Observer effects in a remote population of large-headed capuchins, Sapajus macrocephalus

Human observers often are present when researchers record animal behavior, which can create observer effects. These effects are rarely explicitly investigated, often due to the assumption that the study animal is habituated to or unaffected by a human’s presence. We investigated the effect of human pressure gradients on a remote population of large-headed capuchins, Sapajus macrocephalus, looking specifically at the effects of number of observers, distance to observers, and distance to the research base. We conducted this study over 4 months in the Pacaya-Samiria Nature Reserve, Peru, and collected 199 two-minute focal samples of capuchin behavior. We found that capuchin monkeys fed less when human observers were closer to the focal individual, when more observers were present, and when capuchins were closer to the research base. We found no other consistent differences in capuchin monkey behavior across the measured human pressure gradients, although capuchins directed a high proportion of their vigilance toward humans (29% in adults and 47% in infants). Our results support the hypothesis that human pressure gradients influence animal behavior. Given the proportion of human directed vigilance, we recommend that all studies that use human observers to record animal behavior consider human-directed vigilance, record the number of observers, as well as the observer-focal animal distance, to check for these effects.

Reply to Grote H. (2018). Commentary: Intentional Observer Effects on Quantum Randomness: A Bayesian Analysis Reveals Evidence Against Micro-Psychokinesis. Frontiers in Psychology 9:1350. doi: 10.3389/fpsyg.2018.01350.

No abstract since it is a Reply to a Comment.

Metrics on Restaurant Ordering Behavior

The academic literature analyzing the behavior and interactions among commensals at a table generally resorts to experimental settings with volunteer decision makers or focuses on receipts issued at actual restaurants. The experimental approach widens the potential scope of the phenomena that can be analyzed but is subject to observer effects, with decision makers being aware of the fact that their actions are being monitored. The approach using receipts is not subject to observer effects but limited in its scope by lacking interactions with the commensals and the data that can be collected. In the current article, we make extensive use of a data set collected by restaurant personnel following specific instructions. They gathered information on a number of decisions made at the table throughout the whole meal without the commensals being aware that they are being monitored. As a result, we are able to examine empirically the importance that the choices of the first-person ordering (the leader) may have for the decisions made by the other commensals at the table. In particular, we study the similarity of orders—in terms of dishes, drinks, and prices—between the table leader and the other commensals. Our results reveal that table leaders, both male and female, have a considerable influence on the choices made by other commensals under a variety of different scenarios. We also describe the differences arising when males and females act as table leaders, as well as the influence that specific payment arrangements have on the ordering behavior of the commensals.

Virtual Reality Camera Technology Facilitates Sampling of Interactions Between Reef Piscivores and Prey

Predation is an important process influencing the structure of fish communities. There are multiple approaches used to quantify predatory interactions, and all approaches are beneficial but have their limitations. For example, food habit studies only represent results of successful predation events, direct observations by divers are time limited by both depth and temperature as well as observer effects, acoustic approaches cannot directly identify species, and video has field-of-view constraints when using standard cameras. While no approach is without constraints, the recent availability of small off-the-shelf virtual reality (VR) video cameras that can be used in marine environments offers a more spatially comprehensive field-of-view for conducting studies of community composition and species interactions both on the seafloor and in the overlying water column. Here, we demonstrate an approach for collection and analysis of data from stationary VR video to quantify predator-prey interactions at subtropical reefs in Gray’s Reef National Marine Sanctuary (NW Atlantic). This approach does not substitute for other widely used census and behavioral research approaches but augments those with unique analytical products and interpretation.

Testing the Waters: Behavior across Participant Pools

We leverage a large-scale incentivized survey eliciting behaviors from (almost) an entire undergraduate university student population, a representative sample of the US population, and Amazon Mechanical Turk (MTurk) to address concerns about the external validity of experiments with student participants. Behavior in the student population offers bounds on behaviors in other populations, and correlations between behaviors are similar across samples. Furthermore, non-student samples exhibit higher levels of noise. Adding historical lab participation data, we find a small set of attributes over which lab participants differ from non-lab participants. An additional set of lab experiments shows no evidence of observer effects. (JEL C83, D90, D91)

Habituation is not neutral or equal: Individual differences in tolerance suggest an overlooked personality trait

In behavioral studies, observer effects can be substantial, even for habituated animals, but few studies account for potential observer-related phenomenon empirically. We used wild, habituated chacma baboons to explore two key assumptions of behavioral ecology (i) that observers become a “neutral” stimulus and (ii) that habituation is “equal” across group members. Using flight initiation distance (FID) methods within a personality paradigm, the behavioral responses of baboons suggested that observers were not perceived as neutral but instead viewed as a high-ranking social threat. Habituation was also not equal across group members, with repeatable individual differences more important than contextual factors (e.g., habitat) in determining the distance at which baboons visually oriented or displaced from observers. A strong correlation between individual visual tolerance and displacement tolerance (i.e., convergent validity) indicated a personality trait. We offer several suggestions for how to account for these factors and minimize potential bias in future studies.