For the last couple of weeks we have heard a bird (at least I think it is a bird) calling almost every night. It is a series of short, high pitched whistling sounds (it sounds like there are several birds making the sound). We haven't seen the bird because it is dark outside of course. We live on a farm (Far North Coast of NSW) so there is no light pollution that could be upsetting the birds, especially as they continue to call after we have gone to bed and all of our lights are out.
More info required sorry, can't help you :(
Some birds that could call at that time though:
Bush Stone-Curlew, Common Koel, Channel-billed Cuckoo, Willie Wagtail, Blackbirds... and I'm out for now... Although obviously nocturnal birds also would call then :)
Cheers,
Scott.
Maybe not a bird - do you have flowering eucalyptus, if so, could be Grey Headed flying foxes.
See it! Hear it!
Mid-North Coast NSW