Can Animals Tell When It's Going To Rain?

Dogs get restless. Cows lie down. Birds fly low. Frogs get noisy. For centuries, people have watched animals for clues that rain or storms were on the way.

Some of these observations are probably coincidence, and plenty belong firmly in the folklore category. But the basic idea that animals can react to approaching weather has some science behind it.

Animals don't necessarily "predict" rain. But many are extremely sensitive to changes in their surroundings, including some of the same atmospheric changes that occur before a storm.

What Changes Before It Rains?

Rain doesn't arrive in isolation. An approaching weather system can bring changes in air pressure, humidity, temperature, wind, light and even sound before the first drops reach the ground.

Humans can notice some of these changes too. You may have felt the air become unusually humid before a summer thunderstorm or noticed the wind shift as dark clouds approached.

For animals whose survival depends on detecting subtle changes in their environment, those signals may be much more important.

Can Animals Sense Changes in Air Pressure?

One of the strongest scientific explanations for weather-related animal behavior involves barometric pressure.

Atmospheric pressure often falls as a low-pressure system or storm approaches. Research has shown that some animals and insects can respond to these pressure changes.

For a small flying insect, for example, stormy weather isn't merely inconvenient. Strong winds and heavy rain can make flying dangerous. Detecting falling pressure and changing behavior before conditions deteriorate could provide a real survival advantage.

Birds may also alter their feeding, migration or flight behavior as weather conditions change, although their responses involve a combination of environmental cues rather than a built-in rain forecast.

Humidity May Be Another Clue

Before rain, relative humidity often rises. Many animals are sensitive to moisture in ways humans aren't.

Amphibians are an obvious example. Frogs and toads depend heavily on moist conditions, and rainy or humid weather can trigger increased activity, movement and calling.

Insects may respond to humidity as well. Changes in moisture can affect flight, feeding and reproduction, which in turn can affect the animals that eat them.

That can create a chain reaction. If insects begin flying lower or behaving differently, birds and other insect-eating animals may follow them.

Why Do Birds Sometimes Fly Low Before Rain?

The old saying that low-flying birds mean rain may contain a grain of truth, but the explanation isn't quite as simple as "birds know a storm is coming."

Birds often follow their food.

Changes in humidity, temperature, wind and air pressure can affect the altitude and activity of flying insects. If insects stay closer to the ground, swallows and other aerial insect-eaters may hunt lower too.

So low-flying birds can sometimes accompany changing weather, but they aren't a reliable substitute for a forecast.

What About Cows Lying Down?

"Cows lie down when rain is coming" is one of the most familiar pieces of weather folklore.

Unfortunately, cows also lie down when they're resting, chewing their cud or simply feel like lying down.

Researchers have studied cattle behavior in relation to temperature and other environmental conditions, but there's little reason to treat a field full of reclining cows as a dependable rain forecast.

This is a good example of how weather folklore develops: people remember the afternoon when the cows lay down and it poured an hour later, while forgetting all the dry afternoons when the cows did exactly the same thing.

Dogs, Cats and Approaching Storms

Many pet owners are convinced their dogs or cats know when a storm is approaching.

There are several plausible reasons.

Dogs have extraordinarily sensitive hearing and may detect distant thunder before we do. Animals may also notice changes in wind, pressure, humidity, static electricity, smells or the behavior of people and other animals around them.

A dog that becomes restless well before a thunderstorm therefore isn't necessarily predicting the future. It may simply be receiving information about the approaching storm earlier than its owner is.

Frogs Really Do Have a Connection to Rain

If any animal deserves its reputation as a rain enthusiast, it's probably the frog.

Many frogs become more active during wet and humid conditions because moisture protects them from drying out. Rain can also create temporary pools and other breeding habitat.

Male frogs often call vigorously during favorable breeding conditions, which is one reason loud choruses of frogs have long been associated with rain.

They're not forecasting rain in the human sense. They're responding to conditions that frequently occur with it.

Can Animals Detect Thunderstorms Before Humans Can?

Sometimes, yes—but that isn't the same as predicting them.

Animals may detect distant thunder, pressure changes, shifting winds, increasing humidity and other environmental signals before those signals become obvious to us.

Some species also possess sensory abilities that humans don't have, or have only weakly. That makes seemingly mysterious behavior less mysterious once we understand what the animal may actually be detecting.

Where Science Turns Into Folklore

Humans have used animal behavior to forecast weather for thousands of years, producing sayings about everything from woolly bear caterpillars to groundhogs.

The problem is that anecdotes are very good at becoming traditions and not very good at proving cause and effect.

If a spider builds a web and rain follows, we remember it. If the spider builds a web and nothing happens, there's no story to tell.

Scientists need repeated observations under controlled conditions before concluding that a particular behavior reliably corresponds with a particular weather event.

Some animal responses to atmospheric conditions are well supported. Others remain plausible but uncertain. And quite a few traditional weather signs are simply folklore.

Animals Aren't Weather Forecasters—But They Are Weather Watchers

A bird doesn't need to know that the barometer is falling. A frog doesn't need to understand relative humidity. An insect doesn't need a radar map.

They simply need to respond to the environment around them.

That's what makes animal weather lore so interesting. Beneath some of the exaggeration and superstition is a genuine biological ability to detect subtle changes in air, moisture, wind and temperature.

Animals probably can't tell us whether it will rain at 3:00 tomorrow afternoon. But they may notice that the weather is changing before we do—and sometimes that's enough to make an old bit of folklore seem surprisingly accurate.