Kythnos & Kea, 20.-28.04.2023

For us, springtime means Aegean time: This year, we headed for the two Western Cyclades islands Kythnos and Kea. Although situated close to the mainland, these islands haven’t been visited by herpetologists too often. Our most recent literature was a survey by GRILLITSCH & TIEDEMANN (1984), a paper by CATTANEO (1990) on snakes and a publication of BROGGI (2021) on the semi-aquatic herpetofauna of Kythnos. In particular, we were interested to see the local subspecies of Podarcis erhardii (Aegean Wall Lizard) on Kythnos, as so far, we had hardly seen pictures of these Lacertids. The neighboring island of Kea however is supposed to have no Podarcis at all – and we wanted to check this.

On Google Earth, Kythnos and Kea look quite similar – but they are strikingly different: Kythnos is a barren, treeless island which had been cultivated extensively for barley fields. Abandoned terraces, drystone walls and ancient donkey trails are witnesses of this agricultural past. Nowadays, there is hardly any farming at all on the island – off-season it is a lonely and very silent place.

In contrast to this, Kea is a remarkably green island with the mountains overgrown by beautiful oak forests (Quercus macrolepis). This island seems to be a popular weekend destination for people from the Athens area: This caused a (not always beautiful) construction boom with holiday houses spreading over the coastal hills. Water consumption on the island seems to be high; at least all brooks and wetland places described in literature were completely dry.

From a geological perspective, Kythnos is a part of the western Cyclades Island chain, separated from Greek mainland by roundabout 400 m water depth. In contrast to this, Kea is an appendix of the mainland with water depth of only about 100 meters to adjoining Attica, but almost 400 meters to Kythnos. This results in significant differences in the specific herpetofauna of both islands.

Here is what we found on these islands.

Kythnos has the reputation of a notorious windy island and this held true but we also enjoyed some warm sunny afternoons. As described above, Kythnos in spring has something of lost place – which creates a magic atmosphere but makes herping difficult sometimes: The old trails are completely overgrown by thorny scrub. The steep hills and valleys are pathless. Not a beginners’ island!

Anyhow: Out of 12 species which have been reported from Kythnos we came across 9. The most abundant reptiles are Podarcis erhardii and Mediodactylus kotschyi, of course. Furthermore, Chalcides ocellatus seems to be widespread on the island, although it is rather secretive. Lacerta trilineata seems to be widespread but usually in low numbers. Hemidactylus turcicus was found under stones (not photographed).

Regarding the semi-aquatic herpetofauna we came across Pelophylax kurtmuelleri and Mauremys rivulata at several places – even at some new and so far undescribed sites. As large parts of the valleys are hardly accessible, additional stations can be supposed. Furthermore, there also have been records of Bufotes viridis in the past. However, we didn’t find this species – although its existence on the island still seems likely. 

The only snakes seen were Telescopus fallax and Dolichophis caspius. Other snake species which have been reported for Kythnos are Zamenis situla and Platyceps najadum (requires confirmation).

The westernmost Cyclades Island has – according to literature – no Podarcis erhardii. And to make it short: This seems to be true. But the situation is even worse: In their review, TIEDEMANN & GRILLITSCH noted that also Mediodactylus kotschyi seems to lack on Kea, and we didn’t see this species as well. So, the most abundant reptile is Chalcides ocellatus which inhabits the island from the beaches to the mountain tops. Lacerta trilineata occurs on Kea, but only in small numbers and rather local. It is a strange experience exploring a presumably perfect lizard habitat without noticing the noise of a any lizard escaping into the vegetation. An empty island!

As we only had two days on Kea, we cannot exclude the hidden existence of Podarcis erhardii on the island, but it seems rather unlikely. This circumstance gives another indication that – in biogeographic terms – Kea is no Cyclades Island but a part of the mainland (at the adjoining Attica coast, Podarcis erhardii also does not occur).

In their review, TIEDEMANN & GRILLITSCH mention that Podarcis erhardii occurs on Spanopoula, a rock off the Kea north coast. However, the authors didn’t collect any specimen and it is not known if these lizards belong to the mainland or the Cycladic form of Podarcis erhardii. Unfortunately, due to strong wind, this island was inaccessible during our stay.

Given the absence of small lizards on Kea it is surprising that the island is populated by at least five snake species: TIEDEMANN & GRILLITSCH mention Platyceps najadum, Elaphe quatuorlineata, Telescopus fallax and “Coluber sp.”. The latter one refers to a sighting in 1935 which they interpret as Hierophis gemonensis. This seems doubtful however, and possibly “Coluber sp.” refers to Zamenis situla, which also occurs on the island (DUSEJ, 1986). Furthermore, CATTANEO reports the occurrence of Natrix natrix. During our short stay, we saw Zamenis situla as well as Elaphe quatuorlineata. 

Phenotype:

The Kythnos Wall Lizards have been described as subsp. thermiensis. Males show greenish backs and brownish flanks. The specific characters of the Kythnos population are black-spotted throats and the fact that the dark markings on the flanks tend to be heavier and more extensive as on other islands. Furthermore, males may show rows of blue ocelli on flanks or large blue spots on shoulders. Anyhow, we believe that these characters are within the variability range of Podarcis erhardii on other Western and Central Cyclades. Hence, in terms of coloration and pattern they represent “typical” Cyclades Wall Lizards.

Given that, the most surprising fact is that the lizards on Kythnos significantly differ from their closest relative on neighboring Serifos, Podarcis erhardii erhardii with its prominent yellow coloration. Instead, the Kythnos lizards resemble Podarcis erhardii mykonensis, as it can be seen on Mykonos or Andros.

This illustrates that

A) the current subspecies nomenclature doesn’t make much sense and

B) genetically closely related populations may have significant phenotype plasticity.

Another example for such phenotype plasticity is the throat color: The majority of the Kythnos lizards has white throats (with black spots), but about 10% show orange throats. It appears that such orange throated specimens only occur in the rich, humid habitats (close to brooks or wetlands). Hence, it could be assumed that throat color in this case is determined rather by environment conditions (such as food resources), not by genetics.

Behavior:

Unlike other island populations (such as Serifos or Andros), Podarcis erhardii on Kythnos is rarely seen in pairs (we only noticed one pair basking together on a stone). Also, the copulation efforts we observed were rather violent and didn’t indicate familiarity between the mating partners (see pictures in this report). However, we do not know the reason for such different behavior patterns on the respective islands. In case of Kythnos and Serifos these differences are particularly remarkable, as these islands are quite similar in habitat conditions and population density. As both populations are closely related, it appears that genetics have a minor impact on social behavior of these lizards. This could be an interesting field for future research.

Broggi, M. F. (2021) - The decline of the herpetofauna populations related to open water resources on Aegean islands using the example of Kythnos: Biodiversity Journal, 2021,12 (4): 825–831

Cattaneo, A. (1990) - I serpenti delle isole greche di Kythnos e Kea (Cicladi occidentali).: Att. Soc. ital. Sci. nat. Mus. civ. Stor. nat. Milano 131(11): 209 – 219

Dusej, G. (1986) - Zum Vorkommen der Leopardnatter Elaphe situla (Linnaeus 1758) auf Kea (NW-Cycladen).: Salamandra 22 (2/3): 213-214

Grillitsch, H., Tiedemann, F (1984) - Zur Herpetofauna der griechischen Inseln Kea, Spanopoula, Kithnos, Sifnos, Kitriani (Cycladen), Alonissos und Piperi (Nördliche Sporaden).: Annalen des Naturhistorischen Museums in Wien – 86B: 7 - 28.