Life history traits explain vulnerability of endemic forest birds and predict recovery after predator suppression

Abstract

New Zealand’s native forest bird species with high taxonomic levels of endemism (deep endemics) are more vulnerable to decline than species that arrived and speciated more recently. Here we use national-scale local occupancy data to show that three endemism-linked life-history traits account for greater vulnerability of deep-endemic species in the extant forest avifauna, but also that other, more subtle traits and mechanisms favour rather than hinder endemic persistence. We suggest that these traits together provide a basis for predicting changes in local occupancy following suppression of introduced mammalian predators in different landscapes. Our analyses disentangle the limiting effects of forest area, predation, and food availability for different species. They support understanding that predation by introduced mammals is the primary cause of forest bird declines and limitation today, but suggest that large tracts of native forest are essential for future restoration of endemic forest avifauna, even following suppression of introduced mammalian predators. We predict that with fewer predators (1) deep-endemic species would most successfully and rapidly recover in large tracts of warm forest, (2) scarcity of forest or food would limit recovery in larger-bodied, less mobile species and in mobile cavity-nesters, and (3) interspecific competition would become influential and produce community reassortment.

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

“…Tītitipounamu belong to the New Zealand endemic family Acanthisittidae, while miromiro are part of the Australo-Papuan family Petroicidae and endemic to New Zealand at the species level. We chose these model species to investigate the effects of food availability on reproductive success along an elevational gradient, because (1) they have significantly declined since human colonisation of New Zealand (Parlato et al 2015); (2) but they still coexist with mammalian predators in diverse podocarp-broadleaved forest and have the potential to benefit from large-scale pest mammal suppression; and (3) their current vulnerability and life-history traits differ, resulting in tītitipounamu having experienced larger declines in warmer forests or at lower elevation than miromiro (Elliott et al 2010;Walker et al 2019aWalker et al , 2021. Both species are small, tītitipounamu 5-7 g and miromiro 10-13 g (Moeed & Fitzgerald 1982;O'Donnell & Dilks 1994;Peace 2010), and use vegetation from ground level to the upper understory while foraging either on the ground, by gleaning, or scanning for prey (O'Donnell & Dilks 1994;Peace 2010).…”