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Abstract

White-faced capuchins, (thus capuchins, predictably emit huh vocalizations at high rates within dense fruit patches. We sought to determine why white-faced capuchins at the La Selva Biological Station, Costa Rica produce these food-associated calls. Here we analyze the contexts in which this intra-group vocalization was emitted, including the spatial responses elicited from other troop members. A cumulative 26.6 h of continuous focal samples and 3314 spectrograms (including 1643 huhs) were analyzed from a study troop with 16 focal subjects. The mean individual rate of huhs was greater (1) during foraging versus nonforaging activities; (2) during fruit foraging compared to both visual searching for foraging sites and foraging for arthropod prey; and (3) when the nearest neighbor was within a 10 m radius of the focal animal compared to when the nearest neighbor was at greater distances. A huh also predicted a significant increase in nearest-neighbour distance; on average, mean nearest-neighbor distance increased 3 m within 2 min following a huh vocalization. Null models of change in mean nearest-neighbor distance over time were generated from the original data set by treating predetermined time points (140 s intervals) in the focal recordings as if those points marked instances at which huhs were produced by the focal subject. No significant alterations in nearest-neighbor distance were detected within time lags up to 100 s in these null models, supporting the conclusion that huhs are causally linked with subsequent increases in nearest-neighbor distances. Huhs were most evident when capuchins were within dense fruit patches, but these calls were produced across all foraging contexts. Our results suggest that huhs may not be food calls in the usual sense (i.e. informing others of the location of food sources to be shared), but may be more appropriately described as spacing calls. Huhs probably act to increase foraging efficiency by reducing overlap in foraging areas with other troop members.