Just guessing as I have not done this before...
Code:
WHILE COUNTER <= 2      ' 4.608sec Loop time (Loop for 30 mins = 781)
      INTCON.0 = 0
     @ SLEEP
     COUNTER=COUNTER+1
     'IF  GPIO.3= 0  THEN COUNTS 'Bird at box (it's not dark) so continue counting
WEND
I hope someone else will jump in on this...