Estimation of Vital Rates for the Hawaiian Gallinule, a Cryptic, Endangered Waterbird

Abstract

Vital rates describe the demographic traits of organisms and are an essential resource for wildlife managers to assess local resource conditions and to set objectives for and evaluate management actions. Endangered waterbirds on the Hawaiian Islands have been managed intensively at state and federal refuges since the 1970s, but with little quantitative research on their life history. Information on the vital rates of these taxa is needed to assess the efficacy of different management strategies and to target parts of the life cycle that may be limiting their recovery. Here, we present the most comprehensive data to date on the vital rates (reproduction and survival) of the Hawaiian gallinule Gallinula galeata sandvicensis, a behaviorally cryptic, endangered subspecies of wetland bird endemic to the Hawaiian Islands that is now found only on Kaua‘i and O‘ahu. We review unpublished reproduction data for 252 nests observed between 1979 and 2014 and assess a database of 1,620 sightings of 423 individually color-banded birds between 2004 and 2017. From the resighting data, we estimated annual apparent survival at two managed wetlands on O‘ahu using Cormack–Jolly–Seber models in program MARK. We found that Hawaiian gallinules have smaller mean clutch sizes than do other species in the genus Gallinula and that clutch sizes on Kaua‘i are larger than those on O‘ahu. The longest-lived bird in our dataset was recovered dead at age 7 y and 8 mo, and the youngest confirmed age at first breeding was 1 y and 11 mo. In 4 y of monitoring 14 wetland sites, we confirmed three interwetland movements on O‘ahu. In our pooled dataset, we found no statistically significant differences between managed and unmanaged wetlands in clutch size or reproductive success, but we acknowledge that there were limited data from unmanaged wetlands. Our best supported survival models estimated an overall annual apparent survival of 0.663 (95% CI = 0.572–0.759); detection varied across wetlands and study years. First-year survival is a key missing component in our understanding of the demography of Hawaiian gallinules. These data provide the foundation for quantitative management and assessment of extinction risk of this endangered subspecies.

Landscape genetics identifies streams and drainage infrastructure as dispersal corridors for an endangered wetland bird

“…Rallidae species have colonized oceanic islands all over the world, but are reluctant fliers when not dispersing (Ripley et al., 1977). Although genetic (Miller, Mullins, Haig, Takano, & Garcia, 2015) and observational (Takano & Haig, 2004; Worthington, 1998) evidence of long‐distance (~120 km) movements over open ocean water exist for the Marianas common moorhen, no movements of Hawaiian gallinules have been observed between the two islands they inhabit (Kaua`i and O`ahu, ~138 km apart), despite extensive mark–recapture efforts (Dibben‐Young, 2010; van Rees et al., 2018). There is accordingly some uncertainty with regard to the willingness of Hawaiian gallinules to disperse over open ocean.…”

Interisland genetic structure of two endangered Hawaiian waterbirds: The Hawaiian Coot and Hawaiian Gallinule

“…Conversely, Hawaiian Gallinules are thought to be highly sedentary and to maintain territories year-round (Bannor and Kiviat 2002). Despite the sedentary nature of Hawaiian Gallinules, they have colonized wetlands (either unoccupied or created through restoration and management) as numbers increased post-decline (based on genetic data; van Rees et al 2018b), and intraisland dispersal events have been observed (van Rees et al 2018a). Differences in dispersal propensity are postulated to have played a role in how the population decline influenced genetic diversity (Sonsthagen et al 2017).…”

Predicted effects of landscape change, sea level rise, and habitat management on the extirpation risk of the Hawaiian common gallinule (Gallinula galeata sandvicensis) on the island of O‘ahu

“…Most wetlands support small numbers of gallinules (five–30 individuals), although two larger wetland complexes may support subpopulations of ∼100 (C van Rees, 2018, unpublished data). To our knowledge, the O‘ahu population of gallinules is an effectively closed system, with no published records of movements between O‘ahu and Kaua‘i ( Banko, 1987 ; van Rees et al, 2018a ), although biannual waterbird surveys show extremely rare occurrences of gallinules on the Big Island, Maui, and Molokai, so the possibility of movement cannot be excluded. Demographic data used for this study were taken from van Rees et al (2018a) , and were collected from fourteen wetland sites on the island from different time periods from 1979–2017.…”

“…We generated baseline model parameter values using information on reproduction and survival from van Rees et al (2018a) , with support and supplementation from data on related taxa (e.g., Common moorhen, Gallinula chloropus ; Table 2 ). Even though Hawaiian gallinules do not breed until age 2, there is no evidence of age structure in survival rate beyond year 1 ( van Rees et al, 2018a ). Accordingly, we modeled survival using two age classes: hatch year (hatching to age 1), and after hatch year (age 1+ or adult).…”

“…The discrete distribution of Hawaiian gallinules on O‘ahu makes them an excellent study system for spatially explicit PVA ( Walters, Crowder & Priddy, 2002 ), and their current existence in many small subpopulations warrants attention to the impacts of stochastic elements of population dynamics as well as to deterministic drivers of decline. The uncertainty in demographic parameter estimates for this taxon ( van Rees et al, 2018a ), and difficulty of studying them in the field means that vital rate sensitivity analysis could aid in prioritizing field study and data collection ( Morris & Doak, 2002 ). The management dependence of this subspecies also raises questions about the efficacy of management alternatives.…”