Ki‘ai Moku: Predator proof
Sometimes, fences bring freedom.
In Hawaii, habitat loss and invasive species have left little room for native plants and animals. And feral cats and dogs attack seabirds. Rats and mice steal eggs from endangered birds and snack on the seeds of rare plants. Introduced snails and chameleons have munched rare native tree snails close to oblivion.
At Kaena Point on the northwest tip of Oahu, the state Department of Land and Natural Resources tried to protect nesting habitat for seabirds. They closed off the area to motor vehicles and began trapping rats and other predators. It helped – Laysan albatross, moli; and wedge-tailed shearwaters, uau kani; began nesting among the native plants and in the dunes of this coastal ecosystem. In 2011, more than 3,000 shearwaters chicks hatched; and by 2012, 61 pairs of albatross took turns sitting atop their single egg.
Unfortunately, control efforts only reduced the number of predators; it didn’t stop them. In a typical year, 15 percent of seabird hatchlings were killed. Periodically, stray dogs wandered into the reserve with catastrophic results. In 2006, 113 shearwaters were killed in a single night. The DLNR decided to build a fence.
Predator-proof fencing has been used extensively in New Zealand, but it has only recently gained favor in Hawaii. It offers a promising solution for ongoing struggles like those at Kaena. Rather than ongoing trapping to remove predators, resource managers can create protected “islands” where native plants and animals have a chance to recover.
On Maui, two fenced enclosures are being built on the windward side of the West Maui Mountains at Makamakaole. One is for Newell’s shearwaters, or ao, and the other is for Hawaiian petrels, or uau. Both species nest in underground burrows and are vulnerable to attack by rodents, mongoose and feral cats. The fences are designed to keep these hungry creatures out. First Wind, which built Kaheawa wind farm, is creating the 4-acre enclosures as part of its seabird mitigation program to address impacts caused by the towers.
The Makamakaole fences will be similar to the one at Kaena. The mesh on these predator-proof fences is so small that even two-day-old mice can’t crawl through. The fence will be topped with a metal hood to keep any animals from climbing over, and a skirt extends along the base to keep animals from burrowing under.
Once the first enclosure at Makamakaole is complete, invasive animals will be removed and sound systems will be installed that broadcast seabird calls to attract prospecting birds. If they land to investigate, they may find home in one of the 50 artificial burrows.
Erica Thoele, supervisor of habitat conservation plan compliance with First Wind, says: “Hopefully they’ll think this is a safe place and build a nest.”
Crews will trap for predators along a 100-yard perimeter outside the fence in case any seabirds decide to nest nearby. Ongoing monitoring will help evaluate whether seabirds are using the artificial burrows or digging their own nests in the enclosure.
Monitoring at Kaena Point has shown promising results. The 700-yard fence was completed in March 2011 and protects 59 acres of coastline from predators. There have been dramatic increases in seabird productivity now that the rats have been removed – a 25 percent increase in the number of albatross nesting at Kaena, and a doubling of the number of wedge-tailed shearwater chicks fledging.
Native plants are also showing signs of recovering with more abundant fruits, seeds and seedlings than had been observed prior to removing predators. The fences may keep the hungry critters out, but well-behaved humans are still welcome at Kaena. Double-door gates along the fence allow access to the reserve.
Fencing projects elsewhere in the state are in the works. The Oahu Army Natural Resources Program built “snail” fences to protect rare native snails from rats, mice, Jackson’s chameleons, and the invasive rosy wolf snail. A new fence will be built next year at Kilauea Point National Wildlife Refuge to enclose nearly 8 acres of habitat for six different species of breeding seabirds.
Plans are in process for a fence on Lanaihale to protect uau nesting habitat. Learn more about predator-proof fencing at Kaena by visiting the website hawaii.gov/dlnr/chair/pio/nr/2011/NR10225.pdf.
* 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.