Studying the Algarve's amphibians

Perezi’s Frog

Amphibians (frogs and toads, newts and salamanders) require moist conditions and freshwater to breed in. Consequently, Mediterranean climates, with their long hot and dry seasons, present them with a great challenge. Nevertheless, amphibians do occur in these areas where damp places with freshwater exist such as around ponds, lakes or streams. This localised existence means, however, that they are very vulnerable and entire populations or even linked populations can be easily wiped out by development or by water pollution (for example by agricultural chemicals). Amphibians are made more susceptible to environmental threats by the fact that they are all too easy to overlook; they are often inconspicuous and generally nocturnal.

Torchlight surveys

The Alvor Estuary area of Portugal, where A Rocha has its field centre at Cruzinha, is rich in amphibians and over the years, twelve species have been recorded: two species of salamander, two species of newt, four toad species and four species of frog. Yet regular systematic surveys of amphibians have not been undertaken so far. In March 2003, Alan Preece carried out the first amphibian surveys in the area, partly to see how any such regular systematic surveys might be undertaken in future. Amphibians were surveyed using the "torchlight technique," checking potentially suitable water bodies with a high-powered torch shortly after sunset. Nine water bodies, including ponds, ditches and large puddles, were surveyed. The amphibians found were recorded and the salinity and temperature of the water measured at each locality.

The three species which were found during these surveys were Perezi's Frog (Rana perezi), the Natterjack Toad (Bufo calamita) and Bosca's Newt (Triturus boscai).

Perezi's Frog (formerly classified as the Marsh Frog) occurs across the Iberian peninsula and into the south of France. On the survey, it was seen in four of the ten water bodies, often in some numbers. It appears to be common in the Alvor area and even when it could not be seen, its calls could be heard. This species can apparently utilise most types of water available, and was even present in water that was brackish. The survey period (14-18th March) appeared to be part of the breeding period for this species as a pair were found clasped together ("in amplexus") indicating imminent spawning.
The Natterjack Toad has a distribution across western and central Europe, occurring throughout Portugal. It was widely heard calling and was found in shallow puddles on a night following rainfall where it too was seen breeding. The Natterjack Toad has a specialised reproductive strategy that relies on such short-lived pools.
Bosca's Newt is similarly widespread across Portugal, but is otherwise found only in western Spain, being endemic to the western Iberian Peninsula. A single specimen was found in a ditch.

Future work

Surveying amphibians effectively is difficult. Amphibians are most easily found in the breeding season when they tend to be more visible and are present in suitable water bodies in higher concentrations than at other times.

The "torchlight technique" is fairly effective but suffers from two problems: torchlight surveys of heavily vegetated sites are relatively unproductive, and the charge on the high output torches that are used has a limited life which reduces survey time. Studying the calls that frogs and toads make, particularly during the breeding season, can help in defining their abundance and location. Each frog and toad species has a specific call and can be identified on this basis. During this study, Natterjack Toads were successfully identified and located at a distance of at least 500 m. Unfortunately, newts and salamanders are silent and cannot be located this way.

One other way of determining what species of amphibians are present, and one that works outside the breeding season, is to identify their refugia. Refugia are those protected sites, often under the cover of rocks and logs in shaded and damp areas, where amphibians can survive the hot, dry summer of the Algarve. Searches of refugia do however pose problems; at best, valuable microhabitats are disturbed and at worst they, or the animals they contain, are destroyed. Good environmental practice dictates that if refugia are disturbed by their covering rock or log being lifted up, this should be done in such a way that the cover can be restored to exactly where it was. Any animals found underneath the cover should be removed before it is replaced to avoid being crushed and should then be released next to the refugia so that they can rebury themselves safely. Care should also be taken during refugia searches as they may also contain venomous animals such as snakes or scorpions.

The next step in any systematic study of amphibians in the Alvor Estuary area will be to prioritise those water bodies that are amphibian rich so that they can be regularly studied. This will be done by eliminating the higher salinity water bodies and highlighting preferred breeding sites by mapping frog and toad calls and noting the presence of egg chains and clumps ("spawn").

Studying amphibians poses particular problems; yet, if a case is to be made for the preservation of these creatures in an area, then as much as possible about their abundance and diversity needs to be known.

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Alan Preece can be contacted at adpreece@lineone.net More details on the amphibians of the Alvor area can be had from A Rocha Portugal: portugal@arocha.org