We don’t just mate. We are earthquake indicators too.

The next time you take a walk in San Ruffino Lake, Central Italy, and saw toads around, relax, enjoy the beautiful scenery and be rest assured that you won’t experience any earthquake while you are there.

Dr Rachel Grant of the Open University in UK was carrying out a daily observational study on the behavior of common toads, Bufo Bufo, in San Ruffino Lake, a common breeding site for them, when she observed unusual toad breeding behaviors. This happened around the time when an earthquake struck L’Aquila, Italy, in 2009. There were no clues as to how the toads sensed the impending earthquake but the population declined by 96% in the breeding site 5 days before the earthquake occurred. The lake is situated 74.29 Km away from the earthquake epicentre.

spawningBufo Bufo is usually found on land and, only during their breeding season, in water bodies such as ponds and lakes. There are usually more males than females in the breeding sites and competition to pair with females occur. Males will grab the opportunity to cling on to the back of a female that is heading towards the breeding site (as can be seen from the 1st picture). Those who fail to find an available female will attempt to displace the attached male (shown in the 2nd picture).
FIGHT!!

The successful pair will proceed to the spawning sites where spawning occurs. The males usually hang around after his first spawn and attempt to carry out subsequent mating with another female during the entire breeding season. The success rate is usually very low due to the competition for females.

View normal Bufo Bufo spawning behaviour here.

What was unusual for the toads in San Ruffino Lake was that it was in the midst of the spawning period and the number of breeding pairs suddenly dropped to zero 3 days before the earthquake. There were very little breeding pairs from the period of the earthquake to the last aftershock. Fresh spawns were only observed 6 days before the earthquake and 6 days after the last aftershock. No fresh spawn were observed in the period before the last aftershock, meaning that no breeding took place at all.

The most probable reason for the decline in population was that the toads were fleeing to higher grounds for safety, to prevent themselves from being killed by falling objects. There were various speculations about how the toads detect the impending disaster but there are no existing concrete evidence for support.

This amazing observation which happened to take place during the period of a natural disaster shows us how intricately life is linked to the environment. Having this knowledge at the back of our minds, keep a look out for toads in spring, if you happened to be in Europe, and be thankful to have this natural earthquake indicator around you.

References:

To-be-published journal:
“Predicting the unpredictable; evidence of pre-seismic anticipatory behaviour in the common toad,” by R. A. Grant & T. Halliday. The Zoological Society of London, 31 Mar 2010. URL: http://www3.interscience.wiley.com/journal/123337858/abstract

Journal:
N. B. Davies & T. R. Halliday, 1979. Competitive Mate Searching in Male Common Toads, Bufo Bufo. Animal Behaviour, 27, 1253-1267.

Article:
Toads can ‘predict earthquakes’ and seismic activity, by Matt Walker. BBC News, 31st March 2010. URL: http://news.bbc.co.uk/earth/hi/earth_news/newsid_8593000/8593396.stm (accessed on 5th April 2010).

Photographs:
“Mating Toads” by nutmeg66. Flicker, 25th March 2009. URL: http://www.flickr.com/photos/rachel_s/3385386089/ (accessed on 8th April 2010).

“Common toads (Bufo bufo) in amplexus” by nutmeg66. Flicker, 25th March 2009. URL: http://www.flickr.com/photos/rachel_s/3385386087/ (accessed on 8th April 2010).

Video:
“Common Toads in their spawning lake” by slaphed. YouTube videos, 25th March 2010. URL: http://www.youtube.com/watch?v=rlNz87LTj4s

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