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The strategies that animals use to obtain valuable resources are affected by resource quality and availability (e.g. spatial distribution), population dynamics (e.g. competitor-to-resource ratio) and individual characteristics (e.g. competitive ability). Theoretical papers and field observations suggest that aggressive resource competition, particularly by individuals with high competitive ability, increases as the competitor-to-resource ratio increases. On the other hand, individuals with low competitive ability should adopt a scramble competitive strategy, for example by expanding their home range or utilizing resources at suboptimal times. We tested these theoretical predictions in male house mice, Mus musculus domesticus, by experimentally manipulating the distribution of a desirable resource, a running wheel. Four male mice were exposed to three treatments (zero, one or four running wheels present) using a repeated measures design. We found that aggression increased as the competitor-to-resource ratio increased. In addition, mice with high competitive ability had species-typical nocturnally biased activity and running wheel use patterns, while mice with low competitive ability had more diurnally biased activity and running wheel use patterns. Our results show that aggression encourages less competitive mice to adopt a scramble competitive strategy through temporal partitioning and provides empirical evidence for the predictions of resource defence theory.

The prevalence of stable behavioural differences between individuals of a species (i.e. personality) is puzzling because it indicates that there are limits on animals’ behavioural plasticity and, therefore, optimality of behaviour. Personality may result from individual state characteristics (e.g. morphology or physiology). In turn, these characteristics can lead to differential fitness outcomes for individuals. Cognitive processing of environmental information may be such a characteristic. We developed a subjective personality assessment for Amazona amazonica. We then assessed whether personality predicted a cognitive state difference in attention bias, as measured by the proportion of balks and errors when performing a spatial foraging task in the presence of a passive human observer. Attention biases occur either because individuals attend more quickly to certain environmental stimuli, or because they cannot disengage their attention from such stimuli. Two factors, ‘neuroticism’ and ‘extraversion’, accounted for 66% of the total variance in personality. There was individual variation between parrots’ scores on both personality factors and both factors were temporally consistent over 1 year. There was a significant correlation between neuroticism and attention bias. Evolutionarily, attention biases are selected for because the fitness cost of failing to attend to potential threats is much greater than the cost of expending energy attending to benign stimuli. Therefore, cognitive biases such as attention bias are logical candidate cognitive states driving stable personality differences. Our findings show that differences in personality in A. amazonica are correlated with attention bias, a biologically relevant difference in cognition.

If fearfulness is stable, consistent and trait-like, then valid measures of fearfulness should be stable, consistent and independent of influences unrelated to fear. We assessed the validity of six fear measures using Japanese quail, Coturnix coturnix japonica, a common species in fear research. Measures were made during emergence, novel object, novel food and predator surprise tests. These were considered to have internal validity if they were stable over 18 days, when we controlled for nonexperimental variables including season of testing and cage location. We determined convergent and discriminant validity by factor analysis of fear measures plus measures of sociality, activity level and repetitive behaviour. Fear measures with good convergent validity showed agreement in their factor loadings. Those with good discriminant validity loaded on to different factors from nonfear measures. Most of the fear measures examined were moderately stable over time, but only half had good discriminant validity. Convergence was good among measures from the same test but poor across tests. Measures from each fear test loaded separately. Overall, flight distance and freezing duration in the predator surprise test and amount eaten in the novel food test showed the best internal, convergent and discriminant validity. When we considered only these three measures, convergence remained higher among measures from the same test than from different tests. Fearfulness thus appeared somewhat unstable over time and inconsistent across situations, which, if true across species, greatly limits the utility of fear tests.

The effects of age, sex and previous experience on colour avoidance in northern bobwhites, Colinus virginianus , were evaluated. First, unlearned colour preferences were determined by measuring pecking by 52 1-day-old bobwhite chicks at pinheads of four colours. The number of first pecks and the total number of pecks varied significantly among colours ( P =0·011 and P green>yellow>red. There were no clear sex differences in pecking preference. A second experiment used a two-cup avoidance test to evaluate the effects of sex and previous experience on avoidance of coloured grain by juvenile bobwhite. Forty 11-week-old birds were pre-exposed for 7 days to either multi-coloured or undyed food, and then tested for 5 days for avoidance of red or blue food. Red food was avoided relative to undyed food (preference ratio=0·426, P =0·004), whereas blue food was not avoided. Sex of bird, pre-exposure to coloured food, and day of test had no significant effect on colour avoidance. Finally, 26 of the same birds were retested at the age of 31 weeks for avoidance of blue and red food. Results indicated no change in colour avoidance with age. Although these experiments failed to replicate a sex difference in colour avoidance that we found in a previous study, they did demonstrate that bobwhites show an unlearned aversion to red which is persistent and resistant to extinction. Because red is a common warning colour in insects, this aversion may be an adaptation for avoiding aposematically coloured prey.