Christmas boobook lores and throat, yellow eyes, legs and feet. It is approximately 26–29 cm in length and 130-190 grams in weight with the female slightly larger than the male. The double-noted hoot, "boo-book," has a clucking quality with the second note usually lower in pitch. The begging call of juveniles is a high-pitched trill. Vocalisations are similar to those described for the Southern Boobook "N. novaeseelandiae" and include individual variation in advertisement calls. This may be useful in estimating owl densities as radio-tracking can be impractical in some terrains. A recording, courtesy of Richard Hill and Owl Pages http://www.owlpages.com/sounds/Ninox-natalis-2.mp3 Its natural
Penelope Diane Olsen Penelope Diane Olsen Dr Penelope Diane Olsen is an Australian ornithologist and author. She has worked with CSIRO as an experimental officer and an Honorary Research Associate as well as being an ARC Postdoctoral Fellow at the Australian National University. She is also internationally recognised as an expert on raptors and was involved in the conservation work on Norfolk Island for the Norfolk Island Boobook. She was President of the Australasian Raptor Association 1984–1989. In 1997 she was awarded the Royal Australasian Ornithologists Union's D.L. Serventy Medal for excellence in published work on birds in the Australasian region. Since 2003