Evidence of dominant parasympathetic nervous activity of great cormorants (Phalacrocorax carbo).

The characteristics of autonomic nervous activity were examined on captive great cormorants Phalacrocorax carbo hanedae, using a power spectral analysis of heart rate variability. Heart rates were calculated from recordings of the electrocardiograms of the birds via embarked data loggers. We investigated the effects of blockades of the sympathetic or parasympathetic nervous systems using the indices of autonomic nervous activity such as high frequency (0.061-1.5 Hz) component, low frequency (0.02-0.060 Hz) component and the low frequency power component to high frequency power component ratio. Resting heart rate (85.5 +/- 6.1 bpm) was lower than the intrinsic heart rate (259.2 +/- 15.3 bpm). The heart rate drastically increased after the injection of the parasympathetic nervous blocker, on the other hand it slightly decreased after the injection of the sympathetic nervous blocker. The sympathetic, parasympathetic and net autonomic nervous tones calculated from heart rate with and without blockades were 40.9 +/- 27.6, -44.5 +/- 7.4 and -29.5 +/- 9.0%, respectively. The effect of the parasympathetic nervous blockade on low frequency and high frequency power was greater than that of the sympathetic nervous blockade. Those data suggested that the parasympathetic nervous activity was dominant for great cormorants.