Signs of a changing season

Out walking the dogs today I observed classic signs of a changing season. Nature is on the move. How appropriate, especially considering the official beginning of fall, the autumnal equinox, occurs at 4:05 a.m. on Friday, September 23. Hours of daylight are getting shorter and the creatures of the Earth, big and small, are taking note.

The shortening of daylight is a signal for migrating species to get moving. I saw bluebirds gathering in groups of 5 or 6 today, and the last of the hummingbirds have been loading up on sugar water at the hummingbird feeder in our yard. Meanwhile, Monarch butterflies are drinking nectar and gaining strength and energy for their long flight south.

Scientists have wondered for years how creatures know where to go when they migrate. Do they have a built-in GPS system? Perhaps, although not in the way we think of it. It's not like the computer in our car that guides us from here to there. A detection and sensitivity to Earth's magnetic field may help some species on their path. Others, like birds that migrate, may use the Sun and stars to point the way.

The adult male ruby-throated hummingbird.

I always marvel at the seemingly frail hummingbirds. These tiny ones travel all the way to Mexico and Central and South America for the winter. The adult males leave first. They are gone by now. The most common hummingbirds here, the ruby-throated, have a distinctly red spot on the throats of the males. Adult females depart next. Surprisingly the juvenile hummers, the ones born this summer, leave last - and they have never made the trip before! Chances are the hummers you see at your sugar water feeders now are the juveniles. The young males and females tend to look similar. The young males do not have the distinctive red throat markings yet.

Nothing is as spectacular as the Monarch butterfly migration. The Monarchs you see flying around right now are just a couple of weeks old. This is normally the life span of an adult Monarch. Except the ones born in August don't die that young. They keep living and begin heading south to the Gulf Coast of the U.S. or the mountains of Mexico. And they have never made the trip before! How do they know where to go?

Their great, great, grandparents made the migration last fall. They departed Mexico to head north in the spring and died. But not before laying eggs that develop into new adult Monarchs who continue the journey north. They die after a few weeks but new offspring continue the journey. The Monarchs travel north at a rate corresponding to the spring development of the milkweed plant. The female Monarch lays eggs on the milkweed and the caterpillars feed on the milkweed.

Monarch butterflies by the thousands resting on trees in the mountains of Mexico after migration. They will await the warmth of the spring sun to signal them to begin migrating north for summer.

So when you observe the Monarchs flying around our area during the next few weeks, wish them well. They are embarking on a journey of over 1,000 miles, riding the warm thermals upward and pushed along by the autumn winds. The Monarchs that survive will most likely overwinter in the high elevation of the mountains of central Mexico. There they will hang on trees by the thousands and rest in the cooler air, waiting for the warming sun of spring to signal them to begin the journey north. Amazing.

There are many good websites with information about the life of the Monarch. HERE is one I recommend. And don't forget to visit The Monarch Trail on the Milwaukee County grounds on Watertown Plank Road. It is a favorite resting spot for migrating Monarchs and a wonderful setting to watch them. More info on The Monarch Trail website HERE.