The 'regime shift extinctions' hypothesis and mass extinction of waterbirds in Hawaiʻi

Abstract

Studies of biodiversity loss commonly imply that species extinctions occurred as a direct result of initial human settlement and thus are attributable to stewardship failures of Indigenous Peoples. However, recent studies have suggested this assumption is not supported by the evidence, prompting a global re-evaluation of existing assumptions. To assess the relationship between human arrival in the Hawaiian Islands and documented declines in waterbird biodiversity, we reviewed empirical evidence from palaeoecological studies. We first identified the time period that extinct Hawaiian waterbird species were last observed within the fossil record. We then evaluated four hypotheses proposed to explain drivers of post-settlement Holocene waterbird extinctions: (1) the overkill hypothesis; (2) the deforestation hypothesis; (3) the climate change hypothesis; (4) the species introductions hypothesis. Of the 18 extinct waterbird species evaluated in this study, ten were last observed in the fossil record prior to Polynesian arrival, six were last observed in the fossil record during the Polynesian era, and two were last visually observed after European arrival. Extinctions that possibly occurred during the Polynesian era were likely caused by a suite of factors, some anthropogenic and some non-anthropogenic. Our findings contradict previous studies that attributed post-settlement Holocene waterbird extinctions to hunting and deforestation by Native Hawaiians and suggest a future line of inquiry regarding a proposed “'Regime Shift Extinctions Hypothesis” to explain complex impacts of human-mediated and climatic drivers of extinction in the Anthropocene.