A drizzly day, just what Blackbirds like. Which gave me an idea.

First, an explanation. The number of Blackbirds in the park has declined catastrophically in recent decades: down by an order of magnitude, from hundreds to tens. This has happened at a time when the number in the country as a whole is increasing slightly, the number in London is constant despite people paving over their gardens, and the number in nearby Holland Park is also constant.

We think it's caused by the destructive way in which the park shrubberies are managed. In autumn the dead leaves are blown out with leaf blowers, destroying the blackbirds' natural habitat containing the worms and bugs they feed on. The cleared area is then covered with tons of half-rotted leafmould from the dump in the Leaf Yard, which gives the ground that monochrome brown look that gardeners seem to think is neat. The mould contains little animal life, since this has been cooked out of it by the heat of fermentation.

However, it does contain large quantities of nitrates and phosphates from the decayed organic matter. So there is an explosive growth of nettles and thistles, sometimes to head height or more -- which may be good for butterflies, but not for anything else.  Here is a picture of the edge of the Leaf Yard taken on 9 June 2011. In some years it has been worse than this.

Thus, the stuff that was added as a mulch to prevent the growth of weeds has precisely the opposite effect from what was intended. In areas where this is not done -- for example, the east side of the Long Water -- there is far less growth of weeds, and the shrubberies both look better and contain more Blackbirds. But the people who run the park, sitting behind their desks, are unaware of this.

Last year, Roy Sanderson organised a survey of Blackbirds in Kensington Gardens, to see how far numbers had fallen. The people who do the normal monthly counts of park birds, of whom I am one, each took a route to walk at fortnightly intervals, six times between April and June. The results were sad: Roy estimated that the number of permanent Blackbird territories was down to 18.

I had chosen what I thought was likely to be the best route for seeing Blackbirds: up the west edge of Kensington Gardens, skirting Kensington Palace, along the north edge by the Baywater Road, down the east edge along the top of Buck Hill to the Magazine, then down to the bridge and a loop around the Long Water. My walks along this raised 13 to 16 Blackbirds each time.

Last winter there was a sudden influx of Blackbirds. I wondered whether they had merely migrated in and would leave in the spring. But so far the numbers seem to be holding up.

So today I walked exactly the same route I had followed last summer, and saw 26 Blackbirds. Not a gigantic improvement, but mildly encouraging.

There was also a flock of about 30 Goldfinches near the Orangery. These birds, though common in London, have not been numerous in the park for some reason. But recently numbers of Goldfinches and Greenfinches have been rising.