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\n\t\t\tThis essay is adapted from Traversal.
\n\u201cIn the great chain of cause and effect,\u201d Alexander von Humboldt wrote as he was teaching science to read the poetry of nature, \u201cno single fact can be considered in isolation.\u201d
\nWhen the first European colonists made landfall on New Zealand\u2019s shores in Humboldt\u2019s lifetime, the cats and rats that descended from their ships began decimating the native population of black robins \u2014 sparrow-sized birds with yellow-soled feet that had evolved without mammalian predators, mate for life in monogamous pairs, and raise only two chicks per year in cuplike nests close to the ground.
\nBird by bird, claw by claw, there were only seven survivors within a century.
\nBlack robin among other native birds (John Gerrard Keulemans, 1907)
\nDesperate to encourage the survivors to breed, conservationists moved them to Mangere Island, where twenty thousand trees were planted just to provide a hospitable habitat for the robins. But they would not pair \u2014 mysterious are the ways of even a bird\u2019s heart, for it is all a single mystery.
\nTwo of the seven died.
\nAmong the five survivors there was a sole female capable of laying fertile eggs \u2014 a robin so aged that she came to be known as Old Blue. At eight, she had outlived the average black robin twofold. With the survival of the species resting on Old Blue\u2019s near flightless wings, scientists thought that if her offspring were raised by surrogate parents, she would be able to lay more eggs.
\nWarblers were the first designated foster parents, but they failed to feed the chicks enough.
\nTomtits were tried next, but they were too successful as foster parents \u2014 the black robin chicks grew up perceiving themselves as tomtits and wanted to mate only with other tomtits.
\nFinally, the chicks were returned to Old Blue, in whose care they thrived as black robins.
\nA single mother brought a whole species back from the brink of extinction.
\nOld Blue lived to be fourteen and raised eleven chicks. All the black robins in the world today, numbering around 250, are fractal emissaries of her genes \u2014 a winged reminder that immensities of harm can be undone by a single act of tenacious tenderness.<\/p>\n