Breeding Habitat Selection and Conservation of the Grey Nightjar Caprimulgus jotaka in Volcanic Grasslands

Caprimulgidae is an avian family with nocturnal habits and a wide global distribution; 15% of the species in this family face conservation concerns. Grey Nightjar Caprimulgus jotaka has declined dramatically in Japan in recent decades. We investigated the distribution of nightjar territories and nest sites in semi-natural grasslands at the foot of Mt. Fuji, an active volcano. Although these grasslands support high biodiversity including rare species, there is no ecological information on nightjars living in the grassland habitats. Territories were mainly located in and around the lava flow in vast grasslands with sparse woodland, and nests were found only along ridges created by lava flows and not in areas of volcanic fan deposit. Nest sites had larger gravel, more bare ground, and lower mid-height (1–1.5 m) vegetation cover than non-nesting sites. These results suggest that burned, volcanic, semi-natural grasslands provide suitable habitat for nightjars for both the establishment of territories and for nest sites. Semi-natural grasslands are often located on active volcanoes throughout Japan and are artificially maintained through various management practices. Thus, future research should investigate the effects of grassland management and geographical features on the distribution of nightjars in these semi-natural grasslands, to support their conservation.