“The overflight produced a noise that was even impressive to the human observers.” The overflight in question was that of a low-flying Chinook helicopter. It was participating in a recent experiment which was attempting to answer the question ‘Do goats get stressed-out by low-flying helicopters?’ To find out, a group of Dutch investigators exposed five goats not only to a screened animations of a helicopter with accompanying sound effects, but also to a real-world ‘overfly’ by a Chinook at an altitude of just 50m – producing a peak noise level of 110dB.
Results: “The goats reacted alert to the visual and/or acoustic stimuli that were presented in their room. They raised their heads and turned their ears forward in the direction of the stimuli.” None* of the goats, however, displayed any appreciable stress responses, or increased emotional reactivity – even with the Chinook flyover.
Conclusions : “In line with studies performed with other ruminants, goats may be quite resistant to the effects of intense, adverse visual and acoustic stimuli such as the sight and noise of overflying helicopters.”
‘Physiological and behavioral reactions elicited by simulated and real-life visual and acoustic helicopter stimuli in dairy goats’ is published in BMC Veterinary Research 2011, 7:16
 *Though apparently unstressed, one goat did make an attempt to escape.
 The research was commissioned and sponsored by the Royal Netherlands Air Force (RNLAF).
(Thanks to investigator Philip Dröge for drawing out attention to the research)