This year, Monarchs cover a little more ground
The number of Monarch butterflies that reached wintering grounds in Mexico has rebounded 69 percent from last year's levels. But their numbers remain very low. That is according to the World Wildlife Fund.
Last year, the Monarchs covered only 1.65 acres. It was the smallest area since record-keeping began in 1993. This year, the butterflies rebounded to cover 2.79 acres. A formal census was taken by Mexican environmental authorities and scientists.
The orange-and-black butterflies are suffering from loss of milkweed habitat in the United States. They also suffer due to illegal logging in Mexico and climate change.
The Monarchs are unusual. Each year, they make a migration from Canada to Mexico. They find the same pine and fir forests to spend the winter. What's amazing is that they find their way although no butterfly lives to make the round trip.
"It is good news that the forest area occupied by Monarchs this season increased," said Omar Vidal. He is head of the World Wildlife Fund in Mexico. "But let's be crystal clear. It is still the second-smallest forest surface occupied by this butterfly in 22 years of monitoring."
At their peak in 1996, the Monarchs covered more than 44.5 acres. The butterflies' destination is the mountains west of Mexico City.
Lincoln Brower is a leading entomologist at Sweet Briar College in Virginia. He has said that with anything below 4.1 acres, the butterflies "will remain in the danger category." A population covering 9 to 12 acres would be a sign of significant recovery, he said.
The butterfly population has plummeted before. Then it has partially recovered.
In 2001, driving rain and bitter cold killed millions. Scientists speculated that migrating populations would be seriously depleted in 2002. To their surprise, twice as many returned as some had predicted.
In 2004, unfavorable weather, pollution and deforestation caused a drastic decline. But the next year, the butterflies bounced back.
The overall tendency since 1993 points to a steep decline. Each time the Monarchs rebound, they do so at lower levels. The species is found in many countries. Fortunately, Monarchs are not in danger of extinction. But experts fear the migration could be disrupted if very few butterflies make the trip.
The climate of the mountains west of Mexico City normally creates an ideal setting for the Monarchs. Every fall, tens of millions of the delicate creatures fly thousands of miles. They go to their ancestral breeding grounds. Their movement creates clouds of butterflies. They clump together on trees. This forms chandelier shapes of orange and black.
The migration is an inherited trait. No butterfly lives to make the full round trip. It is unclear how they find the route back to the same patch of forest each year.
Some scientists suggest the butterflies may release chemicals. Those could mark the migratory path. The experts fear that if their numbers fall too low, the chemical traces will not be strong enough. Then the Monarchs would not be able to follow the path.
Critical thinking challenge: Name four factors that have a negative impact on butterfly populations.