Garden Birdwatch bunglers?

In the Jan 22 C&AB (‘Rehabilitator casts doubts on survey stats’, page 3), Andy Meads says he thinks that many people who take part in the RSPB’s Big Garden Birdwatch can’t identify the birds in their garden, so that the results of the survey are too inaccurate to be useful.

Andy mentions injured swifts and woodpigeon squabs brought to his rehab centre and wrongly identified. But surely, swifts whizzing about in flocks in the sky (as they typically do) are less likely to be misidentified than injured ones that people pick up? And fledgling birds, too, are often more tricky to identify than adults. Andy cites thrushes and blackbirds getting mistaken. Well, spotty brown young ones are easy to confuse, but adults aren’t.

Injured or lost squabs and fledglings are not really representative of the birds that get counted in these surveys. And, as the RSPB was careful to point out, the Garden Birdwatch scheme results aren’t published as gospel truth - they are broad-brush conclusions that may then be investigated by experts. So, case unproven, Andy! Anyone got any thoughts on this?