The September-October 1997 seismic sequence in the Umbria-Marche regions of Central Italy has been one of the stronger seismic events to occur in Italy over the last thirty years, with a maximum magnitude of Mw = 6.1. Over the last three years, a collection of evidence was carried out regarding non-seismic phenomena, by interviewing local residents using a questionnaire. One particular observation of anomalous animal behaviour, confirmed by many witnesses, concerned a herd of cows, which descended from a mountain close to the streets of a village near the epicentre, a few days before the main shock. Testimonies were collected using a specific questionnaire including data on earthquake lights, spring variations, human diseases, and irregular animal behaviour. The questionnaire was compiled after the L'Aquila earthquake in 2009, and was based upon past historical earthquake observations. A possible explanation for the cows' behavior-local air ionization caused by stress-activated positive holes-is discussed.
Keywords: air ionization; animal behaviour; cows; earthquakes; positive holes.