Design complexity and strength of laterality are correlated in New Caledonian crows' pandanus tool manufacture

Hooded crows (Corvus cornix) manufacture objects relative to a mental template

It was recently found that not only tool-specialized New Caledonian crows, but also Goffin cockatoos can manufacture physical objects in accordance with a mental template. That is, they can emulate features of existing objects when they manufacture new items. Both species spontaneously ripped pieces of card into large strips if they had previously learned that a large template was rewarded, and small strips when they previously learned that a small template was rewarded. Among New Caledonian crows, this cognitive ability was suggested as a potential mechanism underlying the transmission of natural tool designs. Here, we tested for the same ability in another non-specialised tool user-Hooded crows (Corvus cornix). Crows were exposed to pre-made template objects, varying first in colour and then in size, and were rewarded only if they chose pre-made objects that matched the template. In subsequent tests, birds were given the opportunity to manufacture versions of these objects. All three crows ripped paper pieces from the same colour material as the rewarded template, and, crucially, also manufactured objects that were more similar in size to previously rewarded, than unrewarded, templates, despite the birds being rewarded at random in both tests. Therefore, we found the ability to manufacture physical objects relative to a mental template in yet another bird species not specialized in using or making foraging tools in the wild, but with a high level of brain and cognitive development.

Modulation of behavioural laterality in wild New Caledonian crows (Corvus moneduloides): Vocalization, age and function

The New Caledonian crow (Corvus moneduloides) is known for displaying a unique set of tool-related behaviours, with the bird's bill acting as an individually consistently lateralized effector. However, we still fail to understand how such laterality develops, is modulated or even if its expression is consistent across other behavioural categories. Creating the first ethogram for this species allowed us to examine laterality and vocalisations in a population of wild, free-flying New Caledonian crows using detailed analyses of close-up video footage. We revealed the existence of an overall strong left-sided bias during object manipulation only and which was driven by the adult crows of our focal population, the stabilization of individual preferences occurring during the birds' juvenile years. Individually, at least one crow showed consistent side biases to the right and left within different behavioural categories. Our findings highlight previously unknown variability in behavioural laterality in this species, thus advocating for further investigation. Specifically, we argue that a better understanding of the New Caledonian crow's biology and ecology is required if one wishes to pursue the promising comparative road that laterality could be connected to the evolution of tool-making.

Extra food provisioning does not affect behavioural lateralization in nestling lesser kestrels

Costs and benefits of brain lateralization may depend on environmental conditions. Growing evidence indicates that the development of brain functional asymmetries is adaptively shaped by the environmental conditions experienced during early life. Food availability early in life could act as a proxy of the environmental conditions encountered during adulthood, but its potential modulatory effect on lateralization has received little attention. We increased food supply from egg laying to early nestling rearing in a wild population of lesser kestrels Falco naumanni, a sexually dimorphic raptor, and quantified the lateralization of preening behaviour (head turning direction). As more lateralized individuals may perform better in highly competitive contexts, we expected that extra food provisioning, by reducing the level of intra-brood competition for food, would reduce the strength of lateralization. We found that extra food provisioning improved nestling growth, but it did not significantly affect the strength or direction of nestling lateralization. In addition, maternal body condition did not explain variation in nestling lateralization. Independently of extra food provisioning, the direction of lateralization differed between the sexes, with female nestlings turning more often towards their right. Our findings indicate that early food availability does not modulate behavioural lateralization in a motor task, suggesting limited phenotypic plasticity in this trait.

A framework for the comparative study of language

Comparative studies of language are difficult because few language precursors are recognized. In this paper we propose a framework for designing experiments that test for structural and semantic patterns indicative of simple or complex grammars as originally described by Chomsky. We argue that a key issue is whether animals can recognize full recursion, which is the hallmark of context-free grammar. We discuss limitations of recent experiments that have attempted to address this issue, and point out that experiments aimed at detecting patterns that follow a Fibonacci series have advantages over other artificial context-free grammars. We also argue that experiments using complex sequences of behaviors could, in principle, provide evidence for fully recursive thought. Some of these ideas could also be approached using artificial life simulations, which have the potential to reveal the types of evolutionary transitions that could occur over time. Because the framework we propose has specific memory and computational requirements, future experiments could target candidate genes with the goal of revealing the genetic underpinnings of complex cognition.

A Framework for the Comparative Study of Language

Comparative studies of language are difficult because few language precursors are recognized. In this paper we propose a framework for designing experiments that test for structural and semantic patterns indicative of simple or complex grammars as originally described by Chomsky. We argue that a key issue is whether animals can recognize full recursion, which is the hallmark of context-free grammar. We discuss limitations of recent experiments that have attempted to address this issue, and point out that experiments aimed at detecting patterns that follow a Fibonacci series have advantages over other artificial context-free grammars. We also argue that experiments using complex sequences of behaviors could, in principle, provide evidence for fully recursive thought. Some of these ideas could also be approached using artificial life simulations, which have the potential to reveal the types of evolutionary transitions that could occur over time. Because the framework we propose has specific memory and computational requirements, future experiments could target candidate genes with the goal of revealing the genetic underpinnings of complex cognition.

Cryptic asymmetry: unreliable signals mask asymmetric performance of crayfish weapons

Animals commonly use their limbs as signals and weapons during territorial aggression. Asymmetries of limb performance that do not relate to asymmetries of limb size (cryptic asymmetry) could substantially affect disputes, but this phenomenon has not been considered beyond primates. We investigated cryptic asymmetry in male crayfish (Cherax dispar), which commonly use unreliable signals of strength during aggression. Although the strength of a chela can vary by an order of magnitude for a given size, we found repeatable asymmetries of strength that were only weakly related to asymmetries of size. Size-adjusted strength of chelae and the asymmetry of strength between chelae were highly repeatable between environmental conditions, suggesting that asymmetries of strength stemmed from variation in capacity rather than motivation. Cryptic asymmetry adds another dimension of uncertainty during conflict between animals, which could influence the evolution of unreliable signals and morphological asymmetry.

Imitation explains the propagation, not the stability of animal culture

For acquired behaviour to count as cultural, two conditions must be met: it must propagate in a social group, and it must remain stable across generations in the process of propagation. It is commonly assumed that imitation is the mechanism that explains both the spread of animal culture and its stability. We review the literature on transmission chain studies in chimpanzees (Pan troglodytes) and other animals, and we use a formal model to argue that imitation, which may well play a major role in the propagation of animal culture, cannot be considered faithful enough to explain its stability. We consider the contribution that other psychological and ecological factors might make to the stability of animal culture observed in the wild.

Design complexity in termite-fishing tools of chimpanzees (Pan troglodytes)

Adopting the approach taken with New Caledonian crows (Corvus moneduloides), we present evidence of design complexity in one of the termite-fishing tools of chimpanzees (Pan troglodytes) in the Goualougo Triangle, Republic of Congo. Prior to termite fishing, chimpanzees applied a set of deliberate, distinguishable actions to modify herb stems to fashion a brush-tipped probe, which is different from the form of fishing tools used by chimpanzees in East and West Africa. This means that 'brush-tipped fishing probes', unlike 'brush sticks', are not a by-product of use but a deliberate design feature absent in other chimpanzee populations. The specialized modifications to prepare the tool for termite fishing, measures taken to repair non-functional brushes and appropriate orientation of the modified end suggest that these wild chimpanzees are attentive to tool modifications. We also conducted experimental trials that showed that a brush-tipped probe is more effective in gathering insects than an unmodified fishing probe. Based on these findings, we suggest that chimpanzees in the Congo Basin have developed an improved fishing probe design.

Cerebral Lateralization and Its Relationship to Phylogeny and Aggression in Anabantoid Fishes

We examined the relationship between aggression and cerebral lateralization, as expressed by eye-use preference in a mirror-response paradigm, in six species of anabantoid fishes in the teleost family Belontiidae. Our objective was to test the hypothesis that frequency-dependent selection should decrease lateralization at the population level in more aggressive species. The mean laterality index did not differ significantly among the six species, nor did any of the species differ from zero, which suggests that populations of these fishes are neither left- nor right-eye biased. In spite of species differences in aggressive behavior, there was no relationship between population-level laterality and aggression as we had originally predicted. The degree of individual lateralization did differ significantly among some species. A phylogenetic generalized least squares (PGLS) analysis showed that these species differences were not due to phylogenetic distance. Individual laterality was also unrelated to aggression. Fishes in the genus Betta were the most individually lateralized, but varied in the intensity of aggressive behavior they displayed toward the mirrors. Taxa such as paradise fish (Macropodus opercularis and Pseudosphromenus dayi) were intermediate in eye-use preferences and gourami (Trichogaster trichopterus) displayed little cerebral lateralization. We also used the PGLS method to reconstruct ancestral values for individual lateralization in this group of fishes, from which we conclude that the ancestral condition was one of low variance in eye-use preference.