When Looking for Snakes,<\/b><\/p>\n
When Is Enough Really Enough?<\/b><\/p>\n
There\u2019s good news and bad news on the brown treesnake front.<\/p>\n
The bad news practically everyone in Hawai`i already knows. Should the snake find its way to Hawai`i and become established here, it would be a disaster \u2013 for forest birds, f![\"October](\"https:\/\/environment-hawaii.org\/wp-content\/uploads\/2015\/10\/October-2015-cover.jpg\")
or power lines, for babes in their cribs\u2026 The list of troubles Guam has seen from the snake\u2019s introduction there could fill several books.<\/p>\n
The good news?<\/p>\n
At Andersen Air Force Base, on the northern tip of Guam, the U.S. Geological Survey has established a geographically closed population of the snake. With no new snake entry possible \u2013 thanks to a snake-proof fence \u2013 and no snakes able to leave, researchers have the ability to study the efficacy of control tools at known snake densities. And from that, reported Amy Yackel Adams, it has been possible to develop a means of determining when the rapid response teams established to respond to reports of snake invasions on other islands can say, with certainty, that their work there is done.<\/p>\n
Yackel Adams, with the U.S. Geological Survey in Fort Collins, Colorado, along with Bjorn Lardner stationed on Guam from Colorado State University, tackled the difficult subject of how you prove a negative. How, that is, you can state, with a high degree of confidence, that something (the brown treesnake) doesn\u2019t exist in a given area.<\/p>\n
And their research was put to the test a year ago September on the island of Rota, in the Commonwealth of the Northern Mariana Islands, when a brown treesnake was caught in an interdiction trap there.<\/p>\n
The event triggered \u201ca litany of questions, ranging from how did that snake get to Rota, presumably a snake-free island? to was it a lone individual, or part of an incipient population? And how long should our rapid response continue?\u201d<\/p>\n
The event marked the first time a snake had been caught in an interdiction trap on a Mariana island, she noted, \u201cand I was tasked with figuring out how long we respond. The answer needed to be justified \u2013 hence, quantifiable. But how much uncertainty is tolerable?\u201d<\/p>\n
The BTS Rapid Response Team jumped into action. \u201cSuccessful eradication is best implemented when it\u2019s ready and prompt, with a team ready to deploy the day a sighting occurs,\u201d she said.<\/p>\n
\u201cTo detect whether a colonization has occurred is difficult,\u201d she went on to say, \u201cespecially for cryptic species like the brown treesnake and ones that occur at low density.\u201d<\/p>\n
Furthermore, \u201crapid response is costly and cannot continue indefinitely. So when do you call it enough?\u201d she said. \u201cIf you don\u2019t search long enough, you might say there\u2019s no incipient population, which allows the population to expand.\u201d While you can confirm the presence of a population through detection, she continued, “the absence of a population can only be inferred probabilistically.\u201d<\/p>\n
To determine the probability of encountering a snake in an incipient population, Yackel Adams turned to the closed population of snakes in the fenced-in area of five hectares at Andersen AFB. Researchers had established 27 transects through the area, and each snake had been individually tagged. While it was \u201cgeographically closed,\u201d she said, it remained \u201cdemographically open,\u201d with the snakes reproducing naturally.<\/p>\n
By conducting surveys along transects far enough apart to ensure \u201cwe won\u2019t see the same snake twice\u201d in the course of an evening, Yackel Adams and her colleagues were able to determine snake densities and the probabilities associated with detecting a snake at a given level of effort.<\/p>\n
In the closed BTS area, with a population of 117 snakes in five hectares, the average density was 24 snakes per hectare, she said. At that density, she and her fellow researchers \u201cwould expect to find 8.2 snakes on a given night\u201d when they walked 5.94 kilometers of transects, for a detection probability of 0.07 percent.<\/p>\n
But there was a confounding factor that prevented this formula from being applied in Rota \u2013 or anywhere else, for that matter: what Yackel Adams called satiation.<\/p>\n
\u201cOn the island of Rota, there\u2019s a lot more prey than exists on Guam. Guam has rodents at densities of one to 16 rats per hectare,\u201d she noted. On Rota, \u201cthere are 9 to 96 rats per hectare.\u201d<\/p>\n
\u201cSo this will have a bit of an impact on the detection probability. A lot more prey is available.\u201d The tools developed in Guam, a \u201cprey-limited situation,\u201d had to be adjusted downward in a prey-rich situation.<\/p>\n
\u201cPoisson distribution provides the answer,\u201d she said. \u201cIt provides the probability of a given number of events in a fixed interval of space and time, provided you have a known average rate and independence between events. Simply put, you can determine the probability of finding at least one snake.\u201d<\/p>\n
On Rota, personnel with the Rapid Response Team walked no fewer than 639 kilometers, without finding a single snake. \u201cWith 95 percent certainty,\u201d Yackel Adams said, \u201cwe would have detected at least one snake given that level of effort, if the density was .16 snakes per hectare or more.\u201d If the density was as high as one snake per four hectares, the likelihood of detecting at least one snake, with that same level of effort, would be 99 percent, she noted.<\/p>\n
\u201cThis is the first time rapid response has ever quantified the level of certainty associated with a given effort,\u201d she concluded. With more work, she said, the method could potentially be transferred to invasive species other than the brown treesnake.<\/p>\n
<\/p>\n
* * *<\/b><\/p>\n
Parrotfish Need More Protection<\/b><\/p>\n
Talks on fisheries management rarely are quite as straightforward as the report that Edward DeMartini gave on parrotfish in Hawai`i.<\/p>\n
The state, he said at the end of his talk, \u201cshould seriously consider banning nighttime scuba spearfishing.\u201d<\/p>\n
Just as rare was the enthusiastic applause that greeted his blunt recommendation. (That and other recommendations he made were his own, DeMartini took pains to note, and not necessarily those of his employer, the National Marine Fisheries Service.)<\/p>\n
DeMartini looked at the sizes and ages of five species of parrotfish that are commonly taken by fishers.<\/p>\n
\u201cThere are dozens of important reef fish,\u201d he said, \u201cand not much is known about their life history. Especially lacking are rates of growth and sexual maturity.\u201d<\/p>\n
When determining which species to study, he continued, \u201cyou have to consider whether it\u2019s economically or culturally important, and, ideally, also whether it has an important function within the ecosystem.\u201d<\/p>\n
\u201cOne of the groups of fishes which have great ecological importance are parrotfish,\u201d he said, calling out their role as \u201chabitat engineers.\u201d<\/p>\n
Of the seven species of parrotfish in Hawai`i, five are commonly caught by fishers, and all are recorded under the single name of uhu. Given the differences among the five species in their sizes at maturity, DeMartini said, \u201cWe should be hesitant to manage uhu as a single-species taxon.\u201d<\/p>\n
\u201cThe two large-bodied species greatly dominate commercial landings, in terms of biomass,\u201d DeMartini noted, with smaller-bodied species making up a smaller portion of the overall catch.<\/p>\n
\u201cThe fishery is highly selective, with most of the take occurring through the use of nighttime scuba spearfishing,\u201d he said.<\/p>\n
All of the parrotfish are \u201cfemale first sex-changers,\u201d he pointed out, which creates some special challenges for managing the fish.<\/p>\n
\u201cBoth of the large species\u201d \u2013 spectacled and red-lipped parrotfish \u2013 \u201cmature on average at a size that\u2019s several inches greater than the minimum legal size\u201d of 12 inches, he said, adding that the current legal minimum size protects less than 20 percent of redlip parrotfish.<\/p>\n
DeMartini concluded with a series of personal recommendations for state fishery managers, including:<\/p>\n
- \n
- Improve catch records;<\/li>\n
- Change minimum size limits \u2013 notably by increasing the minimum size for the two largest species to 14 inches;<\/li>\n
- Conduct more thorough censuses and improve creel and market surveys for size and species composition for all species, but \u201cespecially for multi-species groups like parrotfishes;” and, finally<\/li>\n
- Seriously consider banning nighttime scuba spearfishing.<\/li>\n<\/ul>\n
Last year, the state Board of Land and Natural Resources passed new rules for the island of Maui that prohibit the take of spectacled and red-lipped parrotfish altogether and set the minimum take size of two other species of uhu at 14 inches. Elsewhere, such takes continue to be legal. The Land Board has also banned scuba spearfishing in West Hawaii.<\/p>\n
<\/p>\n
* * *<\/b><\/p>\n
`Akohekohe Juveniles:<\/b><\/p>\n
Homeless and Sick?<\/b><\/p>\n
Of Hawai`i\u2019s many rare and endangered birds, the `akohekohe (Palmeria dolei<\/i>) has had one of the more stable populations. Found now only on the upper slopes of windward Haleakala, its population has held steady at around 3,800 individuals for years.<\/p>\n
The bird is relatively long lived, with a life expectancy of at least 12 years. And it has a high nest success rate relative to other forest canopy birds.<\/p>\n
\u201cBut with a high survival rate and high nest success, why is its population not increasing?\u201d asked Alex Wang, a graduate student at the University of Hawai`i-Hilo who has been working with the birds for several years.<\/p>\n
<\/b>One of the problems Wang has identified is the presence of disease \u2013 specifically, avian malaria \u2013 at the lower range of the `akohekohe\u2019s habitat, around 1,700 meters elevation.<\/p>\n
\u201cBecause of the introduction of mosquitoes and disease,\u201d Wang said, \u201cthe birds are restricted to high-elevation refugia.\u201d<\/p>\n
But `akohekohe are nectivores, feeding primarily on the nectar of `ohi`a blossoms. `Ohi`a nectar makes up between 50 and 75 percent of the birds\u2019 diet, Wang said.<\/p>\n
Wang developed a hypothesis: `Akohekohe juveniles move to lower elevations in the summer months, following `ohi`a blooms, where they are exposed to malaria. This, he continued, could explain the bird\u2019s static population.<\/p>\n
To test this, he outfitted several birds with transmitters and for two months, the life of the batteries, he followed them around the forest with a handheld antenna.<\/p>\n
He then quantified `ohi`a blossoms by elevation, from 1,450 meters up to 1,950, on two transects. \u201cI counted `ohi`a blooms at all stations,\u201d he said \u2013 to the gasps of his astonished audience.<\/p>\n
The blooms \u201cdecreased dramatically at high elevation sites during the summer,\u201d he found, \u201cbut there was no corresponding increase in low-elevation sites.\u201d<\/p>\n
He found no support for the idea that juveniles emigrated to lower elevations for food. However, he added, \u201c`akohekohe pairs are aggressive and territorial. Their home ranges don\u2019t overlap.\u201d<\/p>\n
While Wang didn\u2019t find any adults at lower elevations, he said, he did find juvenile birds covering wider areas and \u201cdescending into potential malaria zones.\u201d<\/p>\n
\u201cWhat I found corroborates the high adult survival and high nest success already documented,\u201d he explained in a follow-up email, \u201cbut what I found different was that there is likely low juvenile recruitment back into the probably saturated population.\u201d<\/p>\n
\u201cThe high adult survival,\u201d he concluded, \u201cfits with the `akohekohe\u2019s high philopatry\u201d \u2013 its fidelity to a small home range at high elevation. The \u201chigh juvenile output,\u201d he said, will contribute to the bird\u2019s reproductive success \u201conly if the juveniles don\u2019t go to lower elevations.\u201d<\/p>\n
<\/p>\n
* * *<\/strong><\/p>\n
Of Earthworms and Pigs<\/b><\/p>\n
While there are plenty of studies on the effects of feral pigs on native ecosystems in Hawai`i, Noa Kekuewa Lincoln, a researcher with the University of Hawai`i\u2019s College of Tropical Agriculture and Human Resources, has investigated the way those pigs interact with the ecosystems \u2013 specifically, the relationship between pigs and earthworms.<\/p>\n
Earthworms, Lincoln pointed out, are not native to Hawai`i but were here by the early 1800s. About 35 species are now found in the islands and they make up the largest fraction of macrofauna found in Hawaiian soils.<\/p>\n
Pigs eat them, and although earthworms make up somewhere between 1 and 4 percent of gut content in pigs on Hawai`i island, they are the primary source of protein for the pigs, he said. \u201cHence, the vast majority of rooting in forests may be \u2026 pigs looking for earthworms.\u201d<\/p>\n
Lincoln examined earthworm biomass under a range of canopy species. \u201cWithin the same site,\u201d he reported, \u201cearthworm density can vary dramatically.\u201d Under some species of eucalyptus and redwood, he continued, \u201cthere are no earthworms. But you could walk two feet and go from no worms to choke!\u201d Tropical ash canopy is apparently one of the most preferred areas for earthworms.<\/p>\n
Koa also shelters few earthworms, but native forests generally fall \u201cin the middle of the spectrum.\u201d Pasture, especially kikuyu grass, has more.<\/p>\n
\u201cSo I looked at this in terms of pig rooting,\u201d Lincoln said. \u201cAlmost all the rooting we were seeing is in direct correlation to the amount of earthworms in the soil.\u201d<\/p>\n
Also, he went on to say, \u201cthe impacts of rooting aren\u2019t equal under different forest canopies. \u2026 If you have a tropical ash forest on a steep slope, expect lots of rooting and erosion.\u201d<\/p>\n
\u201cIf we think about pig rooting correlating to time spent in forest areas, this has big implications for how we designate and manage forests,\u201d he said. \u201cIf we set up eucalyptus forests as hunting areas, the hunters will be disappointed.\u201d On the other hand, \u201cif we\u2019re going to try to lower pig populations in an area,\u201d he said, it\u2019s a waste of time if those efforts are focused on areas invaded by tropical ash or other trees that enhance rooting.<\/p>\n
\u201cThere\u2019s lots of speculation that before earthworms were introduced, pigs in Hawai`i were much smaller, and were limited by protein availability in their diet,\u201d he said. \u201cAs everything has moved toward pasture grasses, we\u2019ve greatly increased earthworm habitat, presumably increasing the abundance and vitality of pigs as well.\u201d<\/p>\n
Conversely, he concluded, if pastureland is converted back to native forest, \u201cit may lower pig vitality by altering overall land use.\u201d<\/p>\n
<\/p>\n
* * *<\/b><\/p>\n
Hawai`i\u2019s Bees: An Experiment<\/b><\/p>\n
In Translocation<\/b><\/p>\n
Hawai`i has some 60 species of native Hylaeus<\/i> yellow-faced bees, seven of which are candidates for protection under the federal Endangered Species Act. In an effort to boost the population of one candidate species, Hylaeus anthracinus, <\/i>found on the Kona coast of the Big Island, Karl Magnacca undertook to translocate several hundred of them from Puako, where they are relatively abundant, to three sites at Pu`uhonua o Honaunau National Historic Park in South Kona.<\/p>\n
In a poster presentation at the Hawai`i Conservation Conference, Magnacca noted that a century ago, the bee occurred widely along the leeward coasts of Hawai`i island, from South Point, in Ka`u, up to South Kohala. Now, the isolated South Point population \u201cis extremely small,\u201d he wrote, and \u201cRecent extensive surveys have found no surviving populations in South Kona and only a few suitable sites.\u201d<\/p>\n
\u201cThis combination of large-scale declines and extirpation from historic sites with continued high numbers in some areas makes H. anthracinus<\/i> ideal for testing translocation as a conservation tactic,\u201d Magnacca wrote. And although translocation has been done for birds and plants, until Magnacca translocated the bees, it had not been attempted for any native insect.<\/p>\n
Magnacca, supported by the O`ahu Army Natural Resources Program, chose three sites in Pu`uhonua o Honaunau to release the bees captured at Puako, beginning last January. One site, Alahaka Bay, had a good mix of native vegetation and relatively few ants. Another site, at the start of the coastal trail, had vegetation quality described by Magnacca as \u201cmedium\u201d and abundant big-headed ants (Pheidole megacephala<\/i>). The third site, at the royal grounds, had \u201clow\u201d quality vegetation and also many big-headed ants.<\/p>\n
Six months later, the 100 bees that had been released at Alahaka had become an established population, with nesting observed in coral rocks, Magnacca reported.<\/p>\n
\u201cBees were not able to establish at the other two sites even after a second, larger release in April 2015,\u201d Magnacca wrote. \u201cThis suggests that the presence of large numbers of aggressive ants is the biggest barrier to [the bees\u2019] existence in their historic range.\u201d<\/p>\n
Could ant control help out the bees? Magnacca was asked.<\/p>\n
\u201cUnfortunately, there doesn\u2019t seem to be a good way of controlling ants,\u201d he replied by email. \u201cSheldon Plentovich did some experiments eradicating them from offshore islets on O`ahu and found that they tend to just be replaced by other species, which are sometimes even worse. If big-headed ants are in one area, if you get rid of them, it might be ant-free for a couple of years, but then long-legged ants show up and soon they\u2019ve taken over.<\/p>\n
\u201cAnd of course, on the main islands, it\u2019s much more difficult to get rid of them, because there\u2019s usually a nearby population they can move back in from over land. You could keep them under control, but that would require a huge effort of baiting \u2013 and, of course, as soon as you stop they come back.\u201d<\/p>\n
\u2014 Patricia Tummons<\/i><\/b><\/p>\n
<\/p>\n
Volume 26, Number 4 October 2015<\/p>\n","protected":false},"excerpt":{"rendered":"
The annual Hawai`i Conservation Conference, held this year in August at the University of Hawai`i-Hilo, offered hundreds of discussions on a wide range of topics. This month, we continue to report on selected presentations. * * * When Looking … Continued<\/a><\/p>\n","protected":false},"author":1,"featured_media":8409,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[391],"tags":[7],"class_list":["post-8407","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-october-2015","tag-patricia-tummons"],"_links":{"self":[{"href":"https:\/\/environment-hawaii.org\/index.php?rest_route=\/wp\/v2\/posts\/8407","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/environment-hawaii.org\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/environment-hawaii.org\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/environment-hawaii.org\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/environment-hawaii.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=8407"}],"version-history":[{"count":0,"href":"https:\/\/environment-hawaii.org\/index.php?rest_route=\/wp\/v2\/posts\/8407\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/environment-hawaii.org\/index.php?rest_route=\/wp\/v2\/media\/8409"}],"wp:attachment":[{"href":"https:\/\/environment-hawaii.org\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=8407"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/environment-hawaii.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=8407"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/environment-hawaii.org\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=8407"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}