Predator Control
Mongoose, cat, and rat removal at nēnē nesting habitat on Hawaiʻi Island. Game cameras show us what is moving through. Trap nights and nest outcomes tell us whether the work is moving the needle.
What this project does
Mammalian predation is the dominant threat to nēnē on every island except Kauaʻi. The 2019 federal downlisting rule and the 2024 5-Year Review both name mongoose, feral cats, dogs, rats, and pigs as the underlying threat for the species. This project handles the on-the-ground response at nēnē nesting habitat on Hawaiʻi Island: deploying traps, running game cameras to see what is moving through, and measuring whether the work is actually changing what predators meet the birds.
Over 45,000 game camera images have been processed so far, with a machine learning model handling species ID. That feeds back into where traps go next.
Worth flagging upfront: Kauaʻi is mongoose-free, and that one fact explains most of the difference between the Kauaʻi nēnē population (growing, around 2,200 birds as of 2022) and the other islands. On Kauaʻi the more urgent conversation is biosecurity to keep mongoose out, not removal.
The pieces
Nesting habitat coverage
Trap lines and camera grids go where nēnē actually nest, not where access is easy.
Camera-based monitoring
Game cameras and a trained ML model track what is moving through, so predator pressure is something we measure rather than guess at.
Iterating on what works
Trap type, bait, and placement get adjusted based on what the cameras and trap nights are showing.
Community trapping
Trained volunteers running their own lines, with support for trap selection and reporting.
What is in the field
Trap types
AT220 auto-resetting traps for mongoose, Goodnature A18 and A24 self-resetting traps, plus live traps where the situation calls for them.
Game cameras
A grid of cameras covering active and historical nesting areas. Over 45,000 images processed through a trained classifier.
Outcome tracking
Cameras and carcass counts on the predator side. Nest success and gosling survival on the nēnē side. Both have to move.
Adjustments
Trap locations and bait choices move when the data says they should, not on a fixed quarterly schedule.
Two scoreboards
Removals are one measure. Whether more goslings fledge is the one that matters.
Volunteer support
Equipment, training, and a place to log catches for community members running their own trapping lines.
How it works
1. See what is there
Game cameras run continuously across nēnē nesting habitat. The image stream goes through a classifier that flags mongoose, cats, rats, and feral pigs. Nobody wants to be the person eyeballing thousands of empty frames.
2. Place traps where the data says
AT220 mongoose traps, Goodnature A18 and A24 self-resetting traps, and live traps go where the cameras and previous catches point. The HCSU technical report on Hawaiʻi Island documented male feral cat home ranges up to 2,050 ha. At that range size, trapping right at a single nest fails. Trap lines have to cover a buffer.
3. Track outcomes on both sides
Removals and trap nights on one side. Nest success and gosling survival on the other. The HCSU report on Hawaiʻi Island documented an endangered ʻuaʻu (Hawaiian petrel) recovered from a feral cat stomach. For goslings the predator and the habitat are the same.
4. Pull in community reports
Sightings logged on FeralMap feed back into where we look next. Mongoose reports on Kauaʻi go to biosecurity. Mongoose, cat, and rat reports on other islands help us catch pressure outside the current camera footprint.
Operational numbers
Why this matters
Nest success on Kauaʻi (no mongoose) runs at 75 to 82 percent. Nest success at Hawaiʻi Volcanoes National Park (mongoose present) was 58 percent in the comparable Amidon dataset. The 2019 federal downlisting rule put the difference squarely on mongoose. Removing mongoose from nēnē nesting habitat on Hawaiʻi Island is one of the few levers we have on that gap.
Cats add a second pathway. They prey on goslings and they shed Toxoplasma gondii, the most common infectious disease diagnosed in nēnē, with 21 to 48 percent seroprevalence across tested populations. Rats prey on eggs and very young goslings. The control program is built around those three predators because that is where the science points.
Removal counts are not the success metric on their own. Whether nēnē fledge more goslings is.
Get involved
Sign up for updates on training, workshops, and volunteer trapping.
Report sightings
Mongoose, cats, rats, and other invasive animals go on FeralMap. Reports get routed to the right agency by species and island.
Visit FeralMap.com