A Frog at Butrint in southern Albania: What was it?

Enjoying the archaeological site at Butrint—Greek settlement, Roman city, bishopric, Byzantine and then Venetian, but abandoned in the late Middle Ages—at the southern tip of Albania, greater treats of a herpetological kind were in store. The flooded basements of the ruined buildings are home to two of the three species of terrapin in Europe, the European Pond Terrapin (Emys orbicularis) and the Balkan Terrapin (Mauremys rivulata). In another ruin we spotted a frog—the frog shown in the photograph. At the time (April 2010) I looked it up in the 2nd edition of the Collins Field Guide (2002 and 2004, London: Collins) and wrote it down as a Greek Marsh Frog, Rana balcanica, found in southern Albania, southern Macedonia, south-western Bulgaria and Greece. Nick Arnold, the book’s author, noted though that this species is also known as Rana kurtmuelleri and ‘sometimes not regarded as distinct from Marsh Frog’, i.e. Rana ribibunda.

Frog photographed in the archaeological site of Butrint, April 2010

Since the early 2000s the water frogs have been moved into their own genus, Pelophylax. Therefore the Marsh Frog became Pelophylax ribibundus. The specific name balcanica for the Greek Marsh Frog aka Balkan Water Frog has also gone in favour of P. kurtmuelleri because P. balcanica was quickly determined to be the same species as that described by Gayda in 1940. Gayda’s name had priority. According to the The Eponym Dictionary of Amphibians (Beolens, Watkins, Grayson, 2013, Exeter: Pelagic Publishing) nothing seems to be known of who Kurt Müller was except that he collected the holotype in Albania in 1938.

But is P. kurtmuelleri a valid species, distinct from Marsh Frog, P. ribibundus? One group has contended that it is not, and seeing one member of that group was a main author of the Field Guide to the Amphibians & Reptiles of Britain and Europe (Speybroeck, Beukema, Bok van der Voort, London: Bloomsbury) which was published in 2016, it not surprising that the species is not listed other than to note it had been lumped into Marsh Frog.

However, in fact, lots of others have retained P. kurtmuelleri as a valid species. A key example is the influential Amphibian Species of the World. That site contains a very brief summary of, and a link to, each paper that has appeared on the species. For that reason, I am not providing a list of sources at the end of this article.

I find it very difficult to decide on the basis of current evidence who is right since the status of the water frogs of south-east Europe and south-western Asia is both confused and confusing. However, I am disquieted by those who dismiss studies other than those obtained using the limited analysis of mitochondrial DNA (in this particular case they are those lumping the Balkan Water Frog into Marsh Frog) while dismissing biological evidence which could indicate the Balkan Water Frog should be split from Marsh Frog.

It was Schneider, Sinsch and Sofianidou in 1993 who proposed that their balcanicus, later recognised as kurtmuelleri, should be recognised as a species distinct from the more northerly ribibundus. The grounds for the split was biological evidence: the mating calls of the two forms were different. This is part of the summary of their paper:

The mating call of the lake frogs from Thrace resembles in all parameters that of the Rana ribibunda in the terra typica restricta (Guryev, CIS). Accordingly the lake frogs of eastern Greece belong to R. ridibunda. The mating call of these lake frogs consists of 20 pulses/pulse group and of 7 pulse groups/call on the average. Most of Greece is inhabited by the second taxon, Rana balcanica sp. n. [P. kurtmuelleri] Its mating call is characterized by 27 pulses/pulse group and 4 pulse groups/call on average.

In addition to the analysis of the mating calls, small but statistically significant differences were evident in morphological features when the measurements they made were subjected to discriminant analysis.

One bit of possible evidence to suggest the Balkan Water Frog is a valid species was raised by Schneider and his colleagues. In the early 1980s some work had been done on crossing Marsh Frogs proper with water frogs from what was then southern Yugoslavia, which, they suggest, were in all probability, Balkan Water Frogs. The resulting tadpoles had a high mortality and those that few that did survive to maturity, a low fertility, both indicative of hybridisation between two, rather than within one, species.

Overall, as a ‘lumper’ I can see why the ‘splitters’ have a case in recognising the Balkan Water Frog, Pelophylax kurtmuelleri, as a species, even though even more research is still required.

But back to Butrint in 2010. Was the frog I photographed a Balkan Water Frog? There is another species of Pelophylax living in the southern tip of Albania, the Epirus Water Frog, P. epeiroticus. Both species are highly variable in appearance and hybrids between the two have been found. The Epirus Water Frog was only described (by essentially the same group that described balcanica (kurtmuelleri)) in 1984. A group of Slovakian and Czech zoologists have illustrated the differences in morphology and particularly in coloration within and between the species of water frogs that occur in the south-western Balkans. Looking at the photographs and reading the distinguishing features, it appears to me that the frog in my photograph (not ideal because of the reflections obscuring the tympanum) shows characteristics of the Balkan Water Frog, P. kurtmuelleri. The habitat preferences of the Epirus Water Frog (which is apparently common on the edges of the nearby Lake Butrint) given in the 2016 Field Guide also indicate that the flooded basement of an ancient building are not likely to be inhabited by P. epeiroticus. 

I thought a second visit to Butrint, this time in 2017 and also in mid-April, would afford me another look at the frogs within the archaeological site. The terrapins were there but not a frog to be seen. The area I had seen the frog in 2010 was nearly dry but for one corner which had a lot of large tadpoles.