This morning my daughter Zoe (aged 10) took part in the RSPB's Big Garden Birdwatch. She sat at at her bedroom window between 8 and 9am and recorded the maximum number of each type of bird she saw at any given moment in the grounds of our flats. I provided backup support by fetching the binoculars when they were needed and by supplying a (vegetarian) bacon sandwich at the halfway point. The results were much as I would have expected:
Blackbird - 3
Magpie - 2
Wood pigeon - 7
Wren - 1
The 'at any given moment' condition ensures that the same bird never gets counted more than once.