Saturday, January 24, 2015

Where Have all the Monarchs Gone?

Greetings All,
Have you ever wondered where Monarch butterflies go during the long cold winters in Canada and the US?  Well, I have.  Ever since I was a young girl I have been enthralled with monarch butterflies. Some of my fondest childhood memories are of collecting monarch butterfly caterpillars from the milkweed plants in our back field.  Munching on the leaves were wildly black, yellow and white striped caterpillars.  Their skin was so soft, like velvet.

Monarch Butterfly Caterpillar (c)2007 Derek Ramsey Licensed under GFDL 1.2 via Wikimedia Commons

I'd pluck a few leaves containing caterpillars, place them in a jar with a perforated lid and watched as they increased their body weight 2700 times by eating the toxic leaves of the milkweed!  I placed a small twig with a horizontal branch inside the jar and observed with amazement as a caterpillar would attach by its rear end and transform into a pale green chrysalis with gold dots right before my eyes!

Monarch Butterfly Cocoon by Greyson Orlando  Licensed under CC BY 3.0 via Wikimedia Commons

Days later an adult monarch butterfly would emerge with folded wings.  Once dry, the monarch's wings would unfurl and a beautiful orange butterfly with black stripes emerged.  It was the miracle of metamorphosis!  I released this seemingly fragile creature and watched as it took flight.  Little did I know at the time that the monarch was about to perform another miracle.
In 1937 a Canadian zoologist, Dr. Fred A. Urquhart set out to discover where the monarch butterflies spend the winter.  He did the nearly impossible, tagging butterflies in an attempt to determine their migration route.  The answer came nearly 4 decades later!  Urquhart's wife, Norah, wrote a letter to Mexican newspapers asking for sightings and help with tagging since the butterflies didn't appear to be overwintering in the US.  Kenneth Brugger, a man living in Mexico City, proved to be the key that unlocked the mystery. On January 9, 1972 he phoned Urquhart excitedly proclaiming "We have found them - millions of monarchs - in evergreens beside a mountain clearing!".

Now here we were standing in El Rosario Sanctuary in the central highlands of Mexico witnessing this amazing spectacle for ourselves.  Millions of monarch butterflies were hanging from the boughs of Oyamel fir  trees!

El Rosario Sanctuary (the dark blobs are butterflies!)
We watched in awe as the butterflies reacted to changes in cloud cover.  When the sun came out they'd open their wings and start fluttering about.

Monarchs in El Rosario

Just as soon as a cloud obscured the sun, they would return to their roosting site and close their wings exposing their darker tan undersides.

Monarchs in El Rosario
We also learned how to tell the difference between a male and a female monarch.  Males have thin vein pigmentation and black pouches on the hindwings where they store pheromones.  Females have thick vein pigmentation and no black pouches on the hindwings as shown.

Female Monarch                    Male Monarch
Today there are 14 sanctuaries (6 are open to the public) in the Monarch Butterfly Biosphere Reserve. Here is a map of the reserve showing the location of the sanctuaries in the Transvolcanic Mountains of Mexico.

Map of Monarch Biosphere Reserve

The land is communally owned by a group of families and is called an ejido.   The ejidatarios are responsible for protecting the forest and hence the Monarchs within the sanctuaries.  In past years illegal logging was a serious threat to the forest and the overwintering sites of the butterflies.  Today illegal logging has all but stopped and the number of hectares containing trees with roosting Monarchs has increased.  The local people now realize how important the forest is in protecting their watersheds, preventing landslides and of course harboring the Monarchs during the winter.  The ejidatarios now make a living through ecotourism and sustainable forestry practices.  Now it's up to Canada and the US to protect the Monarchs when they are up north.  The use of pesticides and habitat destruction are serious threats.  Milkweed, the plant larvae feed on exclusively, is considered a noxious weed by some people, which means it is often destroyed

The next day we visited another Sanctury called Chincua.  The effect was the same, awe.

Monarch in Chincua Sanctuary
How can such delicate creatures fly up to 3000 miles to reach the fir forests of Central Mexico?  How do they know when to head south?  How do they know how to get there?  Today the answers to these questions are beginning to be understood through the work of Dr. Urquhart, Dr. Lincoln Brower, a research professor at Sweet Briar College, and more recently Dr. Chip Taylor, director of  Monarch Watch.  Each fall around the month of September the Monarchs undergo a physiological change which shuts off their drive to mate and reproduce.  These changes are triggered by shorter days and colder temperatures.   This "migratory generation" makes the long migration south. Monarchs east of the Rocky Mountains funnel together over the state of Texas as the head south into Mexico.  Here is a map showing their flight pattern.

Migration Pattern of the Monarch Butterfly

It's not entirely clear how Monarchs find their overwintering sites each year.  Somehow they know the way even though they've never made the journey before.  In fact, they are the great-great grandchildren of the Monarchs that left the previous spring from Mexico.  Some believe that the butterflies use visual and olfactory cues and possibly the Earths magnetic field to make their way south to the overwintering sites.

The last Sanctuary we visited is called Piedra Herrada.  A steep climb brought us to the overwintering site at nearly 10,000 feet.  As we were observing the colony, I noticed that a large clump of butterflies suddenly took flight.  When I looked through my binoculars I could see birds feeding on the butterflies.  Monarchs are toxic to most animals throughout their entire life cycle.  In all fairness they do warn potential predators of their toxicity with their bright orange coloration.  There are only 3 predators known to have evolved defenses against the Monarchs toxic exoskeleton.  We were witnessing one of these predators, the Black-headed Grosbeak!

Black-headed grosbeak Eating a Monarch!
These birds go for the muscle-laden thorax with their heavy bills and have a higher tolerance to the toxin of the Monarchs.  The other two predators are the Black-backed Oriole and the Black-eared Mouse. We had the privilege of spending nearly 2 hours in the Sanctuary.  It was a particularly sunny day making the Monarchs more active.  Here's a video clip of this amazing spectacle.

It was perfect for us as it made for great photos and videos but not so good for the Monarchs who need to be conserving energy for the long trip back north in mid-March. In fact the Monarchs choose these high elevation overwintering sites as they hover around freezing. This causes the Monarchs to be less active hence conserving energy.
During sunny days, the Monarchs are warm enough to drink water and nectar from some of the forest flowers.

Monarch Drinking Nectar
All too soon it was time to leave.  I was overcome with emotion and began to cry.  Not out of sadness but joy at being privileged to witness such an amazing natural phenomenon.  The Monarchs thrilled me as a child with there miraculous feat of metamorphosis and now as an adult I was witnessing the equally miraculous feat of migration!  As we were loading into the bus, Paty one of our guides brought me a tag that one of the locals had found. Could it be the tag Marc saw on the climb to the colony but failed to pick up?  I paid 50 pesos for the tag and will send the info to Monarch Watch so they can determine the origin of the butterfly who wore this tag.  Here is a photo of the ting tag once fixed to the underside of the monarch's wing.

Monarch Tag

The Monarchs had one more surprise for us.  As we were leaving the Sanctuary, hundreds were flying along the road.  Our bus had to slow to a crawl to avoid hitting and killing Monarchs.  In fact you get fined 500 pesos for each butterfly you kill.  The monarch police were out ensuring that motorists slow down.  Here is a short video clip capturing the scene.

What an amazing day spent with the Monarchs.  A special thanks to our wonderful guides Astrid and Paty for sharing the Monarchs amazing story with us.  Here's to the Monarch, long may you fly!
We hope all is well back home.
Peggy and Marc

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