Reactions of Grey Herons (Ardea cinerea) to seismic tremors

Abstract

Earthquakes are usually a matter of seconds and while experiencing the phenomenon few observe the behaviour of the animals during the phenomenon. On 22 November 1995, at 06:16 hrs Israel Standard Time, an earthquake of a magnitude (Mw) of 7.2 on the Richter scale shocked Eilat, Israel. I first observed unusual behaviour at about 06:00 hrs when flocks of several avian species flew north. Also, a flock of about 50 Grey Herons (Ardea cinerea), that roosted on the salt pans, became increasingly restless and eventually took to the air at 06:08 hrs. Our primary objective was to describe the sensitivity exhibited by the flock of Grey Herons to the tremors which continued to occur for weeks after the initial shock. Observers remained at the salt pans for a week after the initial shock and noted if flock members displayed any physical discomfort (e. g., shaking wings, jumping or hopping without lift off) during the day, and prior to flying off, owing to no reasonable disturbance. Subsequently, the Seismology Division, Institute for Petroleum Research and Geophysics supplied data of tremors recorded for the same period. A total of 37 tremors of Mw=3.9 or more were recorded. Majority of the tremors were Mw=4.1, but an equal number of 4.4 and 4.5 combined were also recorded. Grey Herons reacted at all levels, although they appeared to ignore some tremors that were less than Mw=4.2. However, the Herons took to the air when tremors were stronger than Mw=4.3. Human observors partially felt tremors between the magnitudes of Mw=4.1 to 4.4, but all stronger tremors were felt. One of the interesting and consistent observations was that the birds showed the first signs of restlessnes about 30–60 seconds prior to the human observors ability to feel the tremors.