Memory in wild mountain chickadees from different elevations: comparing first-year birds with older survivors

The function of episodic memory in animals

The best-known example of episodic memory in animals came from food-storing birds. One of the beauties of the food-storing system was that inherent in the behaviour were the elements that (at the time) made up episodic memory: what, where and when. While there were then already plenty of data on animals' ability to put together what and where, the addition of the time element in animals' memory and its testing was one that was both new and experimentally challenging. It has, however, led to an increasing variety of examples showing that animals can put together all three informational components. If episodic memories can be described as those memories that make any one of us who we are, why should non-human animals have such memories? Here, we argue that episodic memories play a significant functional role in the lives of real animals, in particular, enabling them to make decisions about how they might or should act in their future. We support our argument with data from a range of examples, focussing on data from the field.This article is part of the theme issue 'Elements of episodic memory: lessons from 40 years of research'.

Spatial cognitive ability is associated with longevity in food-caching chickadees

Cognitive abilities are hypothesized to affect survival and life span in nonhuman animals. However, most tests of this hypothesis have relied on interspecific comparisons of indirect measures of cognitive ability, such as brain size. We present direct evidence that individual variation in cognitive abilities is associated with differences in life span in a wild food caching bird. We measured the spatial cognitive abilities and tracked the life span of 227 mountain chickadees (Poecile gambeli) in their natural environment and found that individuals with better spatial learning and memory abilities involved in food caching lived longer. These results confirm that enhanced cognitive abilities can be associated with longer life in wild animals and that selection on cognitive abilities can lead to increased life span.

Food quality influences behavioural flexibility and cognition in wild house mice

Environmental change is frequent. To adjust and survive, animals need behavioural flexibility. Recently, cognitive flexibility has emerged as a driving force for adjusting to environmental change. Understanding how environmental factors, such as food quality, influence behavioural and/or more costly cognitive flexibility. Here, we investigate the effects of high-quality versus standard food as well as the effects of different housing conditions on both types of flexibility. Our results show that mice that experienced a poorer diet under seminatural conditions showed greater behavioural but not cognitive flexibility. For cage-housed mice, the results were less clear. However, mice fed a poorer diet performed better in innovative problem-solving, thus showing enhanced cognitive flexibility, which was not apparent in the reversal learning paradigm. The observed differences were most likely due to differences in motivation to obtain food rewards. Additionally, animals on poorer diet had lower brain volume, usually related to lower cognitive task performance at the between-species level. Thus, our study emphasises the importance of environmental conditions on behavioural flexibility at the within-species level, highlights that different test paradigms may lead to different conclusions, and finally shows that cage housing of wild animals may lead to patterns that do not necessarily reflect natural conditions.

Genes and gene networks underlying spatial cognition in food-caching chickadees

Substantial progress has been made in understanding the genetic architecture of phenotypes involved in a variety of evolutionary processes. Behavioral genetics remains, however, among the least understood. We explore the genetic architecture of spatial cognitive abilities in a wild passerine bird, the mountain chickadee (Poecile gambeli). Mountain chickadees cache thousands of seeds in the fall and require specialized spatial memory to recover these caches throughout the winter. We previously showed that variation in spatial cognition has a direct effect on fitness and has a genetic basis. It remains unknown which specific genes and developmental pathways are particularly important for shaping spatial cognition. To further dissect the genetic basis of spatial cognitive abilities, we combine experimental quantification of spatial cognition in wild chickadees with whole-genome sequencing of 162 individuals, a new chromosome-scale reference genome, and species-specific gene annotation. We have identified a set of genes and developmental pathways that play a key role in creating variation in spatial cognition and found that the mechanism shaping cognitive variation is consistent with selection against mildly deleterious non-coding mutations. Although some candidate genes were organized into connected gene networks, about half do not have shared regulation, highlighting that multiple independent developmental or physiological mechanisms contribute to variation in spatial cognitive abilities. A large proportion of the candidate genes we found are associated with synaptic plasticity, an intriguing result that leads to the hypothesis that certain genetic variants create antagonism between behavioral plasticity and long-term memory, each providing distinct benefits depending on ecological context.

Environmental harshness does not affect the propensity for social learning in great tits, Parus major

According to the harsh environment hypothesis, natural selection should favour cognitive mechanisms to overcome environmental challenges. Tests of this hypothesis to date have largely focused on asocial learning and memory, thus failing to account for the spread of information via social means. Tests in specialized food-hoarding birds have shown strong support for the effects of environmental harshness on both asocial and social learning. Whether the hypothesis applies to non-specialist foraging species remains largely unexplored. We evaluated the relative importance of social learning across a known harshness gradient by testing generalist great tits, Parus major, from high (harsh)- and low (mild)-elevation populations in two social learning tasks. We showed that individuals use social learning to find food in both colour-associative and spatial foraging tasks and that individuals differed consistently in their use of social learning. However, we did not detect a difference in the use or speed of implementing socially observed information across the elevational gradient. Our results do not support predictions of the harsh environment hypothesis suggesting that context-dependent costs and benefits as well as plasticity in the use of social information may play an important role in the use of social learning across environments. Finally, this study adds to the accumulating evidence that the harsh environment hypothesis appears to have more pronounced effects on specialists compared to generalist species.

Cognitive flexibility in urban yellow mongooses, Cynictis penicillata

Cognitive flexibility enables animals to alter their behaviour and respond appropriately to environmental changes. Such flexibility is important in urban settings where environmental changes occur rapidly and continually. We studied whether free-living, urban-dwelling yellow mongooses, Cynictis penicillata, in South Africa, are cognitively flexible in reversal learning and attention task experiments (n = 10). Reversal learning was conducted using two puzzle boxes that were distinct visually and spatially, each containing a preferred or non-preferred food type. Once mongooses learned which box contained the preferred food type, the food types were reversed. The mongooses successfully unlearned their previously learned response in favour of learning a new response, possibly through a win-stay, lose-shift strategy. Attention task experiments were conducted using one puzzle box surrounded by zero, one, two or three objects, introducing various levels of distraction while solving the task. The mongooses were distracted by two and three distractions but were able to solve the task despite the distractions by splitting their attention between the puzzle box task and remaining vigilant. However, those exposed to human residents more often were more vigilant. We provide the first evidence of cognitive flexibility in urban yellow mongooses, which enables them to modify their behaviour to urban environments.

High temperatures during early development reduce adult cognitive performance and reproductive success in a wild animal population

Global warming is rapidly changing the phenology, distribution, behaviour and demography of wild animal populations. Recent studies in wild animals have shown that high temperatures can induce short-term cognitive impairment, and captive studies have demonstrated that heat exposure during early development can lead to long-term cognitive impairment. Given that cognition underpins behavioural flexibility and can be directly linked to fitness, understanding how high temperatures during early life might impact adult cognitive performance in wild animals is a critical next step to predict wildlife responses to climate change. Here, we investigated the relationship between temperatures experienced during development, adult cognitive performance, and reproductive success in wild southern pied babblers (Turdoides bicolor). We found that higher mean daily maximum temperatures during nestling development led to long-term cognitive impairment in associative learning performance, but not reversal learning performance. Additionally, a higher number of hot days (exceeding 35.5 °C, temperature threshold at which foraging efficiency and offspring provisioning decline) during post-fledging care led to reduced reproductive success in adulthood. We did not find evidence that low reproductive success was linked to impaired associative learning performance: associative learning performance was not related to reproductive success. In contrast, reversal learning performance was negatively related to reproductive success in breeding adults. This suggests that reproduction can carry a cost in terms of reduced performance in cognitively demanding tasks, confirming previous evidence in this species. Taken together, these findings indicate that naturally occurring high temperatures during early development have long-term negative effects on cognition and reproductive success in wild animals. Compounding effects of high temperatures on current nestling mortality and on the long-term cognitive and reproductive performance of survivors are highly concerning given ongoing global warming.

What's in a mate? Social pairing decisions and spatial cognitive ability in food-caching mountain chickadees

While researchers have investigated mating decisions for decades, gaps remain in our understanding of how behaviour influences social mate choice. We compared spatial cognitive performance and food caching propensity within social pairs of mountain chickadees inhabiting differentially harsh winter climates to understand how these measures contribute to social mate choice. Chickadees rely on specialized spatial cognitive abilities to recover food stores and survive harsh winters, and females can discriminate among males with varying spatial cognition. Because spatial cognition and caching propensity are critical for survival and likely heritable, pairing with a mate with such enhanced traits may provide indirect benefits to offspring. Comparing the behaviour of social mates, we found that spatial cognitive performance approached a significant correlation within pairs at low, but not at high elevation. We found no correlation within pairs in spatial reversal cognitive performance at either elevation; however, females at high elevation tended to perform better than their social mates. Finally, we found that caching propensity correlated within pairs at low, while males cached significantly more food than their social mates at high elevations. These results suggest that cognition and caching propensity may influence social mating decisions, but only in certain environments and for some aspects of cognition.

Food-caching mountain chickadees can learn abstract rules to solve a complex spatial-temporal pattern

The use of abstract rules in behavioral decisions is considered evidence of executive functions associated with higher-level cognition. Laboratory studies across taxa have shown that animals may be capable of learning abstract concepts, such as the relationships between items, but often use simpler cognitive abilities to solve tasks. Little is known about whether or how animals learn and use abstract rules in natural environments. Here, we tested whether wild, food-caching mountain chickadees (Poecile gambeli) could learn an abstract rule in a spatial-temporal task in which the location of a food reward rotated daily around an 8-feeder square spatial array for up to 34 days. Chickadees initially searched for the daily food reward by visiting the most recently rewarding locations and then moving backward to visit previously rewarding feeders, using memory of previous locations. But by the end of the task, chickadees were more likely to search forward in the correct direction of rotation, moving away from the previously rewarding feeders. These results suggest that chickadees learned the direction rule for daily feeder rotation and used this to guide their decisions while searching for a food reward. Thus, chickadees appear to use an executive function to make decisions on a foraging-based task in the wild. VIDEO ABSTRACT.

Food-caching chickadees with specialized spatial cognition do not use scrounging as a stable strategy when learning a spatial task

Social animals may use alternative strategies when foraging, with producer-scrounger being one stable dichotomy of strategies. While 'producers' search and discover new food sources, 'scroungers' obtain food discovered by producers. Previous work suggests that differences in cognitive abilities may influence tendencies toward being either a producer or a scrounger, but scrounging behaviour in the context of specialized cognitive abilities is less understood. We investigated whether food-caching mountain chickadees, which rely on spatial cognition to retrieve food caches, engage in scrounging when learning a spatial task. We analysed data from seven seasons of spatial cognition testing, using arrays of radio frequency identification-enabled bird feeders, to identify and quantify potential scrounging behaviour. Chickadees rarely engaged in scrounging, scrounging was not repeatable within individuals and nearly all scrounging events occurred before the bird learned the 'producer' strategy. Scrounging was less frequent in harsher winters, but adults scrounged more than juveniles, and birds at higher elevations scrounged more than chickadees at lower elevations. There was no clear association between spatial cognitive abilities and scrounging frequency. Overall, our study suggests that food-caching species with specialized spatial cognition do not use scrounging as a stable strategy when learning a spatial task, instead relying on learning abilities.

Adding the neuro to cognition: from food storing to nest building

Typically, investigations of animal cognition couple careful experimental manipulations with examination of the animal's behavioural responses. Sometimes those questions have included attempts to describe the neural underpinnings of the behavioural outputs. Over the past 25 years, behaviours that involve spatial learning and memory (such as navigation and food storing) has been one context in which such dual or correlated investigations have been both accessible and productive. Here I review some of that work and where it has led. Because of the wealth of data and insights gained from that work and song learning before it, it seems that it might also be useful to try to add some neurobiology to other systems in animal cognition. I finish then, with a description of recent work on the cognition and neurobiology of avian nest building. It is still relatively early days but asking questions about the cognition of nest building has already shown both neural correlates of nest building and that learning and memory play a much greater role in this behaviour than previously considered. While it is not yet clear how putting these components together will be synergistic, the examples of song learning and food storing provide encouragement. Perhaps this might be true for other behaviours too?

Learning with lacertids: Studying the link between ecology and cognition within a comparative framework

Cognition is an essential tool for animals to deal with environmental challenges. Nonetheless, the ecological forces driving the evolution of cognition throughout the animal kingdom remain enigmatic. Large-scale comparative studies on multiple species and cognitive traits have been advanced as the best way to facilitate our understanding of cognitive evolution, but such studies are rare. Here, we tested 13 species of lacertid lizards (Reptilia: Lacertidae) using a battery of cognitive tests measuring inhibitory control, problem-solving, and spatial and reversal learning. Next, we tested the relationship between species' performance and (a) resource availability (temperature and precipitation), habitat complexity (Normalized Difference Vegetation Index), and habitat variability (seasonality) in their natural habitat and (b) their life history (size at hatching and maturity, clutch size, and frequency). Although species differed markedly in their cognitive abilities, such variation was mostly unrelated to their ecology and life history. Yet, species living in more variable environments exhibited lower behavioral flexibility, likely due to energetic constrains in such habitats. Our standardized protocols provide opportunities for collaborative research, allowing increased sample sizes and replication, essential for moving forward in the field of comparative cognition. Follow-up studies could include more detailed measures of habitat structure and look at other potential selective drivers such as predation.

Natural variation in developmental condition has limited effect on spatial cognition in a wild food-caching bird

Laboratory studies show that increased physiological burden during development results in cognitive impairment. In the wild, animals experience a wide range of developmental conditions, and it is critical to understand how variation in such conditions affects cognitive abilities later in life, especially in species that strongly depend on such abilities for survival. We tested whether variation in developmental condition is associated with differences in spatial cognitive abilities in wild food-caching mountain chickadees. Using tail feathers grown during development in juvenile birds, we measured feather corticosterone (Cortf) levels and growth rates and tested these birds during their first winter on two spatial learning tasks. In only 1 of the 3 years, higher feather Cortf was negatively associated with memory acquisition. No significant associations between feather Cortf and any other measurement of spatial cognition were detected in the other 2 years of the study or between feather growth rate and any measurement of cognition during the entire study. Our results suggest that in the wild, naturally existing variation in developmental condition has only a limited effect on spatial cognitive abilities, at least in a food-caching species. This suggests that there may be compensatory mechanisms to buffer specialized cognitive abilities against developmental perturbations.

Manipulating actions: a selective two‐option device for cognitive experiments in wild animals

Advances in biologging technologies have significantly improved our ability to track individual animals' behaviour in their natural environment. Beyond observations, automation of data collection has revolutionized cognitive experiments in the wild. For example, radio-frequency identification (RFID) antennae embedded in 'puzzle box' devices have allowed for large-scale cognitive experiments where individuals tagged with passive integrated transponder (PIT) tags interact with puzzle boxes to gain a food reward, with devices logging both the identity and solving action of visitors. Here, we extended the scope of wild cognitive experiments by developing a fully automated selective two-option foraging device to specifically control which actions lead to a food reward and which remain unrewarded. Selective devices were based on a sliding-door foraging puzzle, and built using commercially available low-cost electronics. We tested it on two free-ranging PIT-tagged subpopulations of great tits Parus major as a proof of concept. We conducted a diffusion experiment where birds learned from trained demonstrators to get a food reward by sliding the door either to the left or right. We then restricted access of knowledgeable birds to their less preferred side and calculated the latency until birds produced solutions as a measure of behavioural flexibility. A total of 22 of 23 knowledgeable birds produced at least one solution on their less preferred side after being restricted, with higher-frequency solvers being faster at doing so. In addition, 18 of the 23 birds reached their solving rate from prior to the restriction on their less preferred side, with birds with stronger prior side preference taking longer to do so. We therefore introduce and successfully test a new selective two-option puzzle box, providing detailed instructions and freely available software that allows reproducibility. It extends the functionality of existing systems by allowing fine-scale manipulations of individuals' actions and opens a large range of possibilities to study cognitive processes in wild animal populations.

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.

Challenges in Linking Cognition and Survival: A Review

Linking cognitive performance with fitness outcomes, measured using both reproductive and survival metrics, of free-living animals is crucial for understanding the evolution of cognition. Although there is increasing evidence showing a link between cognitive traits and reproductive success metrics, studies specifically exploring the link between cognition and survival are scarce. We first explore which cognitive traits related to survival have been investigated in free-living animals. We also discuss the challenges associated with investigating the links between cognition and survival. We then review studies that specifically consider survival of animals of known cognitive abilities that are either free-living or in captivity and later released into the wild. We found nine studies exploring cognitive traits in wild populations. The relationships between these cognitive traits and survival were equivocal. We found a further nine studies in captive-reared populations trained to predator cues and later released into the wild. Training to recognize predator cues was correlated with increased survival in the majority of studies. Finally, different individual intrinsic characteristics (i.e., age, body condition, personality, sex) showed varied effects between studies. We argue that finding ecologically relevant cognitive traits is crucial for gaining a better understanding of how selection impacts certain cognitive traits, and how these might contribute to an individual’s survival. We also suggest possible standardized, easy to implement, cognitive tests that can be used in long-term studies, which would generate large sample sizes, take into account intrinsic characteristics, and provide an opportunity to understand the mechanisms, development and evolution of cognition.

Social dominance has limited effects on spatial cognition in a wild food-caching bird

Social dominance has long been used as a model to investigate social stress. However, many studies using such comparisons have been performed in captive environments. These environments may produce unnaturally high antagonistic interactions, exaggerating the stress of social subordination and any associated adverse consequences. One such adverse effect concerns impaired cognitive ability, often thought to be associated with social subordination. Here, we tested whether social dominance rank is associated with differences in spatial learning and memory, and in reversal spatial learning (flexibility) abilities in wild food-caching mountain chickadees at different montane elevations. Higher dominance rank was associated with higher spatial cognitive flexibility in harsh environments at higher elevations, but not at lower, milder elevations. By contrast, there were no consistent differences in spatial learning and memory ability associated with dominance rank. Our results suggest that spatial learning and memory ability in specialized food-caching species is a stable trait resilient to social influences. Spatial cognitive flexibility, on the other hand, appears to be more sensitive to environmental influences, including social dominance. These findings contradict those from laboratory studies and suggest that it is critical to investigate the biological consequences of social dominance under natural conditions.

The genetic basis of spatial cognitive variation in a food-caching bird

Spatial cognition is used by most organisms to navigate their environment. Some species rely particularly heavily on specialized spatial cognition to survive, suggesting that a heritable component of cognition may be under natural selection. This idea remains largely untested outside of humans, perhaps because cognition in general is known to be strongly affected by learning and experience.^1-4 We investigated the genetic basis of individual variation in spatial cognition used by non-migratory food-caching birds to recover food stores and survive harsh montane winters. Comparing the genomes of wild, free-living birds ranging from best to worst in their performance on a spatial cognitive task revealed significant associations with genes involved in neuron growth and development and hippocampal function. These results identify candidate genes associated with differences in spatial cognition and provide a critical link connecting individual variation in spatial cognition with natural selection.

Seasonal variation in reversal learning reveals greater female cognitive flexibility in African striped mice

Cognitive flexibility describes the ability of animals to alter cognitively mediated behaviour in response to changing situational demands, and can vary according to prevailing environemental conditions and individual caracteristics. In the present study, we investigated (1) how learning and reversal learning performance changes between seasons, and (2) how cognitive flexibility is related to sex in a free-living small mammal. We studied 107 African striped mice, Rhabdomys pumilio, in an arid semi-desert, 58 during the hot dry summer with low food availability, and 49 during the cold wet winter with higher food availability. We used an escape box task to test for learning and reversal learning performance. We found that learning and reversal learning efficiency varied seasonally by sex: females tested in summer were faster at solving both learning and reversal tasks than males tested in winter. Performance varied within sex: males tested in winter showed faster learning compared to males tested in summer. During reversal learning, females tested in summer were more efficient and solve the task faster compared to females tested in winter. We suggest that seasonal cognitive performance could be related to sex-specific behavioural characteristics of the species, resulting in adaptation for living in harsh environmental conditions.

Food discovery is associated with different reliance on social learning and lower cognitive flexibility across environments in a food-caching bird

Social learning is a primary mechanism for information acquisition in social species. Despite many benefits, social learning may be disadvantageous when independent learning is more efficient. For example, searching independently may be more advantageous when food sources are ephemeral and unpredictable. Individual differences in cognitive abilities can also be expected to influence social information use. Specifically, better spatial memory can make a given environment more predictable for an individual by allowing it to better track food sources. We investigated how resident food-caching chickadees discovered multiple novel food sources in both harsher, less predictable high elevation and milder, more predictable low elevation winter environments. Chickadees at high elevation were faster at discovering multiple novel food sources and discovered more food sources than birds at low elevation. While birds at both elevations used social information, the contribution of social learning to food discovery was significantly lower at high elevation. At both elevations, chickadees with better spatial cognitive flexibility were slower at discovering food sources, likely because birds with lower spatial cognitive flexibility are worse at tracking natural resources and therefore spend more time exploring. Overall, our study supported the prediction that harsh environments should favour less reliance on social learning.

Great tits who remember more accurately have difficulty forgetting, but variation is not driven by environmental harshness

The causes of individual variation in memory are poorly understood in wild animals. Harsh environments with sparse or rapidly changing food resources are hypothesized to favour more accurate spatial memory to allow animals to return to previously visited patches when current patches are depleted. A potential cost of more accurate spatial memory is proactive interference, where accurate memories block the formation of new memories. This relationship between spatial memory, proactive interference, and harsh environments has only been studied in scatter-hoarding animals. We compare spatial memory accuracy and proactive interference performance of non-scatter hoarding great tits (Parus major) from high and low elevations where harshness increases with elevation. In contrast to studies of scatter-hoarders, we did not find a significant difference between high and low elevation birds in their spatial memory accuracy or proactive interference performance. Using a variance partitioning approach, we report the first among-individual trade-off between spatial memory and proactive interference, uncovering variation in memory at the individual level where selection may act. Although we have no evidence of harsh habitats affecting spatial memory, our results suggest that if elevation produced differences in spatial memory between elevations, we could see concurrent changes in how quickly birds can forget.

Dealing with the unexpected: the effect of environmental variability on behavioural flexibility in a Mediterranean lizard

Harsh and variable environments have been hypothesized to both drive and constrain the evolution towards higher cognitive abilities and behavioural flexibility. In this study, we compared the cognitive abilities of island and mainland Aegean wall lizards (Podarcis erhardii), which were expected to live in respectively a more variable and a more stable habitat. We used four proxies of behavioural flexibility: a neophobia assay, a problem-solving test and a spatial + reversal learning task. Surprisingly, the two populations did not differ in neophobia or problem-solving. Insular lizards, however, outperformed mainland conspecifics in an initial spatial learning task, but were less successful during the subsequent reversal learning. Our results thus seem to indicate that the effect of environmental variability on cognition is complex, as it may favour some, but not all aspects of behavioural flexibility.

Specialized spatial cognition is associated with reduced cognitive senescence in a food-caching bird

Senescence, the gradual reduction and loss of function as organisms age, is a widespread process that is especially pronounced in cognitive abilities. Senescence appears to have a genetic basis and can be affected by evolutionary processes. If cognitive senescence is shaped by natural selection, it may be linked with selection on cognitive abilities needed for survival and reproduction, such that species where fitness is directly related to cognitive abilities should evolve delayed cognitive senescence likely resulting in higher lifetime fitness. We used wild food-caching mountain chickadees, which rely on specialized spatial cognition to recover thousands of food caches annually, to test for cognitive senescence in spatial learning and memory and reversal spatial learning and memory abilities. We detected no signs of age-related senescence in spatial cognitive performance on either task in birds ranging from 1 to 6 years old; older birds actually performed better on spatial learning and memory tasks. Our results therefore suggest that cognitive senescence may be either delayed (potentially appearing after 6 years) or negligible in species with strong selection on cognitive abilities and that food-caching species may present a useful model to investigate mechanisms associated with cognitive senescence.

Variation in reversal learning by three generalist mesocarnivores

Urbanization imposes novel challenges for wildlife, but also provides new opportunities for exploitation. Generalist species are commonly found in urban habitats, but the cognitive mechanisms facilitating their successful behavioral adaptations and exploitations are largely under-investigated. Cognitive flexibility is thought to enable generalists to be more plastic in their behavior, thereby increasing their adaptability to a variety of environments, including urban habitats. Yet direct measures of cognitive flexibility across urban wildlife are lacking. We used a classic reversal-learning paradigm to investigate the cognitive flexibility of three generalist mesocarnivores commonly found in urban habitats: striped skunks (Mephitis mephitis), raccoons (Procyon lotor), and coyotes (Canis latrans). We developed an automated device and testing protocol that allowed us to administer tests of reversal learning in captivity without extensive training or experimenter involvement. Although most subjects were able to rapidly form and reverse learned associations, we found moderate variation in performance and behavior during trials. Most notably, we observed heightened neophobia and a lack of habituation expressed by coyotes. We discuss the implications of such differences among generalists with regard to urban adaptation and we identify goals for future research. This study is an important step in investigating the relationships between cognition, generalism, and urban adaptation.

Testing the greater male variability phenomenon: male mountain chickadees exhibit larger variation in reversal learning performance compared with females

The greater male variability phenomenon predicts that males exhibit larger ranges of variation in cognitive performance compared with females; however, support for this pattern has come exclusively from studies of humans and lacks mechanistic explanation. Furthermore, the vast majority of the literature assessing sex differences in cognition is based on studies of humans and a few other mammals. In order to elucidate the underpinnings of cognitive variation and the potential for fitness consequences, we must investigate sex differences in cognition in non-mammalian systems as well. Here, we assess the performance of male and female food-caching birds on a spatial learning and memory task and a reversal spatial task to address whether there are sex differences in mean cognitive performance or in the range of variation in performance. For both tasks, male and female mean performance was similar across four years of testing; however, males did exhibit a wider range of variation in performance on the reversal spatial task compared with females. The implications for mate choice and sexual selection of cognitive abilities are discussed and future directions are suggested to aid in the understanding of sex-related cognitive variation.

Testing the greater male variability phenomenon: male mountain chickadees exhibit larger variation in reversal learning performance compared with females

The greater male variability phenomenon predicts that males exhibit larger ranges of variation in cognitive performance compared with females; however, support for this pattern has come exclusively from studies of humans and lacks mechanistic explanation. Furthermore, the vast majority of the literature assessing sex differences in cognition is based on studies of humans and a few other mammals. In order to elucidate the underpinnings of cognitive variation and the potential for fitness consequences, we must investigate sex differences in cognition in non-mammalian systems as well. Here, we assess the performance of male and female food-caching birds on a spatial learning and memory task and a reversal spatial task to address whether there are sex differences in mean cognitive performance or in the range of variation in performance. For both tasks, male and female mean performance was similar across four years of testing; however, males did exhibit a wider range of variation in performance on the reversal spatial task compared with females. The implications for mate choice and sexual selection of cognitive abilities are discussed and future directions are suggested to aid in the understanding of sex-related cognitive variation.

Testing the greater male variability phenomenon: male mountain chickadees exhibit larger variation in reversal learning performance compared with females

The greater male variability phenomenon predicts that males exhibit larger ranges of variation in cognitive performance compared with females; however, support for this pattern has come exclusively from studies of humans and lacks mechanistic explanation. Furthermore, the vast majority of the literature assessing sex differences in cognition is based on studies of humans and a few other mammals. In order to elucidate the underpinnings of cognitive variation and the potential for fitness consequences, we must investigate sex differences in cognition in non-mammalian systems as well. Here, we assess the performance of male and female food-caching birds on a spatial learning and memory task and a reversal spatial task to address whether there are sex differences in mean cognitive performance or in the range of variation in performance. For both tasks, male and female mean performance was similar across four years of testing; however, males did exhibit a wider range of variation in performance on the reversal spatial task compared with females. The implications for mate choice and sexual selection of cognitive abilities are discussed and future directions are suggested to aid in the understanding of sex-related cognitive variation.

Multiple genetic loci affect place learning and memory performance in Drosophila melanogaster

Learning and memory are critical functions for all animals, giving individuals the ability to respond to changes in their environment. Within populations, individuals vary, however the mechanisms underlying this variation in performance are largely unknown. Thus, it remains to be determined what genetic factors cause an individual to have high learning ability and what factors determine how well an individual will remember what they have learned. To genetically dissect learning and memory performance, we used the Drosophila synthetic population resource (DSPR), a multiparent mapping resource in the model system Drosophila melanogaster, consisting of a large set of recombinant inbred lines (RILs) that naturally vary in these and other traits. Fruit flies can be trained in a "heat box" to learn to remain on one side of a chamber (place learning) and can remember this (place memory) over short timescales. Using this paradigm, we measured place learning and memory for ~49 000 individual flies from over 700 DSPR RILs. We identified 16 different loci across the genome that significantly affect place learning and/or memory performance, with 5 of these loci affecting both traits. To identify transcriptomic differences associated with performance, we performed RNA-Seq on pooled samples of seven high performing and seven low performing RILs for both learning and memory and identified hundreds of genes with differences in expression in the two sets. Integrating our transcriptomic results with the mapping results allowed us to identify nine promising candidate genes, advancing our understanding of the genetic basis underlying natural variation in learning and memory performance.

Food caching in city birds: urbanization and exploration do not predict spatial memory in scatter hoarders

Urbanization has been shown to affect the physiological, morphological, and behavioral traits of animals, but it is less clear how cognitive traits are affected. Urban habitats contain artificial food sources, such as bird feeders that are known to impact foraging behaviors. As of yet, however, it is not well known whether urbanization and the abundance of supplemental food during the winter affect caching behaviors and spatial memory in scatter hoarders. We aim to compare caching intensity and spatial memory performance along an urban gradient to determine (i) whether individuals from more urbanized sites cache less frequently and perform less accurately on a spatial memory task, and (ii) for the first time in individual scatter hoarders, whether slower explorers perform more accurately than faster explorers on a spatial memory task. We assessed food caching, exploration of a novel environment, and spatial memory performance of wild-caught black-capped chickadees (Poecile atricapillus; N = 95) from 14 sites along an urban gradient. Although the individuals that cached most in captivity were all from less urbanized sites, we found no clear evidence that caching intensity and spatial memory accuracy differed along an urban gradient. At the individual level, we found no significant relationship between spatial memory performance and exploration score. However, individuals that performed more accurately on the spatial task also tended to cache more, pointing to a specialization of spatial memory in scatter hoarders that could occur at the level of the individual, in addition to the previously documented specialization at the population and species levels.

Smart is the new sexy: female mountain chickadees increase reproductive investment when mated to males with better spatial cognition

Understanding the evolution of inter and intraspecific variation in cognitive abilities is one of the main goals in cognitive ecology. In scatter-caching species, spatial memory is critical for the recovery of food caches and overwinter survival, but its effects on reproduction are less clear. Better spatial cognition may improve pre-breeding condition allowing for earlier reproduction. Alternatively, when mated to males with better spatial memory, females may be able to invest more in reproduction which may allow increased offspring survival and hence higher fitness. Using wild food-caching mountain chickadees, we found that when environmental conditions were favourable for breeding, females mated to males with better spatial cognition laid larger clutches and fledged larger broods than females mated to males with worse cognitive performance. Our results support the hypothesis that females may increase their reproductive investment to gain indirect, genetic benefits when mated to high-quality males with better spatial cognitive abilities.

The repeatability of cognitive performance: a meta-analysis

Behavioural and cognitive processes play important roles in mediating an individual's interactions with its environment. Yet, while there is a vast literature on repeatable individual differences in behaviour, relatively little is known about the repeatability of cognitive performance. To further our understanding of the evolution of cognition, we gathered 44 studies on individual performance of 25 species across six animal classes and used meta-analysis to assess whether cognitive performance is repeatable. We compared repeatability (R) in performance (1) on the same task presented at different times (temporal repeatability), and (2) on different tasks that measured the same putative cognitive ability (contextual repeatability). We also addressed whether R estimates were influenced by seven extrinsic factors (moderators): type of cognitive performance measurement, type of cognitive task, delay between tests, origin of the subjects, experimental context, taxonomic class and publication status. We found support for both temporal and contextual repeatability of cognitive performance, with mean R estimates ranging between 0.15 and 0.28. Repeatability estimates were mostly influenced by the type of cognitive performance measures and publication status. Our findings highlight the widespread occurrence of consistent inter-individual variation in cognition across a range of taxa which, like behaviour, may be associated with fitness outcomes.This article is part of the theme issue 'Causes and consequences of individual differences in cognitive abilities'.