Avoidance without flight: actor and timescale in the spatial responses of an arboreal primate to human presence

Animals that share landscapes with people must balance the avoidance of human disturbance against the costs of avoidance itself, and movement is the currency in which this trade-off is paid. Because the distance between an animal and a person is a joint property of two trajectories, however, a change in that distance need not reflect movement by the animal. We examined how an energy-conservative, time-minimizing primate, the mantled howler monkey ( Alouatta palliata ), responds spatially to a recurring and mobile human presence in an agroforestry landscape, decomposing the response according to who moves and over what timescale. Using 3,116 synchronous 15-min records of group and nearest-worker locations, worker numbers, worker activity and sound levels collected across 112 days, we analysed the probability and geometry of movement, partitioned changes in monkey–worker distance into monkey- and worker-generated components, and modelled day-scale space use against daily disturbance dose. Groups moved in only 14% of intervals, and the probability of moving was unrelated to worker numbers, sound level or proximity to workers. When groups did move, their movements were not oriented away from the nearest worker (mean resultant length = 0.08), a result robust to day-level dependence, to permutation tests preserving within-day trajectory structure, and to correction for effective sample size. Approximately 63% of the magnitude of change in monkey–worker distance was generated by the worker’s rather than the monkeys’ movement. Over whole days, groups maintained greater distance from workers when more workers were present (≈21% per standard deviation of daily worker number) without any increase in their own travel. This day-scale separation was itself substantially human-generated: it persisted when monkey positions were held fixed, was absent when worker positions were held fixed, and was attenuated by controlling for the kind of work being done. Reactive flight is therefore not how these monkeys respond to people, and the separation that does emerge over longer timescales cannot be attributed to the monkeys without further evidence. Energetic constraint remains a plausible framework for the absence of costly avoidance movement, but it is not tested here. Our results show that proximity-change metrics can overstate active avoidance when the human party is itself mobile. Significance statement Wild animals increasingly live among people, and avoiding human disturbance is widely assumed to mean moving away from it. But moving is costly, especially for animals that conserve energy by resting most of the day, and the distance between an animal and a person depends on both of them. Studying an arboreal monkey with exactly this energy-conserving lifestyle, we separated two things usually conflated in studies of avoidance: whether an animal actively moves away when a person is near, and whether it ends up further from people over longer periods. The monkeys did not flee: they were no more likely to move when workers were numerous or close, and when they did move their movements were not aimed away from workers. Most of the moment-to-moment change in how far apart they were came from the people moving. On days with more people the groups were further away, but much of that separation, too, was produced by where the work happened rather than by the monkeys relocating. Avoidance can be far less active than proximity measures suggest.