I watch birds and search electricity pylons for signs of nesting birds - sad eh!. I reckon a pylon does NOT have a nest (they are not visible fom the ground) if i watch continuously for an hour and i see no activity. If there is a nest i reckon on seeing some activity within 1 hour, may be at minute 1 or in the 60th minute or anywhere in betweeen. Yesterday i could only watch a pylon for 1/2 an hour. I saw nothing so i think i am 50% certain there is no nest. If i went today, watched for 1/2 hour and saw nothing how certain could i then be that there is no nest. I guess 75%, but can't work out a proof. Then, how many 1/2 hour random negative visits would i need to make to be at least 90% sure that there is no nest? NB This is now a mathematical question only, nothing to do with birds per se.
Thanks in advance.
Thanks in advance.