Swallows stage for migration on electrical wires at Spring Lake State Fish and Wildlife Area in Southern Tazewell County.
DENNIS ENDICOTT/PEORIA AUDUBON SOCIETY
As August unfolds with its usual dose of heat and humidity, nature is reacting to the shortening of daylight hours. After the summer solstice on June 20th, the amount of daylight hours declines.
MIKE MILLER
The sun rises a little later and sets a little earlier each day. In July, we lose around 43 minutes. In August the pace of the shortening day increases, so that we lose an additional 71 minutes of daylight. The farther north you go, the pace of daylight loss is much greater. One would think that this shortening of daylight would give us a reprieve from the heat and humidity. Thanks to the thermal lag that is caused by warm earth and atmosphere, temperature doesn’t reduce as noticeably as the length of the day. In fact, our average high temperature only falls by around 3 degrees in August.
This decrease in daylight is one of the main events that triggers birds to start migration from their northern nesting grounds to where they will eventually overwinter.
In August, many species of birds will gather and stage for migration. Along the Illinois River, the first birds to stage their migration are the various swallow species. There are seven species of swallows regularly found in Illinois. It is a sure sign that we are in the dogdays of summer when we see swallows sitting side-by-side stretched out along electrical wires. These mixed flocks can number into the thousands. These flocks, known as a flight, gulp, or swoop of swallows, are made up of both seasoned migrants and young of the year. They are quick to take to the wing and always seem to launch into flight just as soon as you get your binoculars focused on them. Always the acrobat, a flight of swallows is grace on the wing.
August’s normally dry weather causes lower water levels. Along backwaters of the Illinois River, this causes expanses of mudflats to form as the water recedes. These mudflats are teaming with aquatic invertebrates emerging from their larval stage into adulthood.
The timing is perfect for another group of migrants built for taking advantage of this movable feast: Enter the shorebird. Several species of Plovers, Stilts, Avocets, and Sandpipers all flock to the mudflats. Their migration is timed to follow these seasonal mudflats south.
Mudflats in August soon turn into verdant green swaths of vegetation, as wet soil plants begin to grow. By the end of August, the mudflats have disappeared and so have the shorebirds. They are enroute to far-flung corners of the southern hemisphere. Shorebirds have some of the longest migration treks of any bird species. To the Avocet that graces our wetland in August, we are but one stop on its 4,000-mile journey.
The plants that grow in the mudflats are in a hurry. They must grow and produce seed before the fall rains come. By October, the mudflats will be underwater, and the plants will release their seeds. It’s this combination that sets the stage for the last wave of migrants to visit: Waterfowl. Ducks and geese have been triggered to move by the shorter days. They stage their migration to coincide with fall rain. As rivers and backwaters rise, the seed produced by moist soil plants will fuel their migration south.
Shortening of daylight doesn’t only trigger bird migration, it is the driving force for plants to end their annual growth cycle. Trees begin changing the chemistry of their leaves. Nutrients and sugars are drawn into the branches, setting the stage for the spectacle of fall colors. Seeds mature to ensure the next generation of plants can survive. Insects deploy their strategy for surviving winter by going dormant or laying eggs that overwinter. Some like the Monarch Butterfly and dragonflies will take a lesson from the birds and migrate.
The seasonal ebb-and-flow is an important trigger for us as well. While we might regret the loss of long days, we can take a clue from nature. There is an innate sense of urgency in birds, insects, plants and all living things on Earth. Human beings are tied to the same planetary clock. Shorter days will result in increasing darkness. How we prepare for the darkness will shape our fate. Will we come out of the other side with energy to spare, or will we struggle? Even though the daylight is fading, August is still a month with more light than darkness. Daylight will still reign until the Fall Equinox on Sept. 22. So, get out and allow your soul to soak in the sunlight.