It got me thinking. Obviously we all agree, but is it a straightforward loss? Is there more to it?
Perhaps the biggest change is flocking; we now have a situation that is normal for North America and rainforests, which is they are largely birdless apart from 'the flock' which contains everything. I saw a comment ages ago that the return of the Sparrowhawk meant birds behaved differently, as they flock to avoid predators. It stuck in my mind. Just now the excellent Steve Gale at North Downs and Beyond tweeted 'a spectacular gathering of finches - 550 Brambling, 450 Chaffinch, 125 Linnet.' That's a lot of finches. And that's a lot of finches in one place and not somewhere else.
Why do birds flock? I guess because it helps them find food, and helps when predators are around. If there were no predators, would birds flock less if when they find food they can have it all? Would there be 55 flocks of 10 Brambling scattered round Surrey rather than one of 550?
And the second point is that baseline we hear about, the records from the 19th century of masses of birds, right through to the 1970s and 1980s; those were years of busy keepering, of crows and hawks being shot on sight. So the 'natural' baseline is in fact an unnatural baseline; it was the numbers of songbirds you get when you take predators out.
So there we have it; a couple of random ideas. With no data to support. And a happy new year to you