Hornbill Nests

Pair Bonding and Trust

©Karl Svendsen
Southern yellow billed hornbill (Tockus leucomelas).

Hornbills, specifically yellow-billed, red-billed and grey, have a remarkable nesting strategy. After the summer rains when there is adequate mud around, the female secrets herself away in a natural cavity in a tree, which is lined with mud for insulation and the entrance is completely sealed off with mud and excreta bar a slit for her bill to receive food from her mate. Once inside she moults her tail and flight feathers to line the nest and make space for her brood. During her incarceration she is completely reliant on her partner to care for her and should he neglect his duties, she may die.

Such ‘trust’ is built up before the nesting season through elaborate and incessant courtship displays and pair bonding. For this reason, hornbills have only one mate for the season, i.e. are monogamous, onto which they mutually lavish all their attentions.

Pairs will feed together prior to mating and the male will bring nuptial gifts to the female to build up her fat reserves and convince her of his capabilities as a provider. While foraging the pair will hesitate regularly to call and display. They fly to a prominent perch, usually a treetop, where they will bow to one another, wings raised above their backs and cluck in an increasingly urgent manner.

Newly Dressed

©Nigel Dennis
Yellow hornbill male feeding female at their nest (Tockus flavirostris)

Once the chicks are about half grown the female breaks out of the nest, dressed in a newly emerged set of feathers, and together she, the male and the chicks reseal the chicks into the nest.

The parent birds then feed the chicks together. The chicks keep their tails erect while in the nest to conserve space inside the cavity while they grow.

This also protects their vital flight feathers from damage.

Prime Real Estate

©Roger de la Harpe
African grey hornbill (Tokus nasutus) at the entrance to his nest with food for the female.

The specifications for a prime piece of hornbill real estate include a hole at a height above the ground of about 4 metres. The cavity must be 20 cm wide with the floor of the nest about 10 cm below the entrance lip which should only be about 2.5 cm tall.

It is of paramount importance that a chimney is present in the cavity into which the chicks may crawl to hide from danger. So important are these specifications that hornbills may reuse nest sites year after year. The chicks and female keep the inside clean by climbing up to the entrance and defecating with force out of the slit.

After the chicks finally break out of the nest cavity at the end of their epic nesting experience, the family remains together for a couple of weeks during which time the adults continue to feed the chicks. After three weeks they become independent.

By Megan Emmet