A stenoecious breeding passerine as indicator of environmental change : the case of ‘Sylvia conspicillata’, Malta

Abstract

It has been widely shown how bird communities in Europe, including the Mediterranean, are sustaining significant declines and processes of biotic homogenisation, especially those that are connected to an agricultural landscape. Nevertheless the monitoring of these same birds as indicators, has become a vital tool in discerning the underlying causes, in an attempt to focus conservation efforts. In Malta, an already species impoverished group of islands, the need for understanding and halting declines is even higher and as yet practically unanswered. By analysing the local population trends of the 'Spectacled Warbler' ('Sylvia conspicillata'), within a context of ongoing environmental changes, this study set out to identify the key impacting factors on this particular species, applicable to a wider array of breeding birds. The species chosen has exhibited its perceived vulnerability to changes, with a significant range contraction in the last decades, making it ideal for such research. The situation presented is far from straightforward, depicting how in modern anthropogenic landscapes bird populations are limited by multiple stressors from dealing with natural limiting factors. One of the noteworthy long term impacts is the loss of valuable low-intensity farmland habitat due to two simultaneous processes: land abandonment of marginal areas and intensification of practices in the more fertile areas. It is moreover shown how the increase in tree planting and in regenerating maquis habitat is limiting the distribution of those birds suffering declines. Euryoecious species on the other hand are benefiting from these changes and seem to be narrowing the niche of the 'Spectacled Warbler'. Therefore, it goes to show that the Maltese Islands require a holistic plan on land-use practices, incorporating agricultural policy, so that stenoecious species are not excluded from any conservation efforts and ultimately that not only alpha diversity increases, but also beta diversity is enhanced.