An intentional cohesion call in male chimpanzees of Budongo Forest

Abstract

Many social animals travel in cohesive groups but some species, including chimpanzees, form flexible fission–fusion systems where individuals have some control over group cohesion and proximity to others. Here, we explored how male chimpanzees of the Sonso community of Budongo Forest, Uganda, use communication signals during resting, a context where the likelihood of group fission is high due to forthcoming travel. We focused on a context-specific vocalisation, the ‘rest hoo’, to investigate its function and determine whether it is produced intentionally. We found that this call was typically given towards the end of typical silent resting bouts, i.e., the period when individuals need to decide whether to continue travelling after a brief stop-over or to start a prolonged resting bout. Subjects rested longer after producing ‘rest hoos’ and their resting time increased with the number of calls produced. They also rested longer if their calls were answered. Furthermore, focal subjects’ resting time was prolonged after hearing others’ ‘rest hoos’. Subjects called more when with top proximity partners and in small parties and rested longer if a top proximity partner called. We also found an interaction effect between rank and grooming activity, with high-ranking males with a high grooming index calling less frequently than other males, suggesting that vocal communication may serve as a cohesion strategy alternative to tactile-based bonding. We discuss these different patterns and conclude that chimpanzee ‘rest hoos’ meet key criteria for intentional signalling. We suggest that ‘rest hoos’ are produced to prolong resting bouts with desired partners, which may function to increase social cohesion.

Bold and bright: shy and supple? The effect of habitat type on personality–cognition covariance in the Aegean wall lizard (Podarcis erhardii)

Abstract

Animals exhibit considerable and consistent among-individual variation in cognitive abilities, even within a population. Recent studies have attempted to address this variation using insights from the field of animal personality. Generally, it is predicted that animals with “faster” personalities (bolder, explorative, and neophilic) should exhibit faster but less flexible learning. However, the empirical evidence for a link between cognitive style and personality is mixed. One possible reason for such conflicting results may be that personality–cognition covariance changes along ecological conditions, a hypothesis that has rarely been investigated so far. In this study, we tested the effect of habitat complexity on multiple aspects of animal personality and cognition, and how this influenced their relationship, in five populations of the Aegean wall lizard (Podarcis erhardii). Overall, lizards from both habitat types did not differ in average levels of personality or cognition, with the exception that lizards from more complex habitats performed better on a spatial learning task. Nevertheless, we found an intricate interplay between ecology, cognition, and personality, as behavioral associations were often habitat- but also year-dependent. In general, behavioral covariance was either independent of habitat, or found exclusively in the simple, open environments. Our results highlight that valuable insights may be gained by taking ecological variation into account while studying the link between personality and cognition.

Perceptual grouping and detection of trial-unique emergent structures by pigeons

Abstract

Detecting global patterns in the environment is essential to object perception and recognition. Consistent with this, pigeons have been shown to readily detect and locate geometrically arranged, structured targets embedded in randomized backgrounds. Here we show for the first time that pigeons can detect and localize trial-unique targets derived solely from global patterns resulting from periodicity, symmetry and their combination using randomly generated segments of black and white local elements. The results indicate pigeons can perceptually segment and detect a wide variety of emergent global structures and do so even when they are unique to each trial. The perceptual and cognitive mechanisms underlying this discrimination likely play important roles in the abilities of how pigeons, and likely other birds, detect and categorize the properties of natural objects at different spatial scales.

Disentangling help-seeking and giving up: differential human-directed gazing by dogs in a modified unsolvable task paradigm

Abstract

Dogs are renowned for ‘looking back’ at humans when confronted with a problem, but it has been questioned whether this implies help-seeking or giving up. We tested 56 pet dogs from two breed groups (herding dogs and terriers) in a modified unsolvable task paradigm. One reward type (food or toy) was enclosed in a box, while the respective other reward was accessible. With both reward types, human-directed gazing in relation to the box was significantly positively correlated with interaction with the box, as long as an alternative was available. This suggests that both behaviours served to attain the unavailable reward and reflected individual motivation for the inaccessible vs the accessible reward. Furthermore, we varied whether the owner or the experimenter was responsible for handling the rewards. In the owner-responsible group, dogs rarely gazed at the experimenter. In the experimenter-responsible group, dogs preferentially directed box-related gazing (prior to or after looking at or interacting with the box) at the owner. Still, they gazed at the experimenter significantly longer than the owner-responsible group. Conversely, toy-related gazing was directed significantly more at the experimenter. Thus, dogs adjust their gazing behaviour according to the people’s responsibility and their current goal (help-seeking vs play). Gaze duration did not differ between herding dogs and terriers. We conclude that dogs use gazing at humans’ faces as a social problem-solving strategy, but not all gazing can be classified as such. Dogs’ human-directed gazing is influenced by the social relationships with the persons, situational associations, and context (unsolvable problem vs play).

Individuality, species-specific features, and female discrimination of male southern white rhinoceros courtship calls

Abstract

Male vocalizations associated with courtship can play a key role in mate selection. They may help females obtain information about males’ quality and identity and/or may contain species-specific properties that help prevent interspecies breeding. Despite vocalizations being a prominent part of the courtship of white rhinos, the role that they play in white rhino breeding behaviour has not been extensively studied. Both southern (SWR) and critically endangered northern white rhino (NWR) males intensively vocalize during courtship with hic calls. We examined these calls and found that call properties differed between NWR and SWR males. In addition, we found that individual SWR males could be identified with a high degree of accuracy using their hic calls and that the signature information capacity in hic calls would allow females to individually recognize about 11 adult males living in or moving through their home-ranges, which may help with mate selection. Then, we conducted playback experiments with wild anoestrus SWR females. The females discriminated between the NWR and SWR hic calls and between the SWR hic and SWR pant calls. However, we only found differences in the latency of observed behaviours, not in their duration or in the intensity of females’ reaction. This might suggest that females which are not in oestrus are not highly responsive to a male’s motivation (i.e., seeking contact or mating), but are more interested in assessing his dominance status or familiarity. Ultimately, our results indicate that courtship hic calls encode information which might help females choose mating partners.

Mirror self-recognition in gorillas (Gorilla gorilla gorilla): a review and evaluation of mark test replications and variants

Abstract

Mirror self-recognition (MSR), widely regarded as an indicator of self-awareness, has not been demonstrated consistently in gorillas. We aimed to examine this issue by setting out a method to evaluate gorilla self-recognition studies that is objective, quantifiable, and easy to replicate. Using Suarez and Gallup’s (J Hum Evol 10:175–183, 1981) study as a reference point, we drew up a list of 15 methodological criteria and assigned scores to all published studies of gorilla MSR for both methodology and outcomes. Key features of studies finding both mark-directed and spontaneous self-directed responses included visually inaccessible marks, controls for tactile and olfactory cues, subjects who were at least 5 years old, and clearly distinguishing between responses in front of versus away from the mirror. Additional important criteria include videotaping the tests, having more than one subject, subjects with adequate social rearing, reporting post-marking observations with mirror absent, and giving mirror exposure in a social versus individual setting. Our prediction that MSR studies would obtain progressively higher scores as procedures and behavioural coding practices improved over time was supported for methods, but not for outcomes. These findings illustrate that methodological rigour does not guarantee stronger evidence of self-recognition in gorillas; methodological differences alone do not explain the inconsistent evidence for MSR in gorillas. By implication, it might be suggested that, in general, gorillas do not show compelling evidence of MSR. We advocate that future MSR studies incorporate the same criteria to optimize the quality of attempts to clarify the self-recognition abilities of gorillas as well as other species.

Flexibility and rigidity in hunting behaviour in rodents: is there room for cognition?

Abstract

Predatory hunting is a complex species-typical behaviour involving different skills, some of which may include learning. This research aims to distinguish between rigid and flexible parts in live-insect hunting behaviour in nine herbivorous and granivorous rodent species, and to find out whether there is room for cognition in this activity. In laboratory experiments, all species studied manifest skilful attacks towards insects in a manner that is typical for specialised predators chasing a fleeing prey. Voles demonstrate a “core” and somewhat primitive scheme of a hunting pattern: approaching a potential victim, biting it, and then seizing and handling. Hamsters display the tendency to start their attacks by actions with paws, but they can achieve success only using teeth as well. Gerbils can successfully use both paws and teeth to start the attack, which brings their hunting behaviour closer to that of specialised rodent predators. We revealed variability in the display of hunting in different species, methods of seizing the prey, and the number of attempts to attack an insect before catching it. We found specific flexible fragments within the “bite–grasp–handle” bouts that can be precursors for adaptive phenotypic variations and include some cognitive attributes. We hypothesise that the divergence and specialisation of predatory behaviour in rodents can be based on the natural fragmentation of the original hunting patterns, that is, on the loss or recombination of particular behavioural elements. We consider a possible link between the fragmentation of hunting behaviour and social learning in different classes of animals and conjecture an intriguing correlation between predatory activity, cognitive skills and personal traits in rodents.

Digital embryos: a novel technical approach to investigate perceptual categorization in pigeons (Columba livia) using machine learning

Abstract

Pigeons are classic model animals to study perceptual category learning. To achieve a deeper understanding of the cognitive mechanisms of categorization, a careful consideration of the employed stimulus material and a thorough analysis of the choice behavior is mandatory. In the present study, we combined the use of “virtual phylogenesis”, an evolutionary algorithm to generate artificial yet naturalistic stimuli termed digital embryos and a machine learning approach on the pigeons’ pecking responses to gain insight into the underlying categorization strategies of the animals. In a forced-choice procedure, pigeons learned to categorize these stimuli and transferred their knowledge successfully to novel exemplars. We used peck tracking to identify where on the stimulus the animals pecked and further investigated whether this behavior was indicative of the pigeon’s choice. Going beyond the classical analysis of the binary choice, we were able to predict the presented stimulus class based on pecking location using a k-nearest neighbor classifier, indicating that pecks are related to features of interest. By analyzing error trials with this approach, we further identified potential strategies of the pigeons to discriminate between stimulus classes. These strategies remained stable during category transfer, but differed between individuals indicating that categorization learning is not limited to a single learning strategy.

A promising novel judgement bias test to evaluate affective states in dogs (Canis familiaris)

Abstract

The judgement bias test represents one of the most applied tools to evaluate animals’ optimistic/pessimistic attitude and to infer their emotional and welfare state accordingly. The judgement bias test (JBT) has been used several times with dogs (Canis familiaris), in most cases using a spatial test that evaluates the dog’s attitude towards a bowl placed in ambiguous positions (located between two unambiguous trained positions associated with opposite outcomes). Results are contrasting and methodological and statistical caveats emerged: dogs struggled to learn the association between unambiguous positions and their outcomes, they hardly discriminated between adjacent locations and they might be influenced by researchers. Therefore, we propose a novel paradigm, aimed at easing the learning process and at achieving more reliable measures. Improvements of the novel paradigm are the increased difference between payoffs of trained locations, the reduction of the number of trials and of their length and the removal of the potential influence of researchers. Results showed that 98% of dogs reached the learning criterion and that their learning appeared more stable: dogs behaved differently between the two trained stimuli and the variability of responses towards these stimuli was lower than the one towards ambiguous stimuli. Behavioural analyses confirmed that dogs fully learned outcomes associated with trained stimuli and that they were hesitant towards ambiguous stimuli. Furthermore, dogs managed to successfully discriminate between each pair of adjacent locations. These results suggest that this protocol is a promising tool to assess judgement biases in dogs and to evaluate their affective state.