The meeting of the Society of Conservation Biology in Hilo last summer was a veritable feast for science junkies and journalists interested in the latest research on issues relating to Hawai`i’s troubled native species.
Our reporting on some of the highlights of the meeting continues. (Our initial report may be found in the September article of Environment Hawai`i.)
Wide-ranging Cats, Wide-ranging Impacts
The tiny palila, an endangered Hawaiian honeycreeper, has stood up in court against the sheep, goats, and mouflon of Mauna Kea that were eating it literally out of house and mamane-tree home. But now it faces another threat: feral cats.
Since 1998, between 8 and 11 percent of palila nests have been victimized by cats, according to a study by Dan Goltz, Christopher Murray, Alison Agness and Paul Banko of the USGS. The researchers summarized their work on a poster exhibited at the SCB meeting.
Over a period of 18 months, the team tracked five male and three female cats, all of which had been trapped on Mauna Kea and outfitted with radio collars. Some of their findings were eye-popping. The range of the males averaged more than 30 square kilometers, with one tomcat covering a territory three times that size – 95 square kilometers. The range of females was a much more modest 4.7 square kilometers on average.
What does this mean? As the authors dryly summarize, “local control efforts will be complicated by immigration,” and “landscape-level control will be very difficult.”
Feral cats are a problem on Maui as well – and not just in the mountain areas. Fern Duvall, Maui wildlife biologist for the state Department of Land and Natural Resources, looked at what cats were doing to wedge-tailed shearwaters and the rarer Bulwer’s petrels, birds that breed in coastal colonies.
His depressing findings: of the burrows he monitored, 41 percent had sustained “cat predation events.”
The birds’ own behavior seemed to exacerbate the cats’ impact. April and May were the worst months for predation, when the noise of breeding pairs seemed to attract the cats. August and September were the next worst, when noisy chicks alerted the cats to the colonies.
Duvall found that some of the smaller colonies of birds were vulnerable to total failure, while larger colonies saw the loss of returning adults and both late-stage chicks and adults. By contrast, colonies of birds on Molokini islet, where cats are absent, enjoyed high reproductive rates, illustrating the severity of the cats’ impact on birds nesting on the larger island.
One of the great obstacles to protecting the birds is the presence of large colonies of feral cats that are often “adopted” by people who believe the cats do no harm, Duvall says. The seabirds are right on the coast, often in areas close by the cat colonies. They’re not noticed by the people who tend the cats, he adds, since the birds fly in to their nests well after dark and are gone before sunlight.
“Very often the same [cat] colonies that are being fed are those that are preying on seabirds,” he adds. Often Duvall gets calls reporting bird deaths, although the callers may not know the cause. “It’s cats,” he says. “They’ll go through and kill birds – once as many as 37 adults in one colony in just one night.”
On occasion, the Maui Humane Society has had people move cats, “but the colonies come right back,” he says.
— Patricia Tummons
Aliens in the Alaka`i
The Alaka`i Swamp on Kaua`i is one of the most remote spots you can find in Hawai`i. Yet even in this high-elevation rainforest, far from farm fields and fruit orchards, Hawai`i’s native moths are not safe from the alien wasps introduced to control farm pests.
That’s according to Lawrence Henneman and Jane Memmott of Great Britain’s University of Bristol, who, in a painstaking study, collected more than 60 species of caterpillars from swamp vegetation and reared them in the laboratory to determine whether they had been attacked by parasitioid wasps. (These are wasps that insert their eggs in the bodies of living caterpillars; a wasp rather than a moth eventually develops).
The researchers found that between 5 and 12 percent of the caterpillars they collected harbored the wasps, but they estimate that up to 35 percent of all caterpillars may be attacked by wasps (often, the initial wasp attack kills the caterpillars outright; thus those caterpillars would not have been collected for study). Most of the wasps infesting the caterpillars are species that were introduced to eradicate farm pests.
Wasps weren’t the only problem for native caterpillars; the researchers also found that ladybugs-which were introduced to control aphids but also eat moth eggs-have moved into the Alaka’i Swamp in the past year.
If there’s any good news in this story, it’s that the alien wasps attacking Alakai`s native caterpillars all are species that were introduced to Hawaii before 1950. That means contemporary pest management programs are doing a better job of selected biocontrol agents that stay where they’re released and attack mainly the target species.
(Memmott and Henneman’s work was reported in the August 17 edition of Science.)
— Cynthia A. Berger
Nene Failing to Thrive: Is Junk Food to Blame?
Populations of the Hawaiian goose – the beloved nene – are looking kind of peaked lately. In addition to a low number of adults attempting to breed each season, many of the goslings they produce don’t survive the year.
Many scientists suspect poor nutrition may be responsible. At Hawai`i Volcanoes National Park, biologists Kathleen Sherry and Darcy Hu decided to assay the nutritional quality of a variety of plants and then conduct in-the-field taste tests to see which high-protein native plants were palatable to the young goslings. Sherry and Hu described their work in a poster that was exhibited at the meeting of the Society of Conservation Biologists.
In the hope that eventually some of the nutritious plants could be sown in the park, Sherry and Hu restricted their evaluation to native plants and those that were introduced by Polynesians. Protein content of each plant was analyzed by scientists at the University of Hawai`i-Manoa. Any plant that scored 12 percent protein or higher was then offered up to the goslings.
“I did foraging trials with the goslings on 12 species of plants,” Sherry says. “One of the plants was later demoted to exotic,” so it was removed from consideration. The smorgasbord of proteinaceous plants was served up to three different broods of goslings in their natural, wild setting, with the nene families themselves setting the times.
“All were different,” Sherry says of the three broods’ responses. “Some of the goslings tried everything and were very adventurous. Some stuck with their parents and didn’t try anything that the adults didn’t eat.”
“Tit appeared that the favorites among the goslings tested were Agrostis avenacea, Oxalis corniculata, a Polynesian introduction, then Digitaria setigera,” Sherry says. The first is a native Hawaiian grass; oxalis is a sorrel; and the third is a type of crabgrass that is either indigenous or a very early introduction.
Now Sherry is planting those and eight other species in brooding areas at the park. “We’re hoping to see whether free-flying birds are actually going to utilize the plants in a meaningful way and whether we can proceed to larger-scale tests,” Hu says. The area currently being planted totals little more than 1 acre within a larger 13-acre pen. “Adult nene fly in and out,” Sherry says, “and many tend to bring their goslings there,” since the park does supplemental feeding at the site during the breeding season.
“Our goal is to help restore nene populations by enhancing habitat with native plants rather than focusing solely on increasing the nutritional quality of alien habitat – for example, by mowing grasslands,” Sherry says. “We’re trying to keep the nene as wild as possible while helping them achieve a self-sustaining wild population. And, of course, we’re constantly struggling with predation and roadkills.”
The next step, Hu says, is a more exhaustive search of historical records in an effort to learn what the nene used to eat: “What was it that sustained the larger populations that we may be missing now?” she says. “It could be extinct species that we can’t recapture.”
— Patricia Tummons
Volume 12, Number 4 October 2001
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