Distributing Risk

When and endangered species is limited to a single location, one chance event can erase it from existence. In Australia, ecologists have found a way to hedge the bets of the black-eared miner.

By Douglas Fox

Two hours ago the last scratchy FM radio signal sputtered out. One hour ago, the pavement gave way to a dirt road that now alternates between washboard stutter and smooth dusty dunes as it weaves through an unending maze of spider-branched mallee trees. Driving with me are two volunteer rangers, Marilyn and Brian.

The place we’re touring is Gluepot Reserve, located in the parched red interior of South Australia and home to the world’s last remaining viable population of black-eared miner birds (Manorina melanotis).

Like any old-growth mallee forest, Gluepot is an untidy place, with dry leaves and tattered bark strewn across the ground. That messiness is exactly what makes it uptown for black-eared miners because it harbors a metropolis of insects just waiting to be plucked and devoured by an enterprising bird.

But this paradise could vanish at any time. Australia is nothing if not a land of wildfires and old growth mallee, with wood-shaving ground litter and dangling bark that rate just behind rocket fuel in terms of combustibility.

“If a fire went through here,” says Marilyn, throwing me a glance from the steering wheel, “it could wipe out every black-eared miner.”

And it’s not just the black-eared miner that’s playing extinction roulette: this is a common dilemma, faced by conservation managers whenever the endangered species they’re trying to protect is limited to a single location. Just one chance event—a fire, flood, hurricane, or epidemic—can erase such a species from existence.

And so it is that here in Australia, a team of ecologists decided to hedge the black-eared miner’s bets. They undertook the immodest step of capturing some of these precious feathered few and moving them to other locations in hopes of distributing the risk by building viable populations elsewhere that would survive even if Gluepot went up in smoke.

But accomplishing that is no small task, and compelling these birds to set up shop in a new neighborhood is no mere matter of releasing a few individuals and hoping for the best. It’s true that conservation biologists have successfully captured and released species such as the eastern wild turkey (Meleagris gallopavo silvestris), which aren’t terribly social. But the black-eared miner is an unwieldy candidate for translocation. It’s one of the most socially complex bird species known. In the wild, several breeding pairs cooperate as a coterie. Each coterie also includes a dedicated corps of helper birds that constantly gather food for the young. Several of these coteries, in turn, cooperate as a colony.

The helpers in particular are so attuned to the young they’re feeding that they choose each one’s food according to its age. For the first few days, it’s a high-protein mix of spiders, flies, and nectar. But once a youngster ventures from the nest, the helpers work extra hard to bring them lerps, tiny sugar-igloos built by psyllid bugs—high-octane lollipops to meet the adolescent’s growing energy demands.

In other words, to raise young and repel predators, the entire colony must function as a seamless unit. So, if you want black-eared miners to thrive after you release them, then somehow you’ve got to reconstitute an entire bird society.

This is the task that was undertaken, and the results were stellar: five colonies were translocated in 2000 and 2001, all of them staying together at the release site, with some of them breeding again within as little as 15 days after release. The observations coming out of this effort could provide a framework for using translocation to spread the risk of extinction for other socially complex species.

The black-eared miner was pushed into its current crisis by human factors. After World War II, much of the land where old-growth mallee thrived was cleared for agriculture and sheep grazing. That brought a second threat to the miners’ doorstep: the yellow-throated miner (Manorina flavigula), which readily interbreeds with black-eared miners and is hybridizing them out of existence. Unlike their black-eared brothers, yellow-throateds need standing water to survive—and artificial ponds found on sheep lands provided that aplenty. So yellow-throated miners expanded, encroaching on black-eared miner colonies, diluting them away. By the mid-1990s, the only known surviving population of black-eared miners was a ragtag group of ten or so colonies scattered in and around Murray-Sunset National Park in Northwest Victoria.

Then in late 1996, a substantial black-eared miner population was discovered on the Gluepot Sheep Station. Gluepot was purchased by the nonprofit group Birds Australia, which is now restoring Gluepot to its natural state, including filling in ponds.

What makes Gluepot attractive for black-eared miners is that it harbors old-growth mallee that hasn’t burned in at least 50 years. But the fire drought won’t last forever. During recent decades, several wildfires—some bigger than Gluepot—have charred large swaths of mallee lands nearby.

This ticking time bomb spurred a team to begin moving intact black-eared miner colonies from Gluepot to Murray-Sunset, 110 miles away. Gluepot and its surroundings contained 200 colonies—more than enough for a viable meta-population—and so the near-term plan was to move up to eight of those colonies to Murray-Sunset in hopes of boosting its flagging population of ten colonies back toward viability (no formal calculations have been done, but minimum viable population size for black-eared miners probably lies in the range of 50-100 colonies). The long-term goal was to have two geographically separate, ecologically viable populations of black-eared miners to safeguard against chance calamities at one location.

The appointed morning of capture was September 24, 2000. When the first glow appeared on the eastern horizon, 20 mist nets were already deployed around the nests and across the oft-used flight paths of the chosen colony.

In the gray half-light, a bleary-eyed black-eared miner stirred from its perch, flitted toward a neighboring tree, and flumped into a net. It dropped silently into the net’s pocket and with nary a neep, was snatched into a gunnysack.

The team easily kept pace with the early birds, but then came the first breeding female. She tumbled into the net with a scathing squawk that electrified the entire colony. Almost instantly, five more well meaning birds arrived to investigate and careered into the same net. From then on, it was chaos for birds and humans alike.

After two hours of running around, the team had captured most of the colony, and by the end of the day, all but two of the noisy little neepers were bagged, gagged, and ready to go on the truck ride of their life—the three-hour rattle-bump to Murray-Sunset.

During September, October, and November 2000 and 2001, five colonies (as many as conditions permitted) were captured and moved. The biggest concern was keeping the social fabric of the colonies intact, and for this the dependent young were enlisted. Nestlings and fledglings are particularly vulnerable—especially in new environments—and so translocation programs generally steer clear of them. But in the case of the black-eared miner, the risk of moving fragile young seemed to be worth it. “Helping at the nest is one of their most social activities,” says Mike Clarke, the La Trobe University ecologist who oversaw the project. “We hoped the stimulus of feeding young would be the glue that held colonies together.”

As a result, only colonies with dependent young (either nestlings or fledglings) were moved. In addition to providing a social center of gravity, the team hoped that the nonflying and poorly flying young would anchor the colony close to its site of release.

This, at least, was the plan.

The moment of truth came on a lazy Monday afternoon in the Murray-Sunset mallee—the day the first colony was released: September 25, 2000.

Beneath a drifting herd of cumulonimbus, the colony’s four fledglings perched in the tree where they’d been released; in a circle around that tree sat seven cages, each containing several pent-up adults.

And then, with the team watching through binoculars, those cages were opened.

As though following some plan, the adults gathered in a nearby tree and called to one another. Through human eyes, they seemed to be taking roll call, seeing who had survived. And then as a single squawking mass they took to the air, wheeled in the sky and headed north.

They left the fledglings behind. “We could hear them, nee nee nee, just getting softer and softer until they were out of hearing range,” recalls Rohan Clarke (no relation to Mike Clarke), one of two La Trobe University PhD students spearheading the project. “We were pretty dejected because we thought that might be it.” And so in the deepening quiet, all thoughts turned to the fledglings: recapturing them and packing them back into the truck for the six-hour ride to a captive breeding center.

But 15 minutes later, the gallows talk was interrupted by the cries of black-eared miners. The birds reappeared, every single one of them, from over a far dune. They alighted at the release sight and began feeding the fledglings.

In total, five colonies were moved from Gluepot to Murray-Sunset during 2000 and 2001 with excellent results. Three of the five colonies resumed breeding within eight weeks of their release at Murray-Sunset, and one colony bred within 15 days. A fourth colony bred 12 months after release. The colonies also stayed intact and generally remained within a kilometer of their release site for at least two months.

Everyone understood the inherent risk involved in moving entire black-eared miner colonies—the translocation specialists who reviewed the project proposal even made the unusual gesture of wishing the team lots of luck.

And so it should come as no surprise that the plan included a clear exit strategy in case the capture of a colony went awry. The team decided ahead of time that if an entire colony wasn’t captured (with the possible exception of a few very peripheral helpers), then at the end of the day, the capture would be aborted and caged birds would be released. To keep this option open, nests and nestlings weren’t disturbed until all grown birds were captured and the explicit decision was made to proceed beyond the point of no return. A second exit strategy was available for the release phase: if a colony stopped cooperating after its release, then any dependent young were moved to a captive breeding program that was on standby.

But keeping individual colonies together was just one piece of a larger puzzle. “On a broader level, you’re not just moving one colony,” says Mike Clarke. “You’re trying to establish a meta-population.” Planning for this began by choosing release sites that considered the birds’ social structure. Black-eared miners are a female-dispersing species: young females won’t breed until they’ve left their natal colony and joined another. So, colonies need to be spaced closely enough that dispersing females can find new homes. At Murray-Sunset, the team situated release sites about 2 kilometers from existing local colonies and from each other, duplicating the natural spacing that’s seen in Gluepot.

Any translocation should take the meta-population into account, but it’s especially important for species whose young disperse to mate with other groups. For the black-eared miners, the planning succeeded: as little as five days after release, new birds (dispersed from local colonies) began hitching up with translocated colonies, and after a year, one of the translocated colonies had adopted five local birds.

What’s more, the entire translocation was one huge experiment. “In this case,” points out Rohan Clarke, “the overall translocation was a trial. That tends to get forgotten because it was so successful.” In fact, the project compared two release protocols: one in which colonies were released directly into the wild at Murray-Sunset, and the other in which colonies were first released into an outdoor, tree-enclosing aviary for three to seven days and then gradually released into the wild.

The team found that the direct release into the wild worked just as well as gradual release—and at a fraction of the cost.

The project also provided more general ways for gauging success. The team tagged five adults in each colony with radio transmitters. This way, they could locate colonies that tried to give them the slip, or track individuals if a colony simply dispersed and vanished overnight. In addition, every bird was banded with a nontransmitting bracelet, allowing the team to detect when individual birds dispersed from one colony to another.

Because translocation projects are infrequently published in the peer reviewed literature, wildlife managers often find themselves flying in the dark. So, incorporating experimental design can ensure that the process is gradually honed and that optimal results are achieved over time.

Back in Gluepot, the fire gamble continues. In 2002, the reserve experienced two near misses—lightning-strike fires on adjacent properties that were extinguished by rain. But at least the black-eared miner’s odds are improving: five colonies have been moved.

About the Author:

Douglas Fox is a freelance science writer who splits his time between Australia and California.

For More Information:

Clarke, R.H, R.L. Boulton, and M.F. Clarke. 2002. Translocation of the socially complex black-eared miner (Manorina melanotis): a trial using hard and soft release techniques. Pacific Conservation Biology 8(4):223-234.

Clarke, R.H., I.R. Gordon, and M.F. Clarke. 2001. Intraspecific phenotypic variability in the black-eared miner (Manorina melanotis); human-facilitated introgression and the consequences for an endangered taxon. Biological Conservation. 99:145-155.

Illustration © Christopher Zacharow/SIS

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