Population dynamics of reintroduced forest birds on New Zealand islands

Abstract

Aim We studied dynamics of four populations of New Zealand forest birds for 5–9 years after reintroduction to islands. We primarily aimed to predict whether these populations were viable, and what, if any, management was needed to maintain them. However, the small scale of these islands also provided an opportunity to study density‐dependent population growth over a short time frame. Location We studied New Zealand robin (toutouwai, Petroica australis) and stitchbird (hihi, Notiomystis cincta) populations reintroduced to Tiritiri Matangi, a 220‐ha offshore island near Auckland, and saddleback (tieke, Philesturnus carunculatus) and stitchbird populations reintroduced to Mokoia, a 135‐ha island in Lake Rotorua. These islands are free of mammalian predators, but have highly modified habitat following clearing and regeneration. Methods We closely monitored each population, individually marking all or most of the birds and in some cases experimentally manipulated population density or food supply. We used model selection procedures to understand factors affecting survival, fecundity and dispersal, and developed stochastic simulation models. Results The Tiritiri Matangi robin and Mokoia saddleback populations grew without management and appear to be viable. Both showed strong evidence of density‐dependent growth, with fecundity (saddlebacks) and juvenile survival (both populations) declining with increasing density. Neither stitchbird population appears viable without management and supplementation experiments showed reproduction and/or survival to be limited by food supply. The Tiritiri Matangi population appears viable as long as supplementary feeding continues. However, the Mokoia population has a high mortality rate regardless of supplementary feeding, resulting in tenuous viability even with intensive management. Mokoia stitchbirds suffer from infection by Aspergillus fumigatus, a pathogenic fungus that is prevalent in highly modified habitats and more abundant on Mokoia than Tiritiri Matangi. Main conclusions Some forest birds can thrive in regenerating forest on islands and strong evidence of density dependence can be detected in such populations in as little as 5 years. This allows density‐dependent models to be developed, providing guidance when island populations are harvested for further translocations. Other species are limited by food supply in regenerating environments, a problem potentially overcome by management. However, prevalence of A. fumigatus may render highly modified environments uninhabitable by some species regardless of management.

Conservation biology for suites of species: Demographic modeling for Pacific island kingfishers

“…Population models based on surrogates may provide an appropriate and accurate means of managing translocated and reintroduced populations. Some have suggested that useful population models can be developed after studying a reintroduced population for five years (Armstrong et al, 2002). However, model accuracy and utility might be improved even more rapidly if managers were armed with generalized population models based on surrogates prior to release.…”

Successful island reintroductions of New Zealand robins and saddlebacks with small numbers of founders

“…We also assessed extinction probability using stochastic matrix models based on and Armstrong et al's (2002) analysis of the reintroduced robins on Tiritiri Matangi Island and Armstrong et al's (2005) analysis of the reintroduced saddleback population on Mokoia Island. Both models included demographic stochasticity in births, deaths and sex ratio of offspring, with births sampled from the Poisson distribution and deaths and sex sampled from the binomial distribution.…”

Effect of supplementary feeding on reproductive success of hihi (stitchbird, Notiomystis cincta) at a mature forest reintroduction site

“…Estimates from both groups are compared to literature reporting reproductive success from other hihi populations (nest success and number of fledglings produced; Makan et al 2014). We also incorporated age as a variable into our analysis, because previous studies on hihi found age to influence reproductive success (Armstrong et al 2002;Low et al 2007). …”