Introduction

Stimuli that pose physical challenges to animals and initiate stress responses through disturbance of physical or chemical tissue parameters are called physical stressors, whilst stimuli that are perceived as a threat following comparison with innate

predispositions or previous experience and initiate stress responses are called emotional stressors (Day et al., 1999; Jankord and Herman, 2008). Stress responses involve activation of the hypothalamo-pituitary-adrenal (HPA) axis and the secretion of glucocorticoids (Selye, 1974). When birds respond to emotional stressors with

activation the HPA axis they also experience fear, and fear can be defined as a state or situation in which an animal is responding to an environmental threat (LeDoux, 1996; Rodrigues et al., 2009). Although fear cannot be measured directly, behavioural

variables considered to be associated with fear can be measured. An animal in a state of fear might express avoidance behaviours, flight or escape behaviours, or assume

immobility postures, such as crouching or freezing (Jones, 1996), and the expression of such behaviours can be measured in controlled tests. These measurements can then be used to infer the degree of fearfulness of animals, where individuals that show

behaviours consistent with higher levels of fearfulness are considered to be in a higher state of fear than individuals that show lower levels of fearfulness. Behaviour tests of fear typically measure responses of subjects to novel or startling stimuli, and two tests commonly used in birds are the novel object and open field tests (Jones, 1996; Miller et al., 2006). Birds that take longer to pass or peck a novel object are considered to have higher levels of fearfulness than birds that take shorter times (Miller et al., 2005). Similarly, silent, inactive birds that defaecate less in an open field test are considered to be more fearful than active birds (Gallup et al., 1976; Jones and Mills, 1983). The tonic immobility test is also widely used as a measure of fear in birds, where individuals more susceptible to tonic immobility induction and with longer durations of tonic immobility are considered to be more fearful (Gallup, 1979; Jones, 1986). Although fear is difficult

to measure, studies of fearfulness in birds are important from animal welfare and

production perspectives, and in relation to understanding personality in animals (Boissy, 1995; Rushen et al., 1999; Carere et al., 2005; Miller et al., 2005; Cockrem, 2007). Corticosterone is the primary glucocorticoid secreted when birds respond to stressors (Carsia and Harvey, 2000), and Japanese quail (Coturnix coturnix japonica) that experienced emotional stressors 0 or 55 min before tonic immobility or open field testing showed higher levels of fearfulness than control quail left undisturbed before behaviour testing (Satterlee et al., 1993; Satterlee and Marin, 2006). These results raise the question of whether or not elevated plasma corticosterone concentrations were responsible for the stressor-induced increases in fear behaviour in these quail. Exposure to an emotional stressor activates neural pathways involved in the generation of stress responses (see Day et al., 1999), whereas treatment of birds with corticosterone does not activate these pathways. Instead, treatment of birds with corticosterone simulates the rise in plasma corticosterone concentrations that occur during stress, and any measured effects on fear behaviour can be ascribed to the actions of corticosterone, rather than the experience of stress per se. The present study was conducted, therefore, to determine if corticosterone is responsible for the stressor-induced increases in fearfulness reported in other populations of quail. Japanese quail were treated with corticosterone at three different concentrations in their drinking water for 21 days. The concentrations of corticosterone were chosen to elevate mean plasma corticosterone in treated birds to within the physiological range for quail. Between day 6 and 17 of corticosterone treatment, the behaviours of treated and untreated birds were measured in the tonic immobility test on two occasions, and in novel object and open field tests. There is evidence that social behaviour in birds is also related to activity of the HPA axis (Jones et al., 2002). The runway test has been used in studies of sociality in birds, where birds that spend more time closer to conspecifics are considered to be more social (Suarez and Gallup, 1983). The behavioural responses of quail in a runway test of sociality were, therefore, also measured in the present study during corticosterone treatment. Blood samples were collected for measurement of plasma corticosterone concentrations, and daily corticosterone intakes were calculated for individual birds, in order to determine relationships between corticosterone and behaviour in tests of fear and sociality in quail.

Avian personalities have been extensively studied, particularly in great tits (Parus major), and can be defined as suites of correlated behaviours that are consistent across different situations and over time (Carere and Eens, 2005; Groothuis and Carere, 2005). Personalities vary along a continuum, but individuals can be classified as having either proactive or reactive personalities. It has been proposed that birds with proactive personalities might be less fearful than birds with reactive personalities (Cockrem, 2007). If birds are to be classified into personality groups on the basis of relative levels of fearfulness, then behavioural responses of individual birds in tests designed to

measure fear should be consistent. In other words, if a bird showed relatively low levels of fearfulness in one behaviour test of fear, then the same bird should show similar levels of fearfulness if it were subjected to the same test again, and it should also show relatively low levels of fearfulness in similar tests. Studies in quail and chickens (Gallus domesticus) have shown that individual birds can consistently express low or high levels of fearfulness in a range of behaviour tests (Mills and Faure, 1986; Jones, 1987; Jones, 1996). In the present study, the effects of corticosterone treatment on the consistency of behavioural responses in quail were investigated by using various statistical analyses to calculate the repeatability of the tonic immobility test, and the reliability of the three behaviour tests of fear in treated and untreated birds.