Managing microclimates for southern yellow-billed hornbills in the Kalahari Desert, South Africa

South Africa’s Kuruman River Reserve in the southern Kalahari Desert is home to the southern yellow-billed hornbill. These hornbills rely on camelthorn trees for their nesting cavities. However, the declining tree population and rising temperatures pose a threat to their nesting success; nestlings exposed to hot temperatures grow slowly and experience issues with fledging. Researchers from the University of Cape Town, who have been supplying hornbills with nest boxes to cope with nesting habitat loss, have noticed an alarming decline in breeding success within their study population due to rapidly increasing regional temperatures, leading them to believe that without intervention, these birds could be facing local extinction in the coming decades. Already, researchers observed a decline in nesting success from 58% to 17% between 2008 and 2019. They found that nesting success drops below 50% when air temperatures exceed 95°F during the nesting period.

The same researchers have designed a new insulated nest box to mitigate the negative impact of high temperatures on nesting success. Preliminary results from a pilot experiment suggest that the insulated boxes positively influence nestling growth, with a 50% increase in nestling weight compared to the nestlings in non-insulated control boxes that can trap heat inside and further stunt nestling growth. With support from the Wildlife Adaptation Innovation Fund, the University of Cape Town’s FitzPatrick Institute of African Ornithology and the Department of Biological Sciences extended this study to a second breeding season to increase their sample size and effectively determine if the insulated nest boxes can be widely installed.

The new nest boxes were made from pinewood with plywood shading panels and each box had a temperature data logger that tracked maximum daily nest temperatures. Weekly measurements were also taken of chick body mass and leg length after hatching to assess growth and health. By the end of the project, researchers found that insulated boxes reduced nest temperatures by about 5.4°F which significantly improved chick growth and nesting success. In insulated boxes, 86% of nesting attempts fledged at least one chick, while in uninsulated boxes, only 8.5% of nesting attempts fledged at least one chick. In other words, over 90% of the nests in uninsulated nesting boxes failed completely. This simple insulated nest box proved to be extremely successful in reducing high temperature extremes inside nest boxes, ultimately bolstering nestling growth and hatching success.