The Swallows are flying very low today, just above the house and trees. According to the saying that means we should expect rain, although it is lovely and sunny at the moment. Apparently it's all to do with the air pressure. Swallows feed on the wing, so they are flying where the insects are flying. When the air is hot and dry (high pressure) the insects are carried up on the thermals and can fly high easily. In low pressure there is more water vapour in the atmosphere and the insects can't fly as easily so tend to be lower down.
Yesterday the Swallows were very high up in the sky ... but it rained a little bit later in the day! We'll just have to see whether they've got it right and it rains later today.
Weather update: It's now three hours later and it's raining. Perhaps there's something to these old sayings!