Tests of inferential reasoning by exclusion in Clark's nutcrackers (Nucifraga columbiana)

Through an animal's eye: the implications of diverse sensory systems in scientific experimentation

'Accounting for the sensory abilities of animals is critical in experimental design.' No researcher would disagree with this statement, yet it is often the case that we inadvertently fall for anthropocentric biases and use ourselves as the reference point. This paper discusses the risks of adopting an anthropocentric view when working with non-human animals, and the unintended consequences this has on our experimental designs and results. To this aim, we provide general examples of anthropocentric bias from different fields of animal research, with a particular focus on animal cognition and behaviour, and lay out the potential consequences of adopting a human-based perspective. Knowledge of the sensory abilities, both in terms of similarities to humans and peculiarities of the investigated species, is crucial to ensure solid conclusions. A more careful consideration of the diverse sensory systems of animals would improve many scientific fields and enhance animal welfare in the laboratory.

Through the eyes of a hunter: assessing perception and exclusion performance in ground-hornbills

Logical inference, once strictly associated with spoken language, is now reported in some non-human animals. One aspect of logical inference, reasoning by exclusion, has been traditionally explored through the use of the cups task (cup A and cup B, if not cup A, then exclude cup A and select cup B). However, to fully understand the factors that drove the evolution of logical processes in animals, this latter paradigm needs to cover a taxonomically broader spectrum of species. In this study, we aimed to test the capacity of Southern ground-hornbills (Bucorvus leadbeateri) to show exclusion performance in a two-way object-choice task. First, we determined whether subjects could perceive and choose correctly between two containers (one rewarded, one unrewarded) using visual or acoustic cues (sensory phase). If successful, individuals were then presented with three experimental conditions (test phase): Full information (content of both cups revealed), Exclusion (content of the empty cup revealed), and Control (no content revealed). During the sensory phase, ground-hornbills succeeded in choosing the rewarded container only in the visual modality. Birds were able to select the rewarded container more than would be expected by chance in the Full information condition, but their performances were equal to chance in the Control condition. The without-learning performance of two individuals within the Exclusion condition indicates that this task is not trivial, which invites further investigation on this species' capacity to represent the dependent relationship between the cups (true logical inference).

Exclusion in the field: wild brown skuas find hidden food in the absence of visual information

Inferential reasoning by exclusion allows responding adaptively to various environmental stimuli when confronted with inconsistent or partial information. In the experimental context, this mechanism involves selecting correctly between an empty option and a potentially rewarded one. Recently, the increasing reports of this capacity in phylogenetically distant species have led to the assumption that reasoning by exclusion is the result of convergent evolution. Within one largely unstudied avian order, i.e. the Charadriiformes, brown skuas (Catharacta antarctica ssp lonnbergi) are highly flexible and opportunistic predators. Behavioural flexibility, along with specific aspects of skuas' feeding ecology, may act as influencing factors in their ability to show exclusion performance. Our study aims to test whether skuas are able to choose by exclusion in a visual two-way object-choice task. Twenty-six wild birds were presented with two opaque cups, one covering a food reward. Three conditions were used: 'full information' (showing the content of both cups), 'exclusion' (showing the content of the empty cup), and 'control' (not showing any content). Skuas preferentially selected the rewarded cup in the full information and exclusion condition. The use of olfactory cues was excluded by results in the control condition. Our study opens new field investigations for testing further the cognition of this predatory seabird.

Inference by exclusion in the red-tailed black cockatoo (Calyptorhynchus banksii)

Inference by exclusion is the ability to select a given option by excluding the others. When designed appropriately, tests of this ability can reveal choices that cannot be explained by associative processes. Over the past decade, exclusion reasoning has been explored in several non-human taxonomic groups, including birds, mainly in Corvids and Parrots. To increase our understanding of the taxonomic distribution of exclusion reasoning and, therefore, its evolution, we investigated exclusion performances in red-tailed black cockatoos (Calyptorhynchus banksii), an Australian relative of the Goffin cockatoo (Cacatua goffini), using a food-finding task. Cockatoos were required to find a food item hidden in 1 of the 2 experimenter's hands. Following training sessions in which they reliably selected the closed baited hand they had just been shown open, each individual was tested on 4 different conditions. Critical to demonstrating exclusion reasoning was the condition in which they were shown the empty hand and then offered a choice of both closed hands. The performance of all birds was above chance on all experimental conditions but not on an olfactory and/or cuing control condition. The results suggest that the birds might be able to infer by exclusion, although an explanation based on rule learning cannot be excluded. This first experiment in red-tailed black cockatoo highlights the potential of this species as a model to study avian cognition and paves the pathway for future investigations.

Examination of long-term visual memorization capacity in the Clark's nutcracker (Nucifraga columbiana)

Clark's nutcrackers exhibit remarkable cache recovery behavior, remembering thousands of seed locations over the winter. No direct laboratory test of their visual memory capacity, however, has yet been performed. Here, two nutcrackers were tested in an operant procedure used to measure different species' visual memory capacities. The nutcrackers were incrementally tested with an ever-expanding pool of pictorial stimuli in a two-alternative discrimination task. Each picture was randomly assigned to either a right or a left choice response, forcing the nutcrackers to memorize each picture-response association. The nutcrackers' visual memorization capacity was estimated at a little over 500 pictures, and the testing suggested effects of primacy, recency, and memory decay over time. The size of this long-term visual memory was less than the approximately 800-picture capacity established for pigeons. These results support the hypothesis that nutcrackers' spatial memory is a specialized adaptation tied to their natural history of food-caching and recovery, and not to a larger long-term, general memory capacity. Furthermore, despite millennia of separate and divergent evolution, the mechanisms of visual information retention seem to reflect common memory systems of differing capacities across the different species tested in this design.

Reasoning by exclusion in the kea (Nestor notabilis)

Reasoning by exclusion, i.e. the ability to understand that if there are only two possibilities and if it is not A, it must be B, has been a topic of great interest in recent comparative cognition research. Many studies have investigated this ability, employing different methods, but rarely exploring concurrent decision processes underlying choice behaviour of non-human animals encountering inconsistent or incomplete information. Here, we employed a novel training and test method in order to perform an in-depth analysis of the underlying processes. Importantly, to discourage the explorative behaviour of the kea, a highly neophilic species, the training included a large amount of novel, unrewarded stimuli. The subsequent test consisted of 30 sessions with different sequences of four test trials. In these test trials, we confronted the kea with novel stimuli that were paired with either the rewarded or unrewarded training stimuli or with the novel stimuli of previous test trials. Once habituated to novelty, eight out of fourteen kea tested responded to novel stimuli by inferring their contingency via logical exclusion of the alternative. One individual inferred predominantly in this way, while other response strategies, such as one trial learning, stimulus preferences and avoiding the negative stimulus also guided the responses of the remaining individuals. Interestingly, the difficulty of the task had no influence on the test performance. We discuss the implications of these findings for the current hypotheses about the emergence of inferential reasoning in some avian species, considering causal links to brain size, feeding ecology and social complexity.

Inferential reasoning and egg rejection in a cooperatively breeding cuckoo

Inferential reasoning-associating a visible consequence with an imagined event-has been demonstrated in several bird species in captivity, but few studies have tested wild birds in ecologically relevant contexts. Here, we investigate inferential reasoning by the greater ani, a cooperatively breeding cuckoo in which several females lay eggs in one nest. Prior to laying her first egg, each female removes any eggs that have already been laid by other females in the shared nest. After laying her first egg, however, each female stops removing eggs, presumably in order to avoid accidentally rejecting her own. But are anis using inferential reasoning to track the fate of their eggs in the communal nest, or is egg ejection governed by non-cognitive determinants? We experimentally removed eggs from two-female nests after both females had laid at least one egg and used video recording to verify that both females viewed the empty nest. We waited until one female (A) laid an egg in the nest, and video recorded the behavior of the female that had not yet re-laid (B). We predicted that if capable of inferential reasoning, female B should infer that the new egg could not be her own and she should remove it. Five out of five females tested failed to make this inference, suggesting that egg removal is either determined by the female's reproductive status or by the amount of time elapsed between egg removal and re-laying. This apparent cognitive constraint may have implications for the evolutionary stability of the anis' unusual breeding system.

Exclusion performance in dwarf goats (Capra aegagrus hircus) and sheep (Ovis orientalis aries)

Using a comparative approach, we investigated the ability of dwarf goats and sheep to use direct and indirect information about the location of a food reward in an object-choice task. Subjects had to choose between two cups with only one covering a reward. Before making a choice, subjects received information about the baited (direct information) or non-baited cup (indirect information). Both goats and sheep were able to use direct information (presence of food) in the object choice task. After controlling for local enhancement, we found that goats rather than sheep were able to use indirect information (i.e., the absence of food) to find a reward. The actual test setup could not clarify whether individual goats were able to inferentially reason about the content of the baited cup when only shown the content of the non-baited cup or if they simply avoided the empty cup in that situation. As browsing species, feral and wild goats exhibit highly selective feeding behaviour compared to the rather unselective grazing sheep. The potential influence of this species-specific foraging flexibility of goats and sheep for using direct and indirect information to find a food reward is discussed in relation to a higher aversion to losses in food acquisition in goats compared to sheep.