In 1976, conservationist Don Merton disembarked from a boat in tempestuous seas and ascended 600 feet up a rock stack known as Little Mangere Island.
This spit is a tiny member of the Chatham Islands, which rest 400 miles east of New Zealand’s South Island. Little Mangere covers just 37 acres, a mere blip in an endless ocean. Nearby is the larger Mangere Island, which is dwarfed by Pitt Island to the east, which lies south of the main isle of the group, Chatham Island, a relative Gargantua at 360 square miles in area.
In the 1870s, when European naturalists first visited the Chathams, numerous avian populations thrived. Like the famous endemism on the Galápagos Islands, birds had evolved odd traits in these isolated habitats. One such species was the black robin, known as the karure to the native Moriori and kakaruia to the Maori. Unlike most passerines, the black robin had developed a limited flying ability over the centuries. With no need to leave the Chatham Islands, the capacity to soar great distances became unnecessary. When non-native humans arrived, carrying rats and cats, however, this trait became a fatal flaw.
As foreign predators arrived, populations plummeted. By the early 1900s, black robins had disappeared from every island in the Chathams save one: Little Mangere. For a while, this tiny home fostered a decent colony, but, by 1972, only 18 birds remained alive.
In 1975, that figure had dropped to seven, including just two females. So, Don Merton hatched a plan to save the robins, which required him to scale a vertical cliff to rescue the heptad.
Merton’s conservation team had seeded Mangere Island with 20,000 rooted cuttings, hoping to provide a larger suitable habitat for the robins. They ascended Little Mangere with netted traps, snared the birds, rappelled the rocks, and hoped the robins would survive the turbulent boat ride to a new Eden.
The robins made it safely to Big Mungere Island, where they managed to breed. However, they did not produce enough offspring to sufficiently recover. By 1979, the original seven had diminished to just five. If the robins were to continue existence on Earth, we required a new plan.
One aspect of the black robin’s lives that made rebounding difficult involved their breeding patterns. Researchers had only observed pairs laying two eggs per year, not exactly a formula for population explosion. However, Merton noticed one bird lose a nest in a storm. Instead of simply having to skip a breeding season, the bird actually produced a second nest with additional eggs. Merton ideated something genius: if scientists could snag the first round of eggs from the robins and “cross-foster” them with another species, the robins might produce a second clutch, thereby doubling the output of a single pair.
Some species of birds cross-foster in the wild, albeit parasitically. Cuckoos lay eggs in the nests of other birds, so the other species will raise the cuckoos as their own. Biologists have utilized the technique to save avian species, including the California condor, which was cross-fostered with turkey vultures.
Merton placed black robin eggs in the nests of Chatham Island tomtits, which began to rear the endangered young. The approach began to pay dividends until the downside of cross-fostering appeared. Sometimes, the fostered species will imprint on the host species, meaning they believe themselves to be the host species. They try to breed with the hosts, which obviously doesn’t work. In the case of the robins, this misadjusted breeding impulse was the opposite of the desired goal. To compensate, Merton’s team had to time the hatchings, so they could remove chicks before they imprinted.
When they began to reunite the cross-fostered robins with their parents, the population started to increase!
This success wasn’t a miracle salve, however. The attempts to grow robin numbers illustrate just how tricky the process can be.
Researchers noticed the birds laid a decent amount of their eggs on the rims of their nests, leaving them vulnerable to falling out. The team began to move the eggs toward the center of the nests, which helped the population grow. However, the more rim-laying birds that survived to produce offspring meant that their rim-laying genetic predispositions passed from generation to generation. The researchers noticed more and more birds laying eggs toward the outer reaches of nests. If the trend continued, black robins would not survive without humans intervening to move the eggs. Though the original impetus for the intervention produced positive results, scientists were forced to cease giving that specific type of aid when the number of robins laying rim eggs reached 50%.
Thankfully, the intercession had produced enough population growth that they could let nature take over, in regards to laying eggs. Eventually, the percentage of robins errantly laying eggs dipped to nine.
Down the line, researchers introduced black robins to multiple islands. They have become the poster species for rehabilitation in New Zealand, though they still face a grim future.
This species perfectly depicts just how dire the situation is when an animal is critically endangered, endangered, or vulnerable. Today, the black robin is officially listed as a “vulnerable” species by the IUCN. This designation is three steps above “extinct in the wild.” A veritable success story. Yet, only 300 black robins are currently alive. This fact highlights just how much jeopardy a critically endangered species encounters.
Further, every single black robin living descended from one female, named Old Blue. So far, the species seems viable, but genetic bottlenecking is a serious concern. And, though the numbers seem stable overall, the birds have not thrived on every island. On Mangere, the robins are down to just 30 individuals.
More work needs to be done to ensure the survival of this adorable avian. Human intervention led to their downfall; hopefully, human intervention can rebalance the future. For now, things look far less grim than they did 50 years ago, all thanks to a man scaling a cliff to save the handful of living black robins and an altruistic bend from some nearby tomtits.
Further Reading and Exploration
Karure / Kakaruia / Chatham Island black robin – New Zeland Department of Conservation
Black Robin – IUCN Red List
The extraordinary survival story of the black robin – Australian Geographic
Once a global conservation success story, New Zealand’s black robin in trouble again – The Guardian
Remembering Don Merton and a bird called ‘Old Blue’ – Predator Free NZ
Human-Assisted Spread of a Maladaptive Behavior in a Critically Endangered Bird – National Institute of Health
Black robin recovery plan – New Zealand Department of Conservation