Amphibians are poikilothermic, which means their body temperature fluctuates with the environment because they lack internal mechanisms to generate heat, like birds or mammals. The rich amphibian community of Peñalara faces low winter temperatures typical of a high mountain area, but we did not really know the extent to which animals endure low temperatures inside their winter shelters.
This question prompted us to insert devices which are capable of measuring and recording temperature for a whole year, under the skin of common toads. To do this, we had the valuable assistance of Dr. Luis María Carrascal, an expert in the study of the influence of environmental temperature on fitness, distribution, abundance and feeding of vertebrate animals.
At the end of the breeding season last year (May-June), we captured some male common toad in three ponds of the park, and implanted the devices capable of recording body temperature every two hours, to accumulate data during an annual cycle. The common frog is the only amphibian species of the Peñalara Massif whose large size allows the insertion of such a device. This year we have been able to return to find the implanted toads and to our relief, all were well, carrying the devices without any problem.
After removing the devices and reading the information they have collected, we were left speechless by the "physiological feat" of these animals during the winter and early spring: they spent more than four months of the year at temperatures between 0.2 and 1.5 °C!
In addition, we have found that the animals of the three different lakes (some very distant from each other), maintain very similar temperatures throughout year, noting the generality of the response of the toads to the temperature, in spite of the environmental heterogeneity of the lakes and that they were only three individuals. On the other hand, in the warmer seasons, body temperature of the toads fluctuates around 15 °C rarely exceeding 20 °C, due to their nocturnal activity and because they select havens where their bodies can retain moisture and they are not overheated by the intense summer sunlight.
This information on the ecology of common toads in Peñalara opens up a whole range of new questions, and helps us to understand the influence of temperature on the development of chytridiomycosis and to infer the possible effect of global warming on their populations, taking into account their thermoregulatory behaviour and therefore improve our ability to better conserve amphibians in our Guadarrama Mountains.