Mark A. Whiteside

Selection on behavioural traits during ‘unselective’ harvesting means that shy pheasants better survive a hunting season

Recreational hunting can disrupt the population structure or alter the morphology of target populations. More subtly, such hunting may alter the behaviour of individuals in the target population, especially if individuals are culled nonrandomly. We assayed the behavioural temperaments of a sample of hand-reared and released pheasants, Phasianus colchicus. We could place birds on a behavioural continuum between bold or fast and shy or slow. Individual differences could not be explained by sex or mass. Birds were released into the wild and we followed their fate over a single hunting season. Birds that survived the hunting season were shyer or slower as juveniles than the original population mean. Males that died of disease or predation were relatively bold or fast as juveniles, while females dying of disease or predation were relatively shy or slow. Males that were bold or fast as juveniles were shot early in the season compared to females. Unselective hunting can skew the expression of behaviours in released gamebirds. This skew may explain why released birds subsequently fail to reproduce or are especially likely to die of natural causes once the hunting season has finished, and hence why it is difficult to establish wild populations of these species through reintroduction to an area where shooting takes place.

Differential participation in cognitive tests is driven by personality, sex, body condition and experience

Failure to participate in a cognitive test may result in sampling biases when measuring inter-individual variation in cognitive performances in both captive and wild populations. This would be problematic if particular classes of individuals consistently fail to participate, skewing data and making generalisations or comparisons difficult. We presented 144 pheasant chicks, raised under standardised conditions, with a battery of cognitive tests to investigate whether sex, body condition or personality traits, measured by differences in latencies to explore a novel object, novel environment or unknown conspecific, predicted individual variation in voluntary participation across 37 test sessions. In general, participation increased across testing sessions, yet patterns of participation differed with sex and body condition. Males with a high body condition were more likely to participate in early test sessions compared to males with a low body condition or females. While participation among males in high body condition was consistent across sessions, males with a low body condition and females, regardless of body condition, were more likely to participate in later, rather than earlier sessions. Individuals also showed repeatable behaviours across time and different contexts, revealing not only that the exploration of novelty, but also that the order that subjects entered the testing arena and their latencies to acquire a freely available meal-worm reward may be considered valid proxies for different personality traits. During each test session, those individuals that were among the first to voluntarily enter the testing arena were more likely to participate in subsequent trials. Moreover, when isolated in the testing arena, individuals that rapidly acquired a freely available meal-worm, positioned on the testing apparatus, were also more likely to participate in a cognitive test. Our findings therefore reveal that sex, body condition and personality traits, along with habituation to the testing paradigms, all play important roles in determining whether or not particular individuals participate in cognitive tests. Sampling biases may therefore misrepresent our understanding of variation in cognitive performance in wild and captive populations, making individual differences in cognition difficult to interpret.

Diet complexity in early life affects survival in released pheasants by altering foraging efficiency, food choice, handling skills and gut morphology

Behavioural and physiological deficiencies are major reasons why reintroduction programmes suffer from high mortality when captive animals are used. Mitigation of these deficiencies is essential for successful reintroduction programmes. Our study manipulated early developmental diet to better replicate foraging behaviour in the wild. Over 2 years, we hand-reared 1800 pheasants (Phasianus colchicus), from 1 day old, for 7 weeks under different dietary conditions. In year one, 900 pheasants were divided into three groups and reared with (i) commercial chick crumb, (ii) crumb plus 1% live mealworm or (iii) crumb plus 5% mixed seed and fruit. In year two, a further 900 pheasants were divided into two groups and reared with (i) commercial chick crumb or (ii) crumb plus a combination of 1% mealworm and 5% mixed seed and fruit. In both years, the commercial chick crumb acted as a control treatment, whilst those with live prey and mixed seeds and fruits mimicking a more naturalistic diet. After 7 weeks reared on these diets, pheasants were released into the wild. Postrelease survival was improved with exposure to more naturalistic diets prior to release. We identified four mechanisms to explain this. Pheasants reared with more naturalistic diets (i) foraged for less time and had a higher likelihood of performing vigilance behaviours, (ii) were quicker at handling live prey items, (iii) were less reliant on supplementary feed which could be withdrawn and (iv) developed different gut morphologies. These mechanisms allowed the pheasants to (i) reduce the risk of predation by reducing exposure time whilst foraging and allowing more time to be vigilant; (ii) be better at handling and discriminating natural food items and not be solely reliant on supplementary feed; and (iii) have a better gut system to cope with the natural forage after the cessation of supplementary feeding in the spring. Learning food discrimination, preference and handling skills by the provision of a more naturalistic diet is essential prior to the release of pheasants in a reintroduction programme. Subsequent diet, foraging behaviour, gut morphology and digestive capabilities all work together as one nutritional complex. Simple manipulations during early development can influence these characteristics to better prepare an individual for survival upon release.

Multiple behavioural, morphological and cognitive developmental changes arise from a single alteration to early life spatial environment, resulting in fitness consequences for released pheasants

Subtle variations in early rearing environment influence morphological, cognitive and behavioural processes that together impact on adult fitness. We manipulated habitat complexity experienced by young pheasants (Phasianus colchicus) in their first seven weeks, adding a third accessible dimension by placing elevated perches in their rearing pens mimicking natural variation in habitat complexity. This simple manipulation provoked an interrelated suite of morphological, cognitive and behavioural changes, culminating in decreased wild mortality of birds from complex habitats compared with controls. Three mechanisms contribute to this: Pheasants reared with perches had a morphology which could enable them to fly to the higher branches and cope with prolonged roosting. They had a higher propensity to roost off the ground at night in the wild. More generally, these birds had more accurate spatial memory. Consequently, birds were at a reduced risk of terrestrial predation. The fitness consequences of variation in early rearing on behavioural development are rarely studied in the wild but we show that this is necessary because the effects can be broad ranging and not simple, depending on a complex interplay of behavioural, cognitive and morphological elements, even when effects that the treatments provoke are relatively short term and plastic.

Do detour tasks provide accurate assays of inhibitory control

Transparent Cylinder and Barrier tasks are used to purportedly assess inhibitory control in a variety of animals. However, we suspect that performances on these detour tasks are influenced by non-cognitive traits, which may result in inaccurate assays of inhibitory control. We therefore reared pheasants under standardized conditions and presented each bird with two sets of similar tasks commonly used to measure inhibitory control. We recorded the number of times subjects incorrectly attempted to access a reward through transparent barriers, and their latencies to solve each task. Such measures are commonly used to infer the differential expression of inhibitory control. We found little evidence that their performances were consistent across the two different Putative Inhibitory Control Tasks (PICTs). Improvements in performance across trials showed that pheasants learned the affordances of each specific task. Critically, prior experience of transparent tasks, either Barrier or Cylinder, also improved subsequent inhibitory control performance on a novel task, suggesting that they also learned the general properties of transparent obstacles. Individual measures of persistence, assayed in a third task, were positively related to their frequency of incorrect attempts to solve the transparent inhibitory control tasks. Neophobia, Sex and Body Condition had no influence on individual performance. Contrary to previous studies of primates, pheasants with poor performance on PICTs had a wider dietary breadth assayed using a free-choice task. Our results demonstrate that in systems or taxa where prior experience and differences in development cannot be accounted for, individual differences in performance on commonly used detour-dependent PICTS may reveal more about an individuals prior experience of transparent objects, or their motivation to acquire food, than providing a reliable measure of their inhibitory control.

The repeatability of cognitive performance: a meta-analysis

Behavioural and cognitive processes play important roles in mediating an individuals 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’.

Variation in female mate choice and mating success is affected by sex ratio experienced during early life

Females vary in their mate choice and consequent fitness outcomes. Individual differences may be explained by conditions experienced early in life. We tested whether the sex ratio at which young pheasants, Phasianus colchicus, were reared affected their adult sexual behaviour. Females reared in equal sex ratios discriminated strongly between males of differing attractiveness in choice tests and had the lowest variance in mating success. Conversely, females reared in female-biased sex ratios showed little discrimination between males based on their attractiveness, and exhibited highly skewed mating success with the majority gaining no copulations, but a quarter each gaining more copulations than any other female in the study. Early life environmental determination of variation in female choice could explain the lack of uniformity in mate choice and hence maintain variation in male traits in the face of directional sexual selection.

Males and females differentially adjust vigilance levels as group size increases: effect on optimal group size

A strong motivation for one individual to aggregate with others is to reduce their vigilance because other group members provide coverage and warning of approaching predators. This collective vigilance means that a focal individual is usually less susceptible to predation than when alone. However, individuals differ in their vigilance levels depending on status and context. They may also differ in how they adjust their vigilance levels as group size changes. This flexibility in response means that the collective vigilance of a group, and hence its optimal size, is not intuitive. We demonstrate, in both natural and experimental systems, that male and female pheasants, Phasianus colchicus, in harems differentially adjusted their vigilance levels as harem size changed. Females became less vigilant as harems became larger, and benefited by increasing their foraging time. Conversely, males became more vigilant as harems became larger. We calculated the collective probability that a harem would detect a predator. Within natural harem sizes, a male and two females exhibited the highest probability of collective detection, with decreases as more females joined. This optimal harem size matched the average harem size observed at our study site. Females may join harems for benefits of collective vigilance. Despite both sexes having a shared interest in larger harems for mating benefits, optimal harem size is influenced by trade-offs in a nonsexual behaviour, vigilance. This results in males with relatively small harems, females associating with less preferred males and each male being surrounded by fewer females than he could mate with.

The quick are the dead: pheasants that are slow to reverse a learned association survive for longer in the wild

Cognitive abilities probably evolve through natural selection if they provide individuals with fitness benefits. A growing number of studies demonstrate a positive relationship between performance in psychometric tasks and (proxy) measures of fitness. We assayed the performance of 154 common pheasant (Phasianus colchicus) chicks on tests of acquisition and reversal learning, using a different set of chicks and different set of cue types (spatial location and colour) in each of two years and then followed their fates after release into the wild. Across all birds, individuals that were slow to reverse previously learned associations were more likely to survive to four months old. For heavy birds, individuals that rapidly acquired an association had improved survival to four months, whereas for light birds, slow acquirers were more likely to be alive. Slow reversers also exhibited less exploratory behaviour in assays when five weeks old. Fast acquirers visited more artificial feeders after release. In contrast to most other studies, we showed that apparently ‘poor’ cognitive performance (slow reversal speed suggesting low behavioural flexibility) correlates with fitness benefits in at least some circumstances. This correlation suggests a novel mechanism by which continued exaggeration of cognitive abilities may be constrained. This article is part of the theme issue ‘Causes and consequences of individual differences in cognitive abilities’.

Erratum to: Differences in social preference between the sexes during ontogeny drive segregation in a precocial species

The work was jointly funded by the University of Exeter, the Game and Wildlife Conservation Trust, a Royal Society Small Project Grant awarded to JRM and an ERC Consolidator Grant (616474) awarded to JRM.