Invertebrate food supply and reproductive success of two native forest passerines along an elevational gradient

Predation by mammals has been identified as the primary limiting factor of Aotearoa New Zealand native birds. Consequently, the ranges of many native forest bird species have contracted to cooler and higher elevation tracts of forest that support fewer introduced mammals. However, lower elevation forests are likely to be intrinsically more productive and able to sustain larger bird populations if control of mammalian pests removes predation as a primary limiting factor.