Tuesday, May 21, 2024

Achieving functional eradication of invasive snakes to benefit avian conservation – The Applied Ecologist

EcologyAchieving functional eradication of invasive snakes to benefit avian conservation – The Applied Ecologist


Melia Nafus summarises how, alongside colleagues, they applied an Adaptive Resource Management process across three field phases of snake removal. This enabled an evaluation of whether eradication was achievable and whether it was necessary to achieve an avian response.

Invasive snakes

Invasive species, particularly predators, harm natural ecosystems and are a leading driver in global biodiversity loss. Invasive snakes often cause substantial ecological harm as they expand into areas in which they may not have predators and where native species have little behavioral defense against them. For example, the brown treesnake, which arrived on the small island of Guam shortly after World War II, caused significant or total population loss to almost every native forest bird.

The ko’ko’ (Guam rail [Gallirallus owstoni]), a bird endemic to Guam that was extirpated by snakes, running across a forested patch on Cocos Island © U.S. Geological Survey, public domain. Photographer: Peter Xiong

While a considerable amount of research has been done on the ecological effects of invasive snakes, especially the brown treesnake, there is little known about how to manage or eradicate snakes and allow native species to recover. There are no successful, large-scale examples of eradicating an established invasive snake. Likewise, there have been no invasive snake removal efforts that have been successful enough to result in the recovery of a species once decimated by their presence.

A brown treesnake (Boiga irregularis) eats a gecko © U.S. Geological Survey, public domain. Photographer: Melia Nafus

Most research on invasive snake control has occurred on brown treesnakes, which has helped build a successful containment program that has kept them on Guam, a small island in the Pacific Region, and prevented their establishment in new locations. However, research and control programmes have not yet established a technique to control or suppress snakes to recover native vertebrates that have been affected by their introduction.

Adaptive Resource Management

Adaptive Resource Management (ARM), which is a specialized form of creating a structured decision process, can be used to navigate uncertainty and learn while taking management actions. ARM uses a multi-step process and begins with identifying the primary outcome/goal of the management action, as well as any indicators that can be used to evaluate progress towards the final goal.

Once that is done,  scientists or resource managers can take immediate action, while monitoring the progress of indicators and documenting how well the decided upon actions yielded the desired result. If insufficient progress within a treatment interval is made, then the approach is changed through an interactive, adaptive process to improve the likelihood of achieving the final goal that was selected at the beginning of the process.

A brown tree snake investigates its surroundings by flicking its tongue © U.S. Geological Survey, public domain. Photographer: Melia Nafus

This process can be repeated indefinitely until the desired outcome is achieved. By taking this approach, uncertainty at the start is explicitly identified and a repeatable management approach is documented to create both an adaptable and replicable strategy.

Findings

When facing uncertainty around optimal brown tree snake removal techniques with a goal of recovering birds, ARM was an appealing and successful approach to test how individual control tools contributed to brown treesnake population suppression for vertebrate conservation goals. The ARM approach allowed for the evaluation of strengths and weaknesses of individual actions as they related to the goal of snake suppression for avian conservation and recovery.

Graphical abstract summarising the study © Nafus et al, 2024

A pathway was developed that allowed for snake suppression sufficient enough to observe an increase in activity of birds in the control area, provided the area was surrounded by a snake-exclusion barrier. The approach also identified that using live birds as a form of control, although expensive, was essential if bird recovery was the desired outcome. This finding was somewhat contradictory towards prior opinion that birds should not be used as control tools because mice are less expensive and remove equal numbers of snakes, challenging previously established wisdom on best practice approaches to snake control.

This work establishes the value of ARM in refining management decisions and actions when there is considerable uncertainty at the onset. The work sets the stage for further studies that may identify approaches or techniques to eradicate invasive snakes and begin the process of recovering species struggling to co-exist with these predators.

Read the full article “Adaptive resource management: Achieving functional eradication of invasive snakes to benefit avian conservation” in Journal of Applied Ecology.

Check out our other content

Most Popular Articles