Behaviour under conditions of mild stress shows consistent patterns in all vertebrates: exploratory behaviour, boldness, aggressiveness covary in the same way. The existence of highly consistent individual variation in these behavioural strategies, also referred to as personalities or coping styles, allows us to measure the behaviour under standardized conditions on birds bred in captivity, link the standardized measurements to the behaviour under natural conditions and measure natural selection in the field. We have bred the great tit (Parus major), a classical model species for the study of behaviour under natural conditions, in captivity. Here, we report a realized heritability of 54±5% for early exploratory behaviour, based on four generations of bi-directional artificial selection. In addition to this, we measured hand–reared juveniles and their wild–caught parents in the laboratory. The heritability found in the mid–offspring–mid–parent regression was significantly different from zero. We have thus established the presence of considerable amounts of genetic variation for personality types in a wild bird.

Personalities are general properties of humans and other animals. Different personality traits are phenotypically correlated, and heritabilities of personality traits have been reported in humans and various animals. In great tits, consistent heritable differences have been found in relation to exploration, which is correlated with various other personality traits. In this paper, we investigate whether or not risk–taking behaviour is part of these avian personalities. We found that (i) risk–taking behaviour is repeatable and correlated with exploratory behaviour in wild–caught hand–reared birds, (ii) in a bi–directional selection experiment on ‘fast’ and ‘slow’ early exploratory behaviour, bird lines tend to differ in risk–taking behaviour, and (iii) within–nest variation of risk–taking behaviour is smaller than between–nest variation. To show that risk–taking behaviour has a genetic component in a natural bird population, we bred great tits in the laboratory and artificially selected ‘high’ and ‘low’ risk–taking behaviour for two generations. Here, we report a realized heritability of 19.3±3.3% (s.e.m.) for risk–taking behaviour. With these results we show in several ways that risk–taking behaviour is linked to exploratory behaviour, and we therefore have evidence for the existence of avian personalities. Moreover, we prove that there is heritable variation in more than one correlated personality trait in a natural population, which demonstrates the potential for correlated evolution.

Phenology refers to the periodic appearance of life-cycle events and currently receives abundant attention as the effects of global change on phenology are so apparent. Phenology as a discipline observes these events and relates their annual variation to variation in climate. But phenology is also studied in other disciplines, each with their own perspective. Evolutionary ecologists study variation in seasonal timing and its fitness consequences, whereas chronobiologists emphasize the periodic nature of life-cycle stages and their underlying timing programmes (e.g. circannual rhythms). The (neuro-) endocrine processes underlying these life-cycle events are studied by physiologists and need to be linked to genes that are explored by molecular geneticists. In order to fully understand variation in phenology, we need to integrate these different perspectives, in particular by combining evolutionary and mechanistic approaches. We use avian research to characterize different perspectives and to highlight integration that has already been achieved. Building on this work, we outline a route towards uniting the different disciplines in a single framework, which may be used to better understand and, more importantly, to forecast climate change impacts on phenology.

Individuals of many species differ consistently in their behavioral reaction to mild novel challenges. Suites of these behaviors are referred to as behavioral syndromes or personalities. Personality traits are often phenotypically and genetically correlated. Therefore, animal personalities are generally considered as broad characteristics, with one underlying genetical and physiological mechanism that is expressed across situations and contexts. Because there are carryover effects between situations, animals are not entirely flexible in their behavior in each situation. This may cause behaviors to seem nonadaptive in isolated situations. To test whether individuals with different personalities could react differently to changes in their environment, we studied context dependence of personalities in the great tit (Parus major). We tested birds categorized as either fast or slow explorers for their latency to come back to a feeding table after a mild startle (risk-taking behavior) in a nonsocial followed by a social context. We found that the relation between exploratory behavior and risk-taking behavior depended on the social context. Females in general returned later in the social test, while male reaction to the presence of a conspecific was dependent on their behavioral type. Slow males thereby reacted to the behavior of the companion and fast males did not. These results show that although personalities have a rigid structure the relation between personality traits is context dependent. These results are discussed in the perspective of the adaptive significance and maintenance of personalities.