Saturday, 21 April 2012

A damp morning at BGM

I didn’t expect to find much at Bowling Green Marsh yesterday morning as the tide was out, but as it was forecast to rain I thought I’d go there anyway so that I could hide in the hide. It was actually dry at first & quite pleasant as I mostly had the hide to myself. The best on offer were about 60 Black-tailed Godwits, a Little Grebe, a few Teal & 2 Swallows. I stayed there for a while before wandering down to the estuary view-point where there were several Redshank & a couple of Curlew on the mud. 

Gloomy Exe Estuary
As the rain was still holding off, I went down to the Goat Walk, the furthest point from the hide. As soon as I got there the heavens opened. I normally carry a brolly in my scope back-pack, but I must have taken it out at some stage. By the time I got back to the hide I was drenched.

The scene had changed since I left. Instead of the 2 Swallows, there were now about 30 Swallows & a few House Martins hurtling about low over the marsh. It was fantastic to watch.  It was still bucketing down, so I just sat there watching them & waiting for it to ease up so that I could get back to the van without getting even wetter.

I Googled 'Swallows' & 'rain' following their appearance during the downpour. It turns out that there's an old saying involving Swallows & the weather:

"Low flies the Swallow, rain to follow. When Swallows fly high the weather will be dry".

Well, I don't know about predicting the rain, but they were certainly happy to hunt in it. There is however a scientific basis for the old saying. Swallows feed on insects which they mainly catch in mid-air. The ability of bugs to fly is effected by air pressure & water vapour content. Low air pressure, associated with rain, tends to lead to a higher water vapour content, and cool & windy conditions. This all makes it more difficult for bugs to fly & they therefore tend to stay close to the ground. During high pressure, associated with clear sunny days, there is less vapour in the air making it easier for bugs to fly & thermals develop helping to carry them  higher. The Swallows simply follow their dinner.

No comments:

Post a Comment