Integrated Management of Alien Predators

Science Center Objects

Small mammals (including three species of rats and one species of mongoose) and social Hymenoptera (order of insects including ants and yellowjacket wasps) form two groups of alien predators in Hawaiian ecosystems. The combined impact of these predators has resulted in substantial loss or reduction of native biota in the Pacific. Furthermore, given the past successes of managing or excluding feral ungulates and, in some instances, invasive alien plants, control of alien predators is one of the highest research priorities among federal land management agencies in Hawai‘i. Small mammals and social Hymenoptera form a complex of multiple stressors whose impact and control have many parallels that lend them to co-management in native ecosystems. Both groups undergo seasonal fluctuations in populations, are attracted to baits, and respond to chemical control. 


‘Elepaio in the hand

Hawai‘i ‘elepaio. Photo: C. Gagorik

A high priority of natural resource managers is research to evaluate how integrated management of alien predators can aid the recovery and increase the resiliency and stability of mesic montane forests of Hawaii Volcanoes National Park (HAVO). These forests have been listed as globally imperiled by the International Union for Conservation of Nature (IUCN) and contain biologically rich sites that support many rare, declining, and threatened or endangered species. Ecosystem restoration at HAVO began in the 1970s with the pioneering removal and exclusion of feral ungulates, which resulted in or is leading toward recovery of the native tree canopy across broad and diverse swaths of mesic montane forest. More recently, a program to stabilize rare plants has led to the reintroduction or augmentation of more than 22 native taxa, including 10 federally listed species. Additionally, select invasive weed species are being controlled, yet the recovery of native understory vegetation and invertebrate and vertebrate communities has been limited.

Ants and aphids at Kipuka Pua‘ulu

Ants tending aphids on a plant in Kipuka Pua‘ulu in Hawai‘i Volcanoes National Park. Photo: R. Peck 


New methods are needed to continue the restoration of biotic communities following these major first steps. Among the most urgent needs of management are new tools and strategies for controlling suites of invasive vertebrate and invertebrate predators that together prey on native species, thereby destabilizing their populations, and disrupt critical food webs and pollination networks. Our research will investigate the interactions of a key vertebrate predator and two invertebrate predators with a wide range of native species, and we will demonstrate techniques for how their impacts can be reduced.  Rodents and social Hymenoptera (ants and wasps) are the most widespread and ecologically disruptive invasive animals on islands. As predators of both animals and plants, they have altered Pacific island ecosystems by disrupting native communities and exterminating endemic species. Ecological impacts of these individual invasive species are generally well-documented, but the combined impacts of invasive vertebrate and invertebrate predators are poorly understood.

Based upon previous work, the invasive predators expected to have the greatest impacts on these mesic montane communities are the black rat (Rattus rattus), the western yellowjacket wasp (Vespula pensylvanica), and the Argentine ant (Linepithema humile). Rats are ubiquitous and omnivorous and pose a major predatory threat to native birds while also reducing native plant vigor, survival, and reproduction. Yellowjacket wasps are seasonally irrupting predators of native arthropods that are important as foods of birds, and they disrupt native pollination webs by usurping nectar resources. Argentine ants likely impact arthropod communities in ways that are similar to yellowjackets, but their limited distribution in HAVO may not warrant further consideration. Our work will reveal for the first time the cumulative impacts of these important predators in mesic montane ecosystems of HAVO.  Broad-area control methods suitable for use in Hawaiian forests allow for measuring the ecological benefits and practical costs of removing a suite of invasive predators. Following the removal of introduced ungulates, ongoing suppression of invasive weeds, and reintroduction and augmentation of rare plant populations, the removal or control of alien predators is the next important step towards restoring habitats for endangered and declining forest birds and increasing protections for rare and endangered plants and insects in HAVO.

Project Objectives:

PIERC volunteer measures the leg of a Hawai‘i ‘elepaio

A PIERC volunteer measures the tarsus (lower leg) of a Hawai‘i ‘elepaio. Photo: A. Powell

The objective is to demonstrate how montane mesic communities can be restored by eliminating or significantly reducing the interference of invasive small predators with the behavior, reproduction, survival, and natural interaction among native birds, insects, and plants. In particular, we will determine the response of key native plant and animal species to the integrated management of high-impact predators that impede ecosystem recovery even after ungulate removal and weed control.

Yellow-jacket wasp on an ‘ōhi‘a flower

Yellow-jacket wasp on an ‘ōhi‘a flower. Photo: C. Hanna


Highlights and Key Findings:

Field studies and data collection were completed in 2017.

Data analysis and manuscript prepartion will continue during 2018.