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The floater's dilemma: use of space by wild solitary Azara's owl monkeys, Aotus azarae , in relation to group rangesThe fate and behaviour of animals that leave their natal group (‘floaters’) is usually poorly understood, which can limit the understanding of a species' population dynamics. Attempted immigrations can have serious negative effects on residents who therefore may forcibly reject intruders. Consequently, floaters face a dilemma: they need to leave their natal range to find a breeding territory while trying to avoid potentially lethal rejections from established groups. To examine the hypothesis that floating Azara's owl monkeys avoid established groups temporally, we compared time-matched locations of floaters and groups with randomly selected distances. To examine the hypothesis that floaters avoid established groups spatially, we compared the utilization distribution overlap indices (UDOIs) for core areas of floaters and groups with randomly expected UDOIs. Based on average home range sizes and areas of overlap between floaters, we estimated the floater density in the study area to be 0.2e0.5 per group. The temporal avoidance hypothesis was not supported, since time-matched distances were smaller than distances of random locations, and not larger as predicted under this hypothesis. The spatial avoidance hypothesis, in contrast, was supported, with smaller UDOIs for core ranges than predicted. In conclusion, solitary owl monkeys seem to solve the floater's dilemma by trying to stay in relatively close proximity to groups while still avoiding their core ranges. Floaters thus maximize the number of groups with which they have contact, while being able to leave a group's territory quickly if detected by residents. While no marked sex differences in patterns were detected, there was a strong stochastic element to the number of floaters of a particular sex, thus resulting in a locally uneven operational sex ratio. This, in turn, can have important consequences for various aspects of the population dynamics.
Home-range use of wild solitary Azara's owl monkeys (Aotus azarae) in relation to group ranges in Formosa, ArgentinaLittle is known about the secret lives of subadult owl monkeys that have left their natal group to "float" in the population, before they find a new group or die. Groups are territorial, and in suitable habitat territories take up all available space. Thus, “floaters” cannot avoid overlapping with established groups while roaming, and may be attacked by groups that are trying to avoid take-overs. We hypothesized that floaters minimize temporal and/or spatial overlap with groups. Using location data of 23 floaters and surrounding groups (range 23-96 (25-973), median=42 (93) locations for floaters (groups)), we determined home-range sizes and home-range overlaps. Temporal avoidance was analyzed by comparing floaters’ distances to groups during simultaneous observations to distances between randomly selected location pairs of floaters and groups. Spatial avoidance was investigated by comparing the actual Utilization Distribution Overlap Indices (UDOIs) for 50% kernels of floaters and groups against UDOIs derived from randomized home-ranges. We predicted greater distances for parallel observations and lower spatial/home range overlap. Linear mixed models did not suggest temporal avoidance (parallel=361.8m vs. 381.5m), but UDOIs were smaller than expected based on randomized ranges (0.012 vs. 0.014). It seems that floaters do not monitor exact locations of groups closely enough to avoid them completely, but preferentially use areas outside the core home range of groups. Funding to EFD: NSF-BCS-0621020/1219368/1232349, NSF-REU 0837921/0924352/1026991 and NIA- P30 AG012836-19