Signs of Fall 8: Let’s All Fall Behind!

Photo by Pixabay

(Click here to listen to an audio version of this blog!)

Last weekend we changed back over to Standard Time. This “fall behind” change in our clocks does nothing to alter the total amount of sunlight we get in a day but it does change our perception of the lengths of day and night. Supposedly, we get an extra hour’s sleep on that first Sunday morning after the time change, although many of us, I am sure, just got up a bit earlier on clock time than we usually do on a Sunday.

All sorts of studies have explored the impacts of the Fall and Spring time change. The Fall, with its promise of that extra hour of sleep, seems more benign than the Spring change which takes that hour away. One researcher referred to both changes as a type of “jet lag.” Sleep pattern disruptions, headaches, and mood changes were the dominant symptoms, and like jet lag the symptoms go  away within a few days.  The Spring change, though, had some potentially serious consequences: for several days after the “spring ahead” clock change there is, an increase in work-related injuries, and, possibly (although there are conflicting studies on this) an increase in morning traffic accidents. Interestingly, according to a 2012 study published in the Journal of Applied Psychology, for several days after the Spring time change office workers also increased their on-the-job “cyberloafing” Internet time. Maybe web surfing is an adaptive way to avoid accidents and injuries!

Izzy. Photo by D. Sillman

Mornings now are just a little more sunlit than they were before the clock shift and afternoons and evenings are a little less.  When Deborah takes our dog, Izzy, for her morning walk at 7 am it is a bit more sun-lit than under Daylight Time. A flashlight, though, is still helpful. The full darkness of the late fall and early winter mornings will soon be upon us.

We are racing toward the Winter Solstice (December 21 this year) when the North Pole will be tipped as far away from the sun as it goes these days. On the Winter Solstice we will have an hour less sunlight than we do today (just 9 hours and 6 minutes).  Do you remember the Summer Solstice back on June 21? We had 15 hours and 3 minutes of sunlight that day.

Anyway, our shifts from Daylight Savings to Standard times do not affect organisms other than humans, but the on-going transitions of day length and darkness do affect almost every plant and animal species around us.

Photo by D. Sillman

I used to be able to closely watch the impacts of the shortening day lengths and colder temperatures on my late, pet box turtle, Spider. He would get sleepier and sleepier as the days got shorter through the Fall. I started keeping him exclusively in the house as the temperatures got cooler, but the decreasing time of sunlight pulled him into a torpor that lasted all winter. In turtles that live in outside environments this seasonally induced dream-state leads all the way into a true hibernational homeostasis. Even keeping him in the relatively constant temperature of my dining room (where his terrarium was located), though, he could not resist the physiological changes of the season. He would eat his last nightcrawler of the year sometime in late October and wouldn’t have another until the first or second week in March.

Shortening day lengths are the prime stimuli for many of our summer birds to begin their southward migrations. They need to fatten up and leave the area well before food supplies are gone and cold weather has settled in, so getting a benign physiological nudge from the shortening light periods is a great evolutionary advantage. The hummingbirds, the tanagers, the grosbeaks, the robins, most of the bluebirds and many other species, each tune into their specific day length stimuli and then build up their fat layers and head out toward their overwintering regions.

Even humans respond to the shortening day lengths, although the pattern of this response is not always the same in all people. Thyroid hormone seems to either go up or get more active in most people in the winter. Logically, it stimulates metabolic rate and heat production especially through the metabolism of carbohydrates and possibly also stimulates metabolic heat generation in the body’s brown fat deposits. Cortisol levels also go up in the winter probably acting to shift metabolism over to using fats (both stored and dietary) for energy. But all of these responses are really quite muted compared to other mammalian species that have not developed technologies that protect them from the great stresses of winter.

Photo by D. Sillman

Plants have all sorts of photo-receptor proteins that respond to day length. These proteins are especially sensitive to the duration of the dark periods. It is the length of the night that drives plant species to flower, or make seed, or senesce. The cessation of chlorophyll production in deciduous tree leaves and its accelerated breakdown reveals the formerly hidden accessory pigments and generates the beautiful color displays of the autumn trees. The red maples were among the first trees to have their leaves turn color and then fall. Oaks and beech trees are among the last to have their leaves turn and may keep their leaves all through the winter.

I was riding my bike down on Roaring Run Trail a few days before the fall time change and noticed that the ridges surrounding the Kiski River had a distinct pattern of bare and leafed trees. The bare trees were mostly red maples, the same trees we had so clearly seen in the spring with their early red haze of flower and leaf buds, and the leafed trees were mostly oaks. The visual clarity of the species abundance (so many more red maples than oaks!) was striking!