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Data collection
This protocol is extracted from research article:
Time-space–displaced responses in the orangutan vocal system
Sci Adv, Nov 14, 2018; DOI: 10.1126/sciadv.aau3401

Seven females with known reproductive history (one nulliparous, two primiparous, and four multiparous) were tested, composing the total female resident population of the Ketambe forest block (3°41′N, 97°39′E, June 2010 to March 2011, Aceh, Sumatra, Indonesia), all of which were highly habituated to the presence of human observers—a condition unique to this site in the whole island resulting from continuous observations for nearly 40 years. Subjects were presented with single pseudorandomized exposures (to maximize the neutralization of order effects, that is, no two subjects were presented with the same order of models, and any specific model was as equally probable to have been presented first, second, third, or fourth to the maximum extent possible) of four predator models—a human experimenter walking on all fours along the forest floor draped over with a sheet with one of four different types of print: tiger patterned [a natural predator historically known to predate on orangutans at this site (50)], color patterned (abstract pattern), white with multicolored spots, and plain white. Forest felids are silent ambush hunters. Accordingly, during the design of this study, we thought that predator playbacks would not necessarily constitute a more realistic simulation than an actual predator model on the forest floor conspicuously presented in front of the subjects. All subjects were tested individually (see the Supplementary Materials). When the subject was between 5- and 20-m height in the forest understory, feeding, resting, or slowly moving, and having exhibited no vocal behavior or having encountered no conspecific in the previous 5 hours, the model moved past in front of the subject on the forest floor. The model halted for 2 min once the subject viewed it, after which the model moved out of sight. Experiments were never conducted in the same location in the forest to avoid habituation. Each individual was exposed only once to each model, and models were always presented to each individual at least 5 days apart. All calls produced by the subjects after the presentation of the predator model were alarm calls typically produced under conditions of moderate to acute danger (51).

Upon sighting the predator model, subjects typically halted the activity in which they were engaged and exhibited signals of distress, such as urinating and defecating, while monitoring the forest floor while the predator model was present and after it had already left. These behaviors indicated that the subjects had effectively seen the model, allowing the experiment to proceed, even when there was no vocal response.

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