The dynamics and conservation of a spatially subdivided avian population in a fragmented landscape

Abstract

Many bird species have declined in abundance in the agricultural regions of southern Australia, The mechanisms underlying these declines and the viability of the remaining populations are largely unknown, A number of species exist as spatially subdivided populations in heavily fragmented landscapes. Metapopulation and source-sink theory have influenced thinking on the dynamics of subdivided populations, but the general applicability of these theories is uncertain. I examined the dynamics of a subdivided population of the Rufous Treecreeper Climacteris ruta, a declining woodland passerine, occupying a fragmented, agricultural landscape in southwestern Australia. I determined if local populations could replace themselves without immigration and estimated population growth rates for the periods 1998-1999 and 1999-2000. I also examined the influence of movement between local populations on the viability of the entire subdivided population. Out of four geographically defined local populations, only one was above replacement, and only in one year of the study. Fledgling productivity and recruitment in the remainder were not sufficient to compensate for breeding female mortality. Long-term population growth estimates were <1 for all local populations, but variability in demographic rates suggested that the status of these populations may fluctuate over time. Also, there appeared to be sufficient movement between local populations, and into the study area from nearby habitat remnants, to slow or halt any decline in local population size, Within- and between-local-population processes appeared to be important to the viability of the treecreeper population during the two years of the study, and this is consistent with the general principles of metapopulation theory. I compared the dynamics of the treecreeper population occupying the fragmented landscape with one occupying a continuously wooded landscape and found that the latter had population growth rates >1, suggesting it may be an important population source and vital to the regional viability of the species.