I realise the reason for the one hour sample and only to count total of species at same time. But I may see many different birds outside the one hour window that did not visit in the allotted hour. Could the form have a section to note these birds, not counting for overall total, but indicating which individual species visited during the day? Hope this makes sense.
David, This sort of question occurs every year. The danger with citizen science is that people might try to add in the birds that did not arrive on that particular day etc. Why this count works well is that it is able to deal with huge returns (500,000+) and missing birds in one garden average out those that turn up unexpectedly in others gardens. It is important that we are accurate about what is seen and also what is not seen, as much as that hurts our own wish to record a lot.
There are always comments about how accurate this survey can be but every year it matches extremely closely to other more structured surveys.
Of course, in an ideal world we would love to hear about all the birds and other animals in your garden outside of the hour time frame, but the purpose of this survey is to just capture a snapshot of what is in your garden, and a great way for people to do that is to note what is seen in an hour. Don't forget you can always keep us up to date with what you see in your garden on this forum!