First subfossil Holocene avian breeding burrows in volcanic rocks of the Tibesti Mountains (Chad)

We report here the discovery of subfossil subterranean bird burrows in the Tibesti, the Sahara’s highest mountains (Chad). In the Enneri Gonoa area, thousands of these burrows were found in cliffs of ignimbrite rock. Their morphology was studied in detail during a field survey in May 2024, one year after their discovery. Their distribution in the areas of western Tibesti, where the volcanic rock ignimbrite crops out in Enneris, also became clear. Several bird species construct subterranean nesting structures. We suggest burrow-digging bee-eaters, hirundines or kingfisher species are the probable producers. These species do not longer breed in the Tibesti Mountains but may have thrived here during the African Holocene Humid Period (~ 9500 to ~ 6500 cal yr BP) only to vanish from the region with progressing aridification. Our findings represent not only the first subfossil subterranean avian breeding structures but also provide evidence of the former bird populations in the Tibesti region during the more humid climate of the early to mid-Holocene.