If you go to Google in the US, Mexico, and most of Western Europe and western South America (but not Canada, where they’re celebrating Simone de Beauvoir), you’ll see the screenshot below. When you click on it (do so), you’ll learn what it’s celebrating: the 41st anniversary of the discovery of the “Mountain of Butterflies”: the most famous overwintering site of Monarch butterflies (Danaus plexippus) in the world. It’s truly one of the most marvelous sights in nature, and I hope to see it some day.
Monarchs overwinter at several sites in the western U.S. and Mexico; the “Mountain of Butterflies” is in the Mariposa Monarca Biosphere Reserve in Mexico.
The life cycle of the butterfly is complex; you can read about it here. They go through four generations per year, with only the final generation migrating to southern sites to overwinter (adults of the first three generations live 2-6 weeks, the overwintering one 6-8 months). The movement to the northern breeding sites is gradual, with the insects heading farther north generation by generation. In contrast, the trip south is done by single adults, who fly from the U.S. to Mexico in one big go. (As shown below, Monarchs from the eastern U.S. overwinter in Mexico; those from the Western U.S. in coastal California.)
It’s amazing to ponder how natural selection could create this behavior, as the sequential northern migration, as well as the one-shot southern migration to the same sites year after year (it’s not clear how the insects find their way), and the knowledge of when to start migrating—all of these are somehow coded in each individual’s DNA. What a marvelous thing the butterfly’s genes have done to keep themselves alive and replicating in a harsh environment!
Below is a video of the Mexican site with some spectacular shots of the huge masses of overwintering butterflies, estimated at over 150 million individuals. The shots of the butterflies begin about 2:30:
Here, from the USDA website, are the flight paths south, and an animated gif showing their sequential movement south this year:
The absence of the butterfly image in Canada is a bit curious, for the Mexican overwintering site was discovered by a team led by Canadian zoologists, Fred and Norah Urquhart, with the collaboration of Catalina Trails and Ken Brewer.
It does show images in southern Ontario. Interesting the heavy East Indian accent describing the mariposas in Mexico.
Don’t birds take note of all that breakfast, lunch, and dinner available on the wing? Didn’t see any in the vid.
Birds quickly learn that monarchs are rather poisonous, filled with a toxin from the milkweed plants that the larvae eat. Here is a bluejay learning the lesson: http://biology-forums.com/index.php?action=gallery;sa=view;id=1367
There is a minor flyway from SoCal and Las Cruces, NM. We are trying to propagate butterfly plant to encourage their increase here.
They are wonderful. Thanks for this posting.
A wrinkle in doing that is that some of the popularly sold milkweed plants sold for helping the butterflies actually cause harm because they cause the butterflies to not migrate and this results in the extinction of those lineages. Here is some info: http://entomologytoday.org/2015/01/16/planting-the-wrong-kind-of-milkweed-may-harm-monarch-butterflies/
Thanks for that. I have found several sites with info on milkweed varieties available for my area and one which cautions which to use. Will pursue this accordingly.
I love Monarchs. I grow swan plants outside my kitchen windows so I can watch them through their life cycle each year. So far this year mostly all I’ve seen is the new growth disappearing like magic as it gets munched away. Numbers increase markedly in February. I don’t know where ours go in the winter, but it would be warm enough north of Auckland.
Holy smokes, I had no idea the Monarch was so widely spread! From Wikipedia:
Hi
google.ca is showing the butterfly image and text now, at least to those of us in Canada.
Jim
This may be overstating it. I’m guessing that many of the details of the migration pattern are coded in the environment rather than in the butterfly DNA.
For instance, the stepwise northern migration is probably not a result of each generation trying to cover a fixed fraction of the distance. Rather, the butterflies move north until the weather feels right for stopping, and the next generation departs when the weather feels right for departing. It just so happens that it takes several such cycles to reach a place where the weather is stable enough for them to stay put for the remainder of the summer.
The environmental cues might include available food sources or other factors as well as temperature. The point is that there’s most likely a seasonally moving sweet spot of butterfly habitat, and the migration follows that, rather than being genetically programmed with a specific itinerary.
I stand by what I said, which was that the butterflies know when and where to migrate. That they use environmental cues to do this is not surprising; they’d HAVE TO. But tell me how they get back to one spot in Mexico without that being somehow genetically based. It clearly involves assessing the environment, but that assessment is in the genes.
I agree that the assessment criteria are coded in the genes. But that’s not the same as saying the particular migration pattern we observe is coded in the genes (which is what you seemed to be saying). The pattern is the product of those assessment genes operating in a seasonally changing environment. I predict that a different environment, with different seasonal variations (say as a result of global climate change), would produce a different migration pattern, indicating that some of the information that determines the pattern is not coded in the DNA.
Could it be that every first class male passes on a return address… (am I banned?) 😉
I thought that most long-distance migrants relied on day-length rather than weather for “travel instructions.”
(Which raises the thought that global warming is going to be even harder on those spp!)
Very interesting and amazing to see such vast numbers crowded together in the trees. I have spent many pleasant hours watching monarch butterflies and caterpillars in my garden, although they have been scarce the last several years.
From the link about the life cycle: “It is amazing how the four generations of monarch butterflies works out so that the monarch population can continue to live on throughout the years, but not become overpopulated.”
But not become overpopulated…sounds off to me; like “for the good of the species.”