I took part in the RSPB Garden Birdwatch today, and spent an hour noting down the maximum number of each species of bird visiting the garden within the selected hour. As well as being quite fun, and a good way of encouraging people to notice the bird life going about its business in their gardens or local parks, it's also a scientific exercise, gathering important data about the temporal and geographic changes in species numbers. While there is inevitably a small amount of statistical noise introduced because the participants are mostly not scientists, the enormous number of participants and broad coverage of the UK would be impossible without the participation of the public, so it's a valuable exercise.

As I did my hour of observation, I was aware of a familiar non-scientific urge creeping in. Despite that fact that I know very well that a survey period in which few or no birds are observed is as scientifically valuable as one which huge numbers of birds are reported, you can't help feeling disappointed and frustrated -- if it's your garden -- when you get a pathetic avian turnout of a couple a few tits, two robins and a blackcap. I would never note down birds that weren't there (as a scientist, that would rank alongside armed robbery in severity), but that didn't stop me sitting there urging birds (in my mind) to come and visit the garden.

We get a good range of species visiting the garden, in reasonable numbers. Blue tits, great tits, coal tits, and small, bouncy puffball flocks of long tailed tits are regular visitors, along with a pair of robins, a pair of blackcaps (in the winter), blackbirds, dunnocks, wrens, chaffinches and occasional bullfinches. We also had groups of house sparrows (though sadly they seem to have reduced in numbers last year), the ubiquitous magpies and wood pigeons, and rare but startling visits from a sparrowhawk. Of course, that's a cumulative collection of birds, over the course of hours or days, and in any randomly selected hour, we would be unlikely to see more than a small sub-set of those species, which is why my observation hour was so disappointing.

I did see a sparrowhawk flying over the garden during the hour, but the instructions tell you (sternly) to count only those birds actually in your garden. Curses.

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