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| The St Kilda Wren was on the front cover of W.H. Hudson's pamphlet which was published by the Society for the Protection of Birds - forerunner of the RSPB |
IN a pamphlet published in 1894, W.H. Hudson asserted that the St Kilda Wren - a sub-species of the bird familiar on the mainland - had been extirpated by unscrupulous collectors.
Happily, he was wrong. The bird was not extinct - and it is the subject of a study on 'island gigantism' published in the most recent edition of the Evolutionary Journal of the Linnaean Society.
It seems odd to apply the term 'gigantism' to such a diminutive species - but apparently it can occur, as discovered by Charles Darwin, on islands when species evolve in a different way from their mainland counterparts.
At between 13 and 16 grammes, the St Kilda Wren can be twice the size of a mainland Wren which typically weighs in at 7-10g.
The authors of the new study on gigantism note that the former typically lives in very open and often sheer cliff face habitats which tend to be predator-free.
They also have longer bills and there may also be differences in song.
Unfortunately, the Evolutionary Journal is a bit of a soup, full of unfamiliar academic jargon which makes it difficult to follow.
By contrast, though written more than 130 years ago and flawed in its conclusions, the commentary of Hudson is much more accessible to the contemporary birder.
He writes of the St Kilda Wren: "This small feathered creature is a dweller among the rocks near the sea, and it frequently nests in crevices and holes just above highwater mark on the shores of places which the Great Auk once haunted.
"It will be remembered that, about nine or ten years ago, Charles Dixon found this wren quite common at S. Kilda, where it was the only small bird resident all the year.
"It differed from the Common Wren in its habits and more powerful song, its paler ground colour and its more distinct markings and stouter legs and feet.
"On account of these distinguishing characters, it was described as a new species - Troglodytes hirtensis.
"It is now believed by ornithologists that the St Kilda Wren is not specifically distinct from the Wren of the mainland but that it is a variety, or race, which has diverged from the parent form during the long centuries of its isolated life on that wintry island where not a tree or shrub exists.
"Species, sub-species or variety, it matters little, what concerns us just now is the following fact.
"No sooner had the news gone abroad that "lone St Kilda’s isle" possessed one little songbird of her own - a Wren that differed somewhat from the familiar Wren - than it was invaded by the army of collectors who did not mind its distance from the mainland so long as they secured something for their cabinets.
"And the result of their invasion is that the St. Kilda Wren no longer exists."
Cliff faces on St Kilda provide an all-year habitat for the island's 'giant' Wrens (photo: Stephen Hodges via Wikimedia Commons)
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