Fenced sanctuaries deliver conservation benefits for most common and threatened native island birds in New Zealand

Abstract

Island species are disproportionately threatened with extinction, and invasive species are the primary driver of biodiversity loss. Globally, eradicating invasive mammals from small oceanic islands has led to the recovery of threatened populations, but eradicating mammals from large islands and continents is more challenging. In New Zealand, conservation organizations have established a large network of fenced sanctuaries that use predator‐proof fencing to exclude invasive mammals and conserve native flora and fauna. Yet, critics question if sanctuaries meet these targets, given a lack of evidence on outcomes. We surveyed birds in three sanctuaries and three paired sites on New Zealand's North Island to investigate whether sanctuaries increase bird population densities relative to sites with minimal mammal control. Densities of nine endemic bird species were higher in sanctuaries compared to unprotected sites (0.27–9.00 more birds/ha), but we found no significant difference in mean population densities for introduced and biogeographically recent native species. These findings provide compelling evidence that fenced sanctuaries effectively conserve native island bird populations, and affirm predictions that native species are more likely to benefit from invasive mammal eradications than introduced species. New Zealand's novel approach to recovering rare species holds great promise for conserving biota at risk from invasion in other global hotspots of endemism.

Long‐term biodiversity trajectories for pest‐managed ecological restorations: eradication vs. suppression

“…Within ecosanctuaries, deeply endemic avifauna, frequently established or supplemented by translocation, showed greatest benefits compared with recent natives or introduced species. There is a growing literature reporting higher vulnerability of native species to invasive predators, relative to introduced species (Salo et al 2007, Fukasawa et al 2013, and our species-specific results (Appendix S2: Table S2) were consistent with previous studies (Ruffell and Didham 2017, Bombaci et al 2018, Fea et al 2020. Traits linked to an evolutionarily reduced predator escape response are likely the primary mechanism explaining this trend (Cassey 2001, Bromham et al 2012, Parlato et al 2015.…”

“…For example, ring‐fenced exclosures defending against large mammalian predators have improved nest survival and productivity for native lapwing ( Vanellus vanellus ) in the UK’s lowland wet grasslands (Malpas et al 2013), and gopher tortoise ( Gopherus polyphemus ) in southeastern U.S. forests (Smith et al 2013). Densities of numbats ( Myrmecobius fasciatus ), a native marsupial, increased in Australia’s Scotia and Yookamurra ecosanctuaries (Hayward et al 2015), as did endemic forest avifauna in New Zealand ring‐fenced ecosanctuaries (Miskelly 2018, Bombaci et al 2018, Drummond and Armstrong 2019), with biodiversity spillover into surrounding landscape (Tanentzap and Lloyd 2017, Fitzgerald et al 2019).…”

“…Previous studies in terrestrial ecosanctuaries on New Zealand’s mainland have focused on biodiversity outcomes for multiple taxonomic groups at a single study site (e.g., Gillies et al 2003), or within one taxonomic group across several sites (e.g., Pierce and Westbrooke 2003, Ruffell and Didham 2017, Bombaci et al 2018, Fea et al 2020). A comprehensive national review across diverse taxa can reveal new insights into broad biodiversity outcomes under different restoration regimes.…”

Australian birds could benefit from predator exclusion fencing

“…To date, over 50 fences have been erected for the protection of nesting seabirds (Cooper, 2013). Predator exclusion fences in New Zealand alone protecting more than 30 bird species behind 28 fences (Burns, Innes, & Day, 2012), 15 fences >25 ha; Innes et al, 2019), with reports of widespread recovery of forest birds and restored ecosystem function as a result of predator exclusion fencing (Bombaci, Pejchar, & Innes, 2018;Miskelly, 2018). In Europe (Mayer & Ryan, 1991) and North America (Malpas et al, 2013), game birds and waders are regularly protected using both long term fencing such as peninsula fences, and short-term fencing to opportunistically protect individual nests.…”

A Consideration of Mesopredator Release and New Zealand's Predator Free Plan: A Literature Review

“…Lethal control has been assumed to be beneficial to the biodiversity of the native flora and fauna, as observed in the eradication of exotic predators in the Bay of Plenty Region. However, these islands are closed systems of reduced area that allow for a more comprehensive distribution and implementation of lethal eradication methods over a short period of time (Bombaci et al 2018). Attempting lethal eradication on a larger scale across the entire country will take several decades and introduces compromises to the efficacy of the technique.…”