Data from: Spatial and temporal variation in hornbill densities in Namdapha Tiger Reserve, Arunachal Pradesh, north-east India

Asian hornbill populations are declining across their ranges because of hunting and deforestation. Five of the 32 Asian hornbill species occur in north-east India. However, vital information on their abundance from the region remains scanty. Understanding spatiotemporal variation in densities provides crucial information for formulating effective conservation strategies based on species-specific abundance patterns and population trends. We examined spatiotemporal variation in densities of four hornbill species in the Namdapha Tiger Reserve, a site identified as an important site for hornbill conservation in Asia. We collected data through variable-width line transect sampling (effort=842.1 km) in the non-breeding season from 2009-12 to estimate hornbill densities. We had 458 detections of four hornbill species. We have estimated White-throated Brown Hornbill densities (7.9 birds/km2) for the first time throughout its entire range. The mean Rufous-necked Hornbill densities (6.9 birds/km2) were higher than those reported elsewhere. Great (3.9 birds/km2) and Wreathed Hornbill (16.1 birds/km2) densities were comparable with other sites. The peak densities of all hornbill species in November-December are among the highest reported from Asia. Wreathed Hornbill densities showed temporal variation peaking in November-December (68 birds/km2) and drastically declining by March-April (1.3 birds/km2), indicating seasonal altitudinal movement to low-elevation areas outside the reserve during the breeding season. Our results underscored the spatial variation in hornbill distribution, with low densities of Great and the White-throated Brown hornbills in higher elevations. Our study demonstrates the global importance of Namdapha for hornbills, given its large area and high densities of four hornbill species.亚洲犀鸟种群在其全球分布范围内因狩猎活动与森林砍伐而持续衰退。32种亚洲犀鸟中有5种分布于印度东北部地区，但该区域关于其种群丰度的关键调研数据仍较为匮乏。明晰种群密度的时空变异规律，可为基于物种特异性丰度模式与种群动态制定高效保护策略提供核心支撑。我们针对亚洲犀鸟保护重要位点——纳姆达法老虎保护区（Namdapha Tiger Reserve）内的4种犀鸟的密度时空变异展开研究。我们于2009至2012年的非繁殖季，采用可变距离样线法（variable-width line transect sampling）开展野外调查，总采样里程达842.1公里，以此估算犀鸟种群密度。本次调查共记录到4种犀鸟的458次目击记录。我们首次在白喉棕犀鸟（White-throated Brown Hornbill）的全球分布范围内完成了其种群密度估算，结果为7.9只/平方公里。棕颈犀鸟（Rufous-necked Hornbill）的平均种群密度为6.9只/平方公里，高于其他已有报道的数值。大犀鸟（Great Hornbill）种群密度为3.9只/平方公里，花冠皱盔犀鸟（Wreathed Hornbill）为16.1只/平方公里，二者密度均与其他调查位点的结果相当。所有犀鸟物种在11月至12月达到的种群密度峰值，位列亚洲已报道的同类峰值之首。其中花冠皱盔犀鸟的密度呈现显著的季节动态：11-12月达到峰值（68只/平方公里），而在次年3-4月骤降至1.3只/平方公里，这表明该物种在繁殖季会向保护区外的低海拔区域进行季节性垂直迁徙。我们的研究结果凸显了犀鸟分布的空间异质性：大犀鸟与白喉棕犀鸟在高海拔区域的种群密度普遍偏低。鉴于纳姆达法老虎保护区面积广阔且拥有4种犀鸟的高密度种群，本研究证实了该保护区对于全球犀鸟保护的重要价值。