The house mice predate adults, nestlings, and eggs, and cause island-wide damage to the ecosystem. To combat the non-native house mice, the USFWS plans an island-wide eradiation using a rodenticide toxicant called brodifacoum. Brodifacoum is an anti-coagulant that builds up quickly in the liver of vertebrate species and has been used on other island ecosystems in New Zealand and the Galapagos to remove pests. Although brodifacoum is often efficient in eradicating target pests, there is also a very high risk of poisoning to non-target vertebrate species, like birds. This presents quite a predicament for a small island that is home to several bird species! Especially for the endangered Laysan Duck, a resident species on MANWR that is endemic to the Hawaiian Islands. So how do biologists plan to migrate the removal of the house mice, while still ensuring that the birds of Midway aren’t also impacted? The USFWS plans to, first capture all the Laysan Ducks on MANWR and keep them in captive care during the baiting operation, and second, use bioindicators to monitor toxicant levels in the environment over time.

Bioindicators are species, or groups of organisms, capable of indicating changes in the environment. The classic example everyone knows is the canary in the coal mine, in which canaries were used to indicate the risk to coal mines of methane gases. Well, what if we used canaries…on MANWR? Island Canaries are native to the Canary Island off the coast of Morocco, now widespread as a common pet species, and were introduced to MANWR by military families. The USFWS plans to use these non-native canaries as indicators to monitor the decay of brodifacoum after the baiting application. In addition to Island Canaries, there is another introduced passerine species, the Common Myna that will also be used as an indicator, which are native to Southern Asia but now widespread throughout the world. So how will Island Canaries and Common Mynas be used as indicators?

Island Canary - Photo by Carmen Antaky, USFWS

Part of my summer internship with USFWS was to assist in creating plans to use radio telemetry, a technique commonly used in wildlife studies, to track Island Canaries and Common Mynas after the baiting application of brodifacoum on MANWR. Radio telemetry works similar to your car radio, in which the birds carry little transmitters that emit a frequency or signal, and you can tune your receiver to that signal to track down the bird, much like tuning in to your favorite radio station. Biologists can track the sentinel passerines and monitor their health to understand the impacts of brodifacoum on avian species and the pathways of brodifacoum, or how it is spreading throughout the environment. The survival of the Island Canaries and Common Mynas will indicate to USFWS how much risk is associated with brodifacoum and when it will be safe for Laysan Ducks to return to MANWR.

Agency: U.S. Fish and Wildlife Service

Program: US Fish & Wildlife Service - DFP

Location: Midway Atoll National Wildlife Refuge