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A Blue View: Phenology: Timing is Everything

Rhythm is a dancer—and a strawberry, a coral reef, a peach and a firefly. Nature has its own rhythms, the circadian rhythms, which can be observed from the tiniest microbes to the leaves of colossal trees.

Published September 08, 2015


Photo via Wikicommons.

Circadian rhythms are 24-hour cycles of physical, mental and behavioral changes, guided by the sun. They influence sleep-wake cycles and body temperature—a black bear stirs with the warmth of the sunlit spring, while the dim light of autumn cues hibernation.

They can impact when an animal reproduces or determine the season in which a flower blooms or a tree produces fruit. You’d be hard pressed to find fresh, local corn outside of the summer season.

The study of these cyclical and seasonal changes in nature is called phenology. It helps scientists understand how plants and animals relate to changes in weather and climate within their environment.

But they can’t do it alone…and that’s where you come in. By observing the nature in your own backyard—from the emergence of insects to bird sightings and when leaves first begin to sprout—you can help influence scientific discovery.

Programs like Project Budburst and iNaturalist make it easy to identify and document nature, providing researchers access to global information.

For more ways you can engage in citizen science, click here.

Episode Transcript

You may not think you’re much of a dancer, but never say you don’t have rhythm. All humans, and many other animals, have our own rhythm. It’s called circadian rhythm, and it’s a 24-hour internal clock that regulates our sleep-wake cycle, and even controls some of our physiological processes. And the best part is: we get this rhythm from a star. More precisely, our own Sun.

Like many mammals, humans are most active during the day, spending night to rest and digest. There are clear patterns of brain-wave activity, hormone production and cell regeneration linked to these daily cycles. Researchers are finding that not only what we eat, but also when we eat, exercise and sleep has major consequences for our health. A deregulated sleep-wake cycle increases the risk of cardiovascular disease, obesity and depression. Night shift workers are at high risk, as are airline crews. Jet lag is a circadian-rhythm disruption.

All of nature has a rhythm, too. Corals on tropical reefs spawn annually in a mass synchronized event that occurs on a single night. They take their cue from environmental factors such as water temperature and the light of the moon. In the Northeast, when deciduous trees start to drop their leaves, tourism leaps. The cycle of life for plants, animals, and the Earth itself is seasonal, and sometimes fleeting. Take strawberries. Here in the Mid-Atlantic, they’re really only available for two weeks in June. Or try finding a fresh local peach in February. Fireflies wink ubiquitously, but only on summer nights. Nature has a calendar.

Phenology (FENN ology) is the study of how the biological world times its natural events and cycles. Aldo Leopold, philosopher, naturalist and author of the now-famous collection of essays entitled “A Sand County Almanac,” is considered by many to be the father of this branch of ecology. Leopold began keeping records of the timing of natural events on the landscape of his Wisconsin farm in 1935, and his daughter Nina continued his work until her death in 2011.

What’s fascinating about this data cache is that Nina's start dates—especially those of spring-phenological (FEEN o logical) events, such as the migration of birds and the blooming of flowers—differed from her father's. Beginning in the 1970’s, they occurred 2 to 3 weeks earlier. What changed? Certainly not Earth’s location in the solar system, nor the Sun’s intensity. She pondered: what had changed?

As quaint as it may seem today, the fact that temperatures were rising steadily in Southern Wisconsin was a surprising discovery at that time. As we now know, rising temperatures change the distribution of species and the timing of their reproduction, which is what Nina observed. All too soon, it became clear that this phenomenon was global. She was observing the onset of human-caused climate change.

Species use predictable, annual environmental changes to cue natural events such as breeding or flowering. The increasing light and warmth of spring wakes up groundhogs, just as shorter, cooler days in fall send them back to their burrows.

The Sun is the conductor of this grand symphony, and light and temperature hold the lead chairs. These two factors even impact our moods, as anyone who has ever felt the winter blues can tell you. Psychologists call it SAD…seasonal affective disorder. The prescribed cure? Find a bright spot for your morning coffee. Scientists at Harvard’s Medical School found that bright light stimulates cells in the retina, which in turn connects to the hypothalamus, the brain’s control center for our circadian rhythms.

Phenology and climate change are inextricably linked, and we humans are as vulnerable as bees, birds and frogs to its effects. Learn how to spot nature’s rhythms and become a citizen phenologist yourself by visiting As they say, timing is everything.

A Blue View is produced by the National Aquarium for WYPR. For the National Aquarium, I’m John Racanelli.

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