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El Dia de los Muertos (The Day of the Dead) has now passed and one of nature's most spectacular mass migrations is coming to an end.
The Monarchs that have returned are the grandchildren of those that departed in March - it's still a mystery how these tiny insects know to navigate back to such a specific location but we do know why they return to these forests. The physiology of this area offers great protection from the cold winds that rattle through the region - if they were not so protected they would all surely freeze.
Once they have settled, they form massive clusters, which is believed to have two advantages. Firstly, it offers further protection from bird predation - by presenting a united front, they look like one big creature rather than millions of tiny fragile individuals. Secondly, these clusters make it easier for the Monarchs to warm up. Monarchs need the heat of the sun to become active and it's easier to do this if the Monarchs congregate together as a blanket.
Those lucky individuals that have made it to this over-wintering site will now have another great challenge - to make it through to spring without feeding. These Monarchs will have spent the last few months storing up a healthy fat reserve and they will now have to sustain themselves on this reserve until March. This is why it is the largest Monarchs that are most likely to make it to this site and to survive through winter.
As Professor Chip Taylor says, this has been a very poor year for the Monarchs - poor weather compounded by habitat loss. Conditions during spring and early summer held them back but 6000 acres of potential habitat is being stripped EVERY DAY. That's 2.2 million acres a year! Clearly, there is a lot of work to do if we are to conserve this awesome spectacle and Monarch Watch is one project that you can get involved with if you want to make a difference.
Further Reading:
Next report: Monarchs and the Day of the Dead
Last report: Running with Monarchs Part V
Chip Taylor's Monarch Watch blog