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The effects of stress last for life in birds

16 March 2009 Society for Endocrinology

Researchers have discovered the first direct evidence that exposure to stress in young birds affects the way they react to stress when adult.  This research, presented at the Society for Endocrinology BES meeting in Harrogate, greatly improves our understanding of how the environment during development influences birds’ subsequent physiology, health and survival. 

Exposure to stressful events soon after birth has significant effects on a range of physiological and behavioural responses later in life.  Previous work in mammals has been unable to work out whether this is due to raised stress hormone levels produced by the young or raised stress hormone levels in the mother, transmitted to her offspring through lactation.  To overcome this problem, a team led by Dr Karen Spencer at the University of Glasgow used a bird species, the zebra finch, as a model to study the effects of stress in early life.  In birds, there is no possibility of hormone transfer between the mother and offspring after egg laying. 

The researchers took 34 12-day old sibling pairs of zebra finch chicks.  They simulated a stressful situation by giving one chick from each pair the hormone corticosterone (dissolved in peanut oil) for 16 days.  Corticosterone is the main hormone produced by birds in response to stress.  It causes many changes in behaviour and physiology, helping the bird to cope with stressful stimuli.  The other chick (the control) was just given peanut oil.  When adult (60 days old), all birds were exposed to a stressful situation and researchers measured the amount of corticosterone they produced naturally in response.

Birds exposed to higher corticosterone levels as chicks showed different physiological responses to stress when adult.  When presented with a stressful situation, they showed a larger (p=0.008) and more prolonged (p=0.03) corticosterone response than control birds.  There was no difference in the corticosterone levels of the two groups when resting.  

This study shows for the first time that direct post-natal exposure to raised stress hormone levels can have long term consequences for birds’ physiological stress responses.  In the wild, conditions that cause stress during early life include inclement weather conditions, lack of food and exposure to parasites.  This research suggests a potential mechanism for why this early stress can alter animals’ behaviour and physiology when adult.  Further research is now needed to examine how these changes are related to birds’ long-term health and survival.

Researcher Dr Karen Spencer said:

“Early exposure to stress hormones is known to affect later responses to stressful situations in the adult.  Using the zebra finch as a model provides us with an important tool with which to investigate the role of stress hormones on adult characteristics.  Our results show an individual’s stress response can be re-programmed as a result of post-natal exposure to elevated corticosterone levels.  This indicates that if a bird is exposed to stress early in life, for example through bad weather conditions or lack of food, this has implications for the way it will react to situations throughout its life.  We now want to study how the observed changes in stress hormone response relate to any behavioural changes observed, and in turn to birds’ long term health and survival.” 

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