male and Female seen entering this hollow on numerous occasions over last two days. Checked out from 3:20 = 3:50 - both entered hollow again but only once. Both stayed in hollow or on tree. i left and returned at 5.00pm. No birds present or emerged when I tickled tree so I poled it and found hollow empty with a little bit of bark chewing. Male turns up and made growling noises and flapped wings until I took pole out of hollow.