Yes, I could have ventured out: but I am too old to derive much pleasure from walking about in driving rain getting wet … did I ever enjoy that? … and strict observance of the coronavirus rules and guidelines dictated that I did not take the car out unnecessarily.
Relieving boredom is not an essential reason for taking to the highways or the byways. Thus it came about that, staring through the rain-smeared windows of the house, I paid more attention than I usually would to the wavelets lapping the sides of the bird bath and the resultant spillage on to the paving beneath.
But, apart from watching this spectacle … who says watching paint dry isn’t exciting? … I thought nothing of it.
I looked out over my distinctly wintry garden, heavily powdered with rime whose white particles were also decorating the ice on the bird bath; and I was surprised to see that the ice on which the rime rested was a good one-third of the depth of the bird bath below the top.
That’s strange, I thought through the befuddlement of pre-breakfast confusion; the bird bath was full when I drew the curtains yesterday afternoon when it was still raining; where has the water gone?
My puzzlement extended to wondering whether the water in the bird bath had frozen from the top down or from the bottom up; and again, although the answer to this question took some time to surface, I actually did know that a pond, for example, freezes over from the top down.
Water behaves differently from most compounds when the temperature drops to near or below freezing. When I was a frequent train traveller many years ago, the actual rails came in 60-foot lengths which were joined together by iron fittings called fishplates with a small gap left between the ends of adjacent rails. The carriage wheels passing over these gaps gave rise to the ‘diddly-dum, diddly-dah, diddly-dum, diddly-dah’ sound so characteristic of rail travel for its first hundred years and more. These gaps were called expansion gaps; but they not only allowed the steel rails to stretch a little when the temperature rose on a hot summer day; they also allowed the rails to shrink a little in the middle of winter, making the ‘diddly-dum, diddly-dahs’ more pronounced. But water does it t’other way round; as the temperature approaches 0°C, water expands and the ‘thinnest’ (or lightest) … water is found on the top.
And, although the temperature of the earth’s inner core is thought to be around 5,430 °C, the warmth which reaches earth’s surface from this source is insufficient to unfreeze a frozen bird bath. This must await a rise in the air temperature, which causes a thaw, again from the top down although one might not think so, since the remaining ice floats on the now-contracting, ‘thicker’ meltwater.
So, if you have been counting the birds in your garden during the Big Bird Gardenwatch 2021 – do thaw out or at least clear any ice off the surface of a frozen bird bath. Birds can’t drink ice – they need water.