Is the Western Scrub-Jay (Aphelocoma californica) Really an Underdog among Food-Caching Corvids when It Comes to Hippocampal Volume and Food Caching Propensity?

Linking ecology and cognition: does ecological specialisation predict cognitive test performance?

Variation in cognitive abilities is thought to be linked to variation in brain size, which varies across species with either social factors (Social Intelligence Hypothesis) or ecological challenges (Ecological Intelligence Hypothesis). However, the nature of the ecological processes invoked by the Ecological Intelligence Hypothesis, like adaptations to certain habitat characteristics or dietary requirements, remains relatively poorly known. Here, we review comparative studies that experimentally investigated interspecific variation in cognitive performance in relation to a species’ degree of ecological specialisation. Overall, the relevant literature was biased towards studies of mammals and birds as well as studies focusing on ecological challenges related to diet. We separated ecological challenges into those related to searching for food, accessing a food item and memorising food locations. We found interspecific variation in cognitive performance that can be explained by adaptations to different foraging styles. Species-specific adaptations to certain ecological conditions, like food patch distribution, characteristics of food items or seasonality also broadly predicted variation in cognitive abilities. A species’ innovative problem-solving and spatial processing ability, for example, could be explained by its use of specific foraging techniques or search strategies, respectively. Further, habitat generalists were more likely to outperform habitat specialists. Hence, we found evidence that ecological adaptations and cognitive performance are linked and that the classification concept of ecological specialisation can explain variation in cognitive performance only with regard to habitat, but not dietary specialisation.

Western scrub-jays do not appear to attend to functionality in Aesop's Fable experiments

Western scrub-jays are known for their highly discriminatory and flexible behaviors in a caching (food storing) context. However, it is unknown whether their cognitive abilities are restricted to a caching context. To explore this question, we tested scrub-jays in a non-caching context using the Aesop’s Fable paradigm, where a partially filled tube of water contains a floating food reward and objects must be inserted to displace the water and bring the food within reach. We tested four birds, but only two learned to drop stones proficiently. Of these, one bird participated in 4/5 experiments and one in 2/5 experiments. Both birds passed one experiment, but without attending to the functional differences of the objects, and failed the other experiments. Scrub-jays were not motivated to participate in these experiments, suggesting that either this paradigm was ecologically irrelevant or perhaps their flexibility is restricted to a caching context.

Sex, estradiol, and spatial memory in a food-caching corvid

Estrogens significantly impact spatial memory function in mammalian species. Songbirds express the estrogen synthetic enzyme aromatase at relatively high levels in the hippocampus and there is evidence from zebra finches that estrogens facilitate performance on spatial learning and/or memory tasks. It is unknown, however, whether estrogens influence hippocampal function in songbirds that naturally exhibit memory-intensive behaviors, such as cache recovery observed in many corvid species. To address this question, we examined the impact of estradiol on spatial memory in non-breeding Western scrub-jays, a species that routinely participates in food caching and retrieval in nature and in captivity. We also asked if there were sex differences in performance or responses to estradiol. Utilizing a combination of an aromatase inhibitor, fadrozole, with estradiol implants, we found that while overall cache recovery rates were unaffected by estradiol, several other indices of spatial memory, including searching efficiency and efficiency to retrieve the first item, were impaired in the presence of estradiol. In addition, males and females differed in some performance measures, although these differences appeared to be a consequence of the nature of the task as neither sex consistently out-performed the other. Overall, our data suggest that a sustained estradiol elevation in a food-caching bird impairs some, but not all, aspects of spatial memory on an innate behavioral task, at times in a sex-specific manner.

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.

Differences in relative hippocampus volume and number of hippocampus neurons among five corvid species

The relative size of the avian hippocampus (Hp) has been shown to be related to spatial memory and food storing in two avian families, the parids and corvids. Basil et al. [Brain Behav Evol 1996;47:156-164] examined North American food-storing birds in the corvid family and found that Clark's nutcrackers had a larger relative Hp than pinyon jays and Western scrub jays. These results correlated with the nutcracker's better performance on most spatial memory tasks and their strong reliance on stored food in the wild. However, Pravosudov and de Kort [Brain Behav Evol 2006;67:1-9] raised questions about the methodology used in the 1996 study, specifically the use of paraffin as an embedding material and recalculation for shrinkage. Therefore, we measured relative Hp volume using gelatin as the embedding material in four North American species of food-storing corvids (Clark's nutcrackers, pinyon jays, Western scrub jays and blue jays) and one Eurasian corvid that stores little to no food (azure-winged magpies). Although there was a significant overall effect of species on relative Hp volume among the five species, subsequent tests found only one pairwise difference, blue jays having a larger Hp than the azure-winged magpies. We also examined the relative size of the septum in the five species. Although Shiflett et al. [J Neurobiol 2002;51:215-222] found a difference in relative septum volume amongst three species of parids that correlated with storing food, we did not find significant differences amongst the five species in relative septum. Finally, we calculated the number of neurons in the Hp relative to body mass in the five species and found statistically significant differences, some of which are in accord with the adaptive specialization hypothesis and some are not.

Evolution of cognition

Renewed interest in the field of comparative cognition over the past 30 years has led to a renaissance in our thinking of how cognition evolved. Here, we review historical and comparative approaches to the study of psychological evolution, focusing on cognitive differences based on evolutionary divergence, but also cognitive similarities based on evolutionary convergence. Both approaches have contributed to major theories of cognitive evolution in humans and non-human animals. As a result, not only have we furthered our understanding of the evolution of the human mind and its unique attributes, but we have also identified complex cognitive capacities in a few large-brained species, evolved from solving social and ecological challenges requiring a flexible mind. WIREs Cogni Sci 2011 2 621-633 DOI: 10.1002/wcs.144 For further resources related to this article, please visit the WIREs website.

The synthetic approach to the study of spatial memory: have we properly addressed Tinbergen's "four questions"?

In 1963, Niko Tinbergen suggested that to truly understand the behavior of an animal, the ultimate causes (e.g., adaptive value, evolutionary history) as well as the proximate mechanisms (e.g., neurobiology, development) that result in the production of the behavior must be understood in an integrated framework. We examine whether the study of spatial memory in food storing birds has adequately addressed Tinbergen's questions and highlight the work of Sara Shettleworth, who has made a tremendous contribution to this area of study, and whom this issue honors. Our conclusion is that while the study of food caching and spatial memory in birds has been a very good model of a program of research that has addressed Tinbergen's questions, additional work remains.

Ten years of research into avian models of episodic-like memory and its implications for developmental and comparative cognition

Episodic memory refers to the ability to remember specific personal events from the past. Ever since Tulving first made the distinction between episodic memory and other forms of declarative memory in 1972, most cognitive psychologists and neuroscientists have assumed that episodic recall is unique to humans. The seminal paper on episodic-like memory in Western scrub-jays (Aphelocoma californica) by Clayton and Dickinson [4] has inspired a number of studies and in a wide range of species over the past 10 years. Here we shall first review the avian studies of what-where-when memory, namely in the Western scrub-jays, magpies, black-capped chickadees and pigeons; we shall then present an alternative approach to studying episodic-like memory also tested in pigeons. In the second and third section we want to draw attention to topics where we believe the bird model could prove highly valuable, namely studying development of episodic-memory in pre-verbal children, and the evolution and ontogeny of brain areas subserving episodic(-like) memory.

Problems faced by food-caching corvids and the evolution of cognitive solutions

The scatter hoarding of food, or caching, is a widespread and well-studied behaviour. Recent experiments with caching corvids have provided evidence for episodic-like memory, future planning and possibly mental attribution, all cognitive abilities that were thought to be unique to humans. In addition to the complexity of making flexible, informed decisions about caching and recovering, this behaviour is underpinned by a motivationally controlled compulsion to cache. In this review, we shall first discuss the compulsive side of caching both during ontogeny and in the caching behaviour of adult corvids. We then consider some of the problems that these birds face and review the evidence for the cognitive abilities they use to solve them. Thus, the emergence of episodic-like memory is viewed as a solution for coping with food perishability, while the various cache-protection and pilfering strategies may be sophisticated tools to deprive competitors of information, either by reducing the quality of information they can gather, or invalidating the information they already have. Finally, we shall examine whether such future-oriented behaviour involves future planning and ask why this and other cognitive abilities might have evolved in corvids.

Is bigger always better? A critical appraisal of the use of volumetric analysis in the study of the hippocampus

A well-developed spatial memory is important for many animals, but appears especially important for scatter-hoarding species. Consequently, the scatter-hoarding system provides an excellent paradigm in which to study the integrative aspects of memory use within an ecological and evolutionary framework. One of the main tenets of this paradigm is that selection for enhanced spatial memory for cache locations should specialize the brain areas involved in memory. One such brain area is the hippocampus (Hp). Many studies have examined this adaptive specialization hypothesis, typically relating spatial memory to Hp volume. However, it is unclear how the volume of the Hp is related to its function for spatial memory. Thus, the goal of this article is to evaluate volume as a main measurement of the degree of morphological and physiological adaptation of the Hp as it relates to memory. We will briefly review the evidence for the specialization of memory in food-hoarding animals and discuss the philosophy behind volume as the main currency. We will then examine the problems associated with this approach, attempting to understand the advantages and limitations of using volume and discuss alternatives that might yield more specific hypotheses. Overall, there is strong evidence that the Hp is involved in the specialization of spatial memory in scatter-hoarding animals. However, volume may be only a coarse proxy for more relevant and subtle changes in the structure of the brain underlying changes in behaviour. To better understand the nature of this brain/memory relationship, we suggest focusing on more specific and relevant features of the Hp, such as the number or size of neurons, variation in connectivity depending on dendritic and axonal arborization and the number of synapses. These should generate more specific hypotheses derived from a solid theoretical background and should provide a better understanding of both neural mechanisms of memory and their evolution.

Animal consciousness: a synthetic approach

Despite anecdotal evidence suggesting conscious states in a variety of non-human animals, no systematic neuroscientific investigation of animal consciousness has yet been undertaken. We set forth a framework for such an investigation that incorporates integration of data from neuroanatomy, neurophysiology, and behavioral studies, uses evidence from humans as a benchmark, and recognizes the critical role of explicit verbal report of conscious experiences in human studies. We illustrate our framework with reference to two subphyla: one relatively near to mammals - birds - and one quite far -cephalopod molluscs. Consistent with the possibility of conscious states, both subphyla exhibit complex behavior and possess sophisticated nervous systems. Their further investigation may reveal common phyletic conditions and neural substrates underlying the emergence of animal consciousness.

The development of caching and object permanence in Western scrub-jays (Aphelocoma californica): which emerges first?

Recent studies on the food-caching behavior of corvids have revealed complex physical and social skills, yet little is known about the ontogeny of food caching in relation to the development of cognitive capacities. Piagetian object permanence is the understanding that objects continue to exist even when they are no longer visible. Here, the authors focus on Piagetian Stages 3 and 4, because they are hallmarks in the cognitive development of both young children and animals. Our aim is to determine in a food-caching corvid, the Western scrub-jay, whether (1) Piagetian Stage 4 competence and tentative caching (i.e., hiding an item invisibly and retrieving it without delay), emerge concomitantly or consecutively; (2) whether experiencing the reappearance of hidden objects enhances the timing of the appearance of object permanence; and (3) discuss how the development of object permanence is related to behavioral development and sensorimotor intelligence. Our findings suggest that object permanence Stage 4 emerges before tentative caching, and independent of environmental influences, but that once the birds have developed simple object-permanence, then social learning might advance the interval after which tentative caching commences.