Climate Change and the Monarch Butterfly

Changes in climate affecting the state of Michoacán, Mexico may wreck havoc on the eastern Monarch butterfly's winter sites.  As opposed to the western Monarch which spends its winters along beaches in California, the eastern Monarch must travel up to 3,000 miles to find the perfect combination of temperature and relative humidity. 

 

Oyamel Fir Forests of Michoacán, Mexico

The oyamel fir forests of Michoacán, Mexico experience little, if any, freezing and snow even at 10,000 feet in this mountainous region.  During the 135 days of the over-wintering period, this region is experiencing its dry season with associated low levels of relative humidity.  When the Monarch's do encounter minor, short dips in temperature, they huddle together for warmth.  Historically, concerns related to Monarchs have focused on the effects of deforestation, however, climate change may create more long-term risks.

 

Change in Climate in Michoacán, Mexico

Recently, researchers have noted winter mortality events related to rainfall followed by low temperatures.   Monarch's are very sensitive to drops in temperature which may inhibit their ability to fly (thus increasing possibility of predation) or may result in death.  Ecological niche modeling indicates this region may be uninhabitable by monarchs by 2050 due to increased precipitation.

Examples of mortality events:

January 1981 – storms over 10-day period followed by temps around 23˚F – killed ~42%

February 1992 – storm killed 82% of a small colony

December 1995 – late snow storm killed 6% of Sierra Chincua population

January 2002 – cold/wet storm killed 70-80% of two largest populations in Mexico – following summer had 2nd lowest summer populations recorded (image at right taken after 2002 storm)

 

 

Why don’t they just move farther south

Unfortunately, just as low temps are bad, so are high.  Locations with too high of a temperature may deplete the Monarch's lipid reserve which may cause the monarch’s to move into the reproductive development stage too soon or may cause the migration north to start too soon.  If milkweed hasn't come out of it's hibernation, then there will be no food for the newly hatched caterpillars to eat.  Early reproduction and/or migration can destroy a large population.  Monarchs survive in “relatively narrow microclimate window”.

 

Even if they do find an area with the proper temperatures and precipitation, will there be a habitat for them?

This year, the trees of the wintering site has been infected by bark beetles.  Park officials have cut down over 9,000 fir trees in an attempt to control the infestation but it does appear to be spreading.  The beetles are not new to the area but recent droughts have weakened the fir trees and made them more susceptible to the destruction of bark.  - Yale environment 360 - e360 digest - Bark Beetle Infestation Spreads in Monarch Butterfly Reserve

 

 

 

 

Back to Top ▲