In 1992 the Sardinian Warbler was first recorded breeding in Cyprus. Since then, survey results from Paphos District suggest that the endemic Cyprus Warbler population has declined, while the Sardinian Warbler breeding population has increased and expanded in Paphos District.

Colour-ringed Cyprus and Sardinian Warblers were observed during 2003 to 2005 breeding seasons on seven scrub study plots located across Paphos District. Both species appeared to establish home-ranges without reference to the other species, resulting in considerable interspecific home-range overlap. A playback experiment indicated that Cyprus Warblers reacted equally strongly to conspecific and congeneric song in areas where the two species coexist, but less strongly to congeneric than conspecific song in areas where Sardinian Warblers did not yet breed.

The vegetation composition of Cyprus and Sardinian Warbler home-ranges was very similar. There was no indication that the species competed for nest sites.

Cyprus and Sardinian Warbler have similar breeding biology; they laid similar sized first clutches and had similar chick output per pair for first nesting attempts. However Sardinian Warblers had a higher frequency of second nesting attempts and this resulted in a higher chick output per pair per year than was achieved by Cyprus Warblers. In both species total chick output per year was higher for pairs that nested early. Nest survival was similar for the two species.

Cyprus and Sardinian Warbler diets were very similar. Body condition of both species’ chicks was higher earlier in the breeding season. Cyprus Warblers had higher productivity but lower chick body condition in the zone where their population has declined than in the zone with fewest breeding Sardinian Warblers. Productivity was positively related to arthropod biomass available on different plots for Sardinian Warbler, but not for Cyprus Warbler. There was no evidence of a negative impact of either species on the number or condition of nestlings produced by the congener.