I’ve been a little groggy lately. It’s been hard to stay motivated with the skies turning grey and days getting shorter. Especially after we changed our clocks, falling back into “normal” not-day-light-savings time, it’s like the world is telling me to go to bed right after dinner. I already drink enough coffee. Each year figuring out how to adjust my schedule to fit this new daylight scheme poses challenges, but the problem is not just the end of day-light-savings. It’s the days getting shorter, with Ithaca having less than nine hours of daylight towards the end of December. It’s changes in day length and temperature that signal to all organisms, including humans, the onset of winter. Aware of it or not, this impacts our physiology and mood. But like the forsythia I saw blooming on Thanksgiving day, anomalous weather associated with climate change throws a wrinkle into our rhythms.
We track the weekly trends in the length of days and nights, and shorter days indicate that winter is coming. The oak tree thinks: resorb your nutrients, store your sugar, shed your leaves, prepare for dormancy. It’s also how the monarch butterfly shape-shifts its body and gears up for a 3,000-mile journey to Mexico. The shorter days stimulate hormones that trigger the autumnal generation of monarchs to grow swole, with bigger wings, and to refrain from mating. Then, butterflies face south, and throughout their morning flight keep the sun to their left side. In the afternoon, they keep the sun to their right. In this way, flutterbys integrate their own clock with the position of the sun to find their way to southern overwintering sites. It’s a time-compensated sun compass that’s their tool of navigation. I kid you not. The three other monarch generations per year, which were caterpillars in April, May and June, have none of that with longer days. They are flabby, with shorter wings, and ready to mate.
As part of seasonal cycles, being in tune with the environment makes life livable and ensures our survival. For monarch butterflies, those that don’t start migrating south by mid- to late September typically won’t make it to Mexico. But, if they start too early, there are missed opportunities for bulking up before the journey. Accordingly, butterflies not only pay attention to the shrinking days of autumn, but they also take stock of the relative warmth of days and nights.
The remarkable thing about days getting shorter is that this celestial process is time immemorial. Year after year and millennia after millennia, days get shorter beginning in summer until the winter solstice, and then gradually lengthen until the summer solstice.
Like the butterflies, we primates are not only paying attention to the length of the days, but also to the temperature trends. Has there been a frost yet? Are nights getting colder as days are getting shorter? It’s typically the combination of rigid factors that have a very repeatable cycle of change, like day length across the seasons, and a more variable factor, like night-time temperatures, that jointly shape plant and animal seasonal schedules. Some Octobers are warm and wet, while others are cold and frosty. But shorter days with warm nights in November might be confusing for all species. And worse than confusing, such mixed signals associated with climate change could be devastating.
The humble groundhog is one of our few true hibernators. It’s not unlike an extended winter break, triggered by the changing of the seasons. Their heart rate slows from 80 beats per minute to 5; their body temperature plummets from 99 degrees to 40 degrees; and they slumber in a slow metabolic state by burning stored fat reserves. It’s the joint effect of shorter days and colder nights that gets them on that trajectory of sleeping for five months. But being awoken in February due to a winter heat wave could be ruinous for these creatures.
Organisms like us have a sharp sense of seasonal shifts. We, like most of our ancestors, are fine tuned to the schedules and fluctuations of the seasons. But with the acceleration of global environmental change, those delightfully warm days in winter perhaps conflict with the declining daylight of the approaching solstice. Awareness of nature’s rhythm can guide us. Paying attention can only help. Thinking of yourself as the animal that you are might be the best solution. But be mindful of the anomalies that disrupt our sense of the seasonal cycles. For many organisms, adaptation will be key; for those that fail, extinction looms. We, too, need to stay in touch.
Forsythia blooming in Ithaca on Thanksgiving day 2024
Anurag Agrawal is the James A. Perkins Professor of Environmental Studies in the College of Agriculture and LIfe Sciences. He can be reached at [email protected].
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