brower explains why this question is important. According to Dr. Brewer’s observations in Mexico and in the south eastern U.S., monarchs have been leaving their overwintering sites in Mexico earlier than normal. The reason for this, he says is that the thinned forests are causing drier, warmer air to blow through the overwintering sanctuaries, activating the spring migration prematurely.
If this is true, then monarchs may arrive in northern regions before the danger of frost has passed. “Hard frost results in the withering and drying of the tender newly-emerged milkweed leaves. The problem is until the frost danger has passed, even if monarch eggs or early instars aren’t frozen, the frosted leaves can result in larval starvation. Another problem is that monarchs that arrive too early may not be able to find adequate supply of sprouting milkweeds, so they may keep migrating northwards, and of course, the further they go the worse the problem gets,” Dr. Brewer said.
Ultimately why are Monarch butterflies so important? One of the main reasons is that they migrate every year and when doing so pass over areas where pollination is an issue. Monarchs are pollinators and without them some of the plant life, such as those in deserts, may suffer.
They also teach us profound life’s lessons like unity. Tens of thousands of Monarchs cluster together on a single tree to stay warm.
Every creature on our Planet Earth plays an important role, which in the end benefits mankind, and that begs the question why do we turn around and destroy the very source that sustains us?
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written by Alisha, December 16, 2010
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