On June 29 and 30, about 500 scientists, resource managers, students and others with a stake or interest in Hawai’i’s natural resources filled the ballrooms of the Hilton Hawaiian Village in Waikiki to catch up on the latest studies being undertaken by their peers.
The 2004 Hawai’i Conservation Conference, sponsored by the Hawai’i Conservation Alliance, was built on the theme, “Hawai’i’s Invasive Species Challenges.” Discussions spanned a broad range of topics: from the proper use of rat poisons to new fence designs to alien coral and barnacle invasions.
Here is a summary of just a few of the more than 50 talks presented at the two-day event.
Dave Smith, a resource manager with the Department of Land and Natural Resources’ Division of Forestry and Wildlife, was never able to get really psyched about managing the scant resources on the tiny islet in Kane’ohe Bay called Mokoli’i (also known as Chinaman’s Hat).
The island is owned by the City and County of Honolulu, but its designation as a seabird sanctuary allows DOFAW to do some resource management. For decades, Mokoli’i had been dominated by alien plants, insects and rodents. To many, the future of the island’s few rare native species looked grim.
Mokoli’i did support a struggling population of wedge-tailed shearwaters, but with just one chick found in the islet’s 48 active burrows between 1999 and 2001, the population seemed destined for extinction. The endangered grass Panicum fauriei var. carteri, first collected from the island by Joseph Rock in April 1917, was also hanging on in a “teeny patch of less than a dozen plants,” Smith said.
(In 1978, about the islet’s Panicum population totaled little more than 200 individuals divided among two subunits. In 1983, the grass was placed on the federal endangered species list and the entire islet of Mokoli’i was designated as critical habitat. In 1992, plants in both subunits, which by then numbered fewer than 50 individuals, were relocated to the northeast corner of the islet.)
A U.S. Fish and Wildlife Service recovery plan for the grass written in the early 1990s identifies rats as one of many threats to its survival.
“Rats appear to be gnawing at Scaevola sericea, particularly in the Mokoli’i population. This is detrimental to Panicum fauriei, because, at this site, it is the only other perennial native species stabilizing the soil,” the plan states.
The plan identified rat control as an important recovery effort, yet no systematic eradication effort was attempted on the island.
In October 1999, while on a visit to Mokoli’i to monitor seabird nesting, Smith said he spied a black rat scampering from the shoreline up the steep hillside. The rat quickly disappeared and Smith, paddling away in his kayak at the time, didn’t bother to pursue it, thinking it would be impossible catch it in the dense underbrush. Then in February 2002 Waiahole taro farmer Charlie Reppun called Smith’s co-worker John Polhemus asking how he could help rid rats from the little island, where he had camped as a kid as far back as the 1950’s.
“Predator control involves killing things,” Smith said, and is not for the squeamish. “We usually do not use volunteers for predator control work.” But in Reppun’s case, during a recent visit with friends, he had chased down and killed a rat. Recalling the day he had seen a rat and neglected to pursue it, Smith thought, “These folks not only saw a rat, they chased it down and killed it. These are people with the commitment and passion to work with on a rat eradication project.”
And so a partnership was born. DOFAW, with volunteers from the University of Hawai’i and the east O’ahu community, set out 19 bait stations containing Eaton’s peanut-butter flavored blocks laced with rodenticide, nine cages, and snap traps in March of 2002. (The volunteer group included Paul, Nicholas, Fred, Charlie, David, and Pat Reppun; Vivien Lee; Jane and Martha Beachy; Natcha Enesa; Kaua and Hoala Fraiola; Phaeton, and Kaelenui Dickson.) That month they caught 18 rats. By May and throughout June, not a single rat could be found.
Smith said it took about 80 days of volunteer labor to eradicate rats from the island. With no rats destroying the vegetation or raiding the shearwater burrows, the island’s resources rebounded:
While rats could return to the island, which is a short swim from Kualoa Beach Park, it likely will take some time. UH researchers are already looking for ways to help the birds.
Heather Eijzenga of the UH Botany Department is working with DOFAW on ridding the islet of invasive plants, including Christmasberry, lantana, fleabane and several non-native grasses. “This exotic vegetation alters the island ecosystem and greatly reduces available seabird nesting habitat,” she states in a description of her research posted on her website. Christmasberry especially poses a problem for the birds, she writes: it “covers the island in dense, monotypic stands that prevent shearwaters from accessing the ground beneath.” After having cleared plots of the plant in 2003, “a small number of shearwaters nested in the cleared plots, while none nested in the ‘control’ Christmasberry plots,” she reports.
Low-elevation forests, with more alien species and mosquito-borne disease than the cool uplands, aren’t usually considered the best havens for Hawai’i’s native forest birds. But the recent discovery that ‘amakihi are actually thriving in lowland areas on the Big Island means special care should be taken to protect these forests, says Katerine Schletz, a researcher with the U.S. Geological Survey’s Biological Resources Division. Her lab experiments on ‘amakihi (Hemignathus virens) taken from high and low elevations suggest that the lowland forests are “crucibles of evolution.”
While some researchers have speculated that outside migration or longer breeding seasons have contributed to the large numbers of lowland ‘amakihi, Schletz says the most scientists believe that the birds are developing resistance to avian malaria. While genetic differences between highland and lowland ‘amakihi haven’t yet been discovered, Schletz’s laboratory research on the birds’ responses to infection suggests that the lowlanders are evolving.
In 2002 and 2003, Schletz collected ‘amakihi from the 6,000-foot elevation in Waiakea and from the lowlands of Malama Ki. Because malaria is so prevalent in the lowlands, it took her three months to find unaffected ‘amakihi there. In eight months of netting, she said only 18 out of 111 were unaffected by malaria.
Once she had captured enough disease-free ‘amakihi, some were set aside as a control group, and the rest were stuffed into individual sacks containing mosquitoes infected with avian malaria. Once the birds became infected, Schletz monitored them for 36 days. In that time, two lowland ‘amakihi died, compared to five from the high elevations. Of those that survived, Schletz found several differences between the two groups:
All of these differences suggest that the lowland birds are in an intermediate phase of evolution, Schletz said. While she was still analyzing the physiological basis of the birds’ disease resistance, Schletz added that a logical next step will be to identify any genetic differences between upland and lowland ‘amakihi.
Lowland forests aren’t the only under-rated ecosystem when it comes to native bird habitat. Liba Pejchar, a student with the University of California at Santa Cruz, has found that koa plantations may also prove valuable to the endangered ‘akiapola’au (Hemignathus monroi), whose population hovers at around 1,200 individuals.
‘Akiapola’au are known to be old-growth forest birds with large home ranges. Even so, the birds have been frequenting newer areas, such as reforested pasture, where the trees are less than 15 years old. The birds’ use of new forests has led Pejchar to investigate how they’re using koa plantations and whether the plantations could assist in the species’ survival.
To answer these questions, Pejchar studied the behavior and movement of 10 ‘aki family groups over three years in an open, ohi’a-dominated old-growth forest at Pu’u Akala, a densely vegetated one at Naui, and a koa-dominated plantation at Keauhou Ranch, which had been clear -cut, scarified, and was at the time supporting 10 to 12 year old koa.
In all of the forests, she found that the birds foraged almost exclusively on the dead branches of large koa trees. While reproduction rates among the birds were the same at all three sites, Pejchar found that the birds’ home range sizes and territoriality behaviors varied greatly.
At the 23-hectare Pu’u Akala site, she found that the birds ranges had little or no overlap, compared to the 12-hectare Naui site, where the birds ranges overlapped a lot. At the plantation site, which was roughly the same area as the Naui site, Pejchar found that the bird ranges overlapped 41 percent, which she said suggests “a complete loss of territoriality… Birds don’t need to defend their food because there’s so much of it.”
While ‘akis do need ‘ohi’a (for nesting) and use naio, kolea, and olapa as well, the fact that the koa plantation supported the greatest density of ‘akis suggests that there is a great potential for collaboration between conservationists and foresters, Pejchar said.
Build an eight-meter high pen in a remote lava field, throw in some cats and rats and the like, “sit back, have a beer, and watch the animals try to escape.”
No, it’s not Jeff Burgett’s idea of a good time. It’s what he, as a biologist with the U.S. Fish and Wildlife Service, did back in 2002 to test a New Zealand-designed mammal-proof fence in local conditions against local mammalian pests.
In Hawai’i, resource managers are always trying to find better means of controlling feral ungulates, cats, and rodents – all of which damage native ecosystems in some way.
“Long-term exclusion of all alien mammals from natural areas of Hawai`i has the potential to generate large gains in ecosystem function and populations of impacted native species. However, current effective fence designs from New Zealand had not been tested on lava substrates or with mongoose or mouflon,” writes Burgett and the National Park Service’s Kathleen Misajon.
So in 2002, the USFWS and Xcluder built the pen at The Nature Conservancy’s Kona Hema reserve on the Big Island. Thick wood posts that had been plunged into the ground were fitted with wire mesh and topped with a smooth, sloped hood, curved inward, like a fishhook, at its lower edge to keep animals from crawling over the top.
Once the pen was complete, researchers threw in mice, feral cats, mongooses, black rats, and mouflon sheep. Only seven mice escaped, Burgett said, and that was only because they were tiny enough to slip through pockets between the uneven lava ground and the wire mesh. (A few simple design modifications can fix problem that in the future, he says.) A mongoose and some of the rats were able to climb up under the hood, where, apparently frustrated by their inability to break out, they eventually fell asleep.
While the pen was relatively successful at trapping the animals, it hasn’t been tested against axis deer, which are perhaps the best escape artist of the islands’ invasive mammals and a great threat to Maui’s resources. Deer were not tested in the pen because they aren’t found on the Big Island.
The fence may be effective, but its cost is daunting. “It’s like constructing a wall, not stringing a fence,” Burgett said, adding that it costs about $90 a meter to build from scratch or $74 a meter if retrofitted to an existing pig fence.
If or when this type of fence is ever built, Burgett said that in addition to better mouse-proofing, there needs to be a three meter gap between the fence and surrounding trees to prevent rats from jumping over it, a nearby road to allow easy and regular monitoring, and a mild topography with no big streams.
— Teresa Dawson
Volume 15, Number 3 September 2004
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