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

Hornbill looking at nestbox

South Africa’s Kuruman River Reserve in the southern Kalahari Desert is home to the southern yellow-billed hornbill. These hornbills are cavity nesters, relying 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.

Baby birds inside nestbox

The same researchers have designed a new and 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. 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 will extend this study to a second breeding season in order to increase their sample size and effectively determine if the insulated nest boxes can replace all old nest boxes and be widely installed across the habitat.

All occupied boxes will be monitored with continuous temperature measurements and weekly mother and nestling weigh-ins. Researchers will also test the stress hormones of the birds to assess if the insulated box is reducing heat-induced stress levels. If the project proves to be successful, the insulated “climate-proof” design can be implemented across all nest boxes in the reserve.