Eradication of invasive birds from tropical oceanic islands: lessons learned from studies of common mynas Acridotheres tristis

Many tropical oceanic islands host unique taxa that have evolved in isolation from non-indigenous influences. Some of these endemic taxa are now threatened by man-induced changes that include the introduction of predators, competitors, vegetation and seed dispersers. While considerable progress has been made to eradicate alien mammals from islands, methodologies for the eradication of alien birds lag behind. This paper will discuss findings of recent and on-going attempts to develop eradication techniques for common mynas Acridotheres tristis, invasive birds that have been widely introduced on tropical oceanic islands and are suspected of negative impacts on endemic and indigenous fauna and flora. During the course of these studies, features of common myna behavior and demography on small islands have been discovered that can influence preferred control methodologies; these discoveries also highlight the lack of available basic knowledge of alien invasive bird biology at the inception of most eradication attempts. On Denis Island, Seychelles, mensural and age/sex data have been collected from all caught mynas, revealing new demographic information about the population on this small island, and supporting inferences made from indirect information elsewhere. Experiences with different control methods will be described, highlighting their benefits and disadvantages and how these may vary between island types, and possible risks to endemic taxa from their use. These studies have revealed fundamental requirements for the eradication of populations involving hundreds of mynas and will contribute to the further development of appropriate methodologies, but how widely applicable they will be for other invasive bird species remains to be determined.