Recently, I was told something about Sardinian Warblers (Sylvia melanocephala) pushing the endemic Cyprus Warblers (Sylvia melanothorax) out of some of their range here in Cyprus in recent years. That could be a big deal, with Cyprus Warblers which have such a restricted range to begin with, even if they are currently listed as a species of Least Concern. So, naturally, I took the time to look into it and find some more concrete data on the warblers and their population changes.
I dug up a paper by Derek Pomeroy and Frank Walsh in The Oryx (2002), A European endemic warbler under threat? Population changes in Sylvia warblers on the island of Cyprus. The abstract:
In the early 1990s the Sardinian warbler began nesting in Cyprus, and now has two breeding populations, in the west and north of the island. Observations of the western population show that its range is still expanding and that the endemic Cyprus warbler has declined in the areas colonized by the Sardinian warbler. However, the Cyprus warbler is still present in most of these areas, and hence, although the Cyprus warbler is a species of European Conservation Concern, the current situation requires further study rather than alarm. The Sardinian warbler is the more numerous species at lower altitudes, whilst the Cyprus warbler is more common at higher altitudes, especially above 500 m. Within their areas of overlap, both Cyprus and Sardinian warbler populations occur throughout almost all habitats; natural, semi-natural and agroecosystems. We recommend that monitoring should continue, with more detailed ecological studies.
Comments after reading the paper:
To start with, I’ll just get my naiveté out of the way, by saying I didn’t know that Sardinian Warblers only started breeding in Cyprus in the early 1990s. Prior to then, they were only winter visitors, even though they had been breeding successfully throughout the Mediterranean basin. That was genuinely new info for me, and interesting to learn.
The paper has a couple original findings that they described in the abstract, quoted above. Most importantly, the authors describe how data and personal observations suggest that the species are not in direct competition. It does not appear clear whether they are choosing different habitat features, or using the same resources. They note however the “almost total absence of detailed information on the foods of the two species.
The article’s discussion is also very interesting for its analysis of documented shifts in biogeography of other Sylvia warblers in the Mediterranean basin. For instance, the observed replacement of Balearic warblers (S. sarda balearica by Dartford warblers (Sylvia undata), driving the former to local extinction on Menorca within five years of the first reported breeding of Dartfords there (1975).
They also mention the near total replacement of Spectacled warbler (Sylvia conspicillata) by Sardinians on Malta, albeit in a much less abrupt shift. While the first breeding Sardinians may have occurred in 1884, it was not until 1981 that Spectacled warblers experienced a drastic decline, and they are now very rare on Malta.
The Malta instance is seen as a possible outcome in Cyprus with Cyprus warblers and maybe Spectacled warblers at some later time. Although the population changes don’t appear to be due to direct competition, it is still possible that the extremely generalized Sardinian warblers will replace the endemic species.
Despite the need for more detailed ecological studies needed to better know what is going on, I have not been able to find any articles published on this topic since 2002, leaving the question unanswered, just how are Sardinian warblers replacing Cyprus warblers in the Western part of the island?
Sardinian Warbler (Wikipedia)
Pomeroy D, Walsh F. (2002) Oryx 36 : 342-348.