Alecia J. Carter

Animal personality: what are behavioural ecologists measuring?

The discovery that an individual may be constrained, and even behave sub‐optimally, because of its personality type has fundamental implications for understanding individual‐ to group‐level processes. Despite recent interest in the study of animal personalities within behavioural ecology, the field is fraught with conceptual and methodological difficulties inherent in any young discipline. We review the current agreement of definitions and methods used in personality studies across taxa and systems, and find that current methods risk misclassifying traits. Fortunately, these problems have been faced before by other similar fields during their infancy, affording important opportunities to learn from past mistakes. We review the tools that were developed to overcome similar methodological problems in psychology. These tools emphasise the importance of attempting to measure animal personality traits using multiple tests and the care that needs to be taken when interpreting correlations between personality traits or their tests. Accordingly, we suggest an integrative theoretical framework that incorporates these tools to facilitate a robust and unified approach in the study of animal personality.

How not to measure boldness: novel object and antipredator responses are not the same in wild baboons

Boldness in animal personality studies is measured using a range of different behavioural assays, including responses to novel objects, novel environments and threatening stimuli. These assays should be correlated if they all reflect boldness, but this assumption has rarely been tested. We investigated experimentally whether presentation of threatening stimuli (a taxidermic puff adder, Bitis arietans arietans) and novel object (an unfamiliar food item) both assayed the same personality trait in wild chacma baboons, Papio ursinus. We recorded individual responses to both the snake model and novel foods for 57 baboons encompassing all age–sex classes in two study troops over 3 years. Surprisingly, those individuals that showed the greatest alarm responses to the model snake, that is, the least bold responses, also inspected it for longer. Furthermore, individuals threat responses did not correlate with their response to the novel food. Thus, boldness according to one definition was not related to boldness using another definition. We suggest that threat-directed behaviours did not reflect individual boldness, but instead were indicative of another personality dimension: anxiety. These findings highlight that current boldness assays may not be interchangeable, and in some cases may not measure boldness at all. We stress the value of using multiple assays to measure the personality trait of interest.

Structured association patterns and their energetic benefits in female eastern grey kangaroos, Macropus giganteus

Little is known about the determinants of females social interactions in species with fission–fusion social organization, in which individuals associate with different individuals at different times. Even less is known about social organization in marsupials. We investigated the association patterns of wild female eastern grey kangaroos in southeast Queensland. Female kangaroos had a nonrandom social structure and we present a new methodology for analysing social structure that accounts for the amount of spatial overlap shared by pairs of female kangaroos. This simulation model showed that patterns of association among our female kangaroos were not simply those predicted by their patterns of spatial overlap. Females that associated frequently with certain associates were able to graze for longer because they were less vigilant, and thus were able to benefit from having frequent associates. Female kangaroo social structure was affected by the loss of key members of the society during a period of unusually high predation. Information-theoretical modelling showed that the factors affecting grazing behaviour changed after partial population turnover, with the strength of association between nearest neighbours having a positive effect on grazing behaviour before population turnover and group size having a positive effect on grazing behaviour after population turnover. We propose that social organization within this marsupial is more structured than previously thought.

Personality and plasticity: temporal behavioural reaction norms in a lizard, the Namibian rock agama

Behavioural traits are often plastic and can allow animals important flexibility when environmental conditions vary. However, studies of animal personality suggest that behaviour can be ‘constrained’ to certain behavioural types, leading to consistent differences between individuals. Few studies have investigated the interaction between personality traits and the need for flexibility in individuals over different, naturally occurring situations in the wild. We investigated whether free-living Namibian rock agamas, Agama planiceps, were constrained by personality types or showed behavioural plasticity when their environmental conditions changed dramatically between the dry and rainy seasons. We examined three key behaviours: risk taking as measured by flight initiation distance, time budgets focusing on time spent conspicuous and rates of signalling directed at conspecifics. Risk-taking behaviour of males showed stable between-individual differences, but no between-individual differences in plasticity, supporting previous evidence that antipredator behaviour is determined by personality in this species. Time spent conspicuous showed a response to season, and an interaction between the individual and season, suggesting that behavioural plasticity itself may be a personality trait. In contrast, signalling behaviour changed in response to season but did not vary consistently between individuals. We suggest that where there are reliable environmental cues, individual plasticity will be favoured over consistency in the relevant behaviours.

Individual variation in the relationship between vigilance and group size in eastern grey kangaroos

The mean vigilance of animals in a group often decreases as their group size increases, yet nothing is known about whether there is individual variability in this relationship in species that change group sizes frequently, such as those that exhibit fission–fusion social systems. We investigated variability in the relationship between group size and vigilance in the eastern grey kangaroo (Macropus giganteus) by testing whether all individuals showed decreased vigilance with increased group size, as has been commonly assumed. We carried out both behavioural observations of entire groups of kangaroos and focal observations of individually recognised wild female kangaroos. As in other studies, we found a collective group-size effect on vigilance; however, individuals varied in their vigilance patterns. The majority (57%) of the identified individual kangaroos did not show significant group-size effects for any of the recorded measures of vigilance. The females that did not show a negative group-size effect were, on average, more vigilant than those females that did show a group-size effect, but this difference was not significant. We propose that some females exhibit higher levels of social vigilance than others, and that this social vigilance increases with group size, cancelling out any group-size effect on anti-predator vigilance for those females. Our results therefore suggest that only some prey individuals may gain anti-predator benefits by reducing their time spent scanning when in larger groups. The large amount of variation that we found in the vigilance behaviour of individual kangaroos highlights the importance of collecting and analysing vigilance data at the individual level, which requires individual recognition.

Social networks created with different techniques are not comparable

The recent application of social network analysis to animal populations has provided a tool to quantify group dynamics and individual social positions, which may enhance our understanding of the costs and benefits of sociality and the evolution of behavioural strategies within societies. Despite this, uncertainties remain about whether comparisons can be drawn between studies in which different sampling techniques have been used. We compared social networks constructed from two interaction and three proximity techniques that are frequently used in the literature, at both the ego network and global network levels, using data collected annually for two troops of chacma baboons, Papio ursinus, over 3 years. We obtained very different results at both the global and individual levels, demonstrating the clear distinction between networks built using different interaction and proximity techniques. While interaction techniques may be comparable at the whole global level, proximity techniques were not, and we found the opposite at the ego network level: proximity techniques could be compared whereas interaction techniques could not. As there was a clear distinction between the networks created, caution should be taken when using proximity as a proxy for social interactions (and vice versa) in social network studies. Further, our results showed high variation between troops and study seasons, reemphasizing the importance of incorporating temporal change in the analysis of social networks. Researchers should consider the effects of sampling technique on the networks produced when comparing networks created from different techniques.

Evaluating animal personalities: do observer assessments and experimental tests measure the same thing?

The animal personality literature uses three approaches to assess personality. However, two of these methods, personality ratings and experimentation, have been little compared in captivity and never compared in the wild. We assessed the boldness of wild chacma baboons Papio ursinus using both ratings and experimental methods. Boldness was experimentally assessed when individuals were presented with a novel food item during natural foraging. The boldness of the same individuals was rated on a five-point scale by experienced observers. The ratings and experimental assessments of boldness were found to correlate positively and in a linear fashion. When considered categorically the two approaches showed variable agreement depending on the number of categories assigned and the cut-off criteria adopted. We suggest that the variation between approaches arises because each method captures different aspects of personality; ratings consider personality in absolute terms (using predefined criteria) and multiple contexts, while experimental assessments consider personality in relative terms (using experimental scores relative to the population average) and in limited contexts. We encourage animal personality researchers to consider adopting both methodologies in future studies. We also propose that future studies restrict their analyses to continuous data, since the greatest comparability between methods was found with these data. However, if individuals must be categorised, we suggest that researchers either (a) analyse only those individuals categorised as bold or shy by both ratings and experimental approaches or, if these methods cannot be employed simultaneously, (b) do not use approach-specific criteria but choose a cut-off that can be compared by both approaches.

Cooperative personalities and social niche specialization in female meerkats.

The social niche specialization hypothesis predicts that group‐living animals should specialize in particular social roles to avoid social conflict, resulting in alternative life‐history strategies for different roles. Social niche specialization, coupled with role‐specific life‐history trade‐offs, should thus generate between‐individual differences in behaviour that persist through time, or distinct personalities, as individuals specialize in particular nonoverlapping social roles. We tested for support for the social niche specialization hypothesis in cooperative personality traits in wild female meerkats (Suricata suricatta) that compete for access to dominant social roles. As cooperation is costly and dominance is acquired by heavier females, we predicted that females that ultimately acquired dominant roles would show noncooperative personality types early in life and before and after role acquisition. Although we found large individual differences in repeatable cooperative behaviours, there was no indication that individuals that ultimately acquired dominance differed from unsuccessful individuals in their cooperative behaviour. Early‐life behaviour did not predict social role acquisition later in life, nor was cooperative behaviour before and after role acquisition correlated in the same individuals. We suggest that female meerkats do not show social niche specialization resulting in cooperative personalities, but that they exhibit an adaptive response in personality at role acquisition.

Personality predicts the propensity for social learning in a wild primate

Social learning can play a critical role in the reproduction and survival of social animals. Individual differences in the propensity for social learning are therefore likely to have important fitness consequences. We asked whether personality might underpin such individual variation in a wild population of chacma baboons (Papio ursinus). We used two field experiments in which individuals had the opportunity to learn how to solve a task from an experienced conspecific demonstrator: exploitation of a novel food and a hidden item of known food. We investigated whether the (1) time spent watching a demonstrator and (2) changes in task-solving behaviour after watching a demonstrator were related to personality. We found that both boldness and anxiety influenced individual performance in social learning. Specifically, bolder and more anxious animals were more likely to show a greater improvement in task solving after watching a demonstrator. In addition, there was also evidence that the acquisition of social information was not always correlated with its use. These findings present new insights into the costs and benefits of different personality types, and have important implications for the evolution of social learning.

Personality predicts decision making only when information is unreliable

Phenotypic plasticity in decision making should be selected for when reliable information on current conditions is available. When current information is unreliable, however, selection should favour unresponsive behavioural phenotypes, which might lead to the emergence of personalities. We tested the hypothesis that personality will affect decision making when information is unreliable, but not when it is reliable. We measured two personality traits, boldness and anxiety, in 55 wild chacma baboons, Papio ursinus , by quantifying responses to a novel food and a mild threat, respectively, in repeated field experiments. To assess decision making under different information reliabilities, we recorded foraging decisions in two contexts. We followed the baboons as they foraged naturally with reliable information about their environment (>8900 decisions) and, to manipulate information reliability experimentally, we performed a large-scale in situ foraging experiment during which we provided the study troops with access to experimental food patches (>10u2008000 decisions). Importantly, the baboons could not see the food in the experimental patches until close inspection of them, and thus had unreliable information about patch quality. We found plastic foraging decisions in the presence of reliable cues, but personality-dependent decisions in the absence of such cues. Specifically, bold individuals were more likely to produce, and shy individuals scrounge, in the experimental arena but there was no effect of personality on foraging decisions under natural foraging conditions. Our results clarify the importance of information reliability in the evolution of personality and plasticity. These findings also contribute to our understanding of how individuals, and thus populations, might respond to environmental change in the future.