Staffan Widstrand / Wild Wonders of China / Great pied hornbill (Buceros bicornis) male bird photographed in flight in Hong Bung He, Dehong, Yunnan, China

Neil Aldridge / Southern yellow-billed hornbill (Tockus leucomelas) displays while calling in winter, Kruger National Park, South Africa.

David Tipling / Huli Wigmen from the Tari Valley in Southern Highlands of Papua New Guinea, wearing a bill from Blyth's Hornbill as decoration, August 2011

Edwin Giesbers / Male Sulawesi red-knobbed hornbill (Aceros cassidix) head portrait, captive

Gerry Ellis / Rhinoceros Hornbill (Buceros rhinoceros), southeast Asia

Tui De Roy / Sulawesi Red-knobbed Hornbill (Aceros cassidix) male delivering figs to a female sealed inside hollow nest cavity, Tangkoko Dua Saudara Nature Reserve, Sulawesi, Indonesia

Tui De Roy / Sulawesi Red-knobbed Hornbill (Aceros cassidix) male delivering figs to female sealed inside hollow tree, Tangkoko-Dua Saudara Reserve, Indonesia

Mark Jones / Sulawesi Red-knobbed Hornbill (Aceros cassidix) breeding male in a fruiting Fig tree (Ficus forsteni) 32 meters above the ground in rainforest canopy, Tangkoko-Dua Saudara Nature Reserve, Sulawesi, In...

Mark Jones / Sulawesi Red-knobbed Hornbill (Aceros cassidix) breeding male in fruiting Fig (Ficus forsteni), Tangkoko-Dua Saudara Nature Reserve, Sulawesi, Indonesia

Oscar Dewhurst / Malabar pied hornbill (Anthracoceros coronatus) male in flight. Goa, India. September.

Ann & Steve Toon / Southern redbilled hornbill (Tockus rufirostris), Zimanga game reserve, South Africa.

Staffan Widstrand / Wild Wonders of China / Wreathed hornbill (Rhyticeros undulatus) Tongbiguan Nature Reserve, Dehong, Yunnan, China