Migrating Monarch Butterfly Spectacle -- not just in Mexico!

A monarch butterfly, Danaus plexippus.

I was in Cape May Point, New Jersey, on Saturday, September 18^th, expecting to see migrating hawks. Many birds follow the Atlantic shoreline south during autumn migration. As New Jersey gradually narrows into a tip at its southern end, migrants end up concentrated at the “point” with the Delaware Bay in front of them -- across their path. They sometimes wait a day or two for a north wind to help them across the water. The place can fill up with eagles, hawks, and songbirds. It’s a great place for autumn bird watching.

But this year butterflies stole the show. Monarch butterflies also get funneled to New Jersey’s point. On Saturday there may have been a half a million big orange and black butterflies in the tiny town of Cape May. Butterflies filled the sky. They hung from the flowers and trees. It looked like the town had been transformed into a Walt Disney movie. 

Gathering in a roost for the night. 

On Sunday morning, the wind was just right. The butterflies headed out in orange clouds across the bay. They passed by for hours. It was spectacular.

They are going to Mexico. As unlikely as it sounds, each tiny individual from the summer’s last generation flies the whole distance or dies trying. For some that is a distance of over 3000 miles. They can fly at about 12 miles per hour, for about 50 miles per day.

Once they get to Mexico, they spend the winter in a dormant state in chilly mountain refuges. The migrating generation lives about seven months, which is much longer than the few weeks typical for monarchs born in spring or summer. The migratory generation doesn’t finish developing sexually until the spring following migration. Then they rouse, mate, and start coming back north.

But they don’t have to fly all the way back. The return flight is generational. Individuals fly part of the distance, lay eggs on milkweed plants, and then die. The eggs hatch into caterpillars that eventually become adults that fly further north to lay eggs of their own. After a few generations, each traveling further north, the continent is repopulated all the way to southern Canada. Before you know it, a migratory generation is born and it’s time to migrate again.

Populations from eastern North America fly to Mexico. The western ones tend to end up in southern California.  In cities all over the continent we can glance out of our office windows, even on high floors, and see the big orange butterflies passing by. The last of them will go by around Halloween; they have to beat the first frost. 

There is more information about urban insects in my book,  Field Guide to Urban Wildlife, which will be published by Stackpole Books in spring 2011. 

Sparkling Birds

I took this photo of the World Trade Center Light Memorial this year on 9/11. The normally still columns were filled with thousands of shifting silver dots of light that glittered as they moved. At the time I didn’t know what they were.

They turned out to be migrating birds!

Hundreds of thousands of birds fly over New York City each autumn on their way to their southern winter homes. Light from the sun, moon, and stars helps them navigate. But artificial lights can interfere with their natural abilities to find their way. Unlike most autumn migrants, the birds that flew down Broadway on the night of 9/11 did not pass overhead unseen; instead they flew into the memorial lights. They became disoriented and stayed there, circling, illuminated like silver sparks. 

The lights were turned off five times during the night for 20-minute periods to allow the birds to fly away.

But migrating birds are still in danger. Brightly lit buildings confuse them too; many birds die every year when they fly into office building windows. The phenomenon is gaining recognition and famous sites like the Empire State Building and the Chrysler Building dim their lights from midnight until dawn during fall migration. It saves a lot of birds. Let us hope that it catches on.

You can read more about it here:  'Lights out' help migratory birds


There is more information about urban birds in my book,  Field Guide to Urban Wildlife, which will be published by Stackpole Books in spring 2011.