To many of us, the beginning of spring doesn't only mean longer days and warmer weather -- the new season also brings spring fever: more energy, appetite shifts (a desire for less food and more sex), restlessness and other biological changes. But do animals feel the symptoms of changing seasons, too?
For dogs and other mammals, part of the answer lies in a tiny clump of cells -- called the suprachiasmatic nucleus -- located in the brain's center. These little clusters of neurons are the springs that drive mammalian biological clocks. Because these cells are hooked up to the eyes, they respond to changes in daylight, triggering the release of sleep-inducing hormone melatonin when it's dark. More light, on the other hand, cuts back on the flow of melatonin. A group of Polish veterinarians studying Alaskan husky dogs, for example, found that the huskies' melatonin levels peaked in December, dropped in March and were lowest in June.
What about changes in sex drive? Historically, conception rates for humans have peaked in the spring -- and so do those of deer mice and hares. A study of more than 400 breeding dogs, likewise, found that canine reproductive cycles were most active between February to May.