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August 29, 2012

Monarchs in Migration

What you need to know to watch, and make way for Monarchs on the wing

  • Popular and well studied, monarch butterflies endure many obstacles to survive. Cathy Klein/iStockphoto.com

  • As distinguished as the butterflies are, so too are the monarch caterpillars. Cathy Klein/iStockphoto.com

  • Here a monarch dries her wings after emerging from her chrysalis (cocoon). Cathy Klein/iStockphoto.com

  • During their migration, you may see monarchs roosting in trees waiting out inclement weather to continue their journey south. Jodi Jacobson/iStockphoto.com

  • The milkweed plant serves as nursery and dining room for monarchs.  They feed on the flower’s nectar and lay their eggs on its leaves. Debra Firmani

Among the most popular and well-studied insects, monarchs living east of the Rockies are unique among butterflies for their extraordinary two-way migration between their vast summer breeding range in North America and their overwintering sites in Central Mexico, where they gather by the millions.

(Those living west of the Rockies winter along the California coast.) Weighing only one-fifth as much as a penny, the eastern monarchs fly up to 3,000 miles.

Not all generations of monarchs migrate—summer generations focus on reproduction and live only 2-5 weeks—but those that make the roundtrip migration live up to 9 months.

Delicate timing, navigation, and chemistry
A barrage of unnatural challenges and threats
A chance to make a difference
Tips for observing
A final word
Online resources

Delicate timing, navigation, and chemistry

The mystery of the monarch's migration continues to unfold since overwintering colonies were first discovered in 1975. In addition to roosting nightly, monarchs make frequent stops of two or more days to rest, refuel, and wait for favorable weather and winds. Here are some of the other things we know about their journeys:

  • Changes in daylight hours, temperatures, and the condition of the plants they feed upon cause monarchs to migrate. Survival during their journey depends upon the availability of nectaring flowers to feed upon and trees to roost in along the way.
  • To navigate, they use mountain ranges as landmarks, special UV photo receptors to read the changing position of the sun, and an internal biological clock.
  • Upon arrival at one of only twelve mountain sanctuaries in a small region of Mexico, monarchs cluster tightly on branches of oyamel (o-ee-ya-mel) fir trees.
  • While overwintering, monarchs survive snow and overnight temperatures below freezing by entering a state of diapause, which allows them to live on fat reserves. 
  • Springtime changes in daylight hours and temperatures cause monarchs to head northward to repopulate their North American range, which they accomplish in stages. Overwintering monarchs lay eggs on milkweed emerging in the southern part of their breeding range, and the resulting generation moves northward, laying eggs on milkweed emerging there. It can take three or four generations for monarchs to reach the northernmost portions of their range.

A barrage of unnatural challenges and threats

This past winter was one of the worst on record for monarchs. Hailstorms covered their roosting trees in two inches of ice, and then another 15 inches of rain fell. Monarchs not killed outright by the extreme weather dispersed prematurely, greatly diminishing their chances of survival. Added to such natural threats to monarch survival are many human-caused challenges, such as:

  • Urban and agricultural development, which diminish availability of milkweed.
  • Logging in Mexico (forest thinning increases the risk of freezing, as gaps cause wetting and loss of body heat; heavy winds tear monarchs from their clusters).
  • Killing of milkweed and nectaring wildflowers as a result of the increased use of crops genetically engineered to withstand harsh, non-selective herbicides.
  • Human-caused climate change, as it causes more extreme weather events, stressing monarchs at critical points in their life cycle.
  • Pesticides.

A chance to make a difference

  • Eliminate (or at least minimize) use of pesticides and herbicides in your yard and gardens, particularly non-selective systemic herbicides, such as Roundup®.
  • Plant milkweed and other nectar-bearing flowers in a sunny spot in groups of ten or more. Check with your cooperative extension office for appropriate species.
  • Create a Monarch Waystation in your yard or at your school or place of work.
  • Participate in citizen science projects to help monarchs. For more information brouse our resource list.
  • Encourage elected officials to protect small natural areas that support milkweed and to manage roadside habitat without herbicides and excessive mowing.

Tips for observing

  • Look for concentrations of migrating monarchs along the coastlines of the Great Lakes, Atlantic Ocean, and Gulf of Mexico; in the Midwest corn belt; and funneling through Texas to Mexico.
  • Look for monarchs in your garden, along roadsides, and in abandoned fields or fields of blooming clover or alfalfa.
  • Watch them with binoculars when they soar overhead on tailwinds; in headwinds, they'll be flying close to the ground.
  • Check for overnight roosts in trees during migration.
  • When rain or heavy winds occur, find them roosting in trees as they wait for the right conditions to continue their journey.

A final word

Take time to watch for monarchs, and when you see one—or many—remember all that has gone into their life cycle and survival. And, if you have a yard, try to make it a life-saving place for monarchs to rest and refuel on future migrations.

Online resources

» Monarch Watch
» Journey North
» Cooperative Extension Offices 
» The Monarch Larva Monitoring Project
» Project Monarch Health
» The Xerces Society

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