Biologists from the University of California, Los Angeles, Peter Narins and Sebastiaan Meenderink recorded the mating calls of male coquis along a 13-kilometre transect up the side of El Yunque mountain that took in a wide altitudinal gradient. They then compared these with similar recordings along the same altitudinal gradient obtained 23 years earlier. The results showed that at any given altitude, the call has become shorter and higher pitched.
The pair also compared the physical attributes of 116 male coquis caught in 2006 with those of 170 males caught in 1983 along the same altitudinal gradient. The results indicated that frogs from comparable altitudes are more than ten per cent shorter in length than they were 23 years earlier.
According to the biologists, the observed differences are consistent with a shift to higher elevations for the population. Their results showed, for example, that in 2006, the pitch of the ‘qui’ part of the males’ call was comparable to that of counterparts that lived 83 metres downslope in 1983. ‘If current trends continue unabated, the coqui frog will sound and look quite different before this century is over,’ Narins added.
This story was published in the June 2014 edition of Geographical Magazine