The birds of Norfolk & Lord Howe Islands and the Australasian South Polar quadrant :London :H.F. & G. Witherby,1928.biodiversitylibrary.org/page/58795379
The birds of Norfolk & Lord Howe Islands and the Australasian South Polar quadrant :London :H.F. & G. Witherby,1928.biodiversitylibrary.org/page/58795376
""Dueling beaks?" --- this contact with the beaks continued for at least 15 minutes, interrupted only when one adult pointed its beak vertically at the sky."