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Individuals vary in their cognitive performance. While this variation forms the foundation of the study of human psychometrics, its broader importance is only recently being recognized. Explicitly acknowledging this individual variation found in both humans and non-human animals provides a novel opportunity to understand the mechanisms, development and evolution of cognition. The papers in this special issue highlight the growing emphasis on individual cognitive differences from fields as diverse as neurobiology, experimental psychology and evolutionary biology. Here, we synthesize this body of work. We consider the distinct challenges in quantifying individual differences in cognition and provide concrete methodological recommendations. In particular, future studies would benefit from using multiple task variants to ensure they target specific, clearly defined cognitive traits and from conducting repeated testing to assess individual consistency. We then consider how neural, genetic, developmental and behavioural factors may generate individual differences in cognition. Finally, we discuss the potential fitness consequences of individual cognitive variation and place these into an evolutionary framework with testable hypotheses. We intend for this special issue to stimulate researchers to position individual variation at the centre of the cognitive sciences. This article is part of the theme issue ‘Causes and consequences of individual differences in cognitive abilities’.

Social interactions between animals can provide many benefits, including the ability to gain useful environmental information through social learning. However, these social contacts can also facilitate the transmission of infectious diseases through a population. Animals engaging in social interactions therefore face a trade-off between the potential informational benefits and the risk of acquiring disease. Theoretical models have suggested that modular social networks, associated with the formation of groups or sub-groups, can slow spread of infection by trapping it within particular groups. However, these social structures will not necessarily impact the spread of information in the same way if its transmission follows a “complex contagion”, e.g. through individuals disproportionally copying the majority (conformist learning). Here we use simulation models to demonstrate that modular networks can promote the spread of information relative to the spread of infection, but only when the network is fragmented and group sizes are small. We show that the difference in transmission between information and disease is maximised for more well-connected social networks when the likelihood of transmission is intermediate. Our results have important implications for understanding the selective pressures operating on the social structure of animal societies, revealing that highly fragmented networks such as those formed in fission–fusion social groups and multilevel societies can be effective in modulating the infection-information trade-off for individuals within them.

Living with increasing urbanisation and human populations requires resourcefulness and flexibility in wild animals' behaviour. Animals have to adapt to anthropogenic novelty in habitat structure and resources that may not resemble, or be as beneficial as, natural resources. Herring gulls Larus argentatus increasingly reside in towns and cities to breed and forage, yet how gulls are adjusting their behaviour to life in urban areas is not yet fully understood. This study investigated wild herring gulls' responses to novel and common anthropogenic objects in urban and rural locations. We also examined whether gulls' age influenced their object response behaviour. We found that, out of the 126 individual gulls presented with objects, 34% approached them. This suggests that the majority of targeted gulls were wary or lacked interest in the experimental set‐up. Of the 43 gulls that approached the objects, we found that those tested in urban locations approached more slowly than their rural counterparts. Overall, gulls showed no preference for either novel or common anthropogenic objects, and age did not influence likelihood of approach, approach speed or object choice. Individuals paid most attention to the object they approached first, potentially indicative of individual preferences. Our findings indicated that most herring gulls are not as attracted to anthropogenic objects as anecdotal reports have suggested. Covering up obvious food rewards may thus help mitigate human–gull conflict over anthropogenic food sources.

Urban populations of herring gulls ( Larus argentatus ) are increasing and causing human-wildlife conflict by exploiting anthropogenic resources. Gulls that breed in urban areas rely on varying amounts of terrestrial anthropogenic foods ( e.g ., domestic refuse, agricultural and commercial waste) to feed themselves. However, with the onset of hatching, many parent gulls switch to sourcing more marine than anthropogenic or terrestrial foods to provision their chicks. Although anthropogenic foods may meet chick calorific requirements for growth and development, some such foods ( e.g ., bread) may have lower levels of protein and other key nutrients compared to marine foods. However, whether this parental switch in chick diet is driven by chicks’ preference for marine foods, or whether chicks’ food preferences are shaped by the food types provisioned by their parents, remains untested. This study tests whether chick food preferences can be influenced by their provisioned diet by experimentally manipulating the ratio of time for which anthropogenic and marine foods were available (80:20 and vice versa ) in the rearing diets of two treatment groups of rescued herring gull chicks. Each diet was randomly assigned to each of the 27 captive-reared chicks for the duration of the study. We tested chicks’ individual food preferences throughout their development in captivity using food arrays with four food choices (fish, cat food, mussels and brown bread). Regardless of the dietary treatment group, we found that all chicks preferred fish and almost all refused to eat most of the bread offered. Our findings suggest that early-life diet, manipulated by the ratio of time the different foods were available, did not influence gull chicks’ food preferences. Instead, chicks developed a strong and persistent preference for marine foods, which appears to match adult gulls’ dietary switch to marine foods upon chick hatching and may reinforce the provisioning of marine foods during chick development. However, whether chicks in the wild would refuse provisioned foods, and to a sufficient extent to influence parental provisioning, requires further study. Longitudinal studies of urban animal populations that track wild individuals’ food preferences and foraging specialisations throughout life are required to shed light on the development and use of anthropogenic resource exploitation.

Agonistic and affiliative interactions with group members dictate individual access to resources, and investment in competing for resources is often traded off with other needs. For example, reproductive investment can reduce body condition and, thereby, an individual's ability to win future agonistic interactions. However, group members may also alter their behaviour towards reproductive individuals, such as becoming more or less aggressive. Here, we investigated the social consequences of reproduction in female vulturine guineafowl Acryllium vulturinum, a plural breeder in which females disperse and are subordinate to males. We found opposing patterns for within‐ and between‐sex dominance interactions experienced by females from before to after breeding. Specifically, breeding females became far less likely to win dominance interactions with non‐breeding females after breeding than before breeding, but received considerably fewer male aggressions than non‐breeding females after breeding. Despite a limited sample size, our study reveals that reproduction can have nuanced trade‐offs with dominance and suggests that the study of dominance may benefit from explicitly considering variation in interaction rates as an additional factor affecting individuals. Females often have to trade‐off investment in reproduction versus social status. This study shows that after breeding, females lose more dominance interactions against other females, but that they also receive fewer aggressions from dominant males. The results suggest that breeding causes a change in the status of females, whereby they may need to invest less in same‐sex interactions because of increased access to resources through dominant males.

Wild animal species often use human‐modified environments for foraging and reproduction, but this may require dietary diversification with fitness consequences. The extent to which colonising species successfully exploit such habitats is poorly understood. We used stable isotope analysis of egg yolk to investigate the association between foraging choices and reproductive success in 102 female herring gulls (Larus argentatus) over 3 years in a roof‐nesting, pericoastal breeding colony. Stable isotopes of egg yolk predominantly reflect maternal diet during egg production. We measured δ13C as an indicator of foraging habitat, and δ15N as an indicator of trophic level. We predicted diverse foraging choices across marine, terrestrial and urban environments due to gulls' generalist foraging strategy and the variety of nearby foraging opportunities. We also predicted higher reproductive success associated with marine feeding compared to terrestrial feeding or feeding on human food and refuse, because marine food has historically been gulls' natural food type and has been previously associated with greater reproductive success. Surprisingly, δ13C values indicated predominantly terrestrial foraging for egg production. Egg mass increased significantly with lower δ13C, indicative of more terrestrial feeding. These findings may reflect availability of habitats and foods nearby or indicate adaptive dietary choices. Fledging success increased significantly with elevated δ15N, indicating that mothers feeding at higher trophic levels before laying produced higher quality eggs and/or had superior offspring‐rearing capacity. A high trophic level maternal diet may nutritionally benefit offspring or improve parental condition. Egg stable isotope ratios of δ13C and δ15N were highly repeatable within clutches, enabling us to predict stable isotope values of unsampled eggs from sampled sibling eggs. Our results highlight high usage of terrestrial foods for egg production, whereas marine and anthropogenic feeding were rare. The reasons for this preference warrant further investigation to advance understanding of species that use human‐modified environments. We used stable isotope analysis to investigate the association between foraging choices and reproductive success in roof‐nesting herring gulls. Surprisingly, δ13C values indicated predominantly terrestrial foraging, while fledging success increased with elevated δ15N, indicating that mothers feeding at higher trophic levels produced higher quality eggs and/or had superior offspring‐rearing capacity. Our results highlight high usage of terrestrial foods for egg production; the reasons for this preference warrant further investigation to advance understanding of species that utilise human‐modified environments.

Establishing how collective behaviour emerges is central to our understanding of animal societies. Previous research has highlighted how universal interaction rules shape collective behaviour, and that individual differences can drive group functioning. Groups themselves may also differ considerably in their collective behaviour, but little is known about the consistency of such group variation, especially across different ecological contexts that may alter individuals' behavioural responses. Here, we test if randomly composed groups of sticklebacks differ consistently from one another in both their structure and movement dynamics across an open environment, an environment with food, and an environment with food and shelter. Based on high-resolution tracking data of the free-swimming shoals, we found large context-associated changes in the average behaviour of the groups. But despite these changes and limited social familiarity among group members, substantial and predictable behavioural differences between the groups persisted both within and across the different contexts (group-level repeatability): some groups moved consistently faster, more cohesively, showed stronger alignment and/or clearer leadership than other groups. These results suggest that among-group heterogeneity could be a widespread feature in animal societies. Future work that considers group-level variation in collective behaviour may help understand the selective pressures that shape how animal collectives form and function.

Recent studies suggest that individuals with better problem-solving and/or learning performance have greater reproductive success, and that individuals may thus benefit from choosing mates based on these performances. However, directly assessing these performances in candidate mates could be difficult. Instead, the use of indirect cues related to problem-solving and/or learning performance, such as condition-dependent phenotypic traits, might be favored. We investigated whether problemsolving and learning performance on a novel non-foraging task correlated with sexually selected plumage colouration in a natural population of great tits Parus major. We found that males successful in solving the task had darker blue-black crowns than non-solvers, and that males solving the task more rapidly over multiple attempts (i.e. learners) exhibited blue-black crowns with higher UV chroma and shorter-wavelength hues than non-learners. In contrast, we found no link between behavioural performance on the task and the yellow breast colouration in either sex. Our findings suggest that blue-black crown colouration could serve as a signal of problem-solving and learning performance in wild great tit males. Further research remains necessary to determine whether different sexually selected traits are used to signal cognitive performance for mate choice, either directly (i.e. cognitive performance influencing individual’s health and ornamentation through diet for example) or indirectly (i.e. due to a correlation with a third factor such as individual quality or condition).

Although strategies to conserve biodiversity (e.g., the establishment of reserves and the management of flagship, umbrella, indicator, and keystone species) are valuable, they entail practical and conceptual difficulties. A focus on niche construction and ecosystem engineering, however, could provide new insights and methods for conservation biology. Many organisms modulate the availability of resources to other species by causing state changes in biotic or abiotic materials (ecosystem engineering), in the process frequently changing the selection to which the ecosystem engineers and other organisms are exposed (niche construction). We describe growing evidence that organisms have significant nontrophic impacts on ecosystem structure, function, and biodiversity, and outline established means of identifying key species involved in niche construction. On the basis of this engineering perspective, we propose a number of measures that could be employed to enhance conservation efforts.