Meeting Abstract
The fight-or-flight response is a highly conserved stress response in vertebrates that occurs via the autonomic nervous system: a decrease in parasympathetic (PNS) activity, which promotes self-maintenance ‘rest and digest’ processes, and an increase in sympathetic (SNS) activity, which prepares an animal for danger. The PNS and SNS mostly act on different parts of the body (though the heart is innervated by both) and can be regulated independently, yet until now, most studies of autonomic stress responses in non-model species focused only on the SNS response. We used non-invasive external electrocardiogram loggers to quantify heart rate (HR) and heart rate variability (HRV) indexes that reflect PNS and SNS activity in the streaked shearwater (Calonectris leucomelas), a pelagic seabird. We quantified PNS and SNS responses to the stress of handling, and during recovery in the nest burrow. We show for the first time in a free-living animal that the fight-or-flight response was mediated primarily by a rapid decrease in PNS activity with only a short and small increase in SNS activity. Individuals consistently differed in their fight-or-flight responses within and across years. Birds with a lower body mass index had higher PNS activity and lower HR suggesting that birds with lower energy reserves may maintain high PNS activity to minimise energy expenditure. Using HR and HRV to measure autonomic activity is an effective non-invasive method for studying stress physiology in free-living animals.
