Temporal Ecology of Hawaiian Waterbirds

Abstract

Conventional conservation has largely been informed by spatial ecology research, such as identifying optimal locations for conserving species and their habitats. However, in a rapidly changing world, it is becoming increasingly important to include temporal ecology, how ecological systems change over time, in conservation planning. In Hawai‘i, state and federal entities have created over 6,000 ha of protected wetland habitat for endangered, endemic Hawaiian waterbirds. Sea level rise poses a threat to many of these protected areas, as many of these wetlands are located on lowlands and nearshore. As Hawaiian waterbirds are currently habitat limited, creating new waterbird habitat will be necessary for the persitance of these populations. However, the uncertainty posed by climate change creates challenges for identifying optimal locations for new waterbird habitat that will be resilient to change. Restoration of Hawaiian wetland agroecosystems (loʻi) under an Indigenous Resource Management (IRM) paradigm may offer a sustainable land-scape level solution to expanding Hawaiian waterbird habitat, as the adaptive, social-ecological framework of these systems increases resilience following disturbance. However, incorporating IRM into conventional conservation approaches has been challenging, in part due to biased perspectives of human-wildlife relationships that are based on shortsighted historical ecology research. Moreover, current conservation goals for recovering Hawaiian waterbird populations are largely informed by research on present-day waterbird ecology. Thus, in this dissertation, I aimed to examine the temporal ecology, including past and present-day ecology, of Hawaiian waterbirds to better understand the future trajectory of their populations. My objectives were to: (1) review empirical evidence for the historical ecology of Hawaiian waterbirds; (2) determine impacts of seasonality and nest-site characteristics on nest survival of the Aeʻo (Hawaiian Stilt – Himantopus mexicanus knudseni); (3) quantify projected losses of Hawaiian waterbird nesting habitat due to sea level rise and the potential for Hawaiian wetland agroecosystems to compensate for these losses. In my first study, I found that the empirical evidence supports the notion that climate change and species introductions were major drivers of post-settlement Hawaiian waterbird extinctions during the Holocene, rather than overhunting and deforestation by Hawaiians. In my second study, nest survival of Aeʻo was found to decrease over the course of the nesting season, possibly due to changes in predation pressure. My results indicate that predation of nests by invasive species, particularly mammals that were introduced to Hawai‘i in the 19th century, is one of the largest threats to Aeʻo populations and likely other extant endangered waterbird populations. The preferred nest-site characteristics of Aeʻo do not improve nest survival, and thus continuous management of predators is critical for Aeʻo reproductive success. In my third chapter I found that sea level rise is projected to reduce currently existing potential waterbird nesting habitat across the main Hawaiian Islands by 29%; however, I found that restoration of loʻi systems may more than compensate for these losses. Together, findings from this dissertation research suggest that restoration of Indigenous agroecosystems, coupled with control of invasive vegetation and predators, may expand conservation of endangered, endemic Hawaiian waterbirds beyond state and federally managed protected areas. My findings help to inform how conservation approaches are most effective when viewed through the perspective of temporal ecology.