Corvids can decide if a future exchange is worth waiting for

Time-mapping and future-oriented behavior in free-ranging wild fruit bats

Episodic memory and mental time travel have been viewed as uniquely human traits.1,2,3 This view began to shift with the development of behavioral criteria to assess what is referred to as "episodic-like memory" in animals.4,5 Key findings have ranged from evidence of what-where-when memory in scrub-jays, rats, and bees; through decision-making that impacts future foraging in frugivorous primates; to evidence of planning based on future needs in scrub-jays and tool use planning in great apes.4,6,7,8,9,10,11,12,13 Field studies of these issues have been rare, though there is field-based evidence for future-oriented behaviors in primates.8,10,14,15 We report evidence that free-ranging wild fruit bats rely on mental temporal maps and exhibit future-oriented behaviors when foraging. We tracked young bats as they navigated and foraged, documenting every tree they visited over many months. We prevented the bats from foraging outside for different time periods and monitored their foraging decisions, revealing that the bats map the spatiotemporal patterns of resources in their environment. Following a long period in captivity, the bats did not visit those trees that were no longer providing fruit. We show that this time-mapping ability requires experience and is lacking in inexperienced bats. Careful analysis of the bats' movement and foraging choices indicated that they plan which tree to visit while still in the colony, thus exhibiting future-oriented behavior and delayed gratification on a nightly basis. Our findings demonstrate how the need for spatiotemporal mental mapping can drive the evolution of high cognitive abilities that were previously considered exclusive to humans.

The Inner Lives of Cephalopods

The minds of cephalopods have captivated scientists for millennia, yet the extent that we can understand their subjective experiences remains contested. In this article, we consider the sum of our scientific progress towards understanding the inner lives of cephalopods. Here, we outline the behavioral responses to specific experimental paradigms that are helping us to reveal their subjective experiences. We consider evidence from three broad research categories, which help to illuminate whether soft-bodied cephalopods (octopus, cuttlefish, and squid) have an awareness of self, awareness of others, and an awareness of time. Where there are current gaps in the literature, we outline cephalopod behaviors that warrant experimental investigation. We argue that investigations, especially framed through the lens of comparative psychology, have the potential to extend our understanding of the inner lives of this extraordinary class of animals.

Social influences on delayed gratification in New Caledonian crows and Eurasian jays

Self-control underlies goal-directed behaviour in humans and other animals. Delayed gratification - a measure of self-control - requires the ability to tolerate delays and/or invest more effort to obtain a reward of higher value over one of lower value, such as food or mates. Social context, in particular, the presence of competitors, may influence delayed gratification. We adapted the 'rotating-tray' paradigm, where subjects need to forgo an immediate, lower-quality (i.e. less preferred) reward for a delayed, higher-quality (i.e. more preferred) one, to test social influences on delayed gratification in two corvid species: New Caledonian crows and Eurasian jays. We compared choices for immediate vs. delayed rewards while alone, in the presence of a competitive conspecific and in the presence of a non-competitive conspecific. We predicted that, given the increased risk of losing a reward with a competitor present, both species would similarly, flexibly alter their choices in the presence of a conspecific compared to when alone. We found that species differed: jays were more likely to select the immediate, less preferred reward than the crows. We also found that jays were more likely to select the immediate, less preferred reward when a competitor or non-competitor was present than when alone, or when a competitor was present compared to a non-competitor, while the crows selected the delayed, highly preferred reward irrespective of social presence. We discuss our findings in relation to species differences in socio-ecological factors related to adult sociality and food-caching (storing). New Caledonian crows are more socially tolerant and moderate cachers, while Eurasian jays are highly territorial and intense cachers that may have evolved under the social context of cache pilfering and cache protection strategies. Therefore, flexibility (or inflexibility) in delay of gratification under different social contexts may relate to the species' social tolerance and related risk of competition.

"Distractor" effects in delay discounting of probability by pigeons

Impulsive behavior can be measured by performance on a successive delay-discounting task, in which a response to a stimulus provides a small reinforcer sooner (SS), but in the absence of a response, a larger reinforcer later (LL). Previous research suggests that the presence of a concurrent "distractor" stimulus, to which responding has no programed consequence, can result in increased LL reinforcers. In the present experiments, we used differences in the probability of reinforcement between SS and LL (rather than magnitude of reinforcement) and tested the hypothesis that the concurrent stimulus may become a Pavlovian conditioned stimulus. For the Red-Only group, a response to the SS stimulus resulted in a reinforcer with a low probability (SS), whereas the absence of a response resulted in a reinforcer with a high probability (LL). For the Red-Green group, (analogous to the more typical simultaneous choice between an SS and LL stimulus) the absence of a response to the SS stimulus replaced the SS stimulus with the LL stimulus and a response to the LL stimulus resulted in the reinforcer. Thus, for the Red-Green group, the concurrent stimulus should have been less effective because responding to the concurrent stimulus was not immediately followed by the reinforcer. In Experiment 1, the concurrent stimulus was a yellow key-light; in Experiment 2, it was a houselight. In both experiments, the concurrent stimulus was effective in increasing the number of LL reinforcers and the effect was larger for the Red-Only group than for the Red-Green group.

Waiting for a better possibility: delay of gratification in corvids and its relationship to other cognitive capacities

Self-control, the ability to resist temptation and wait for better but delayed possibilities, is an important cognitive skill that underpins decision-making and planning. The capacity to exert self-control has been linked to intelligence in humans, chimpanzees and most recently cuttlefish. Here, we presented 10 Eurasian jays, Garrulus glandarius, with a delayed maintenance task, which measured the ability to choose a preferred outcome as well as the ability to sustain the delay prior to that outcome. Jays were able to wait for better possibilities, but maximum wait times varied across the subjects. We also presented them with five cognitive tasks that assessed spatial memory, spatial relationships and learning capacity. These tasks are commonly used as measures of general intelligence within an ecological context. Individual performance was correlated across the cognitive tasks, which suggests that there was a general intelligence factor underlying their performance. Performance in these tasks was correlated significantly with the jays' capacity to wait for better possibilities. This study demonstrates that self-control and intelligence are correlated in jays. The fact that this correlation exists in diverse species suggests that self-control is a fundamental feature of cognition. Our results are discussed in the context of convergent evolution.

This article is part of the theme issue ‘Thinking about possibilities: mechanisms, ontogeny, functions and phylogeny’.

Executive Functions in Birds

Executive functions comprise of top-down cognitive processes that exert control over information processing, from acquiring information to issuing a behavioral response. These cognitive processes of inhibition, working memory, and cognitive flexibility underpin complex cognitive skills, such as episodic memory and planning, which have been repeatedly investigated in several bird species in recent decades. Until recently, avian executive functions were studied in relatively few bird species but have gained traction in comparative cognitive research following MacLean and colleagues’ large-scale study from 2014. Therefore, in this review paper, the relevant previous findings are collected and organized to facilitate further investigations of these core cognitive processes in birds. This review can assist in integrating findings from avian and mammalian cognitive research and further the current understanding of executive functions’ significance and evolution.

High associative neuron numbers could drive cognitive performance in corvid species

Corvids possess cognitive skills, matching those of non-human primates. However, how these species with their small brains achieve such feats remains elusive. Recent studies suggest that cognitive capabilities could be based on the total numbers of telencephalic neurons. Here we extend this hypothesis further and posit that especially high neuron counts in associative pallial areas drive flexible, complex cognition. If true, avian species like corvids should specifically accumulate neurons in the avian associative areas meso- and nidopallium. To test the hypothesis, we analyzed the neuronal composition of telencephalic areas in corvids and non-corvids (chicken, pigeons, and ostriches - the species with the largest bird brain). The overall number of pallial neurons in corvids was much higher than in chicken and pigeons and comparable to those of ostriches. However, neuron numbers in the associative mesopallium and nidopallium were twice as high in corvids and, in correlation with these associative areas, the corvid subpallium also contained high neuron numbers. These findings support our hypothesis that large absolute numbers of associative pallial neurons contribute to cognitive flexibility and complexity and are key to explain why crows are smart. Since meso/nidopallial and subpallial areas scale jointly, it is conceivable that associative pallio-striatal loops play a similar role in executive decision-making as described in primates. This article is protected by copyright. All rights reserved.

Intra- and interspecific variation in self-control capacities of parrots in a delay of gratification task

Forgoing immediate satisfaction for higher pay-offs in the future (delayed gratification) could be adaptive in situations that wild animals may encounter. To explain species-differences in self-control, hypotheses based on social complexity, feeding ecology, brain size and metabolic rate have been proposed. To explore these hypotheses in a comparative setting, we tested three macaw species (neotropical parrots)—great green macaws (N = 8), blue-throated macaws (N = 6), blue-headed macaws (N = 6)—and the distantly related African grey parrots (afrotropical parrots; N = 8) in a modified rotating tray task, in which subjects are required to inhibit consuming a constantly available low-quality reward in favour of a high-quality reward that becomes available only after an increasing delay (min. 5 s, max. 60 s). All four species successfully waited for a minimum of 8.3 s ± 11.7 s (group level mean ± SD) with African greys reaching a delay of 29.4 ± 15.2 s, and great green macaws—as best performing macaw species—tolerating delays of 20 s ± 8 s. The best performing African grey individual reached a maximum delay of 50 s, whereas, a great green and a blue-throated macaw tolerated a delay of 30 s max. Females tolerated higher maximum delays than males. Engaging in distraction behaviours enhanced waiting performance across species and all birds were able to anticipate the waiting duration. Our results suggest that both feeding and socio-ecological complexity may be a factor in self-control, but further systematically collected comparative data on self-control of different (parrot) species are required to test the evolutionary hypotheses rigorously.

Learning and motor inhibitory control in crows and domestic chickens

Cognitive abilities allow animals to navigate through complex, fluctuating environments. In the present study, we tested the performance of a captive group of eight crows, Corvus corone and 10 domestic chickens, Gallus gallus domesticus, in the cylinder task, as a test of motor inhibitory control and reversal learning as a measure of learning ability and behavioural flexibility. Four crows and nine chickens completed the cylinder task, eight crows and six chickens completed the reversal learning experiment. Crows performed better in the cylinder task compared with chickens. In the reversal learning experiment, species did not significantly differ in the number of trials until the learning criterion was reached. The performance in the reversal learning experiment did not correlate with performance in the cylinder task in chickens. Our results suggest crows to possess better motor inhibitory control compared with chickens. By contrast, learning performance in a reversal learning task did not differ between the species, indicating similar levels of behavioural flexibility. Interestingly, we describe notable individual differences in performance. We stress the importance not only to compare cognitive performance between species but also between individuals of the same species when investigating the evolution of cognitive skills.

Carrion Crows and Azure-Winged Magpies Show No Prosocial Tendencies When Tested in a Token Transfer Paradigm

To study the evolution of humans' cooperative nature, researchers have recently sought comparisons with other species. Studies investigating corvids, for example, showed that carrion crows and azure-winged magpies delivered food to group members when tested in naturalistic or simple experimental paradigms. Here, we investigated whether we could replicate these positive findings when testing the same two species in a token transfer paradigm. After training the birds to exchange tokens with an experimenter for food rewards, we tested whether they would also transfer tokens to other birds, when they did not have the opportunity to exchange the tokens themselves. To control for the effects of motivation, and of social or stimulus enhancement, we tested each individual in three additional control conditions. We witnessed very few attempts and/or successful token transfers, and those few instances did not occur more frequently in the test condition than in the controls, which would suggest that the birds lack prosocial tendencies. Alternatively, we propose that this absence of prosociality may stem from the artificial nature and cognitive complexity of the token transfer task. Consequently, our findings highlight the strong impact of methodology on animals' capability to exhibit prosocial tendencies and stress the importance of comparing multiple experimental paradigms.

Cuttlefish exert self-control in a delay of gratification task

The ability to exert self-control varies within and across taxa. Some species can exert self-control for several seconds whereas others, such as large-brained vertebrates, can tolerate delays of up to several minutes. Advanced self-control has been linked to better performance in cognitive tasks and has been hypothesized to evolve in response to specific socio-ecological pressures. These pressures are difficult to uncouple because previously studied species face similar socio-ecological challenges. Here, we investigate self-control and learning performance in cuttlefish, an invertebrate that is thought to have evolved under partially different pressures to previously studied vertebrates. To test self-control, cuttlefish were presented with a delay maintenance task, which measures an individual's ability to forgo immediate gratification and sustain a delay for a better but delayed reward. Cuttlefish maintained delay durations for up to 50-130 s. To test learning performance, we used a reversal-learning task, whereby cuttlefish were required to learn to associate the reward with one of two stimuli and then subsequently learn to associate the reward with the alternative stimulus. Cuttlefish that delayed gratification for longer had better learning performance. Our results demonstrate that cuttlefish can tolerate delays to obtain food of higher quality comparable to that of some large-brained vertebrates.

New Caledonian crows keep 'valuable' hooked tools safer than basic non-hooked tools

The temporary storage and re-use of tools can significantly enhance foraging efficiency. New Caledonian crows in one of our study populations use two types of stick tools - hooked and non-hooked - which differ in raw material, manufacture costs, and foraging performance. Using a large sample of wild-caught, temporarily captive New Caledonian crows, we investigated experimentally whether individuals prefer one tool type over the other when given a choice and whether they take better care of their preferred tools between successive episodes of use, safely storing them underfoot or in nearby holes. Crows strongly preferred hooked stick tools made from Desmanthus virgatus stems over non-hooked stick tools. Importantly, this preference was also reflected in subsequent tool-handling behaviour, with subjects keeping hooked stick tools safe more often than non-hooked stick tools sourced from leaf litter. These results suggest that crows 'value' hooked stick tools, which are both costlier to procure and more efficient to use, more than non-hooked stick tools. Results from a series of control treatments suggested that crows altered their tool 'safekeeping' behaviour in response to a combination of factors, including tool type and raw material. To our knowledge, our study is the first to use safekeeping behaviour as a proxy for assessing how non-human animals value different tool types, establishing a novel paradigm for productive cross-taxonomic comparisons.

Dogs wait longer for better rewards than wolves in a delay of gratification task: but why?

Self-control has been shown to be linked with being cooperative and successful in humans and with the g-factor in chimpanzees. As such, it is likely to play an important role in all forms of problem-solving. Self-control, however, does not just vary across individuals but seems also to be dependent on the ecological niche of the respective species. With dogs having been selected to live in the human environment, several domestication hypotheses have predicted that dogs are better at self-control and thus more tolerant of longer delays than wolves. Here we set out to test this prediction by comparing dogs' and wolves' self-control abilities using a delay of gratification task where the animals had to wait for a predefined delay duration to exchange a low-quality reward for a high-quality reward. We found that in our task, dogs outperformed the wolves waiting an average of 66 s vs. 24 s in the wolves. Food quality did not influence how long the animals waited for the better reward. However, dogs performed overall better in motivation trials than the wolves, although the dogs' performance in those trials was dependent on the duration of the delays in the test trials, whereas this was not the case for the wolves. Overall, the data suggest that selection by humans for traits influencing self-control rather than ecological factors might drive self-control abilities in wolves and dogs. However, several other factors might contribute or explain the observed differences including the presence of the humans, which might have inhibited the dogs more than the wolves, lower motivation of the wolves compared to the dogs to participate in the task and/or wolves having a better understanding of the task contingencies. These possible explanations need further exploration.

Decision time modulates social foraging success in wild common ravens, Corvus corax

Social foraging provides several benefits for individuals but also bears the potential costs of higher competition. In some species, such competition arises through kleptoparasitism, that is when an animal takes food which was caught or collected by a member of its social group. Except in the context of caching, few studies have investigated how individuals avoid kleptoparasitism, which could be based on physical strength/dominance but also cognitive skills. Here, we investigated the foraging success of wild common ravens, Corvus corax, experiencing high levels of kleptoparasitism from conspecifics when snatching food from the daily feedings of captive wild boars in a game park in the Austrian Alps. Success in keeping the food depended mainly on the individuals' age class and was positively correlated with the time to make a decision in whether to fly off with food or consume it on site. While the effect of age class suggests that dominant and/or experienced individuals are better in avoiding kleptoparasitism, the effect of decision time indicates that individuals benefit from applying cognition to such decision-making, independently of age class. We discuss our findings in the context of the ecological and social intelligence hypotheses referring to the development of cognitive abilities. We conclude that investigating which factors underline kleptoparasitism avoidance is a promising scenario to test specific predictions derived from these hypotheses.

A novel test of flexible planning in relation to executive function and language in young children

In adult humans, decisions involving the choice and use of tools for future events typically require episodic foresight. Previous studies suggest some non-human species are capable of future planning; however, these experiments often cannot fully exclude alternative learning explanations. Here, we used a novel tool-use paradigm aiming to address these critiques to test flexible planning in 3- to 5-year-old children, in relation to executive function and language abilities. In the flexible planning task, children were not verbally cued during testing, single trials avoided consistent exposure to stimulus-reward relationships, and training trials provided experience of a predictable return of reward. Furthermore, unlike most standard developmental studies, we incorporated short delays before and after tool choice. The critical test choice included two tools with equal prior reward experience-each only functional in one apparatus. We tested executive function and language abilities using several standardized tasks. Our results echoed standard developmental research: 4- and 5-year-olds outperformed 3-year-olds on the flexible planning task, and 5-year-old children outperformed younger children in most executive function and language tasks. Flexible planning performance did not correlate with executive function and language performance. This paradigm could be used to investigate flexible planning in a tool-use context in non-human species.

Decision-making flexibility in New Caledonian crows, young children and adult humans in a multi-dimensional tool-use task

The ability to make profitable decisions in natural foraging contexts may be influenced by an additional requirement of tool-use, due to increased levels of relational complexity and additional work-effort imposed by tool-use, compared with simply choosing between an immediate and delayed food item. We examined the flexibility for making the most profitable decisions in a multi-dimensional tool-use task, involving different apparatuses, tools and rewards of varying quality, in 3-5-year-old children, adult humans and tool-making New Caledonian crows (Corvus moneduloides). We also compared our results to previous studies on habitually tool-making orangutans (Pongo abelii) and non-tool-making Goffin's cockatoos (Cacatua goffiniana). Adult humans, cockatoos and crows, but not children and orangutans, did not select a tool when it was not necessary, which was the more profitable choice in this situation. Adult humans, orangutans and cockatoos, but not crows and children, were able to refrain from selecting non-functional tools. By contrast, the birds, but not the primates tested, struggled to attend to multiple variables-where two apparatuses, two tools and two reward qualities were presented simultaneously-without extended experience. These findings indicate: (1) in a similar manner to humans and orangutans, New Caledonian crows and Goffin's cockatoos can flexibly make profitable decisions in some decision-making tool-use tasks, though the birds may struggle when tasks become more complex; (2) children and orangutans may have a bias to use tools in situations where adults and other tool-making species do not.

A comparative analysis of the dopaminergic innervation of the executive caudal nidopallium in pigeon, chicken, zebra finch, and carrion crow

Despite the long, separate evolutionary history of birds and mammals, both lineages developed a rich behavioral repertoire of remarkably similar executive control generated by distinctly different brains. The seat for executive functioning in birds is the nidopallium caudolaterale (NCL) and the mammalian equivalent is known as the prefrontal cortex (PFC). Both are densely innervated by dopaminergic fibers, and are an integration center of sensory input and motor output. Whereas the variation of the PFC has been well documented in different mammalian orders, we know very little about the NCL across the avian clade. In order to investigate whether this structure adheres to species-specific variations, this study aimed to describe the trajectory of the NCL in pigeon, chicken, carrion crow and zebra finch. We employed immunohistochemistry to map dopaminergic innervation, and executed a Gallyas stain to visualize the dorsal arcopallial tract that runs between the NCL and the arcopallium. Our analysis showed that whereas the trajectory of the NCL in the chicken is highly comparable to the pigeon, the two Passeriformes show a strikingly different pattern. In both carrion crow and zebra finch, we identified four different subareas of high dopaminergic innervation that span the entire caudal forebrain. Based on their sensory input, motor output, and involvement in dopamine-related cognitive control of the delineated areas here, we propose that at least three morphologically different subareas constitute the NCL in these songbirds. Thus, our study shows that comparable to the PFC in mammals, the NCL in birds varies considerably across species.

Self-control in crows, parrots and nonhuman primates

Self-control is critical for both humans and nonhuman animals because it underlies complex cognitive abilities, such as decision-making and future planning, enabling goal-directed behavior. For instance, it is positively associated with social competence and life success measures in humans. We present the first review of delay of gratification as a measure of self-control in nonhuman primates, corvids (crow family) and psittacines (parrot order): disparate groups that show comparable advanced cognitive abilities and similar socio-ecological factors. We compare delay of gratification performance and identify key issues and outstanding areas for future research, including finding the best measures and drivers of delayed gratification. Our review therefore contributes to our understanding of both delayed gratification as a measure of self-control and of complex cognition in animals. This article is categorized under: Cognitive Biology > Evolutionary Roots of Cognition Psychology > Comparative Psychology.

Delayed gratification in New Caledonian crows and young children: influence of reward type and visibility

Self-control underlies cognitive abilities such as decision making and future planning. Delay of gratification is a measure of self-control and involves obtaining a more valuable outcome in the future by tolerating a delay or investing a greater effort in the present. Contextual issues, such as reward visibility and type, may influence delayed gratification performance, although there has been limited comparative investigation between humans and other animals, particularly non-primate species. Here, we adapted an automated 'rotating tray' paradigm used previously with capuchin monkeys to test for delay of gratification ability that requires little pre-test training, where the subject must forgo an immediate, less preferred reward for a delayed, more preferred one. We tested New Caledonian crows and 3-5-year-old human children. We manipulated reward types to differ in quality or quantity (Experiments 1 and 2) as well as visibility (Experiment 2). In Experiments 1 and 2, both species performed better when the rewards varied in quality as opposed to quantity, though performed above chance in both conditions. In Experiment 1, both crows and children were able to delay gratification when both rewards were visible. In Experiment 2, 5-year-old children outperformed 3- and 4-year olds, though overall children still performed well, while the crows struggled when reward visibility was manipulated, a result which may relate to difficulties in tracking the experimenters' hands during baiting. We discuss these findings in relation to the role of contextual issues on self-control when making species comparisons and investigating the mechanisms of self-control.

Unpredictable environments enhance inhibitory control in pheasants

The ability to control impulsive actions is an important executive function that is central to the self-regulation of behaviours and, in humans, can have important implications for mental and physical health. One key factor that promotes individual differences in inhibitory control (IC) is the predictability of environmental information experienced during development (i.e. reliability of resources and social trust). However, environmental predictability can also influence motivational and other cognitive abilities, which may therefore confound interpretations of the mechanisms underlying IC. We investigated the role of environmental predictability, food motivation and cognition on IC. We reared pheasant chicks, Phasianus colchicus, under standardised conditions, in which birds experienced environments that differed in their spatial predictability. We systematically manipulated spatial predictability during their first 8 weeks of life, by either moving partitions daily to random locations (unpredictable environment) or leaving them in fixed locations (predictable environment). We assessed motivation by presenting pheasants with two different foraging tasks that measured their dietary breadth and persistence to acquire inaccessible food rewards, as well as recording their latencies to acquire a freely available baseline worm positioned adjacent to each test apparatus, their body condition (mass/tarsus³) and sex. We assessed cognitive performance by presenting each bird with an 80-trial binary colour discrimination task. IC was assessed using a transparent detour apparatus, which required subjects to inhibit prepotent attempts to directly acquire a visible reward through the barrier and instead detour around a barrier. We found greater capacities for IC in pheasants that were reared in spatially unpredictable environments compared to those reared in predictable environments. While IC was unrelated to individual differences in cognitive performance on the colour discrimination task or motivational measures, we found that environmental predictability had differential effects on sex. Males reared in an unpredictable environment, and all females regardless of their rearing environment, were less persistent than males reared in a predictable environment. Our findings, therefore, suggest that an individual’s developmental experience can influence their performance on IC tasks.

Orangutans (Pongo abelii) make flexible decisions relative to reward quality and tool functionality in a multi-dimensional tool-use task

Making economic decisions in a natural foraging situation that involves the use of tools may require an animal to consider more levels of relational complexity than merely deciding between an immediate and a delayed food option. We used the same method previously used with Goffin´s cockatoos to investigate the orangutans' flexibility for making the most profitable decisions when confronted with five different settings that included one or two different apparatuses, two different tools and two food items (one more preferred than the other). We found that orangutans made profitable decisions relative to reward quality, when the task required the subjects to select a tool over an immediately accessible food reward. Furthermore, most subjects were sensitive to work-effort when the immediate and the delayed option (directly accessible by using a tool) led to the same outcome. Most subjects continued to make profitable decisions that required taking into account the tool functionality. In a final multidimensional task design in which subjects had to simultaneously focus on two apparatuses, two reward qualities and two different tools, the orangutans chose the functional tool to access the high quality reward.

Differences in persistence between dogs and wolves in an unsolvable task in the absence of humans

Despite being closely related, dogs perform worse than wolves in independent problem-solving tasks. These differences in problem-solving performance have been attributed to dogs’ greater reliance on humans, who are usually present when problem-solving tasks are presented. However, more fundamental motivational factors or behavioural traits such as persistence, motor diversity and neophobia may also be responsible for differences in task performance. Hence, to better understand what drives the differences between dogs’ and wolves’ problem-solving performance, it is essential to test them in the absence of humans. Here, we tested equally raised and kept dogs and wolves with two unsolvable tasks, a commonly used paradigm to study problem-solving behaviour in these species. Differently from previous studies, we ensured no humans were present in the testing situation. We also ensured that the task was unsolvable from the start, which eliminated the possibility that specific manipulative behaviours were reinforced. This allowed us to measure both persistence and motor diversity more accurately. In line with previous studies, we found wolves to be more persistent than dogs. We also found motor diversity to be linked to persistence and persistence to be linked to contact latency. Finally, subjects were consistent in their performance between the two tasks. These results suggest that fundamental differences in motivation to interact with objects drive the differences in the performance of dogs and wolves in problem-solving tasks. Since correlates of problem-solving success, that is persistence, neophobia, and motor diversity are influenced by a species’ ecology, our results support the socioecological hypothesis, which postulates that the different ecological niches of the two species (dogs have evolved to primarily be scavengers and thrive on and around human refuse, while wolves have evolved to primarily be group hunters and have a low hunting success rate) have, at least partly, shaped their behaviours.

Better, Not Just More-Contrast in Qualitative Aspects of Reward Facilitates Impulse Control in Pigs

Delay-of-gratification paradigms, such as the famous "Marshmallow Test," are designed to investigate the complex cognitive concepts of self-control and impulse control in humans and animals. Such tests determine whether a subject will demonstrate impulse control by choosing a large, delayed reward over an immediate, but smaller reward. Documented relationships between impulsive behavior and aggression in humans and animals suggest important implications for farm animal husbandry and welfare, especially in terms of inadequate social behavior, tail biting and maternal behavior. In a preliminary study, we investigated whether the extent of impulse control would differ between quantitatively and qualitatively different aspects of reward in pigs. Twenty female piglets were randomly divided into two groups, with 10 piglets each. After a preference test to determine individual reward preference among six different food items, a discrimination test was conducted to train for successful discrimination between different amounts of reward (one piece vs. four pieces) and different qualitative aspects of reward (highly preferred vs. least preferred food item). Then, an increasing delay (2, 4, 8, 16, 24, 32 s) was introduced for the larger/highly preferred reward. Each piglet could choose to get the smaller/least preferred reward immediately or to wait for the larger/highly preferred reward. Piglets showed clear differences in their preference for food items. Moreover, the "quality group" displayed faster learning in the discrimination test (number of sessions until 90% of the animals completed the discrimination test: "quality group"-3 days vs. "quantity group"-5 days) and reached a higher level of impulse control in the delay-of-gratification test compared to the "quantity group" (maximum delay that was mastered: "quality group"-24 s vs. "quantity group"-8 s). These results demonstrate that impulse control is present in piglets but that the opportunity to get a highly preferred reward is more valued than the opportunity to get more of a given reward. This outcome also underlines the crucial role of motivation in cognitive test paradigms. Further investigations will examine whether impulse control is related to traits that are relevant to animal husbandry and welfare.

Economic Decision-Making in Parrots

Economic decision-making involves weighing up differently beneficial alternatives to maximise payoff. This sometimes requires the ability to forego one's desire for immediate satisfaction. This ability is considered cognitively challenging because it not only requires inhibiting impulses, but also evaluating expected outcomes in order to decide whether waiting is worthwhile. We tested four parrot species in a token exchange task. The subjects were first trained to exchange three types of tokens for a food item of low, medium, and high value and successfully learned to exchange these in an order according to their value. Subsequently, they were confronted with a choice between a food item and a token that could be exchanged for higher-quality food. In additional control conditions however, choosing a token led to an equal or lower payoff. Individuals of all species were capable of deciding economically, yet only large macaws outperformed the other species in one of the crucial controls. For some individuals, particularly African grey parrots, the token apparently had an intrinsic value, which prevented them from choosing economically in some control conditions and which should be considered as potentially confounding by future token exchange studies.

High level of self-control ability in a small passerine bird

Abstract

Cognitively advanced animals are usually assumed to possess better self-control, or ability to decline immediate rewards in favour of delayed ones, than less cognitively advanced animals. It has been claimed that the best predictor of high such ability is absolute brain volume meaning that large-brained animals should perform better than small-brained ones. We tested self-control ability in the great tit, a small passerine. In the common test of this ability, the animal is presented with a transparent cylinder that contains a piece of food. If the animal tries to take the reward through the transparent wall of the cylinder, this is considered an impulsive act and it fails the test. If it moves to an opening and takes the reward this way, it passes the test. The average performance of our great tits was 80%, higher than most animals that have been tested and almost in level with the performance in corvids and apes. This is remarkable considering that the brain volume of a great tit is 3% of that of a raven and 0.1% of that of a chimpanzee.

Significance statement

The transparent cylinder test is the most common way to test the ability of self-control in animals. If an animal understands that it only can take food in the cylinder from the cylinder’s opening and controls its impulsivity, it passes the test. A high level of self-control has been demonstrated only in cognitively advanced animals such as apes and corvids. Here, we demonstrate that the great tit, a small song bird that is very good at learning, performs almost in level with chimpanzees and ravens in this test.

Electronic supplementary material

The online version of this article (10.1007/s00265-018-2529-z) contains supplementary material, which is available to authorized users.

Serial reversal learning and cognitive flexibility in two species of Neotropical parrots (Diopsittaca nobilis and Pionites melanocephala)

Serial reversal learning of colour discriminations was assessed as an index of cognitive flexibility in two captive species of Neotropical parrots. Both species showed similar performances across serial reversals and no between species differences were observed. In a second task subjects' performances were assessed after they experienced either a low or high pre-reversal learning criterion. If reversal performances improve through processes of associative learning, a high pre-reversal criterion is expected to strengthen previously learned associations and hence impede post-reversal performances. Conversely, highly reinforced associations may facilitate the use of conditional rules that can be generalised across reversals and improve post-reversal performances. We found that high criterion subjects made fewer post-reversal errors and required fewer trials to reach criterion, than low criterion subjects. Red-shouldered macaws and black-headed caiques may therefore demonstrate capacities for solving serial reversal problems by applying conditional rules, rather than learning solely by associative processes. Such performances coincide with findings in great apes, but contrast with findings in monkeys and prosimians, which generally show impaired reversal performances when trained to a highly rigorous pre-reversal criterion. Overall, these findings suggest an evolutionary convergence of cognitive flexibility between parrots and non-human great apes.

The Development of Motor Self-Regulation in Ravens

Inhibitory control refers to the ability to stop impulses in favor of more appropriate behavior, and it constitutes one of the underlying cognitive functions associated with cognitive flexibility. Much attention has been given to cross-species comparisons of inhibitory control; however, less is known about how and when these abilities develop. Mapping the ontogeny of inhibitory control in different species may therefore reveal foundational elements behind cognitive processes and their evolution. In this study, we tested the development of motor self-regulation in raven chicks (Corvus corax), using two detour tasks that required inhibition of motor impulses to directly reach for a visible reward behind a barrier. One task included a mesh barrier, which partly occluded the reward, and the other task used a completely transparent barrier, the cylinder task. The results suggest that the more visible a reward is, the more difficult it is to inhibit motor impulses toward it, and further, that this inhibitory challenge gradually decreases during development. The mesh barrier is reliably detoured before the animals pass the task with the wholly transparent cylinder. As the majority of the birds begun testing as nestlings, and as we provided them with experiences they normally would not receive in a nest, it is likely that they showed the earliest possible onset of these skills. A control subject, tested at a later age, showed that the mesh detours required no particular training, but that tasks including complete transparency likely require more specific experiences. Adult ravens without explicit training are highly proficient in inhibitory detour tasks, and, together with chimpanzees, they are the best performers of all tested species in the cylinder task. Our results suggest that their skills develop early in life, around their third month. Their developmental pattern of inhibitory skills for detours resembles that of children and rhesus macaques, albeit the pace of development is markedly faster in ravens. Investigating the development of cognition is crucial to understanding its foundations within and across species.

Are parrots poor at motor self-regulation or is the cylinder task poor at measuring it?

The ability to inhibit unproductive motor responses triggered by salient stimuli is a fundamental inhibitory skill. Such motor self-regulation is thought to underlie more complex cognitive mechanisms, like self-control. Recently, a large-scale study, comparing 36 species, found that absolute brain size best predicted competence in motor inhibition, with great apes as the best performers. This was challenged when three Corvus species (corvids) were found to parallel great apes despite having much smaller absolute brain sizes. However, new analyses suggest that it is the number of pallial neurons, and not absolute brain size per se, that correlates with levels of motor inhibition. Both studies used the cylinder task, a detour-reaching test where food is presented behind a transparent barrier. We tested four species from the order Psittaciformes (parrots) on this task. Like corvids, many parrots have relatively large brains, high numbers of pallial neurons, and solve challenging cognitive tasks. Nonetheless, parrots performed markedly worse than the Corvus species in the cylinder task and exhibited strong learning effects in performance and response times. Our results suggest either that parrots are poor at controlling their motor impulses, and hence that pallial neuronal numbers do not always correlate with such skills, or that the widely used cylinder task may not be a good measure of motor inhibition.

A new approach to measuring patience in preschoolers

Patience in children has usually been studied using delay of gratification paradigms. However, another important aspect of patience that has not been well documented is the ability to adjust one's behavior while waiting without an explicit reward as a motivator (e.g., sitting in the doctor's waiting room). To examine this aspect of patience, video-recordings of sixty-one 3- and 4-year olds waiting for two separate 3-min periods were examined and coded for children's spontaneous behaviors. We found that 4-year olds displayed more patient (i.e., staying still) behaviors than 3-year olds during this "waiting paradigm." Interestingly, we also found that children who displayed less patient behaviors during the waiting paradigm were also those who succeeded on a future-thinking task. These findings have important implications for measuring patience in young children and highlight the potential impact of spontaneous behaviors on children's performance in cognitive tasks such as those assessing future-oriented cognition.

Measures of Dogs' Inhibitory Control Abilities Do Not Correlate across Tasks

Inhibitory control, the ability to overcome prepotent but ineffective behaviors, has been studied extensively across species, revealing the involvement of this ability in many different aspects of life. While various different paradigms have been created in order to measure inhibitory control, only a limited number of studies have investigated whether such measurements indeed evaluate the same underlying mechanism, especially in non-human animals. In humans, inhibitory control is a complex construct composed of distinct behavioral processes rather than of a single unified measure. In the current study, we aimed to investigate the validity of inhibitory control paradigms in dogs. Sixty-seven dogs were tested in a battery consisting of frequently used inhibitory control tests. Additionally, dog owners were asked to complete an impulsivity questionnaire about their dog. No correlation of dogs' performance across tasks was found. In order to understand whether there are some underlying behavioral aspects explaining dogs' performance across tests, we performed principle component analyses. Results revealed that three components (persistency, compulsivity and decision speed) explained the variation across tasks. The questionnaire and dogs' individual characteristics (i.e., age and sex) provided only limited information for the derived components. Overall, results suggest that no unique measurement for inhibitory control exists in dogs, but tests rather measure different aspects of this ability. Considering the context-specificity of inhibitory control in dogs and most probably also in other non-human animals, extreme caution is needed when making conclusions about inhibitory control abilities based on a single test.

Reward type and behavioural patterns predict dogs' success in a delay of gratification paradigm

Inhibiting an immediate behaviour in favour of an alternative but more advantageous behaviour has been linked to individual success in life, especially in humans. Dogs, which have been living in the human environment for thousands of years, are exposed to daily situations that require inhibition different in context from other non-domesticated species. One task regularly used to study inhibitory control is the delay of gratification task, which requires individuals to choose between an immediate option of lower value and a delayed option of higher value. We tested sixteen dogs in a non-social delay of gratification task, conducting two different conditions: a quality and a quantity condition. While the majority of dogs failed to wait for more than 10 s, some dogs tolerated delays of up to 140 s, while one dog waited for 15 minutes. Moreover, dogs had more difficulties to wait if the reward increased in terms of quantity than quality. Interestingly, dogs were able to anticipate the delay duration and some dogs developed behavioural patterns that predicted waiting, which seems similar in some respects to 'coping-strategies' found in children, chimpanzees and parrots. Our results indicate that strategies to cope with impulsivity seem to be consistent and present across animal taxa.

Thinking chickens: a review of cognition, emotion, and behavior in the domestic chicken

Domestic chickens are members of an order, Aves, which has been the focus of a revolution in our understanding of neuroanatomical, cognitive, and social complexity. At least some birds are now known to be on par with many mammals in terms of their level of intelligence, emotional sophistication, and social interaction. Yet, views of chickens have largely remained unrevised by this new evidence. In this paper, I examine the peer-reviewed scientific data on the leading edge of cognition, emotions, personality, and sociality in chickens, exploring such areas as self-awareness, cognitive bias, social learning and self-control, and comparing their abilities in these areas with other birds and other vertebrates, particularly mammals. My overall conclusion is that chickens are just as cognitively, emotionally and socially complex as most other birds and mammals in many areas, and that there is a need for further noninvasive comparative behavioral research with chickens as well as a re-framing of current views about their intelligence.

Flexible decision-making relative to reward quality and tool functionality in Goffin cockatoos (Cacatua goffiniana)

Decisions involving the use of tools may require an agent to consider more levels of relational complexity than merely deciding between an immediate and a delayed option. Using a new experimental approach featuring two different types of tools, two apparatuses as well as two different types of reward, we investigated the Goffin cockatoos’ ability to make flexible and profitable decisions within five different setups. Paralleling previous results in primates, most birds overcame immediate drives in favor of future gains; some did so even if tool use involved additional work effort. Furthermore, at the group level subjects maximized their profit by simultaneously considering both the quality of an immediate versus a delayed food reward (accessible with a tool) and the functionality of the available tool. As their performance levels remained stable across trials in all testing setups, this was unlikely the result of a learning effect. The Goffin cockatoos’ ability to focus on relevant information was constrained when all task components (both food qualities, both apparatuses and both tools) were presented at the same time.

Ravens, New Caledonian crows and jackdaws parallel great apes in motor self-regulation despite smaller brains

Overriding motor impulses instigated by salient perceptual stimuli represent a fundamental inhibitory skill. Such motor self-regulation facilitates more rational behaviour, as it brings economy into the bodily interaction with the physical and social world. It also underlies certain complex cognitive processes including decision making. Recently, MacLean et al. (MacLean et al. 2014 Proc. Natl Acad. Sci. USA 111, 2140-2148. (doi:10.1073/pnas.1323533111)) conducted a large-scale study involving 36 species, comparing motor self-regulation across taxa. They concluded that absolute brain size predicts level of performance. The great apes were most successful. Only a few of the species tested were birds. Given birds' small brain size-in absolute terms-yet flexible behaviour, their motor self-regulation calls for closer study. Corvids exhibit some of the largest relative avian brain sizes-although small in absolute measure-as well as the most flexible cognition in the animal kingdom. We therefore tested ravens, New Caledonian crows and jackdaws in the so-called cylinder task. We found performance indistinguishable from that of great apes despite the much smaller brains. We found both absolute and relative brain volume to be a reliable predictor of performance within Aves. The complex cognition of corvids is often likened to that of great apes; our results show further that they share similar fundamental cognitive mechanisms.

Trading up: chimpanzees (Pan troglodytes) show self-control through their exchange behavior

Self-control is defined as the ability or capacity to obtain an objectively more valuable outcome rather than an objectively less valuable outcome though tolerating a longer delay or a greater effort requirement (or both) in obtaining that more valuable outcome. A number of tests have been devised to assess self-control in non-human animals, including exchange tasks. In this study, three chimpanzees (Pan troglodytes) participated in a delay of gratification task that required food exchange as the behavioral response that reflected self-control. The chimpanzees were offered opportunities to inhibit eating and instead exchange a currently possessed food item for a different (and sometimes better) item, often needing to exchange several food items before obtaining the highest valued reward. We manipulated reward type, reward size, reward visibility, delay to exchange, and location of the highest valued reward in the sequence of exchange events to compare performance within the same individuals. The chimpanzees successfully traded until obtaining the best item in most cases, although there were individual differences among participants in some variations of the test. These results support the idea that self-control is robust in chimpanzees even in contexts in which they perhaps anticipate future rewards and sustain delay of gratification until they can obtain the ultimately most valuable item.

Waiting for what comes later: capuchin monkeys show self-control even for nonvisible delayed rewards

Self-control tasks used with nonhuman animals typically involve the choice between an immediate option and a delayed, but more preferred option. However, in many self-control scenarios, not only does the more impulsive option come sooner in time, it is often more concrete than the delayed option. For example, studies have presented children with the option of eating a visible marshmallow immediately, or foregoing it for a better reward that can only be seen later. Thus, the immediately available option is visible and concrete, whereas the delayed option is not visible and more abstract. We tested eight capuchin monkeys to better understand this potential effect by manipulating the visibility of the response options and the visibility of the baiting itself. Monkeys observed two food items (20 or 5 g pieces of banana) each being placed either on top of or inside of one of the two opaque containers attached to a revolving tray apparatus, either in full view of monkeys or occluded by a barrier. Trials ended when monkeys removed a reward from the rotating tray. To demonstrate self-control, monkeys should have allowed the smaller piece of food to pass if the larger piece was forthcoming. Overall, monkeys were successful on the task, allowing a smaller, visible piece of banana to pass from reach in order to access the larger, nonvisible banana piece. This was true even when the entire baiting process took place out of sight of the monkeys. This finding suggests that capuchin monkeys succeed on self-control tasks even when the delayed option is also more abstract than the immediate one-a situation likely faced by primates in everyday life.

Translational research into intertemporal choice: the Western scrub-jay as an animal model for future-thinking

Decisions often involve outcomes that will not materialise until later, and choices between immediate gratification and future consequences are thought to be important for human health and welfare. Combined human and animal research has identified impulsive intertemporal choice as an important factor in drug-taking and pathological gambling. In this paper, we give an overview of recent research into intertemporal choice in non-human animals, and argue that this work could offer insight into human behaviour through the development of animal models. As an example, we discuss the role of future-thinking in intertemporal choice, and review the case for the Western scrub-jay (Aphelocoma californica) as an animal model of such prospective cognition. This article is part of a Special Issue entitled: Tribute to Tom Zentall.

Craving Ravens: Individual 'haa' Call Rates at Feeding Sites as Cues to Personality and Levels of Fission-Fusion Dynamics?

Common ravens aggregate in large non-breeder flocks for roosting and foraging until they achieve the status of territorial breeders. When discovering food, they produce far-reaching yells or ‘haa’ calls, which attract conspecifics. Due to the high levels of fission-fusion dynamics in non-breeders’ flocks, assemblies of feeding ravens were long thought to represent anonymous aggregations. Yet, non-breeders vary in their degree of vagrancy, and ‘haa’ calls convey individually distinct acoustic features, which are perceived by conspecifics. These findings give rise to the assumption that raven societies are based on differential social relationships on an individual level. We investigated the occurrence of ‘haa’ calling and individual call rates in a group of individually marked free-ranging ravens. Calling mainly occurred in subadult and adult females, which showed low levels of vagrancy. Call rates differed significantly between individuals and with residency status, and were correlated with calling frequency and landing frequency. Local ravens called more often and at higher rates, and were less likely to land at the feeding site than vagrant birds. The results are discussed with respect to individual degrees of vagrancy, which may have an impact on social knowledge and communication in this species.

Bonobos and orangutans, but not chimpanzees, flexibly plan for the future in a token-exchange task

Non-human animals, including great apes, have been suggested to share some of the skills for planning that humans commonly exhibit. A crucial difference between human and non-human planning may relate to the diversity of domains and needs in which this skill is expressed. Although great apes can save tools for future use, there is little evidence yet that they can also do so in other contexts. To investigate this question further, we presented the apes with a planning token-exchange task that differed from standard tool-use tasks. Additionally, we manipulated the future outcome of the task to investigate planning flexibility. In the Exchange condition, subjects had to collect, save and transport tokens because they would need them 30 min later to exchange them for food with a human, i.e., "bring-back" response. In the Release condition, the collection and transport of tokens were not needed as no exchange took place after 30 min. Out of 13 subjects, eight solved the task at least once in the Exchange condition, with chimpanzees appearing less successful than the other species. Importantly, three individuals showed a clear differential response between conditions by producing more "bring-back" responses in the Exchange than in the Release conditions. Those bonobo and orangutan individuals hence adapted their planning behavior according to changing needs (i.e., they brought tokens back significantly more often when they would need them). Bonobos and orangutans, unlike chimpanzees, planned outside the context of tool-use, thus challenging the idea that planning in these species is purely domain-specific.

Waiting for better, not for more: corvids respond to quality in two delay maintenance tasks

Self-control, that is, overcoming impulsivity towards immediate gratification in favour of a greater but delayed reward, is seen as a valuable skill when making future-oriented decisions. Experimental studies in nonhuman primates revealed that individuals of some species are willing to tolerate delays of up to several minutes in order to gain food of a higher quantity or quality. Recently, birds (carrion crows, Corvus corone, common ravens, Corvus corax, Goffin cockatoos, Cacatua goffiniana) performed comparably to primates in an exchange task, contradicting previous notions that birds may lack any impulse control. However, performance differed strikingly with the currency of exchange: individuals of all three species performed better when asked to wait for a higher food quality, rather than quantity. Here, we built on this work and tested whether the apparent difference in levels of self-control expressed in quality versus quantity tasks reflects cognitive constraints or is merely due to methodological limitations. In addition to the exchange paradigm, we applied another established delay maintenance methodology: the accumulation task. In this latter task, food items accumulated to a maximum of four pieces, whereas in the exchange task, an initial item could be exchanged for a reward item after a certain time delay elapsed. In both tasks, birds (seven crows, five ravens) were asked to wait in order to optimize either the quality or the quantity of food. We found that corvids were willing to delay gratification when it led to a food reward of higher quality, but not when waiting was rewarded with a higher quantity, independent of the experimental paradigm. This study is the first to test crows and ravens with two different paradigms, the accumulation and the exchange of food, within the same experiment, allowing for fair comparisons between methods and species.

Waiting for better, not for more: corvids respond to quality in two delay maintenance tasks

Self-control, that is, overcoming impulsivity towards immediate gratification in favour of a greater but delayed reward, is seen as a valuable skill when making future-oriented decisions. Experimental studies in nonhuman primates revealed that individuals of some species are willing to tolerate delays of up to several minutes in order to gain food of a higher quantity or quality. Recently, birds (carrion crows, Corvus corone, common ravens, Corvus corax, Goffin cockatoos, Cacatua goffiniana) performed comparably to primates in an exchange task, contradicting previous notions that birds may lack any impulse control. However, performance differed strikingly with the currency of exchange: individuals of all three species performed better when asked to wait for a higher food quality, rather than quantity. Here, we built on this work and tested whether the apparent difference in levels of self-control expressed in quality versus quantity tasks reflects cognitive constraints or is merely due to methodological limitations. In addition to the exchange paradigm, we applied another established delay maintenance methodology: the accumulation task. In this latter task, food items accumulated to a maximum of four pieces, whereas in the exchange task, an initial item could be exchanged for a reward item after a certain time delay elapsed. In both tasks, birds (seven crows, five ravens) were asked to wait in order to optimize either the quality or the quantity of food. We found that corvids were willing to delay gratification when it led to a food reward of higher quality, but not when waiting was rewarded with a higher quantity, independent of the experimental paradigm. This study is the first to test crows and ravens with two different paradigms, the accumulation and the exchange of food, within the same experiment, allowing for fair comparisons between methods and species.

No evidence of temporal preferences in caching by Western scrub-jays (Aphelocoma californica)

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We ask whether scrub-jays prefer earlier cache-retrieval when caching.

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Caching appears similar for trays that come back after 1 h, 25 h, and 49 h.

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Caching appears similar for delays of 7 min and 26 h when no choice of trays is provided.

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We find no evidence of a preference to cache in trays that are more accessible for recovery.

Humans and other animals often favour immediate gratification over long-term gain. Primates, including humans, appear more willing to wait for rewards than other animals, such as rats or pigeons. Another group displaying impressive patience are the corvids, which possess large brains and show sophisticated cognitive abilities. Here, we assess intertemporal choice in one corvid species, the Western scrub-jay (Aphelocoma californica). These birds cache food for future consumption and respond flexibly to future needs. Cache-theft and cache-degradation are time-dependent processes in scrub-jay ecology that might necessitate sensitivity to delays between caching and retrieval. We adopt a caching paradigm with delays of up to 49 h. Across two experiments we find no evidence of a preference for earlier recovery. We highlight the possibility that, although scrub-jays can discriminate between the present and the future, they may not understand how far into the future an event will occur.

Familiarity with the experimenter influences the performance of Common ravens (Corvus corax) and Carrion crows (Corvus corone corone) in cognitive tasks

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We compared the results of corvids in experiments with familiar/unfamiliar humans.

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We investigated behavioural reactions towards familiar and unfamiliar humans.

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Corvids performed significantly better in experiments with familiar humans.

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Corvids did not show more neophobia towards unfamiliar humans.

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Hence, familiarity positively affected the experimental performance of corvids.

When humans and animals interact with one another over an extended time span they familiarise and may develop a relationship, which can exert an influence on both partners. For example, the behaviour of an animal in experiments may be affected by its relationship to the human experimenter. However, few studies have systematically examined the impact of human–animal relationships on experimental results. In the present study we investigated if familiarity with a human experimenter influences the performance of Common ravens (Corvus corax) and Carrion crows (Corvus corone corone) in interactive tasks. Birds were tested in two interactive cognitive tasks (exchange, object choice) by several experimenters representing different levels of familiarity (long and short-term). Our findings show that the birds participated more often in both tasks and were more successful in the exchange task when working with long-term experimenters than when working with short-term experimenters. Behavioural observations indicate that anxiety did not inhibit experimental performance but that the birds’ motivation to work differed between the two kinds of experimenters, familiar and less familiar. We conclude that human–animal relationships (i.e. familiarity) may affect the experimental performance of corvids in interactive cognitive tasks.

Object caching in corvids: incidence and significance

Food caching is a paramount model for studying relations between cognition, brain organisation and ecology in corvids. In contrast, behaviour towards inedible objects is poorly examined and understood. We review the literature on object caching in corvids and other birds, and describe an exploratory study on object caching in ravens, New Caledonian crows and jackdaws. The captive adult birds were presented with an identical set of novel objects adjacent to food. All three species cached objects, which shows the behaviour not to be restricted to juveniles, food cachers, tool-users or individuals deprived of cacheable food. The pattern of object interaction and caching did not mirror the incidence of food caching: the intensely food caching ravens indeed showed highest object caching incidence, but the rarely food caching jackdaws cached objects to similar extent as the moderate food caching New Caledonian crows. Ravens and jackdaws preferred objects with greater sphericity, but New Caledonian crows preferred stick-like objects (similar to tools). We suggest that the observed object caching might have been expressions of exploration or play, and deserves being studied in its own right because of its potential significance for tool-related behaviour and learning, rather than as an over-spill from food-caching research. This article is part of a Special Issue entitled: CO3 2013.

Chimpanzees (Pan troglodytes) can wait, when they choose to: a study with the hybrid delay task

Self-control has been studied in nonhuman animals using a variety of tasks. The inter-temporal choice (ITC) task presents choices between smaller-sooner (SS) and larger-later (LL) options. Using food amounts as rewards, this presents two problems: (a) choices of the LL option could either reflect self-control or instead result from animals' difficulty with pointing to smaller amounts of food; (b) there is no way to verify whether the subjects would not revert their choice for the LL option, if given the opportunity to do so during the ensuing delay. To address these problems, we have recently introduced a new protocol, the hybrid delay task, which combines an initial ITC with a subsequent accumulation phase in which selection of the SS option leads to its immediate delivery, but choice of the LL option then leads to one-by-one presentation of those items that continues only as long as the subject does not eat any of the accumulated items. The choice of the LL option therefore only reflects self-control when the number of items obtained from LL choices during the accumulation phase is higher than what could be received in the SS option. Previous research with capuchin monkeys demonstrated that their apparent self-control responses in the ITC task may have overestimated their general self-control abilities, given their poor performance in the hybrid delay task. Here, chimpanzees instead demonstrated that their choices for the LL option in the ITC phase of the hybrid delay task were confirmed by their ability to sustain long delays during accumulation of LL rewards.