Just 3 Percent of Forest Bird Habitat in Hawai`i Is Protected from Ungulates

posted in: September 2010 | 0

By now, everyone who attends a hearing on a proposed natural area reserve or an application for a fence or any other plan to protect habitat for native Hawaiian species knows the drill. There’s the predictable, earnest testimony from those who support the protection and conservation of native species. And then there’s the rant of the hunters, who claim the proposal represents one more blow to their traditional rights, one more area closed to their sport, one more family who will go without meat on the table because tree-huggers value plants and birds above people.

A presentation at the recent Hawai`i Conservation Conference, held in Honolulu August 4-6, put into some perspective one of the most frequent of the hunters’ laments: that they’re losing ground to conservationists. One of the presenters, Steve Hess of the U.S. Geological Survey’s Pacific Island Ecosystems Research Center, displayed on the big screen behind him a table showing the total area in the main Hawaiian islands that had been cleared of ungulates, the area of potential forest bird habitat; and the area where the two categories overlapped – that is, the area of forest bird habitat that is actually free of pigs, deer, cattle, goats, sheep, and mouflon.

All totaled, just 746.2 square kilometers (184,390 acres) of land in the inhabited islands plus Kaho`olawe have been cleared of ungulates. The area that could potentially be good forest bird habitat is 7,707 km2 if it were ungulate free. Yet hooved animals have been removed from just 266 km2 of good forest bird habitat. In other words, barely three percent of the land that could be used to protect Hawaiian forest birds, among the most endangered in the world, is protected from ungulates.

And there is virtually no significant area in the main Hawaiian islands where all mammalian pests – including cats, dogs, rats, mongooses, and rabbits – have been eradicated, Hess said. While small mammals have been removed from islets, a proposed predator-proof fence at O`ahu’s Ka`ena Point Natural Area Reserve would be the first area of meaningful size (around 50 acres) to protect albatross and wedge-tailed shearwaters from all of them, he noted. (Whether the fence will be built is not settled at this time: for more on the subject, see Teresa Dawson’s “Board Talk” column, elsewhere in this issue.)

Kaho`olawe, where goats have been eradicated, still has cats and rats. Removing these animals would be “logistically challenging,” he says, because of remaining unexploded ordnance on the 115.5 km2 island used for years as a training area for Navy bombers. Still, he adds, Kaho`olawe may become increasingly important as a refuge for seabirds and possibly native plants displaced by sea level rise or as habitat for additional populations of birds threatened with extinction should their existing habitats be wiped out by disasters.

Repeat Performances

The last century saw repeated, concerted efforts to clear forests of ungulates. Pigs and goats were eradicated from Lana`i, only to be replaced with axis deer, mouflon, and pronghorn antelope, thanks to the state’s deference to sport hunters. (The antelope died, but mouflon and deer continue to limit the recovery of vegetation on the island.) Hess notes that in the 1930s, when the Mauna Kea Forest Reserve was fenced, nearly 47,000 feral sheep and more than 2,200 other ungulates were removed by foresters and workers in the federal Civilian Conservation Corps. But, he adds, “populations rebounded when sport hunting became a major management goal of territorial wildlife biologists.” By statehood, the forest reserve was in dire condition – which, however, didn’t stop the state from introducing mouflon-sheep hybrids to improve hunting opportunities. A federal court order in the famous Palila case requires the state to eradicate sheep and mouflon from the mountain, and by Hess’s count, more than 87,000 sheep have been taken from Mauna Kea over the last 75 years. But eradication remains a distant goal. The fence put up 70 years ago is in disrepair and animals continue to migrate into the forest reserve. Each year, the state, through contracted aerial hunts, continues to remove hundreds of mouflon and sheep from the mountain.

Eradication of goats from Hawai`i Volcanoes National Park began in 1968, but wasn’t accomplished until 1984. In 1989, Haleakala National Park became goat-free. One year later, the last goat was taken from Kaho`olawe.

Feral pigs and cattle have been removed from the national parks, some state reserves, and the Hakalau Forest National Wildlife Refuge on the Big Island. Eradication of the ungulates at Hakalau was a long, protracted effort (from 1988 to 2004), Hess notes, “due in part to the large size of one management unit, interspersed areas of continued sustain-yield hunting, high densities of pigs, and relatively late use of snares.” (Hess was too kind to mention that the Piha tract – what he describes as the “interspersed areas of … hunting” – is owned by the state, which does not even attempt to control pigs, cattle, weeds, or any other threat to natural resources in the area.) Keeping pigs out of the refuge “requires maintenance in perpetuity,” Hess said.

* * *
Kahuku Mouflon

Over the years, resource managers have devised ways to remove sheep, goats, and pigs from forest areas. Developing an efficient way to eradicate mouflon – which don’t herd and can leap over high fences – is a work in progress.

But thanks to work done by the National Park Service at the 469 km2 Kahuku unit of Hawai`i Volcanoes National Park, removal of mouflon from this area, acquired in 2003, might happen on an accelerated timetable.

Just eight mouflon were introduced to Mauna Loa in 1968, Hess said during his second presentation at the conservation conference. With the population doubling every 3-4 years, there were an estimated 2,586 mouflon on the former Kahuku Ranch by 2003. The grazing pressure of the animals put at risk the native Hawaiian plants found there, including many that are listed as endangered or threatened, said Hess. Numbers of the animals have declined thanks to hunting pressure over the last decade, but as the population decreases, it gets harder and harder to remove the remaining numbers, he noted. “We need more effective control efforts,” he said.

That need drove Hess and colleagues to study the home ranges of mouflon and attempt to discover ways to bait them. In the process, he discovered that the animals “don’t get around much.” Bait stations set up to lure the animals with feed took two months to gain acceptance and because of the small home ranges, Hess and his team learned that they needed to be spaced less than a kilometer apart.

Much more needs to be done before the National Park Service can settle on an eradication strategy for mouflon. The work of Hess and his colleagues continues. But with the knowledge gained thus far about mouflon behavior, that goal is years closer to being realized.


* * *
The Nasty Side of Cats

Ungulates are herbivorous. Their threat to Hawaiian birds is serious because of the damage they inflict on native vegetation. Feral cats, however, are carnivores, with birds among their favored prey. Despite the menace they pose, removing cats from the wild is extraordinarily hard – and not only because they are intelligent and resourceful.

Feral cats look like domestic cats. Genetically speaking, they are identical. And therein lies one of the biggest obstacles to controlling them. The images most people have of cats and the fond associations they have with them make it hard for many folks to think of these animals as anything other than rascally cartoon characters, cuddly kittens, or cherished companions.

But cats living in the wild have survival skills that make them a lethal threat to many of Hawai`i’s rare and endangered birds. At sea level, feral or abandoned cats have decimated shearwater colonies on Maui. At higher elevations, they are known to prey on ua`u (Hawaiian petrels, orPterodroma sandwichensis), the Hawaiian goose, or nene (Branta sandvicensis) and palila (Loxioides bailleui). According to the U.S. Geological Survey’s Pacific Islands Ecosystem Research Center, up to 11 percent of palila nests are preyed upon by cats each year.

Toxoplasmosis, a disease carried by cats, can be fatal to birds and has even been known to kill an endangered Hawaiian monk seal.

At the conservation conference, Hess discussed some of the remarkable findings he and colleagues have made about the behavior of feral cats on Mauna Kea. After trapping feral cats and fitting them with radio collars, the scientists released them, monitoring their movements and activities. According to Hess, some males had home ranges of up to 8 square miles, the largest home range yet reported in the world. (Home ranges of female cats averaged about 3 square miles.) As Hess notes in a fact sheet on feral cats (available on the USGS PIERC website,http://biology.usgs.gov/pierc), “the significance of these large home ranges and daily movements is that cats threaten nesting birds from great distances. In addition, several cats may hunt in the same area, exposing birds to threats from a host of different cats over a short period of time.” For palila, whose entire range is just 54 square miles, “each male cat represents more than 10 percent of this area.” At night, when birds have settled on their nests, they are especially vulnerable to the mostly nocturnal cats. Yet another factor making palila nestlings exceptionally exposed is their long development period – twice as long as that of continental songbirds.

Colonial Cats: Cheryl Lohr of the University of Hawai`i at Manoa described her efforts to compare the costs of managing stray cat colonies by either trap-neuter-release (TNR) programs or trap and euthanasia (T&E). In recapping the history of cat colonies on O`ahu, Lohr cited Mark Twain’s observation in 1866, when, visiting Honolulu, he saw “tame cats, wild cats, singed cats, individual cats, groups of cats, platoons of cats, companies of cats, regiments of cats, armies of cats, multitudes of cats, millions of cats.”

The situation is little changed today. On O`ahu, hundreds of cat colonies exist, several of them managed under the TNR program. Using a computer model of what might be a typical cat colony, Lohr estimated that an intensive T&E program could eradicate a colony in a year, whereas a TNR program would take at least 20 years to be eradicated – assuming no new recruits. If as few as 3 percent of pet cats are released and join a colony in a given year, the effect of a T&E program would be wiped out in just four years, given cats’ high reproductive rate. Although TNR programs are nearly two and a half times more expensive than T&E, Lohr said, given the ongoing abandonment of cats, perhaps the best policy to deal with the problem is to educate pet owners on the need to keep cats indoors, and spay or neuter them. In a discussion that followed Lohr’s presentation, she noted that it is a waste of time and money to include males in TNR programs. So long as even one intact male cat exists in a colony, all unneutered females are likely to reproduce.

The Scourge of Weeds

“Is there anything in native ecosystems that strawberry guava doesn’t f&*k up?”

That was the question asked by Charles Chimera in his HCC presentation on the puzzling absence of epiphytes and bryophytes – mosses, ferns, lichens, and the like – from strawberry guava (Psidium cattleianum), also known as waiawi, one of the worst invasive plants in Hawaiian forests. Many past studies have looked at the impact of strawberry guava on forest structure, shifts in vegetation, changes in soil chemistry, and the like. Chimera, who works with the Pacific Cooperative Studies Unit of the University of Hawai`i, has been casting his view upward, onto the trunks and branches of trees.

Chimera studied epiphytes in two wet forests where waiawi has invaded: one on Tantalus, O`ahu, another at Kipahulu, in Maui. Trunks of `ohi`a (Metrosideros polymorpha) are typically carpeted with epiphytes. Those of waiawi are bare. One possible explanation Chimera offered was the very structure of the bark. `Ohi`a bark is rough, giving epiphytes and bryophytes a surface they can easily cling to. That of waiawi is smooth and peeling.

Not only does strawberry guava reduce plant diversity on the forest floor, Chimera said, it also reduces it in the upper forest strata – “a loss that could contribute to a decline in invertebrate and bird populations dependent on habitat provided” by these organisms.

Most important of all, he concluded, the loss of bryophytes and epiphytes, combined with the decline in understory cover that occurs in invaded forests, could modify the hydrological cycle, leading to more runoff, less soil moisture, and diminished aquifers.

Pampas Grass: Long a favorite of landscapers for its showy tufts and billowing base, Pampas grass has become the bane of native ecosystems outside its home range of South America. In Hawai`i, two varieties are found: Cortaderia jubata and C. selloana. The former was first noted in the late 1980s in upcountry Maui and in Haleakala National Park. The latter, which is sterile unless both male and female plants are present, was not thought to be much of a threat here – until (naturally) both sexes were recently found.

Brooke Mahnken, Stephanie Miller, Teya Penniman, and Michael Ade of the Maui Invasive Species Committee have been devising methods to control Pampas grass on Maui for more than a decade. Given its ability to cling to steep slopes and to inhabit a broad range of habitats – from low and dry to high and wet – the challenges to eradicate Cortaderia spp. on the island are formidable, as Mahnken explained to his audience at the HCC.

Mahnken reviewed in particular the efforts to eradicate Pampas grass from high-value native forests in East Maui. In 2008, MISC established a field camp in a high-elevation cloud forest at Honomanu, accessible only by helicopter. Each year, MISC staff criss-cross the area, pulling out young plants and poisoning mature ones while mapping the precise location of each individual. In the course of three years (2008-2010), 236 mature plants were discovered and killed, wiping out the Honomanu infestation.

As difficult as the East Maui work was, wiping out infestations elsewhere will test the mettle of even the most ingenious weed-whackers. Pampas grass grows on the sides of steep cliffs in the West Maui mountains. While spraying from helicopters might poison some plants, the technique is risky and expensive in the best weather – and impossible in the rains and wind that more typically buffet the summits. But the most frustrating obstacles to eradication have to be the landowners who continue to believe that Pampas grass alone can satisfy their desire for landscape drama. Even though the plants are on the state list of noxious weeds, landowners have to give their consent before MISC workers can go onto their property to remove the offenders. The low-hanging fruit – Pampas grass in all its glory, heads heavy with thousands of fertile seeds waiting to be carried off by the trades, waving to the MISC workers as they head to the hills – can’t be picked at all.

Patricia Tummons

* * *
Large-Scale Rat Trapping May Aid Cyanea Recovery

Even if ungulates and cats are eradicated from a forested area, rodents — which eat the seeds and fruit of native plants and compete with native fauna for food and habitat — can still limit recovery.

Traps and diphacinone bait are some of the most commonly used tools to control rodents in Hawai`i’s natural areas. But while aerial toxicant dispersal appears to work well for insular areas, like offshore islets, it may not be the silver bullet in all cases. As rat expert Stephen Mosher said at the conservation conference, “We need to know where traps fit.”

Since 1997, the O`ahu Army Natural Resources Program has been using both traps and toxicants. In May 2009, in an effort to find an alternative to toxicants, Mosher, who works both with the Army and with the University of Hawai`i’s Pacific Cooperative Studies Unit, tested the efficacy of a large grid of snap trap boxes, based on rat control practices currently employed by New Zealand’s Department of Conservation.

Members of the O`ahu Army Natural Resources Program (including Mosher), joined by University of Hawai`i’ botany graduate student Richard Pender, set more than 400 snap traps across 26 hectares in an Army-controlled area known as the Kahanaiki Management Unit, a Cyanea superbareintroduction site in the mixed-mesic forest of O`ahu’s Wai`anae mountains.

(Years ago, the U.S. Fish and Wildlife Service tasked the Army with stabilizing the populations of 29 endangered species, including Cyanea superba, that are jeopardized by military training activities in Makua Valley, which is adjacent to Kahanaiki Valley. As part of its stabilization efforts, the O`ahu Army Natural Resources Program has planted some 250 Cyanea superba plants in Kahanaiki Valley. In 2005, according to a FWS report, survivorship ranged from 35 percent to 80 percent. The report also notes that in addition to invasive plants, feral pigs, and fire, rats are considered one of the main threats to Cyanea superba.)

In addition to the traps, the Army/UH team set up tracking tunnels, which were checked daily, as well as motion-sensing cameras to documentCyanea superba fruit predation in both the Kahanaiki unit and in their adjacent control site, the state’s Pahole Natural Area Rerserve.

Based on their tracking data, they found that rat activity at Kahanaiki averaged 28 percent compared to 41 percent at Pahole, according to Mosher’s conference abstract.

Although the team managed to trap 805 rats over the next year, they had problems with slugs constantly eating the bait, whether it was peanut butter, chocolate, coconut, or wax with food additives, Mosher said. Sprinkling salt around the trap wouldn’t help because the forest is pretty messy and damp, he said. He tried putting salt on the peanut butter, but that didn’t help, since the slugs would eat the bait, then die on the trap.

He added that the rat control did not appear to affect invasive wolf snail (Euglandina rosea) populations and preliminary results suggest that the trapping may have improved lama (Diospyros sandwicensis) seedling recruitment and reduced lama seed predation.

Mosher admitted that the trapping effort, which now includes about 480 traps, is a work in progress and that determining its impacts on endangered tree snails in the area (Achatinella spp.) will require long-term monitoring. However, Pender’s efforts to determine whether large-scale rodent control can reduce predation on fruit of the endangered Cyanea superba subsp. superba, also known as haha, suggests that traps alone can make a significant impact in certain areas.

As Pender reported at the conference, he and his team (Mosher, the Army’s Lalasia Bialic-Murphy, and UH’s Aaron Shiels) monitored 36 cyanea trees in Kahanaiki and 42 trees in Pahole every three days for pre-dispersal fruit predation, and found that 47 percent of the fruits in Pahole had been eaten, compared to only four percent in Kahanaiki.

And the cameras showed that black rats (Rattus rattus) were responsible for a lot of that predation. The 13 cameras set up in Kahanaiki documented eight visits to cyanea trees, while the nine cameras at Pahole captured 22.

To measure post-dispersal fruit predation, the team placed mature fruit in the tracking tunnels and checked them daily. They found that rats removed 86 percent of the fruits in Pahole, compared to only 17 percent in Kahanaiki.

To determine whether rodents were killing or dispersing the seeds, the team fed fruits to captive black rats and house mice (Mus musculus). Pender said they found that rats killed all of the seeds, while the mice were “generally disinterested” in the fruit.

In addition to the rat predation, Pender said, research has shown that slugs eat 49 percent of cyanea seedlings.

“Between rats and slugs, there’s little chance for recruitment. … For the restoration of this species, we need to take these two out of the equation,” he said.

Teresa Dawson


Volume 21, Number 3 — September 2010