Sunday, June 10, 2007

Unlikely pair: Diomedea epomorphora meets Dinornis maximus

Tiaroa Head is one of the only places in the world where you can see the Royal Albatross without using a Zodiac. These birds are massive. With a wingspan of 3 metres, they can easily be mistaken for personal aircraft. Their posture while soaring is careless, but precise. Every control surface is primed for maximum efficiency - they can move those huge wings like tentacles, wrapping around every little patch of lift. They're really just self-satisfied jumbo chickens. Grudgingly beautiful, as only an Albatross can be. Perfect sunset drives to the end of the Otago Peninsula can certainly pay off on windy days. But this speed zeppelin of a seabird has only become NZ's largest in the last few hundred years.

Fifteen million years ago, Central Otago was a lake. We know this because the mud, sand and gravel dumped into this lake from the surrounding hills are piled high under the golden tussock and savory scrub of Southland range. Ever since Lake Manuherikia dried up, its dry muck bottoms have been hosed down by every storm that manages to get past Fiordland into the dry rainshadow of the Southern Alps. Each downpour washes the gullies and swirls new tunnels and holes into the soft sediment. Since the Oligocene, the mountains have grown higher and higher until glaciers clung to the tops and crept to the valleys. Relentless grinding by ice turns any solid rock into a heap of pulverized dust the consistency of flour. The wild wind hauls it easily, and piles can accumulate miles away wherever the air slows enough to drop its load. The Germans named this phenomenon first, and we use the term 'loess' (read: luss) for deposits milled by glaciers and sorted by wind.

Until 800 years ago, outlandish birds trotted around New Zealand. That's not to say they don't anymore, it's just that they're so much smaller now. The Giant Moa of Southland stood at twelve feet. It was here, busy grazing during the Norman invasion of England. None are now alive, but Otago is littered with the record of flightless giants and the flying predators that ate them. Lake Manuherikia left the means to save the bones of bird and beast long enough for us to make educated guesses about life in the relatively recent past.

Huge three-toed golem-like grazers with heads smaller than your average chihuahua aren't the smartest animals in the zoo, so it's not surprising that the hundreds of old potholes in Lake Manuherikia sediment contain more than a few Giant Moa skeletons, extinct Kiwi femurs, and Haast Eagle claws. Every time a wandering bird died in the treacherous booby-trapped terrain, it was covered by windblown loess and rain-washed mud. Some skeletons were buried so quickly that they are still assembled correctly. The process is still happening every season, trapping modern mammals, sheep and rabbits together with the ancient forms they have replaced (with the help of human colonizers). Each storm that passes acts as a bulldozer, trencher, and industrial blender all in one - resulting in such confusion of the strata that ancient and modern bones are juxtaposed in unlikely ways.

So maybe I can be excused for spending an hour exposing a rabbit that died five years ago - my vertebrate anatomy suffered from overexcitement, and I realized only too late that my prize had huge front teeth, quite unlike a bird. But we discovered other clues as we poked along on Ray Bell's ranch. We got the idea from a PhD student in Dunedin, Jamie Wood, who directed us to Chatto Creek. Carey Donald joined us for a long weekend holiday from her research in Australia, and we wound through the Otago hills until we saw Jamie's landmark: a lot of old cars and a bridge. That's how we wandered into Mr. Bell's front yard.

He and his wife were busy butchering a deer. A few minutes of explanation, and Ray was happy to show us everything. We were told to wait in his garage while he finished up - amusing ourselves by examining his red '69 T-bird. Left hand drive. "God those yanks can make a beautiful cahr." He had several other vehicles of all ages and kinds scattered along the hill. He opened the back of a segregation-era bus and produced a meter-long pelvis. Imagine something the size of a watermelon comfortably fitting between the major bones. He fitted two drainpipe-size femurs into their sockets as Eric held the pelvis at the appropriate hight. "That's about right then, eh Lofty?" These bones came from up the gully he explained, leaning on his cane while bits of venison dribbled down his apron onto some classic gumboots. Eric's new nickname has stuck. "Ah, bot you're americans eh, ye don't weahr the gumboots then. You can take a look out there anyhow, dry enough yet. Whaddayou think Lofty?"

Eric didn't have to think long. We spent the rest of the afternoon poking about the gully. Among leftover rabbits and sheep, we found a spare bit of odd eggshell and some promisingly hollow little bones. It was enough to show us that we needed to come back. During an extended tour of the Thunderbird, Ray promised to take us out in the truck to see the real hotspot further up the track. We've made our appointment for this Wednesday. The Chatto Creek tavern and bunkhouse is right across the street.

Today is our last day in Dunedin, and the city seems to be trying to redeem its reputation with us by a string of beautifully cold and lucky days of wildlife spotting. By the time we have the Carat packed up, say goodbye to friends and professors, and chow down at Friendly's Noodle house, leaving Dunedin will seem like leaving home - and it's not a moment too soon. We've got mountains to see, bones to find, and straits to cross. The Subduction Recon Team rides again!

PS: this computer is so slow, it won't upload the rest of my sweet pictures. you'll just have to wait. our customer service representative is Helen Wait. if you have complaints, go to Helen Wait.