Behind the folklore: swallows flying high: Do high-flying swallows mean dry weather?

Behind the folklore: swallows flying high: Do high-flying swallows mean dry weather?

Fri, 01/10/2010 - 11:31
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Swallows high – staying dry

Are birds really any good at forecasting the weather?

Before you get all outraged and start demanded my dismissal, what follows is not the ranting of some boorish Richard Keys-alike dinosaur railing against the increasingly high profile of women within the Met Office – it's a simple question about avian behaviour.

If English folklore is to be believed, some of our native birds make for reliable oracles of future weather conditions. The most common form of this particular branch of folklore comes in a neat little rhyming aphorism:

Swallows high – staying dry

Similar predictive abilities have been attributed to swifts, martins and gulls.

So is it in any way true? To a certain extent, yes it is. One thing that these birds all have in common is that they tend to feed on the wing, swooping and diving to pluck insects from the air. As early as 1828, the famed scientist Sir Humphrey Davy, in his book Salmonia, had identified the feeding patterns of swallows as being central to this particular piece of popular wisdom: ""Swallows follow the flies and gnats,"" he wrote, ""and flies and gnats usually delight in warm strata of air."" On fine days, when air pressure is high, tiny insects are swept up high on warm thermal currents rising from the ground, forcing birds to head upwards in search of their lunch. When air pressure is low, and rain is more likely, there's a greater chance that swallows will find tasty morsels of crunchy winged arthropod buzzing around closer to the ground.

There is a major caveat though. Swallows and other birds can doubtless provide an excellent guide to current weather conditions – seeing swallows feeding high on the wing means that pressure is probably high and the weather is probably good. But what they are not is by any means oracular. Just because the weather is warm and dry right now does not mean, as any native of this island knows all too well, that it is going to stay warm and dry for any length of time. What a swallow cannot tell you is whether a massive depression is going to turn up tomorrow and ruin your picnic.

So in short, the popular rhyme ought to be condensed to:

Swallows high – dry

Or, by ignoring the swallows and just looking out of the window:

Not raining – dry

But where's the fun in that?

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