Maui Invasive Species Committee (MISC)

  • A A A
  • Home
  • Careers at MISC
  • Report a Pest
    • Statewide Pest Hotline
    • Coqui Frog
    • Little Fire Ants
    • MISC Target Pests
  • About Us
    • Who We Are
    • Partners
    • Committee Meetings and Minutes
    • Strategic Plan
    • Contact Us
  • Our Work
    • LFA Detector Dog Program
    • Mālama i ka ʻĀina Award
    • Coqui Frog Control Program
    • Invasive Species Articles
    • Press Releases
    • Technical and Scientific Publications
  • MISC Target Pests
    • Coconut Rhinoceros Beetle
    • Red-Vented Bulbul
    • Rapid ʻŌhiʻa Death
    • Little Fire Ant
    • Coqui Frog
    • Miconia
    • Pampas Grass
    • Ivy Gourd
    • Blessed Milk Thistle
    • Fountain Grass
    • Mullein
    • Rubber vine
  • Get Involved!
    • Community Coqui Control Program
      • Make Your Yard Un-Friendly to Coqui Frogs
      • Community Coqui Control Code of Conduct
      • Effects of citric acid on the environment
      • Where are the coqui frogs?
    • Donate
    • Be Our Eyes and Ears
    • Survey for Little Fire Ants
    • Classroom Visits and Presentations
    • Workshops
  • MISC Target Species

Rats triggered changes in the environment of Hawai’i prior to humans settlement

Posted on March 18, 2021 by Lissa Strohecker

  • Lo’ulu palms, like these pictured in the Kahanu Garden in Hāna, Maui, once lined the coast and sheltered understory plants in arid, windswept plains. Photo by Forest and Kim Starr
  • Rats arrived in Hawaiʻi to find a tasty protein-rich meal in the palm seeds of the palms. Photo by Forest and Kim Starr

Palm trees and Hawaiʻi go together like fish and poi, right?  Kind of.  The coconut palms that line the beaches throughout the state are iconic, but are actually relative newcomers to the islands – one of the “canoe plants” brought to the islands by Polynesians. The only palms native to Hawaiʻi belong to the genus Pritcharidia. They won the sea-current lottery, arriving from the eastern Pacific near the Cook Islands and Tonga some 3.5 to 8 million years ago.  Over time, the extreme isolation of the island chain led to the evolution of 23 to 27 endemic species, found only in the islands.

The first Polynesian voyagers arrived to find loʻulu groves lining the coastlines. These palms grew farther inland as well – in the wet rain forests, across wind-swept plains, and on arid leeward slopes. But within a single generation of the first humans, the loʻulu were mostly gone. To better understand when and why they vanished, scientists have peered underfoot, analyzing what was once wind-borne pollen.

The distinctive shape of a grain of pollen gives clues to its ancestry. The hard walls of pollen help preserve it in the fossil record. By examining layers of pollen deposited over time, scientists can better understand what plants formerly grew in an area.

In the late 1990s, researchers collected and analyzed soil samples from Oʻahu’s ʻEwa Plain, west of Pearl Harbor, to better understand the ecological history of the area. The ʻEwa Plain is arid and isolated from stream flow, providing a stable environment in which dirt and debris, including pollen and bones, accumulated over millions of years. The researchers were especially focused on evaporate ponds — areas where water collects after rainfall, then evaporates – and a sinkhole. Both are places with little disturbance that offer excellent conditions for soil sampling; sinkholes act as vaults for the bones of animals that fall in.  

Huelo Islet off the coast of Molokaʻi is one of the few places in Hawaiʻi free of invasive rats. Loulu palms thrive there as they once did when humans first arrived in Hawaii. — FOREST and KIM STARR photo

From these collections of soil, pollen, and animal bones, the researchers read the story of the ʻEwa Plain. At one time, loʻulu stood tall, shrubby ʻaʻaliʻi and other plants formed the subcanopy. Huge, flightless moa nalo – goose-like ducks – and other land and seabirds had populated the area. The layers then reveal a plot twist – a sudden and dramatic decline in the loʻulu populations and the coincident arrival of a new character – the Polynesian rat (Rattus exulans) – their bones making a timestamp in the sinkholes. Other flowering plants, such as the low-growing ʻāweoweo, became dominant around the same time and bird populations plummeted. Only after the loʻulu population had collapsed do humans arrive in the area – as shown by deposits of charcoal. Rats, initially brought by people, spread across the landscape faster than the humans that introduced them.  Early habitat alteration – the use of fire to encourage growth of grasslands for example – likely impacted loʻulu and native animals, but research findings from the ʻEwa Plain has led researchers to conclude that invasive rats likely catalyzed changes in vegetation that led to the initial decline in bird populations.

Today, loʻulu are still present but scattered, found in very low numbers. A mature loʻulu, one of the taller species, stands out – a distinctive marker in the forest. Cultivating palms in landscape settings may be possible by protecting protein-rich seeds from rats, but in the wild, species of loʻulu are increasingly rare and even endangered. The Hawaiʻi Department of Land and Natural Resources has designated seven palm species for protection through the Plant Extinction Prevention Program. Placement on the list means fewer than 50 individual plants remain in the wild. Offshore islets such as Huelo Islet on the North shore of Molokai offer a glimpse into the past, where loʻulu palms thrive on rodent-free islands.   Conservation efforts in other countries have successfully eradicated invasive rats from islands to protect the native species that live there. New Zealand has set a goal of removing rodent predators entirely by 2050. There are efforts in Hawai’i to protect offshore islets and their rare plants and animals. Learn more about them at https://dlnr.hawaii.gov/removerats/

Lissa Strohecker is the public relations and education specialist for the Maui Invasive Species Committee. She holds a biological sciences degree from Montana State University. Kia’i Moku, “Guarding the Island,” is prepared by the Maui Invasive Species Committee to provide information on protecting the island from invasive plants and animals that can threaten the island’s environment, economy, and quality of life.

This article was originally published in the Maui News on August 8, 2020 as part of the Kia‘i Moku Column from the Maui Invasive Species Committee.

Read more Kiaʻi Moku articles


Filed Under: Kia'i Moku Column Tagged With: 2020, native palms in Hawaii, rats in Hawaii

Got Guano?

Posted on March 25, 2015 by Lissa Strohecker

This albatross colony on Midway Atoll is representative of what the historic density of seabirds may have been throughout Hawaiʻi. Declines in the seabird population  have an impact throughout the ecosystem. Photo by Forest and Kim Starr.

This albatross colony on Midway Atoll is representative of what the historic density of seabirds may have been throughout Hawaiʻi. Declines in the seabird population have an impact throughout the ecosystem. Photo by Forest and Kim Starr.

When horticulturalists at Maui Nui Botanical Gardens want to give an extra boost to their most sensitive and critically endangered Hawaiian plants, they bring out the seabird and bat guano. Why guano? It’s the natural nutrient-packed fertilizer that Hawaiian plants are used to.

Prior to the first canoe reaching Hawaiian shores, taloned and feathered beasts ruled these Islands. Scientists estimate that seabird populations on the main Hawaiian Islands were equivalent to what the 18th century explorers found on the Northwest Hawaiian Islands–in other words, plentiful. Some accounts indicate seabirds were so abundant they blackened the sky. And if they could darken the sky with their wings, they were certainly capable of whitening the ground with their poop, aka guano.

Bird droppings may not be welcome on your car, but plants benefit from the splattered remains of a seabird’s meal. Guano is a gift for growing seedlings: high in nitrogen, phosphate, and potassium–nutrients essential for plant development. The more guano drops from the sky, the more plants sprout from the ground. This growth affects the entire ecosystem. As plants decompose, they provide plentiful and nutritious food for insects, nematodes, snails, and assorted detritivores, as well as soil bacteria and fungus.

An ʻuʻau chick in a burrow. Once plentiful, the ground nesting Hawaiian petrel is critically endgangered, threatened by feral cats, mongoose, and barn owls. Photo by Jay Penniman

An ʻuaʻu chick in a burrow. Once plentiful, the ground nesting Hawaiian petrel is critically endangered, threatened by feral cats, mongoose, and barn owls. Photo by Jay Penniman

Hawaii’s seabird populations are only a fraction of what they once were. The ‘ua‘u, or Hawaiian petrel, was once the most abundant seabird in the Islands. Today this burrowing resident is endangered. In Maui County, remnant populations exist atop the summits of Haleakalā on Maui and Lānaʻihale on Lānaʻi. The reason for the species’ decline is simple, yet irreversible. They were gobbled up by people, rats, mongoose, and barn owls; the hillsides where the birds nested are now pastures, golf courses, farms, and shopping centers. Other seabirds, such as the wedge-tailed shearwater, Newell’s shearwater, and Bulwer’s petrel once filled the air with their cries; these species now live in scattered, isolated populations.

If efforts to restore seabird colonies on the main Hawaiian Islands are successful, this may be a site any resident or visitor to Hawaii can see. For now, you have to visit Midway to see Laysan albatross this dense. Photo by Forest and Kim Starr.

If efforts to restore seabird colonies on the main Hawaiian Islands are successful, this may be a site any resident or visitor to Hawaii can see. For now, you have to visit Midway to see Laysan albatross this dense. Photo by Forest and Kim Starr.

Fewer seabirds mean fewer plant fertilizers. We may never fully understand how declines in pelagic bird populations impact the environment in Hawaiʻi, but research on islands in New Zealand offers some insight into what happens when avian populations crash due to introduced predators. Comparing islands that had been invaded by rats with those still dominated by seabirds, researchers found that the soil on rat-infested islands had a much different nutrient composition and pH. Additionally, the types and abundance of insects and other invertebrates varied, possibly due to differing rates of plant growth and nutrient uptake. The scientists concluded that reducing the seabird population triggers effects that cascade through entire ecosystems, down to the smallest microorganism.

Back in Hawaiʻi, there’s an opportunity to find out what happens in reverse–how a seabird-based ecosystem can recover when the invaders are removed. At Kaʻena point on Oʻahu, rats have been eradicated A predator-proof fence now prevents rodents from re-entering the 59-acre protected area. The resurgence of seabirds, with their increasing deposits of poop, will soon boost nitrogen and stimulate the recovery of native plants.

The loss of a single species has implications for the entire ecosystem. In this case, it’s just about the birds, it’s about what they leave behind, what lives off that, and on and on, all the way down.

You can support the restoration of Hawaiian seabird populations. Visit websites for Maui Nui Seabird Recovery Project (www.mauinuiseabirds.org/restoration/) and Hawaiʻi Offshore Islet Restoration Committee to learn more (http://www.hawaiioirc.org/about-us/).

Lissa Strohecker is the public relations and education specialist for the Maui Invasive Species Committee. She holds a biological sciences degree from Montana State University. Kia’i Moku, “Guarding the Island,” is prepared by the Maui Invasive Species Committee to provide information on protecting the island from invasive plants and animals that can threaten the island’s environment, economy and quality of life.

Originally published in the Maui News, February 8th, 2015 as part of the Kia‘i Moku Column from the Maui Invasive Species Committee.

Filed Under: In the field, Invasive Animals, Kia'i Moku Column Tagged With: 2015, fences for rats, Hawaiian seabirds, rats in Hawaii, seabird guano

Like us on Facebook

Get Involved

  • Donate
  • Classroom Visits and Presentations
  • Meetings Minutes
  • Report a Pest
PCSU logo

Contact Us

Maui Invasive Species Committee (MISC)
Office: (808) 573-6472
Press and Media Inquiries: (808) 344-2756
Mailing Address:
PO Box 983, Makawao, HI 96768

Acting Manager / Public Relations: Lissa Strohecker
E-mail: miscpr@hawaii.edu

Special Projects: Teya Penniman
E-mail: miscmgr@hawaii.edu

Statewide Pest Hotline: 808-643-PEST
Report a Pest Online

© 2025 Maui Invasive Species Committee (MISC) • Sitemap • Log in