The SQUEAK call is described in HANZAB as a harsh, creaky preep, usually repeated 4–5 times at intervals of 15–20 seconds. The nocturnal flight call appears to match this daytime vocalisation closely, both in sound and in the spacing between calls.
Typical SQUEAK call given by a bird flying overhead Featured
Typical flight SQUEAK call, perhaps a little distorted by distance
Typical flight SQUEAK call