The animals you can count on to predict weather, according to science

By Jackie Wattles, CNN

(CNN) — Punxatawney Phil, the central character of the annual rite of winter known as Groundhog’s Day, isn’t great at his job. His predictions are wrong more often than they are right.

On Friday, the divining marmot did not see his shadow, indicating an early spring. Though, technically speaking, winter will end on the spring equinox, which falls on the evening of March 19.

But the groundhog is just one of numerous animals that, according to folklore, possess an uncanny ability to forecast the weather, including cows that are said to lie down before early rain and woolly bear caterpillars that are supposedly decorated with less color before a frigid winter.

Most of these associations are unmoored from modern science — but there is an occasional hint of documented fact among the myths.

Phenology is the study of how seasonal events in the lives of plants and animals shift according to the weather and climate, such as how fish or migratory birds respond to the temperature of water and air. (The field of study can be practiced as a hard science, for the record, and is entirely distinct from the pseudoscientific “phrenology.”)

The USA National Phenology Network tracks when ecological markers of spring arrive across the United States — and the season is already in bloom in certain locations on the east and west coasts.

Theresa Crimmins, the director of the USA National Phenology Network, said that while Punxatawney Phil is not a reliable predictor of spring’s arrival, phenology does offer scientific backing for other seemingly superstitious axioms about the natural world.

“People have been observing (environmental conditions) for many millennia, for basically as long as humans have been around,” Crimmins said. “So (a lot of these adages) actually work because they are, in a sense, capturing those relationships between the environmental conditions and plant response.”

But while folklore often supposes animal behavior portends future weather events, in reality, flora and fauna react to weather and climate.

Plants and their predictions

The roots of Groundhog Day lie in traditions that were likely imported to the United States from Germany, where the winter-forecasting animal was a badger rather than a groundhog.

However, numerous tried-and-true proverbs about the natural world come from Native American populations.

“One example is planting corn when oak leaves are the size of a squirrel’s ear,” notes an article on phenology from the University of Wisconsin-Madison. “You know that planting corn has nothing to do with oak leaves or squirrels. However, Native Americans made the observation centuries ago that the soil was warm enough to prevent seeds from rotting, yet it was still early enough to reap a suitable harvest if corn was planted at this time.”

Crimmins points out that there are plenty of other predictors for coming ecological events spelled out in the leaves, berries and flowers of plants.

For example, the shadblow serviceberry is a small tree that is native to parts of eastern North America, and it’s believed that its name came from the fact that it bears flowers at the same time of year that shad fish begin their river migration. The Lenape and other Native American populations made note of the phenomenon long ago and prepared to fish when the plant began to bloom.

Animals and severe weather

The Old Farmer’s Almanac  has aggregated a couple dozen adages about insects, animals and their ability to predict weather patterns.

Some of the claims are dubious. Dogs eating grass, for example, is likely a far less accurate predictor of rain than a meteorologist’s weather report.

But there is research out there that suggests some animals may possess an innate sense that helps them detect when a disaster is on the way.

Golden-winged warblers, for example, evacuated an area of Tennessee more than 24 hours before a devastating string of tornadoes hit the area, according to a December 2014 study published in the journal Current Biology.

The study authors predicted the migrant birds listened to infrasound — sound at frequencies too low for humans to hear — associated with the storms and heeded it as a warning sign.

Researchers in Germany also looked into whether various species of animals could detect an oncoming earthquake. The scientists found that, collectively, animals including cows, sheep and dogs exhibited more activity before an earthquake up to 20 hours in advance, according to a report from Germany’s Max Planck Society, a nonprofit association of research institutes.

Insects and frogs

There is also truth to the notion that crickets can act as nature’s thermometer. The insects are ectotherms, meaning their body temperature changes with that of their surrounding environment — and they routinely chirp faster in warmer weather.

According to Dolbear’s Law, a formula describing this association between crickets and weather, “you can count the number of chirps per 15 seconds, add 40, and that will give you the temperature in Fahrenheit,” the National Oceanic and Atmospheric Administration notes.

Frogs also deliver unique calls when it’s about to rain.

“Many twentieth-century herpetologists have confirmed and clarified the traditional observation that various species of frogs sometimes utter a distinctive vocalization, a ‘rain call,’ a short time before wet weather,” said Dr. Gordon Miller, a professor emeritus of environmental studies at Seattle University, via email.

The calls “are perhaps triggered by a rise in humidity prior to precipitation,” Miller said.

Fact vs. folklore

Other tropes about animals’ ability to predict seasonal conditions, however, are wrong.

The woolly bear — a species of caterpillar, also called the woolly worm — famously is thought to forecast the severity of the impending winter with its colored bands. More black coloring on the insect supposedly indicates harsher conditions on the way.

But in reality, the “caterpillar’s coloring is based on how long (the) caterpillar has been feeding, its age, and species,” according to the National Weather Service. “The better the growing season is the bigger it will grow. This results in narrower red-orange bands in its middle. Thus, the width of the banding is an indicator of the current or past season’s growth rather than an indicator of the severity of the upcoming winter.”

Climate change and phenology

Unusual animal behavior can also be a reaction to a changing climate, Crimmins emphasized. And often not in good ways.

The climate crisis and human development are causing all sorts of ecological problems, Crimmins noted. Bears, for example, are entering hibernation later and arising earlier because of the warmer weather. That can lead to more human-bear interactions  as bears search for food, and there is concern about how shorter hibernation periods are affecting bear pregnancies.

Miller added that, while frogs may be able to foretell incoming rainfall, “with so many amphibian species continuing to decline due to various environmental and climatic factors, perhaps their most clarion call to us today, as Rachel Carson noted of birds in 1962, is their diminishing chorus and growing silence.”

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