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Abstract
Social life is profitable, but it facilitates conflicts over resources and creates interdependence between individuals. Separating highly social animals triggers intense reactions aimed at re‐establishing lost connections. Less is known, however, about behavioural and physiological responses to separation in socially facultative species, where individuals temporarily form groups and may subsequently leave them. Non‐breeding common ravens (Corvus corax) gather in large numbers at feeding and roosting sites, but otherwise spend time seemingly solitary or in small subgroups. We here studied how ravens cope with being socially isolated, and investigated the life characteristics that might explain potential individual differences. For this, we individually separated captive subadult ravens (n = 25) and housed them in physical and visual isolation from their group members across 4 d. During the separation period, we collected behavioural data and measured the amount of immunoreactive corticosterone metabolites from bird droppings to assess the ravens’ physiological stress response. We found behavioural indicators of stress at the start of the separation, when ravens showed higher levels of tension than of comfort – a pattern that reversed at the end of the separation. Furthermore, we found that the upbringing of ravens affected their behaviour during separation. Hand‐raised birds produced more vocalisations in the beginning of the separation, and were less active at the end, while the reverse pattern occurred with parent‐raised ravens. Contrary to our predictions, we did not find differences in hormonal responses between the beginning and end of the separation period or any link between hormonal responses and behaviours. Ravens’ behavioural responses to social separation stress seem to be dependent on their arousal states, although possible links with hormonal reactions remain unclear. Our results show that behavioural reactions are not always linked with hormonal responses to stress, and further emphasise the importance of investigating effects of early‐life experiences.
Highlights
Social life provides animals with many advantages, such as superior protection against predators, more opportunities to acquire information and improved access to resources (Beauchamp 1999, 2013; Galef & Giraldeau 2001; Krause & Ruxton 2002)
Our results show that behavioural reactions are not always linked with hormonal responses to stress, and further emphasise the importance of investigating effects of early-life experiences
We narrowed down the behavioural variables using a principal component analysis (PCA)
Summary
Social life provides animals with many advantages, such as superior protection against predators, more opportunities to acquire information and improved access to resources (Beauchamp 1999, 2013; Galef & Giraldeau 2001; Krause & Ruxton 2002). Stress Response to Social Separation in Ravens disconnection itself can be an adverse experience (Panksepp et al 1978; Cole et al 2015) with potentially harmful consequences (Cacioppo & Hawkley 2003; Cacioppo et al 2011), including for example neuropsychiatric disorders (Fone & Porkess 2008; Colonnello et al 2011; Normansell & Panksepp 2011), cardiovascular disease (Grippo et al 2007a), neuroendocrine disruptions (Grippo et al 2007b), suppressed immune responses (Scotti et al 2015) and even shorter lifespans (Ruan & Wu 2008) It is no surprise that separation from group members is a strong aversive stimulus which triggers a cascade of psychological, physiological and behavioural changes (Panksepp 1998, 2005, 2011; Brunelli & Hofer 2007) priming an individual to re-establish connections with the group (Gamallo et al 1986; Mendoza & Mason 1986; Jones & Harvey 1987; Feltenstein et al 2002; Apfelbeck & Raess 2008). It is essential to understand what the reactions to being separated are in order to improve the accuracy of experimental data
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