Orienting and freezing responses in incubating ptarmigan hens.

Behavior studies and telemetric recordings of heart and respiration rates were performed on five wild and two captive, incubating, willow ptarmigan hens (Lagopus lagopus lagopus) and on four wild, incubating, Svalbard ptarmigan hens (Lagopus mutus hyperboreus). Sounds and sight of approaching humans, egg predators, or dogs near the nests elicited behavior in the hens which we have interpreted as an orienting response (OR) followed by freezing behavior. During both types of behavioral responses, heart rate was reduced from 204 +/- 39 (mean +/- SE) to 119 +/- 26 beats per minute and respiration from 25 +/- 2 to 12 +/- 3 breaths per minute. In wild incubating willow ptarmigan, further approach led to tachycardia and increased respiration. Some birds maintained freezing behavior, while others became restless before flying off. Two of the four incubating Svalbard ptarmigan hens showed the OR followed by freezing behavior accompanied by decreased heart and respiration rates. The other two birds showed flight response, restless behavior accompanied by increased heart and respiration rates. Flight behavior was also typical for willow ptarmigan incubating in captivity. Repeated auditory provocation of incubating hens caused progressive decrement in behavioral and cardiac responses that is interpreted as habituation of the OR.