A Blog by Ed Yong

In Saving A Species, You Might Accidentally Doom It

The black robin is an endearing ball of beaked fluff, found only in the Chatham Islands off the eastern coast of New Zealand. By 1980, there were just five of them left.

They lived in a rocky outcrop about the size of a few city blocks. The precipitous cliffs kept them safe from the cats, stoats and rats that sailors had brought to the islands. But the high winds were too much for these small birds, and most of the survivors had died. With a single breeding pair left—Old Blue and Old Yellow—their future looked bleak.

Don Merton and a team of conservationists mounted a heroic effort to save them. They relocated the tiny population to larger islands and managed their reproduction over many years, transferring their eggs to foster parents for incubation. By 1989, there were 80 robins. By 1998, there were over 200. Once the world’s most endangered bird, the black robin became a flagship example of conservation success.

But it’s also an example of good intentions leading to unintended consequences.

In those early years, when the team was still carefully managing the birds, they noticed that many females laid their eggs on the rims of their nests, rather than the centre. Precarious positions aside, these “rim eggs” were never incubated and never hatched. With the species’ fate hanging in the balance, every egg was precious. The team repositioned the ones on the rims.

Without this move, it’s unclear if the species would have made its dramatic recovery. But it also saddled the robins with a difficult legacy.

Melanie Massaro from Charles Sturt University in Australia has now shown that rim-laying had a strong genetic basis. Under normal circumstances, natural selection would have quickly weeded out the alleles (versions of a gene) behind the behaviour, because any female who carried them would lay doomed eggs. By saving those eggs, the conservationists inadvertently gave the rim-layers a pass, turning their maladaptive behaviour into a neutral one. They allowed for “survival for the not-so-fit”.

Sure enough, the alleles for rim-laying spread through the growing robin population. The speed of this spread became clear when Massaro checked old records of the robins’ behaviour. Old Blue, the last fertile female as of 1980, laid eggs in the normal way. By 1984, there were five females and one laid a single rim egg. By 1989, there were 35 females, of whom 18 (more than half) were rim-layers.

You can see the spread for yourself in the family tree below, which shows the relationships between every breeding robin during the 1980s. Blue circles represent females that lay eggs in the right place; the rim-layers are in red. This is the sort of diagram you can make when a species only has a few dozen survivors, and you know all of them.

Black robin pedigree, 1980-1989. Credit: Massaro et al, 2013. PLOS.
Black robin pedigree, 1980-1989. Credit: Massaro et al, 2013. PLOS.

It’s possible that the robins increasingly laid eggs on rims as a response to their environment, but the pattern in the family tree suggested otherwise. It looked like rim-laying had a strong genetic basis. In fact, it was most probably caused by a dominant allele—a version of a gene that produces rim-laying even when a bird inherits just one copy from either of its parents.

If the team had continued to replace the rim eggs, you could imagine a future when the robins were entirely dependent on humans for their survival. They’d effectively be living in a wild zoo. Consider the domesticated silkworm—the moth that provides us with silk. Five thousand years of coddled breeding at the hands of humans have left these insects unable to fly or feed themselves as adults.

Thankfully, “the black robin just narrowly escaped such a fate,” Massaro wrote.

The team stopped repositioning the eggs in 1990, once robin numbers had bounced back to more promising levels. Natural selection started doing its thing and the proportion of rim-laying females has fallen from 50 percent to around 10 percent. The allele is still around though, hiding from natural selection in the bodies of males, and waiting to pass to another generation.

The goal of conservation isn’t just to save a species temporarily, but to create a wild population that can sustain itself without our help. The black robin shows just how difficult this goal can be. The team saved the bird, but their practices threatened to leave it incapable of breeding on its own. That would have been no use: conservation programmes are laborious and expensive, and can’t go on forever.

As the team write, “Conservation planning has to overcome this fundamental dilemma of rapidly increasing the size of severely endangered populations to avoid immediate extinction but without simultaneously increasing the frequency of detrimental alleles that are already present in the population.”

PS: As per usual, the acknowledgements of the paper detailed what each of the authors did, by their initials. It says who performed the experiments, analysed the data, contributed materials and tools, and wrote the paper. And rather delightfully, it ends with: “Led the team that saved the black robin from extinction: DM.” Well done, Don Merton. Well done.

Reference: Massaro, Sainudiin, Merton, Briskie, Poole & Hale. 2013. Human-Assisted Spread of a Maladaptive Behavior in a Critically Endangered Bird. PLoS ONE http://dx.doi.org/10.1371/journal.pone.0079066

19 thoughts on “In Saving A Species, You Might Accidentally Doom It

  1. The team did the right thing. Had they not saved the rim eggs when the population was extremely low the species may have not survived at all.

    By waiting until the population was larger and had more of a chance of surviving on its own, they allowed natural selection to act on the larger population.

  2. “Led the team that saved the black robin from extinction: DM.”

    If that was all that he ever accomplished, it would still be more than almost all of the rest of us.

  3. I appreciate this article and the dedication of the Black Robin researchers. It shows that our ability to observe and our effort to understand the challenges and constraints a particular animal is living with from its “point of view” is just as important as any powers we have to “rescue”. It takes a lot of humility and compassion to succeed! Indeed “well done”

  4. Was rim laying proven to be harmful, or was that just an opinion? Reading this article I was thinking along the same lines as C. Mason above me.
    The position may be precarious to a human but not necessarily to the animal, I know many animals that live in places I’d not think they could.

    [Rim-laid eggs *never hatched*. – E]

  5. Interesting. I remember reading about the relocation of the black robins when I was in primary school (there was a write-up in a quasi-magazine called “school journal”), but I hadn’t heard about the rim-laying problem.

  6. Out here you lay the edge.

    And the edge is a fickle hellbeast!

    Love her but never trust her, for her heart is full of lye!

  7. Do we have some reason to think that only, or mainly, the rim-laid eggs are the ones carrying the rim-laying gene? Maybe entire clutches from birds that perform rim-laying should be tossed, and replaced with eggs from non-rim-laying mothers, to be nurtured but not tainted by the mutants.

  8. Don Merton was one of the greatest conservationists of all time. He took the last ever photographs of the Bush Wren and New Zealand greater short-tailed bat and he saved the Black Robin and the Kakapo from extinction. R.I.P. Don

  9. I’m curious, if there was just one breeding pair left and 5 individuals total, how did the researchers handle inbreeding and genetic defects? Are all 200+ of these birds pretty much from the same set of parents?

    1. @Jessica: This article pretty much IS how they are dealing with inbreeding; rim laying appears to be a genetic defect that is having to be weeded out of the population. t is to be hoped that there are no more major defects, each makes the breeding process exponentially harder.

  10. Nice write-up of Melanie’s work, Ed – thanks. Don Merton was a pioneering conservationist not just in New Zealand but on many other islands around the world. Many bird species owe their existence to the translocation methods he developed. You can find lots more about Don and his work in the biography I wrote (‘Don Merton: the man who saved the black robin’ by Alison Ballance, 2007): out of print but track it down if you’re interested to know more http://www.goodreads.com/book/show/3701509-don-merton. Cheers Alison

  11. Every black robin now alive is descended from the last fertile female, Old Blue.. I suspect that hatching and breeding from the birds from the rim eggs enabled considerable genetic variation to be maintained in the population and overall may have contributed to the present success of the programme.

  12. Funny that the headline has a note of “doom” in it, whereas the story of the black robin is still a triumph of conservation work and a model for other programs in NZ and around the world.

    “In saving a species there are a difficult moments, but with care and dedication you will probably overcome them.”

  13. This article makes no sense to me. A robins nest is cup shaped with thin wall. How does a robin hen lay an egg on the rim of the nest. It would either fall in or out. It’s like balancing a ball on a paling fence, it would fall one way or the other. Can someone please explain this to me ?

    1. @Jeff ‘rim laying’ is just the inaccurate name given to robins placing eggs in their nest not directly in the center, where they cannot be properly incubated. Off-center laying would be more accurate but cumbersome to say.

      1. Thanks for your reply Kudzu, but it still makes no sense. I breed Australian robins in captivity in large planted aviaries and a robins nest is a small cup shape, that just fits the parents body, where the eggs have no alternative but to be in the centre of it. Ah the mysteries of life. I would really like to know what they are talking about. Like a pic of the position of the rim egg or something.

  14. This got me really curious, so I googled Don Merton, and from his wiki page, I learned that he already passed on in 2011. Still, his legacy is *are* alive and flyin’ though. Well done indeed.

  15. Jeff, the Chatham Island black robin is not actually a robin but so named simply because of a resemblance. In a similar article in New Scientist magazine there is a photo of a nest with a rim egg. The nest is quite wide and shallow, so the rim egg is not ‘balanced’ but just sits away from the centre. You are right, from your description of a robin nest it would not seem possible for a real robin to exhibit this behaviour.

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