First Confirmed Cooperative Breeding of the Brown Hornbill ( Anorrhinus austeni ) in China at the Sino–Lao Frontier

ABSTRACT The Brown Hornbill ( Anorrhinus austeni ), a Near Threatened frugivore, reaches the northern edge of its distribution in southern Yunnan, China, yet breeding had not been previously documented with site‐attributed nests in the country. In April and May 2025, we documented two active nests in the Mengman sector of the Shangyong Protected Area, separated by ~3.5 km. Both involved sealed incubation or brooding by females attended by multiple males, providing the first definitive evidence of cooperative breeding in the species in China. One cavity occurred in a tall Choerospondias axillaris tree and was provisioned with Dysoxylum gotadhora and D. binectariferum fruits, together with insect prey such as mantis and cicadas. The other was in a tall Terminalia myriocarpa tree beside a stream gully, with food deliveries including Ormosia hosiei and Pometia tomentosa fruits. Taken together, these observations establish that A. austeni breeds in China, broaden knowledge of nest tree substrates and diet in this frontier population, and confirm that cooperative social systems persist at the species' northern range limit. Alongside recent records of Oriental Pied ( Anthracoceros albirostris ) and Great Hornbills ( Buceros bicornis ), these findings demonstrate that Shangyong sustains a multi‐species hornbill guild. Safeguarding cavity‐bearing trees, strengthening systematic monitoring, and enhancing transboundary cooperation with Laos are essential to secure these disturbance‐sensitive frugivores at the landscape scale.