Collapse of Breeding Success in Desert-Dwelling Hornbills Evident Within a Single Decade

Rapid anthropogenic climate change potentially severely reduces avian breeding success. While the consequences of high temperatures and drought are reasonably well-studied within single seasons, their impacts over decadal time scales less clear. We assessed effects air temperature (T ) on output southern yellow-billed hornbills ( Tockus leucomelas ; hornbills) in Kalahari Desert a decade (2008–2019). aimed to document trends performance an arid-zone bird during rapid global warming identify potential drivers variation performance. The our study population collapsed monitoring period. Comparing first three seasons (2008–2011) last (2016–2019), mean percentage nest boxes that were occupied declined from 52% 12%, success 58% 17%, fledglings produced per attempt 1.1 0.4. Breeding was negatively correlated with increasing days which T max (mean maximum daily exceeded threshold at male show 50% likelihood engaging heat dissipation behavior [i.e., panting thresh; = 34.5°C)] occurrence season, as well later dates for entry into cavity (i.e., initiation) fewer post-hatch, spent incarcerated by female parent. apparent present even non-drought years; 115 attempts recorded, all 18 had ? 72% > thresh failed (equivalent 35.7°C). This suggests likely primary driver recent, collapse. Based current trends, 35.7°C, above no successful will be entire hornbill season approximately 2027 site. Therefore, findings support prediction may drive declines cause local extinctions despite absence direct lethal extreme events.