abundance estimation

The National Wetland Trust constructed a 1400 m long pest exclusion fence around a 11 hectare site at Rotopiko and all mammals except mice have been eradicated from inside the fenced area. Since the completion of the pest proof fence, the number of roosting birds has increased dramatically. By removing mammalian pests, an unexpected sanctuary has been created for communal roosting birds such as starlings (Sturnus vulgaris) and sparrows (Passer domesticus).

Large-scale bird monitoring can provide valuable insights about drivers of population change across different spatial and temporal scales. Yet, challenging terrain and survey costs hinder the collection of data needed to estimate absolute abundance or population densities for New Zealand’s forest birds. Acoustic sampling is being used more frequently to increase efficiency in avian monitoring and paired sampling facilitates robust density estimation from acoustic data.

In this study I assess the statistical power to detect a significantly greater increase in bird population size on treatment farms than on control farms given that there is a substantial treatment effect. Computer simulations of bird populations on New Zealand sheep/beef farms were used to generate significant changes in bird abundance from (a) controlling predation by introduced small mammals, (b) habitat structural complexity, and (c) an interaction of both.