Tuesday, 14 September 2021

Long-tailed tit perched on branch
Long-tailed tit weighing 7 - 9 grams Photo RSPB

Light as a feather

If you've ever picked up a bird which has had the misfortune to mistake your kitchen window for a patch of blue sky, you can't fail to have been amazed at just how light and insubstantial most small birds are. I'm not including pigeons of course, as the majority of them feast royally on the food we kindly provide and have enough meat on them to feed a family of five for a week. Smaller birds however seem to consist of just a pair of legs, a beak and a handful of feathers.

When giving talks or leading a bird walk, I try to get across just how tough a small bird's life really is, having to contend with the extremes of our weather, the difficulties of finding food and, in turn being the chosen prey item for a range of other birds and animals while weighing 'little more than a teabag'.

I'd used that expression for quite a while so decided it was time to check the facts. So, recently you would have found me in the kitchen, teabag in hand and electronic scales set to zero. Not long before, I had read that our smallest bird, the goldcrest, weighs in at a mere 4 grams but I must admit that this meant nothing to me, having been raised in the dark (but glorious) age of imperial measures when the only weight that mattered to me was the quarter (4 ounces) of sweets I could get for my 3d. Imagine my surprise when the scales revealed that my PG Tips teabag - other brands are available - weighed in at exactly 4 grams. In the spirit of true and accurate research I weighed several other bags and found that most were 4 grams, others 3 grams. I then realized I should check that my information about the goldcrest was right so called on Mr Google to help.

My info wasn't wildly out. Goldcrests weigh between 5 and 7g so really they're the equivalent of less than two teabags ... only of an ounce. The wren, often mistakenly quoted as our smallest bird, is a whopping 8 to 13 grams while the diminutive long-tailed tit weighs in at 7 to 9 grams.

I was finding this more and more interesting! I noticed that while we think of the three hirundines (swallows and martins) and swifts as more or less the same size, swifts at 36 to 50 grams are more than twice as heavy as house martins and swallows, whilst sand martins are lighter still at 13 or 14 grams, about an ounce. Isn't it amazing that these tiny bodies can cover vast distances year after year on their annual migration?

I couldn't resist a quick look at the raptors whose appearance and behaviour is the essence of speed and power but even here appearances are deceptive. The fearsome sparrowhawk which terrorizes the garden birds weighs only between 5 and 11 ounces (that's male/female differences) while the more delicate kestrel is a mere 5 to 7 oz. Peregrines however weigh in at a respectable 1 to 2 lbs. It must be a bit of a shock to have that hit the back of your neck at 100mph!

If I were a real investigative ornithologist I'd start catching midges and try to work out how many of those it takes to make a chiffchaff or how many flies to make a flycatcher but that's going a bit far. Time to pop a goldcrest in the pot and make a cuppa!