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Zealandia (Karori Sanctuary) is a forest sanctuary which is surrounded by a predator-exclusion fence, and is situated in the Wellington city town belt, New Zealand. Following eradication of introduced mammals from within the fence in 1999, 10 species of endemic forest birds were reintroduced between 2000 and 2011, and 2 other species recolonised naturally. Five-minute bird counts were used to assess changes in the Zealandia diurnal forest bird community over 2 time periods: 1995-98 to 2002-05, and 2002-05 to 2013-16, as well as changes over the full 21 year period. Tui (Prosthemadera novaeseelandiae) was the only bird species present before the fence was completed that showed a significant, year-round positive response to mammal removal. Following the recreation of a diverse and abundant endemic bird community post-2005, detection rates for most of the species that were present before 1999 declined significantly. This included highly significant declines in detection rates for 3 native bird species: silvereye (Zosterops lateralis), grey warbler (Gerygone igata) and New Zealand fantail (Rhipidura fuliginosa). These results suggest that populations of the most common and widespread native and introduced birds are only weakly limited by mammalian predation, but can be rapidly outcompeted by restored endemic bird species if predators are removed. The forest bird community in Zealandia is now more similar to that on nearby Kapiti Island (the source site for many of the bird species translocated to Zealandia) than it is to the bird community that existed at the site before the fence was built.