Evaluating the success of functional restoration after reintroduction of a lost avian pollinator

Conservation translocation is a common method for species recovery, where one increasingly frequent objective is restoring lost ecological functions to promote ecosystem recovery. However, few conservation translocation programs explicitly state or monitor function as an objective, limiting our ability to test assumptions, learn from past efforts, and improve management. Here, we evaluated whether translocations of hihi (Notiomystis cincta), a threatened New Zealand passerine, achieve their implicit objective of restoring lost pollination function. Through a pollinator exclusion experiment, we quantified the effects of hihi pollination by comparing fruit set and seed quality in hangehange (Geniostoma ligustrifolium), a native flowering shrub, across sites with and without hihi. Results suggested that other avian pollinators can compensate for and even exceed hihi's contributions to fruit set. Furthermore, although hihi improved seed germination, plants at non-hihi sites achieved similar germination rates by shifting their reproductive investment to produce a greater quantity of seeds with lower germination probability. Therefore, although our study confirms hihi may bring benefits to seed quality, it also highlights the complexity of ecological functions. When an important species is lost, ecosystems may be able to achieve similar function through different means. Our study underscores the importance of stating and monitoring the ecological benefits of conservation translocations when functional restoration is a motivation to ensure these programs are achieving their objectives