The change to Daylight Savings Time last weekend got me thinking about animals and daylight. The creatures in the woods do not have to change their clocks, naturally, but the change in day length plays an important role in their lives.
Since we biologists need a big word for everything, I am going to use “photoperiod” as a way of saying “number of daylight hours each day.” As a side note, some of my other favorite scientific words to use include formicate (sensation of skin crawling), masticate (chew), album graecum (dog droppings that turn white and chalky), and air-water interface (the surface of a water body). Feel free to use these to impress your friends!
Here in the United States, we valued the role of photoperiod in our lives and society so much that we made a decision to change our clocks twice a year to maximize our use of daily photoperiod. Basically, we fool with Mother Nature! Only a handful of nations in the world use Daylight Savings Time, and most are in the Northern Hemisphere.
Why the Northern Hemisphere? In our location on the globe, we see a fairly dramatic change in photoperiod length. Dec. 21st is the winter solstice, with an eight hour photoperiod. In the summer, our longest day is June 21st, with over 15 hours of sunlight-almost twice that of the shortest day! This photoperiod change definitely affects humans; in the winter, it is commonly referred to as Seasonal Affective Disorder, or SAD. We become sad, irritable, disinterested, become sleepless or oversleep, it’s a kind of sunlight-deprived depression basically throwing our well-being off kilter.
Different wildlife species cope with these changes in different ways. If you are a migratory bird, you head south, flying thousands of miles closer to the equator (or the sun), maybe to Central or Southern America. If you are a bear, you find a den to basically sit out winter, snoozing, keeping activity to a minimum, growling if anyone comes too far into your den without first sedating you. If you are a chipmunk, forget about it-you find a warm spot deep in a hole and conk out completely until spring. If you are a turtle, you might lay in the mud, or below the water, allowing parts of your body to freeze until spring thaws. If you are a deer, you slow your bodily functions down so you can get by on a minimal amount of food, then just kind of trudge through the snow until the south-facing slopes open up.
So photoperiod triggers in wildlife the sense that it is time to change behavior patterns, maybe give birth to young, or to migrate back north. We know that photoperiod is not the only trigger for plant and animal species life events, because air temperature also helps bring snow cover to an end, waking up insects, and stimulating plant growth in the spring. In fact, recent studies have shown that migratory birds are heading north days earlier than they did years ago. The sunrise and sunset times have not changed drastically enough to change this behavior, but global temperatures have. But temperature, ground frost, snow cover, and photoperiod are all still seasonally linked.
These combined factors tell wildlife that it is time to resume their higher energy functions-and time for humans to be less sad.
Correction: In last week’s column, I wrote that the DNR has 39,000 employees, when I meant 3,900. In fact, with the number of retirements and employees who have left, we are even smaller. According to our Human Resources specialist in Spooner, we have 2,200 permanent, full time employees; 17 seasonal employees; 11 project employees; and 2,400 part-time employees. However, that last number can be a bit deceiving because some employees hold 2 LTE positions to work year-round; I would estimate there are more like 1,600 LTEs working for the DNR. This would bring the total employee numbers to about 3,800.
Jeremy Holtz is a wildlife biologist with the Wisconsin DNR in Rhinelander, and writes a weekly column in the Star Journal. To contact him, call (715) 365-8999.