Impacts of invasive rats and tourism on a threatened island bird: the Palau Micronesian Scrubfowl

Abstract

SummaryInvasive predators have decimated island biodiversity worldwide. Rats (Rattus spp.) are perhaps the greatest conservation threat to island fauna. The ground nesting Palau Micronesian Scrubfowl Megapodius laperouse senex (Megapodiidae) inhabits many of the islands of Palau’s Rock Island Southern Lagoon Conservation Area (RISL) in the western Pacific. These islands are also heavily visited by tourists and support populations of introduced rats, both of which may act as added stressors for the scrubfowl. Using passive chew-tag and call playback surveys on five tourist-visited and five tourist-free islands, we investigated if rats and tourists negatively affect scrubfowl, and if higher rat activity is associated with tourist presence. Rat detection probability and site occupancy were significantly higher on tourist visited (89% and 99%, respectively) compared to tourist-free islands (52% and 73%). Scrubfowl were detected at significantly more stations on tourist-free (93%) than tourist visited (47%) islands and their relative abundance was higher (2.66 and 1.58 birds per station, respectively), although not statistically significantly. While rat occupancy probability likewise had a non-significant negative effect on scrubfowl numbers across islands, our results show a negative relationship between tourist presence and scrubfowl in the RISL. Our findings also suggest that rat populations may be augmented by tourist visitation in the RISL. Although this situation may not seriously affect the scrubfowl, it may be highly detrimental to populations of other threatened island landbirds.