Monitoring Bird and Rat Behavior to Improve Invasive Species Management

Science Center Objects

Introduced rats are notorious predators of birds and their nests worldwide, but especially on remote islands. Rats (Rattus exulans) first arrived in Hawai‘i with Polynesian colonists about 1,000 years ago, resulting in deleterious consequences for native birds and ecosystems. Since Western contact in 1778, two additional rat species have become established in Hawai‘i, including the highly invasive black rat (R. rattus), which arrived in the late 1800s. Black rats have contributed substantially to the historical loss of native forest bird populations, in part through nest depredation. The USGS is evaluating rat control as a management tool to improve the breeding success of native birds, and to facilitate native plant regeneration to recover native ecosystems.

Overview:

A Hawai‘i ‘elepaio chick is in a nest with an open mouth and being fed by adult bird

An adult Hawai‘i ‘elepaio feeds its chick at the nest in Hawai‘i Volcanoes National Park.

(Credit: Robert W Peck, Hawai‘i Cooperative Studies Unit)

A high priority of natural resource managers is research to evaluate how 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. The USGS is investigating whether predators such as black rats are impeding bird restoration in these recovering forests.

Bird stands in tree with yellow, red and metal bands on legs

Banded Hawai‘i ‘elepaio in Hawai‘i Volcanoes National Park

(Credit: Nicole Richardson)

Hawai‘i ‘elepaio (Chasiempis sandwichensis) are insectivorous forest birds and are common in native montane forest habitat within HAVO. Their nests are relatively accessible for monitoring and are known to be vulnerable to rat depredation. ‘Elepaio nesting success, nest depredation and rat abundance was monitored during 2015-2017 within study plots in HAVO. Monitoring was conducted before and after rodenticide treatment and compared between paired treatment and non-treatment plots.

Project Objectives:

1) Quantify impact of rat depredation on common forest bird species

2) Inform resource managers

  • Forest bird community declining despite improving vegetation structure since ungulate removal, even where avian malaria & pox are not transmitted
  • Are predators impeding bird restoration in forests recovering from browsing impacts of invasive ungulates (goats, pigs, cattle)
  • How to prioritize efforts, given rat populations difficult to reduce or eliminate

Highlights and Key Findings:

Field studies and data collection were completed in 2017.

Data analysis and manuscript preparation will continue during 2018 & 2019.

See the Multimedia tab for video footage of rat predation of bird nests.

White paper with rat footprints attached to ink paper. Ruler shown for scale.

Rat footprints on an ink card taken from a tracking tunnel. These cards were used to calculate rat abundance in study plots in Hawai‘i Volcanoes National Park.

(Credit: Kelly Jaenecke, Hawai‘i Cooperative Studies Unit)