WILD NEIGHBORS: The Duck in the Cave

By Joe Eaton
Friday February 17, 2012 - 11:27:00 AM
Two nene on Kaua'i: relatively normal geese.
Alejandro Barcenas, via Wikimedia Commons.
Two nene on Kaua'i: relatively normal geese.

Yes, it’s another Hawai’i column. “Neighbors” is a relative term.

I’ve written before about the extraordinary birds called Hawai’ian honeycreepers, or more technically drepanine finches (“dreps” for short.) They’re a classic evolutionary radiation: some generalized ancestral finch gave rise to over 50 descendant species with diverse plumage colors and specialized bill shapes and functions. For a long time there’s been speculation as to whether the ancestor originated in Asia and North America. In an earlier piece for a now-defunct magazine, I imagined a house finch or lesser goldfinch flying from California to Hawai’i with the seed of a tarweed—itself the ancestor of the equally extraordinary silversword plants—clinging to its feathers. 

Well, the geneticists have smashed that all to hell. The latest analysis of drepanine phylogeny indicates the founding species was a Eurasian rosefinch—a close relative of our house, purple, and Cassin’s finches, but no cigar. Something else must have introduced the proto-tarweed; maybe the solitaire that gave rise to the Hawai’ian thrushes, or some other North American species that died without issue. 

North American ancestry remains likely for other Hawai’ian birds, though. The nene, or Hawai’ian goose—the state bird, except on Kaua’i where the feral chicken rules—is considered to be an offshoot of the Canada goose. 

Hawai’ian waterfowl are an interesting assortment, with varying degrees of modification for island life. The nene, despite a few quirks like reduced webbing between its toes, is a pretty standard goose. And the koloa, the only surviving native duck, could pass for a female mallard (and in fact is at risk of genetic swamping by introduced mallards.) 

Other ducks evolved in bizarre directions once they reached the islands. An earlier dabbling duck colonization resulted in the moa- nalo lineage: large flightless browsers with heavy beaks like the jaws of a tortoise. The evolution of prickly leaves in island plants of the lobelia family may have been a defensive response to the foraging habits of these birds. Fossil and subfossil moa-nalo remains have been found on all the main islands except Hawai’i, the Big Island. “Moa” is the word for “chicken” in most Polynesian languages and was applied to anything at all poultry-like, as with the giant birds of New Zealand. “Moa-nalo” is a modern coinage; the Hawai’ians left no oral traditions or other records of these birds, not even recipes. 

The most bizarre of all Hawai’ian ducks was discovered about ten few years ago, during the excavation of the Makauwahi Cave on the south shore of Kaua’i. David Burney, a paleoecologist and director of conservation at the National Tropical Botanical Garden, which has three units on Kaua’i, has been digging at Makauwahi for a couple of decades. His work, chronicled in his book Back to the Future in the Caves of Kaua’i, has allowed the reconstruction of a lost ecosystem, which has already begun in the cave’s vicinity. 

Burney has found the remains of other extinct creatures in the cave, but nothing to rival Talpanas lippa, the mole-duck, described in 2009 on the basis of a single specimen from Makauwahi. It was a small duck, about the size of a female mallard, and apparently flightless: Hawai’i’s approximation of a kiwi. Talpa is the Latin word for “mole,” anas for duck. Andrew Iwaniuk, Storrs Olson, and Helen James, authors of the description, concluded that the bird had “reduced visual abilities, as reflected externally by its small orbits and optic foramen.” But it compensated with a hyperdeveloped tactile sense.

“The hole in the skull for the nerve carrying the sense of touch is over ten times the diameter measured in ducks of comparable size, suggesting that it may have been more heavily reliant on the sense of touch for foraging than any living species of bird in the world,” writes Burney. Iwaniuk et al note that the living duck-billed platypus also has an enlarged trigeminal nerve. The platypus relies on electrosensory input as it hunts in murky water; the mole-duck might have done the same. It might be fair to call the bird a platypus-billed duck. 

With its small eyes and sturdy legs, Talpanas appears to have been nocturnal and land-based. There’s nothing remotely like it among contemporary ducks, although ruddy ducks and other stifftails use tactile cues rather than vision to locate prey. Burney’s conclusion is apt: “It seems that we have dug up something that nobody would have even remotely imagined to exist, had it not been for the discovery of these bones.” 

The mole-duck is long gone, of course. Its remains were found below vegetable matter that was carbon-dated as at least 5305 years old, when the cave site was a lake; one more tantalizing piece of a lost world.