Research-driven habituation linked to abandonment of high-altitude refuge in Indochinese gray langurs

Various human disturbances are displacing animals from suitable lowlands to high-altitude refuges worldwide. However, the mechanisms underlying this upward shift remain poorly understood, limiting the development of effective conservation strategies. Studying how animals adjust their habitat selection and utilization patterns in response to human disturbances offer critical insights into the ecological processes shaping their distribution in human-dominated environments. We investigated altitudinal ranging patterns of endangered Indochinese gray langurs ( Trachypithecus crepusculus ) in Wuliangshan National Nature Reserve (WNNR), China, from 2010 to 2019, across early, middle, and late habituation stages. Although vegetation surveys showed substantially higher food availability at 1750 m than at 2150 m and 2550 m, langurs preferred higher altitudes (2000–2600 m) farther from human settlements during early and middle stages. This vertical refuge selection reversed dramatically in the late habituation stage, with langurs shifted to lower altitudes, increased feeding activities there, and exhibited preference for areas below 2000 m outside the WNNR. This downward shift was associated with an increased intake of high-quality food resources (fruits and seeds). Our findings indicate that human activity initially displaced langurs to high-altitude refuges, and that continued habituation by researchers may have facilitated the reoccupation of resource-rich low-altitude habitats. These results underscore that species distribution models and resource selection functions relying solely on species occurrence data risks prioritizing refuges over ecologically superior habitats. We call for more field studies to document the behavioral shifts of study subjects in human-dominated habitats and their cascading impacts on local ecological communities and human societies.