Heart and ventilation rate changes during tonic immobility in Ornate Tinamou (Nothoprocta ornata) and High Andean chicken (Gallus gallus) compared to Chilean Tinamou (Nothoprocta perdicaria)

Sammanfattning: Animals can show different responses to fear for example by playing dead when there is no possibility to escape. This response is called tonic immobility (TI) and is a well-established test of fear to evaluate fearfulness. Long durations of TI are generally considered as high levels of fearfulness. Physiological changes observed during tonic immobility suggest that there are changes in the autonomic nervous system (ANS) strongly involved in this process. The main objective for this study was to analyse duration of tonic immobility and heart and ventilation rate during tonic immobility in three different species; domesticated High Andean chickens (Gallus gallus), wild-caught Ornate Tinamous (Nothoprocta ornata) and Chilean Tinamous born in captivity (Nothoprocta perdicaria). In this study needle electrodes were used to measure heart and ventilation rate. The time following induction of tonic immobility (i.e. after holding the bird on its back for 15 s) was characterized by a large increase in heart and ventilation rate. During tonic immobility a progressive decrease in heart and ventilation rate was observed in all species, significant in all cases except for heart rate between start and end of TI in chickens. The duration of TI was significantly longer in Ornate Tinamou compared to Chilean Tinamou and chickens. The same was observed in latency to first head movement. TI is probably controlled by the autonomic nervous system, but a heart rate variability analysis has to be done in order to determine the different relative contributions of the sympathetic and parasympathetic systems in these species.