competitive release

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).

In New Zealand, ship rats (Rattus rattus) have been implicated in many extinctions, declines, and range contractions of native birds, so ship rats are an important target of predator control. The outcomes of ship rat control operations are difficult to predict due to other factors which affect rat populations including altitude, Nothofagus seedfall, and control of other mammalian pests, particularly brushtail possums (Trichosurus vulpecula) and stoats (Mustela erminea).