Photo by P. Seveh, Wikimedia Commons
Weekend before last we changed back over to Standard Time. The “fall behind” change in our clocks does nothing to alter the total amount of daylight we get in a day, but it does change our perceptions of lengths of day and night. Supposedly we get an extra hour’s sleep on that first Sunday morning after the time change, but 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!
Mornings now are just a little more sunlit than they were before the clock shift and afternoons and evening are a little bit less. I take my dog, Izzy, for her morning walk at 6:30 am, and with the time change there is a bit more light than before. I still need a flashlight, though, and 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 45 minutes less sunlight than we do today (only 9 hours and 17 minutes). Do you remember the Summer Solstice back on June 21? We had 15 hours and 4 minutes of sunlight that day although it might have been raining!
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 have been watching my box turtle get sleepier and sleepier as the days get shorter. I start keeping him exclusively in the house as days of Fall get cooler, but the decreasing time of sunlight pulls his physiology into a torpor that in the turtles that live in outside environments leads all the way into hibernational homeostasis. Even by moving him in to the constant temperatures of my dining room (where his terrarium is located), though, he still cannot resist the physiological changes of the season. He ate his last nightcrawler of the year a couple of weeks ago and won’t have another meal until the first or second week in March. He likes to wait for the price of early strawberries to peak before he starts to get his spring munchies!
Photo by D. Sillman
My housecats (that’s Taz to the left) are incredible hair producing organisms! Brushing them or even just petting them in the spring or summer generates great handfuls of shed hair. The shortening day lengths, though, do act to slow down even their amazing hair production rates. In an outside cat the production of hair without the shedding loss would result in a thick, insulating winter coat. Indoor cats usually don’t build up quite as heavy a hair layer but, at least, they slow down their shedding (a little bit, anyway).
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, thus getting a physiological nudge by the shortening days before the true cold settles in is a great evolutionary advantage. The hummingbirds, the tanagers, the grosbeaks, the robins, most of the bluebirds and many more other species, each tuned into their own specific day length stimuli, put on their fat layers and headed out toward their overwintering regions. I am glad to report that some of the more northern species (like the dark eyed junco) have responded to their own day length stimuli and have started to arrive to overwinter in our area!
Even humans respond to the shortening day lengths, although the pattern of this response is not always the same in all people. Thyroid hormone levels either rise or its hormone receptors become more reactive in most people in the winter. Logically, this 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 mammal species that have not developed technologies (like central heating!) to protect themselves from the great stresses of winter.
Photo by D. Sillman
Plants have all sorts of photoreceptor proteins that respond to day length. These proteins are especially sensitive to the duration of the dark periods in the 24 hour cycle. 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 the Sunday after the fall time change and noticed that the ridges surrounding the Kiski River had a distinctive pattern of bare trees and trees that still had leaves. 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!
So here we are at the end of the Signs of Fall! As they say in The Game of Thrones, “winter is coming!” Get ready!