Adaptive Harvesting of Source Populations for Translocation: a Case Study with New Zealand Robins

Abstract

Reintroductions are conducted frequently throughout the world, and some source populations are harvested repeatedly to provide animals for translocation. The responses of these source populations to harvest should be monitored, and the resulting data used to refine population models will guide management. After North Island Robins ( Petroica longipes) were reintroduced to Tiritiri Matangi, New Zealand, in 1992, the population became a source for robins for additional reintroductions in the region. We constructed an initial model for the population on the basis of the data collected from 1992 to 1998 and used it to predict the population's response to the first translocation of robins from the island in the autumn (March) of 1999. We then analyzed postharvest data on survival (with mark-recapture analysis) and fecundity (with generalized linear-mixed modeling) to reassess and update the model. In the initial model, juvenile survival was assumed to be limited by the island's fixed carrying capacity, with excess juveniles dying over winter; hence, the autumn harvest was expected to cause an immediate increase in juvenile survival. In postharvest analysis, however, most juvenile mortality occurred before autumn, and the best predictor of juvenile survival was the number of breeding pairs present the previous spring (start of the breeding season). Consequently, the updated population model predicted sustainable harvest levels about half those given by the initial model, and this model has been used to guide the number of individuals removed for two subsequent translocations. The ongoing development of the model has been invaluable for assuring conservation authorities that the population is not being unsustainably harvested, which has allowed surplus animals to be used to establish new populations. Our case study illustrates the value of an adaptive approach to harvesting source populations for reintroduction and illustrates the value of such studies for understanding the density-dependent mechanisms regulating populations.

Captive breeding and rearing of critically endangered Mauritius fodies Foudia rubra for reintroduction

“…Even if it was 50% of this estimate (85), removing 12 juvenile fodies a season is unlikely to have had a significant negative impact on the population dynamics of this subpopulation. Dimond and Armstrong [2007] found that a population of North Island robins Petroica longipes with a reproduction rate of 2.32 fledglings per female per year could maintain a carrying capacity of 65 birds with an annual harvest of 12 juveniles.…”

“…Many of these programs have focused on birds of prey [Seddon et al, 2005] and the in-situ rearing of endangered passerines seems to have been restricted to North America [Kuehler et al, 1995[Kuehler et al, , 2000. Translocation of adult passerines onto islands has been successfully used in the Seychelles [Komdeur, 1994] and New Zealand Dimond and Armstrong, 2007].…”

Nesting sites and nesting success of reintroduced red‐crowned parakeets (Cyanoramphus novaezelandiae) on Tiritiri Matangi Island, New Zealand

“…(Dimond & Armstrong 2007). Previous studies on New Zealand parakeets have focused on remnant populations on the New Zealand mainland (Elliot et al 1996) and on a few offshore islands with alien mammalian predators (Greene 2003) that are known to adversely affect nesting birds (O'Donnell 1996).…”

Reintroducing reintroductions into the conservation arena

“…These issues include the rescaling of red list indices, the investigation of other red list criteria than abundance (such as trends or range area), the consideration of genetic processes and the extension of the analysis to the meta-population scale. At an even wider spatial scale, species-based assessments should balance the benefit of local reintroduced populations with the impact to the source population (Dimond & Armstrong, 2007) and other remnant populations (Le Gouar et al, 2008;Mihoub et al, 2011), and here again, the IUCN status, assessed at the regional or global level, provides a promising framework. More generally, whatever the spatial scale considered, we need to go beyond demography and address the wider ecological impacts of translocations (especially those not conducted in the species range), the perception of success by people (Ewen et al, 2014) and the global, macroevolutionary biodiversity benefits of restoring species and populations.…”