Palmyra Atoll has been free of invasive rats for more than three years and native plants and animals are steadily recovering! A team of four researchers recently returned from a 2014 trip to conduct scientific monitoring to determine the impacts of removing non-native rats. Since the last scientific monitoring trip in 2012, both scientific and anecdotal observations show positive early effects of removing invasive non-native rats and are important indicators of potential long-term recovery of native plants and animals.

Using protocols developed by the University of California – Santa Cruz, the team measured presence and abundance by counting seedlings in a specific area (along transects), in long-term vegetation plots, and by counting seedlings around adults trees. Without rats, several native tree species are rebounding. In particular, the naturally prolific Pisonia grandis trees, where many seabirds roost and nest, have increased. With rats removed, Pisonia grandis seedlings are abundant, and three-year old trees that sprouted in 2011 are now towering overhead (photos below). Before the rats were removed, no seedlings of these trees were observed. A recent study by researchers from Standford University found that Pisonia play an important role in both the terrestrial and marine health of the atoll. Seabirds roosting on these trees fertilize soils below, which increases coastal nutrients and the abundance of plankton, thus attracting manta rays to coastlines bordering stands of native forest (You can read the full paper here.)

Key results include:

-Increased numbers of seedlings of native tree species, Pisonia grandis and Pandanus fischerianus, on 56 transects.
-Increased numbers of seedlings of two species that were absent before rat removal, Guettarda speciosa and Cordia subcordata. The team found 11 C. subcordata seedlings where only two were found in 2012; none were observed before rat removal.
-With rats no longer present on the atoll, the numbers of invasive Coconut Palm (Cocos nucifera) seedlings are unfortunately increasing as well. The U.S. Fish and Wildlife Service (USFWS) and The Nature Conservancy (TNC) are investigating a strategy to control invasive Coconut Palms so that native tree species have room to spread and re-establish Palmyra’s native forest. This is an important next step in restoring the atoll.

Fluctuations in invasive ant populations
The team is also monitoring Palmyra’s terrestrial invertebrate response to rat removal. The 2012 survey found increases in the abundance of most of these insects; however, in 2014, the monitoring team found that this trend had reversed. For example, in 2009 the team found on average 6.6 ants per sample. In 2012, they observed an average of 77 ants per sample and, this year, they found 9.9 ants per sample. Palmyra has 10 species of ants, all introduced and most are invasive. Long-term monitoring will be key to understanding this trend and the mechanisms for these fluctuations.

Two new crab species detected

Two new land crab species (Geograpsus grayi and Ocypode cordimanus, above) have been detected on the atoll since the removal of rats. It is possible these crabs were present before rat removal, but kept in such low numbers due to rat predation that they were not observed by scientists. Crabs such as these play an important role at Palmyra as predators and scavengers of other invertebrates.

Seabirds play critical roles on coral atolls by bringing marine nutrients ashore and feeding the plant community. Seabirds are typically longer-lived animals and expected to be slower in returning to the atoll because they need time to prospect for their ideal nesting sites. We are currently monitoring for seabirds using new technologies such as automated acoustic monitoring songmeters. These microphones can be deployed for months at a time, and when brought back to the lab can be analysed to detect any bird calls. In addition, the USFWS is continuing regular monitoring of seabirds and shorebirds throughout the year at Palmyra Atoll. The hope is that species not seen breeding there in many years, such as the Wedge-tailed Shearwater, return and their eerie cries will fill the sky. Some observations indicate that White Tern nests appear to be increasing. In the first round of scientific monitoring, we recorded just one nest along the vegetation transects. This year, we found 18 nests. Black and Brown Noddies are also beginning to use more of the available nesting habitat across the atoll. In 2014, nests were found on six islets, double what was seen on the previous monitoring trip.

Native Species Expected to Rebound on Rat-free Palmyra Atoll

by Sally Esposito on January 28, 2013

Kathleen Goldstein, Island Conservation, 202-841-0295
Evelyn Wight, The Nature Conservancy, 808-587-6277
Joan Jewett, U.S. Fish and Wildlife Service, 503-231-6211
Native Species Expected to Rebound on Rat-free Palmyra Atoll

January 28, 2013

Palmyra Atoll is rat-free one year after a major effort to remove these invasive predators, the U.S. Fish and Wildlife Service, The Nature Conservancy, and Island Conservation announced today.

Removing non-native rats was the top priority for the Palmyra Atoll Restoration Project, a multi-year effort to protect 10 nesting seabird species, migratory shorebirds, the rare coconut crab, and one of the largest remaining native Pisonia grandis forests (a rare flowering tree in the Bougainvillea family) in the tropical Pacific.

Palmyra Atoll, approximately 1,000 miles south of Honolulu, Hawai‘i, is cooperatively managed by the U.S. Fish and Wildlife Service and The Nature Conservancy as a National Wildlife Refuge and a scientific research station. The area includes 25 islets covering 580 acres of land, and thousands of acres of healthy coral reefs. In 2009, the refuge and waters surrounding it were also included in the Pacific Remote Islands Marine National Monument.

Non-native black rats were likely introduced to the atoll during World War II, and the population grew to as many 30,000 rats. The invasive rodents eat eggs and chicks of ground and tree-nesting birds, particularly sooty and white terns. Rats also eat land crabs and the seeds and seedlings of native tree species.

To reverse this trend, in June 2011, the U.S. Fish and Wildlife Service, The Nature Conservancy, and Island Conservation carefully and strategically implemented the removal of the destructive, non-native rats from Palmyra Atoll, using a rodenticide that had been successful in similar projects on other islands. The Palmyra project was the result of more than seven years of planning and research to ensure that native species were not harmed during the removal, and was the first step in a longer-term effort to restore the atoll’s ecological balance.

“This wonderful atoll is again able to thrive the way nature intended—without rats. Palmyra has been infested with rats for so long, there will be benefits to wildlife we didn’t even fully anticipate—such as the explosion of the fiddler crab population that we’re seeing,” said Susan White, Monument Superintendent/Refuge Project Leader, Pacific Reefs National Wildlife Refuge and Monuments Complex, U.S. Fish and Wildlife Service. “Palmyra’s crucial role in sustaining the Pacific oceanscape is solidified because of this remarkable team of exceptionally talented people.”

Using the same proven methods that were used years before to detect the extent of the rat problem on Palmyra, scientists conducted surveys over a month-long period this summer and confirmed that the entire atoll is currently rat-free. In the tropical climate at Palmyra, rats reproduce approximately once every 3-4 months, so conducting surveys one year after the removal effort is sufficient time to detect rats remaining on the atoll. During the summer, the project partners established a network of 286 rat detection stations that covered the entire atoll. Each station was checked four times during the course of one month. Aside from the detection stations, team members spent hundreds of hours scouring the atoll for natural indicators of rat presence. In accordance with observations of the recovery of native species over the past year that suggested that the project was successful, the recent monitoring found no rats after one year.

“Millions of seabirds, trees, crabs and other native species can now thrive in their home without the threat of being eaten by rats. Staff and visitors to the atoll have seen a large increase in the numbers of crabs, insects, seedlings and seabirds. Our collective efforts to bring balance back to Palmyra are working. The scientific rigor, attention to detail, and collaboration is a testament to the integrity and cooperative nature of our partnership,” said Suzanne Case, Executive Director of The Nature Conservancy’s Hawai’i program.

The University of California Santa Cruz Coastal Conservation Action Lab (UCSC-CCAL) is monitoring the response of Palmyra’s terrestrial ecosystem by comparing measures of seabird, shorebird, and plant populations taken before and after rat removal. In the summer of 2012 they found dramatic increases, including:

• Over 130% increase in native tree seedlings (Palmyra has ten locally rare native tree species), and the first record of Pisonia seedlings (no seedlings were observed in 2007 prior to rat removal);
• A 367% increase in arthropods (such as insects, spiders, and crabs); and
• No change in Bristle-thighed Curlews found at Palmyra (special care was taken to ensure this imperiled species was not negatively impacted by the rat removal project)

“With the atoll free of rats, we are already seeing a dramatic increase in many things that rats preyed upon: nesting seabirds, migratory shorebirds, native tree seedlings, and small invertebrates like fiddler crabs. The island is truly rebounding,” said Gregg Howald, North America Regional Director, Island Conservation.

Although Palmyra is rat-free today, the threat of re-introducing rats or other invasive species is present anytime a boat or airplane travels to the atoll. A detailed prevention plan is in place to minimize the threat of non-native species being introduced to the atoll.

The removal of introduced species such as black rats is a proven, effective conservation tool that has been successful on numerous islands across the globe, including the Galapagos archipelago, a multitude of islands in New Zealand, the Channel Islands off the coast of California, and Hawadax Island (formerly ‘Rat Island’) of the Aleutian Island chain in the Alaska Maritime National Wildlife Refuge.

Additional Resources Available:

• Photos –
• Map -

Update: October 2012

October 19, 2012

The USDA-National Wildlife Research Center conducted independent monitoring of the project to evaluate the bait application rate, impact on target population, and ecosystem reaction. The report is complete and available for download here.

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Update: March 2012

March 1, 2012

By: Alex Wegmann, Project Manager, Island Conservation Initial results from an August 2011 monitoring trip to Palmyra Atoll (Palmyra) are available and are positive! Although we continue to see anecdotal observations of birds, plants and invertebrates thriving, ongoing scientific monitoring will determine the impacts of removing non-native rats from Palmyra and the overall success of [...]

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Update: 10 August 2011

August 10, 2011

By: Susan White, Incident Commander One of the many unique aspects of this project is the immediate and ongoing presence of people on the atoll after completion of baiting operations. Often-times when bait is applied to islands to remove rats, there are no people living there afterwards to see what happens right away. At Palmyra, [...]

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Update: 13 July 2011

July 13, 2011

By: Susan White, Incident Commander The operations team successfully ended the application phase of the Palmyra rat removal project. Some team members returned to their homes on June 30th while others continued on with the ship, the Research Vessel Aquila, to other islands in the Pacific to conduct similar projects. A few team members remain [...]

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Update: 27 June 2011

June 28, 2011

By: Susan White, Incident Commander The second full application of bait was completed on June 26th – all aerial and hand broadcast applications, as well as all canopy baiting of palms, has been completed! The team ended on a wonderfully positive note, having completed the mission successfully, despite challenges and long days. An early anecdotal [...]

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Update: 21 June 2011

June 22, 2011

By: Susan White, Incident Commander The first full application of bait that began on June 12th was completed on Father’s Day Sunday, June 19th. This effort required some team members to slog through muck up to their thighs and trudge through water and underbrush to reach the overhanging palm canopy and bait it. The monitoring [...]

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Palmyra Atoll National Wildlife Refuge Restoration Project Status

June 18, 2011

17 June 2011 By: Susan White, Incident Commander On June 12, 2011, after 5 days of on-island training and equipment preparation, our inter-disciplinary team began bait distribution to eradicate rats from Palmyra Atoll. Yesterday, we completed an important milestone: the first round of aerial and hand broadcast bait application was finalized. Ground teams are now [...]

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Record of Decision Signed for Palmyra Atoll Restoration Project

June 8, 2011

On May 29, 2011, the Record of Decision to restore and protect native species and habitats of Palmyra Atoll National Wildlife Refuge by removing all nonnative rats was signed. The full document can be viewed here.

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