Do Swallows Fly Low Before Rain? Weather Lore Tested

Where the saying comes from

A traditional English rhyme says: “Swallows high, staying dry; swallows low, wet will blow.” Versions of it exist across Europe and North America, and farmers watched swallows over their fields for centuries for clues about the weather.

The barn swallow is an ideal bird for this kind of folk forecasting. It lives around farms and villages, feeds in full view over fields and ponds, and hunts in the open air all day long, so its height above the ground is easy to see.

Why insects fly lower before rain

Swallows eat almost nothing but flying insects, such as flies, aphids, small beetles and flying ants. On warm, sunny days the ground heats up and rising currents of warm air, called thermals, carry small, light insects high into the sky. Swallows and swifts then feed tens or even hundreds of meters up.

When a band of rain approaches, the sky clouds over, the sun’s heating weakens and the air often becomes cooler and more humid. Rising air currents die away, so tiny insects are no longer lifted, and many insects stay low in sheltered places near grass, hedges and water. Wind ahead of a front also keeps weak fliers close to the ground. The swallows simply go where the food is.

This means swallows flying low are a sign of cool, cloudy, humid conditions, which often, but not always, come before rain. They are not responding to a mysterious weather sense.

When the saying fails

Swallows also fly low for reasons that have nothing to do with rain:

• On cool mornings and evenings, insects stay low even in settled weather.
• Swallows often hunt just above ponds, rivers and wet meadows, where insects hatch.
• They follow cattle, horses, tractors and even walkers to catch the insects disturbed from the grass.
• Young swallows learning to hunt in late summer often stay close to the ground.

Likewise, swallows may feed high on a humid summer afternoon shortly before a thunderstorm, when strong rising air carries insects upward. The rhyme is a rough rule of thumb, not a forecast.

How swallows hunt insects on the wing

Swallows are aerial insectivores, meaning they catch their prey in flight. A barn swallow hunts with fast, swooping, twisting flights, usually at around 40 km/h (25 mph), and snaps up insects one at a time in its short, wide bill. It typically feeds just 7–8 m (23–26 ft) above the ground or water, and it drinks by skimming the surface with an open bill.

Parents feeding chicks make hundreds of trips a day, bringing a small ball of insects each time. That is why long spells of cold, wet weather in early summer are hard on swallows: when insects stop flying, chicks can starve, and late broods sometimes fail.

What about swifts?

The common swift behaves in a similar way and features in the same weather lore. Swifts often feed very high on fine days, and lower down over lakes and rivers in cool, cloudy weather. They are even more tied to the air than swallows, as explained in swallow vs swift.

Swifts also react to whole weather systems. Studies by the British ornithologist David Lack and later researchers showed that swifts sometimes fly long distances away from approaching areas of low pressure and bad weather, returning when conditions improve. Their chicks can survive these absences by becoming torpid, lowering their body temperature and living off their fat for several days.

Other bird weather lore

Many cultures read the weather from birds. In Britain, the green woodpecker was once called the “rain bird”, because its loud laughing call was thought to foretell rain, though there is no good evidence for this. Another English rhyme says that when seagulls come inland and sit on the sand, fair weather is over. Gulls do often move inland in stormy weather, but they also visit fields, parks and landfills in calm weather to feed.

Some birds can detect tiny changes in air pressure; experiments with homing pigeons in the 1970s showed this clearly. Whether swallows use such a sense is unknown. The best scientific explanation for the old swallow saying remains the simplest: swallows follow insects, and insects follow the weather.

Test the saying yourself

Swallow watching is an easy way to see this link between birds, insects and weather. On a warm, sunny day in summer, look up over a village or a field and you will often see swallows and swifts as tiny dots high overhead. On a cool, gray day, walk beside a pond or a pasture and the same birds may sweep past at knee height, sometimes almost touching the grass.

If you note the height at which swallows are feeding each day, along with the temperature, the cloud cover and whether it rained in the following hours, you will probably find a loose connection: low feeding goes with cool, damp, overcast air. You will also find plenty of exceptions, which is exactly why meteorologists rely on air pressure, satellites and weather models rather than birds.