Using New Zealand's late-Quaternary fossil record to estimate the past distribution and habitats of a relict species (kākāpō: Strigops habroptila)

Abstract

New Zealand's (NZ's) endemic, flightless kākāpō (Strigops habroptila) – the world's heaviest parrot species - reached near-extinction due to human activity and predation by introduced mammals (51 known individuals between 1995 and 1996). Today, kākāpō only survive on managed predator-free sanctuaries (<250 individuals), and rarely breed except during mast events of native rimu trees (Dacrydium cupressinum). Here, we review NZ's Late-Quaternary fossil record in relation to palaeovegetation, and determine whether it can be used to identify the past habitats and distribution of kākāpō. First, we describe the distribution of kākāpō fossils from c. 25ka until the present and the former habitat breadth of kākāpō. Second, by comparing the abundance of kākāpō fossils to those of similar-sized landbirds in each site, we identify how past kākāpō abundance was affected by habitat type. Although we identify that kākāpō exhibit strong taphonomic biases, we show that kākāpō are the fourth-most common bird taxon in NZ's late-Quaternary deposits (1351 Minimum Number of Individuals from 274 sites), and occupied all forests and adjacent habitats, on the NZ mainland prior to human settlement ca. 0.8 ka. However, we find little evidence that kākāpō occupied semi-arid shrublands, the high alpine zone, or most grassland/shrublands during glacial periods. Further, kākāpō were most abundant in humid, high precipitation forests, were rarest in drought-prone, low-rainfall scrub/forests, and were common in many rimu-free habitats. We also determine that contemporary kākāpō occupy a small proportion of their optimal habitat range. Our study demonstrates the value of late-Quaternary (ca. 50 ka to present) fossils for conservation biology and reveals how contemporary data alone can underestimate the habitat breadth of previously more widespread species.